Keywords: Fruit fly
Selfish sperm hijack Overdrive gene to kill healthy rivals
35511Lisa Potter, Phys.org, 2026-03-12 15:14:08.
A new University of Utah-led study has discovered the mechanism behind a decades-old evolutionary mystery—how "selfish chromosomes" cheat the rules of genetic inheritance. The researchers found that rogue chromosomes hijack the Overdrive (Ovd) gene to destroy rival sperm. The study is the first to identify that the Ovd gene acts as a quality control checkpoint during sperm development. Normally, Ovd detects and eliminates abnormal sperm cells. But selfish chromosomes exploit the system to kill competitors, boosting their chances of passing into the next generation. The findings, published in Nature Communications, reveal the biology behind segregation distortion, a phenomenon in which genes sway inheritance in their favor to beat the standard 50/50 odds predicted by Mendelian genetics. The team observed the scheme in two Drosophila species, each carrying completely different selfish chromosomes, which suggests that multiple genetic systems may evolve independently to exploit the same Ovd pathway.
Assessing target genes for homing suppression gene drive
35447Xu, X., Fang, J., Chen, J. et al., The EMBO Journal, 2026-02-06 17:52:26.
Gene drives are engineered alleles that bias their own inheritance in offspring, enabling the spread of specific traits throughout a population. Targeting female fertility genes in a gene drive can be an efficient strategy for population suppression. In this study, we investigated nine female fertility genes in Drosophila melanogaster using CRISPR-based homing gene drives. Employing a multiplexed gRNA approach to prevent the formation of functional resistance alleles, we aimed to maintain high drive-conversion efficiency with low fitness costs in female drive-carriers. Drive efficiency was assessed in individual crosses and had varied performance across different target genes. Notably, drives targeting the octopamine β2 receptor (oct) and stall (stl) genes exhibited the highest drive-conversion rates and were further tested in cages. A drive targeting stl successfully suppressed a cage population with a high release frequency, though suppression failed in another replicate cage with a lower initial release frequency. Fitness costs in female drive carriers were observed in test cages, impacting the overall efficiency of population suppression. Further tests on the fertility of these lines using individual crosses indicated that some fitness costs were due to maternal deposition of Cas9 combined with new gRNA expression, which would only occur in progeny of drive males when testing split drives with separate Cas9 (when mimicking cages with complete drives) but not for complete drive systems. This could enable success in complete drives with higher maternal Cas9 deposition, even if cage experiments in split drives fail. Overall, our findings identify oct and stl as promising fertility targets and demonstrate both the potential and the constraints of fertility-based suppression drives, providing empirical evidence to guide the design and assessment of more efficient population control strategies.
Bisexual releases are as effective as male-only releases to control Drosophila suzukii with the sterile insect technique
35393Alexandra Labbetoul, Simon Fellous, Pest Management Science, 2026-01-23 10:16:56.
The sterile insect technique (SIT) suppresses insect reproduction by repeatedly releasing sterile insects and allowing them to mate with insects of the same species in the wild. While the classical SIT relies on sterile males mating with wild females, there is a debate regarding the risks and benefits of releasing sterile females along with the sterile males (i.e. bisexual releases). In a replicated cage experiment, we compared the effect of unisexual and bisexual sterile releases of Drosophila suzukii on induced sterility. To ensure field-realism, fertile females - wild-F0 freshly emerged from field-collected sweet-cherries - were placed in cages with artificial vegetation and plastic berries. The proportion of fertile females that produced offspring was not significantly different in unisexual and bisexual treatment (45% and 46%, respectively). Excluding females that had not mated (i.e. no sperm in the spermathecae) from the analysis had no influence. These results suggest the release of sterile females does not always affect the efficacy of the SIT. Even though additional phenomena may arise when scaling up from cages to the field, we conclude that sorting females with genetic constructs or robotic systems is probably dispensable in D. suzukii SIT, at least when deployed in confined farming systems.
D. melanogaster meiotic driver Stellate compromises sperm development by impeding a process of nuclear envelope remodeling
35390Xuefeng Meng, Yukiko M Yamashita,, Genetics, 2026-01-23 09:55:19.
Meiotic drive is a phenomenon that violates Mendel’s Law of Equal Segregation, leading to biased transmission of the meiotic driver to the offspring. D. melanogaster Stellate (Ste) is an X-linked meiotic driver that preferentially harms Y-chromosome-bearing spermatids, thereby favoring the transmission of the X chromosome to the next generation. We have recently shown that Ste protein segregates asymmetrically during meiosis I with a strong bias toward the Y-chromosome-inheriting side, leading to the eventual demise of the Y-chromosome-containing spermatids. However, the cellular mechanisms by which Ste protein interferes with spermatid development remain unknown. Here, we show that Ste-containing spermatids are delayed in the process of nuclear envelope remodeling, an essential process during sperm DNA compaction. We show that components of the nuclear lamina (such as Lamin Dm0, and the LEM domain proteins Otefin and Bocks) are rapidly removed during nuclear envelope remodeling during the early stages of normal spermatid development. However, Ste-containing spermatids retained these nuclear lamina proteins for a prolonged time. Their delayed removal is associated with defective formation of the dense complex, which is composed of a bundle of microtubules and serves as a structural support for sperm nuclear morphogenesis. Defective dense complex formation in Ste-containing spermatids led to defective sperm DNA compaction. Together, the present study reveals an unexpected cellular mechanism by which a meiotic driver, Ste, sabotages sperm development.
Drive, suppression and escape from suppression of a selfish chromosome
35382Jackson Ridges, Jackson Bladen, Robert Unckless, Nitin Phadnis, Proc Biol Sci, 21. 2026-01-21 13:39:59.
Meiotic drivers are selfish genetic elements that are predicted to spark rapid intra-genomic arms races with their suppressors. However, the long-term persistence of unsuppressed selfish chromosomes in natural populations violates these theoretical expectations. The Drosophila pseudoobscura Sex-Ratio (SR) chromosome exemplifies this problem, sometimes referred to as the ‘ancient gene drive paradox’. Here, we analyse the evolutionary history of this SR chromosome and show that its genetic architecture and complexity have likely been shaped by a history of drive, suppression and escape from suppression. Our results suggest that the current lack of resistance to the SR chromosome may represent a transient condition awaiting the emergence of new suppressors.
Selfish chromosomes exploit a germline checkpoint to eliminate competing gametes
35349Ridges, J.T., Bladen, J., King, T.D. et al., Nature, 2026-01-10 09:51:42.
Spermatid individualization is a common stage of spermiogenic failure suggesting that a male germline checkpoint may act at this stage during sperm development in Drosophila. However, the molecular identity of such a male germline checkpoint has remained elusive. Here, we show that Overdrive (Ovd), a gene dispensable for male fertility, is required for the selective elimination of post-meiotic spermatids targeted by selfish chromosomes. Gamete elimination occurs during the individualization stage of spermiogenesis, following histone-to-protamine transition failure of targeted spermatids. We show that Ovd is necessary for the selfish behavior of segregation distorters across distantly related Drosophila species, indicating that independent selfish chromosomes use common mechanisms. Our study suggests that the normal function of an Ovd-mediated germline checkpoint involves the elimination of abnormal gametes during male germline development, which is exploited by selfish chromosomes into eliminating competing sperm.
Behavior modification in fruit flies through male annihilation technique: field applications, olfactory mechanisms, and future directions
35329Liu, Wei; Zhang, Sijia; Wang, Guirong, Entomologia Generalis, 45:1565 - 1576. 2026-01-06 14:51:47.
The male annihilation technique (MAT), as a method of insect behavior manipulation, is an environmentally friendly approach that has been successfully applied in over 150 fruit fly eradication programs worldwide. Despite their effectiveness in integrated pest management programs, concerns have long persisted about the safety of the primarily used male lures – particularly regarding the potential toxicity of methyl eugenol (ME). In this review, we propose a novel attractant screening and validation system for the future improvement of male lures, based on recent advancements in functional genomics and genetic manipulation technologies achieved in tephritid fruit flies. This system is built upon our knowledge of tephritid fruit flies’ core olfactory signal transduction pathway (“Male lures → Odorant receptors → Odorant receptor neurons → Glomerulus”). The working pipeline is centered around a transgenic Bactrocera strain with labeled male lure-responsive olfactory receptor neurons (ORNs) as the key targets. Electrophysiological responses and calcium activity serve as the readouts, while the decision criteria focus on increased intensity, stability, and specificity of neural activation induced by candidate compounds. This pipeline, compared to traditional behavior-first methods, enables the efficient screening of computationally identified candidate compounds and provides a foundation for evaluating their field stability and safety. More importantly, it represents a shift from empirical, field-based optimization to a molecularly guided, receptor-based design framework, advancing the development of enhanced male lure solutions for future applications in insect behavior manipulation.
Homing gene drive strains for genetic suppression of agricultural insect pests
35331Yadav, Amarish K.; Tarrand, Ariel E.; Scott, Maxwell J., Entomologia Generalis, 45:1577 - 1590. 2025-12-04 14:52:03.
Agricultural insect pests cause substantial losses in crop productivity each year. Genetic-based strategies provide economical and environmentally friendly ways to limit pests that reproduce sexually. In contrast to conventional genetic methods (e.g. SIT), homing gene drives (HGDs) are potentially capable of suppressing or modifying an entire pest population in a short period of time after releasing a small number of HGD insects. The advent of CRISPR/Cas gene editing tools has simplified the engineering of gene drives, and the progress made on HGDs in various insects in the recent past is encouraging. However, to date HGDs have been developed and evaluated in only a few agricultural pest species. These drives have been designed to suppress populations by targeting genes essential for female development or fertility. Homing gene drive relies on homology directed repair (HDR) of the Cas9-mediated double-stranded DNA break in germ cells. Consequently, the use of other DNA repair pathways such as non-homologous end joining (NHEJ) and micro-homology mediated end joining (MMEJ) can retard homing. Further, establishment of functional resistant alleles through these end-joining pathways is one of the major challenges associated with HGDs. Development of HGDs in some pest species is challenging due to the technical difficulties of making transgenics. Identification and characterization of germline-specific promoters and other regulatory elements to achieve precise HDR (in early meiosis) can facilitate efficient homing. In this review, we highlight the recent progress made towards developing HGDs in agricultural insect pests with insights gained from studies in model organisms (e.g. Drosophila melanogaster).
Variants in Cas9 and nanos regulatory elements modulate activity and reduce resistance allele formation in homing gene drive
35294Ruizhi Zhou, Jie Du, Nicky R. Faber, Jackson Champer, bioRxiv, 2025-11-09 18:15:12.
Gene drive is a novel approach for controlling vector borne disease via either population modification or suppression. Even with high efficiency, though, overall drive performance can be reduced by somatic Cas9 expression and by maternal deposition of Cas9, leading to resistance allele formation. The nanos promoter for Cas9 shows very little leaky somatic expression, but it causes high rates of embryo resistance allele formation in Drosophila melanogaster. By truncating the promoter, we reduced rates of embryo resistance to undetectable levels, but germline cutting in females decreased by over half. Germline cutting and successful drive conversion was eventually lost when only the 5′ UTR was present, though males still retained moderate germline drive efficiency. Several additional methods were tested to improve performance, including additional suppressor elements to the 3′ UTR and introns to increase expression level. The most successful of these was the addition of a second nuclear localization signal, which substantially increased activity when coupled with a full-length or truncated nanos promoter. Overall, these experiments show the potential to modulate Cas9 regulatory elements to achieve desired expression for gene drive applications, while also showcasing the difficulty of obtaining an optimal activity profile.
Effect of male age at the time of irradiation on the sexual performance of sterile Ceratitis capitata males: insights from remating female offspring
35278Edwin Mauricio Ramírez-Santos, Pedro Alfonso Rendón Arana, et al., Insect Science, 2025-11-03 11:19:51.
The Sterile Insect Technique (SIT) is an effective strategy for controlling insect pests, such as the Mediterranean fruit fly (Ceratitis capitata, Wiedemann). The effectiveness of the SIT depends on the ability of the sterile males to mate and their capacity to induce sterility in wild females. This study evaluated how the irradiation age affects their sexual performance, measured by the outcome of female remating events. Males of the GSS VIENNA 8D53− were irradiated at eleven different ages, from 72 h before emergence (pupal stage) to 72 h after emergence (adult stage) and mated with wild females. These females were subsequently allowed to mate with fertile males from the fluorescent TSS VIENNA 8 1260. The presence of fluorescent offspring was used as indicator of second-male paternity. Results showed that males irradiated at post-emergence ages produced the lowest egg-to-pupae conversion rate, indicating a greater ability to prevent females from producing offspring after remating with a fertile male. In contrast, males irradiated at pre-emergence ages were associated with higher numbers of fluorescent offspring. Although no significant differences were found in mating competitiveness (RSI), the outcome of the remating showed differences in the effectiveness of initial matings. These findings highlight the importance of considering the age of flies at time of irradiation in mass-rearing protocols to enhance the efficacy of SIT programs targeting C. capitata and suggest that irradiating males later in their life cycle, such as adult stages or in pupae close to adult emergence, limit offspring if females remate with fertile males in the field.
Developing Y chromosome sex ratio distorters in the model insect Drosophila melanogaster
35259Yael Arien, Chen Zacharia, Elad Yonah, et al., bioRxiv, 2025-10-28 08:24:56.
CRISPR-Cas9 sex ratio distortion (SRD) systems can suppress insect populations by biasing progeny toward males, but realizing such systems requires reliable Cas9 expression from insect Y chromosomes. Here, we tested whether the spermatocyte-specific betaTub85D promoter can drive functional Cas9 expression when inserted on the Drosophila melanogaster Y chromosome. Using CRISPR-mediated homology-directed repair, we generated a Y-linked betaTub85D-Cas9-T2A-eGFP construct and compared its activity with an autosomal counterpart. Whereas autosomal betaTub85D-Cas9 induced strong male-biased sex ratios when paired with an X-poisoning gRNA, the Y-linked construct failed to distort sex ratios and exhibited approximately 2,000-fold reduction in Cas9 transcript abundance. Nonetheless, weak but detectable GFP fluorescence and Cas9 transcripts confirmed partial Y-linked promoter activity. These findings provide the first direct experimental evidence of meiotic sex chromosome inactivation (MSCI) acting on the Drosophila Y chromosome, revealing that meiotic promoters can remain weakly active despite strong repression. This work defines transcriptional limits of the Drosophila Y chromosome and informs the design of next-generation Y-linked gene drives for sustainable insect control.
Pervasive suppressors halt the spread of selfish Segregation Distorter in a natural population
35247Ching-Ho Chang, Tyler Handler, Nick Fuda, et al., bioRxiv, 2025-10-16 09:21:01.
Meiotic drivers are selfish genetic elements that subvert Mendelian inheritance to increase their own transmission, yet they are typically found at low frequencies across natural populations. The factors that limit their spread remain unclear. To investigate this paradox, we studied the Segregation Distorter (SD) system, a selfish coadapted gene complex in Drosophila melanogaster. SD biases its transmission by killing sperm carrying a homologous chromosome bearing a target locus, Responder (Rsp), which appear as satellite repeats. Such selfish killing impairs male fertility and imposes selective pressure on the host genome to evolve resistance, either by deleting Rsp copies or acquiring unlinked suppressors. To characterize the spectrum of Rsp alleles and the frequency of segregating suppressors, we surveyed 90 strains from the Drosophila Genome Reference Panel. Rather than loss of Rsp, we found that over half of the strains (52/90) harbor suppressors located on the X chromosome or autosomes, but not the Y chromosome. The widespread presence of strong suppressors limited the resolution of our genome-wide association mapping; however, recombination analysis identified a strong X-linked suppressor to a ~300 kb interval on the chromosome. Together, our findings suggest that pervasive, multilocus suppression constrains the spread of SD in natural populations.
The Stellate meiotic drive system of Drosophila melanogaster is active in contemporary populations
35215Benjamin K McCormick, Daniel A Barbash, Andrew G Clark, bioRxiv, 2025-10-05 12:58:27.
Meiotic drivers are selfish elements that bias their own transmission so that they are overrepresented among the functional gametes produced. The selective costs imposed by drivers on their hosts may trigger intragenomic conflict, promoting the evolution of suppressors and fueling an ongoing arms race between drivers and suppressors. Stellate (Ste) is an X-linked tandemly arrayed multicopy gene. Its copy number ranges from 3 to more than 300 among Drosophila melanogaster strains from the Global Diversity Lines. In wild-type animals, Ste expression is usually suppressed by homologous piRNAs produced from the Suppressor of Stellate (Su(Ste)) array on the Y chromosome. Derepression of Ste in the absence Su(Ste) results in the formation of proteinaceous crystals in spermatocytes, chromatin compaction defects, reductions in fertility, and female-biased sex ratios arising from under-recovery of Y-bearing sperm. Despite extensive study, the function of the Stellate array and evolutionary significance of its persistence in the genome have remained elusive. It has been suggested to be a now-inactive relic of an ancient meiotic drive system, as perturbations in lab stocks can produce Ste-mediated meiotic distortions. Meiotic drive occurring among natural variants, however, has not been reported. We established crosses between females with high Ste copy number X chromosomes and males carrying low Su(Ste) copy number Y chromosomes and found that the male progeny displayed non-Mendelian sex chromosome transmission. Importantly, deletion of the euSte array in an otherwise matched genetic background rescues this phenotype, demonstrating that Stellate is an active driver in contemporary populations.
D. melanogaster meiotic driver Stellate compromises sperm development by impeding nuclear envelope remodeling
35211Xuefeng M Meng, Yukiko M Yamashita, bioRxiv, 2025-10-02 15:00:55.
Meiotic drive is a phenomenon that violates Mendels Law of Equal Segregation, leading to biased transmission of the meiotic driver to the offspring. D. melanogaster Stellate (Ste) is an X-linked meiotic driver that preferentially harms Y-chromosome-bearing spermatids, thereby favoring the transmission of the X chromosome to the next generation. We have recently shown that Ste protein segregates asymmetrically during meiosis I with a strong bias toward the Y-chromosome-inheriting side, leading to the eventual demise of the Y-chromosome-containing spermatids. However, the cellular mechanisms by which Ste protein interferes with spermatid development remain unknown. Here, we show that Ste-containing spermatids are delayed in the process of nuclear envelope remodeling, an essential process during sperm DNA compaction. We show that Lamin Dm0, a component of the nuclear lamina, is rapidly removed during nuclear envelope remodeling during the early stages of normal spermatid development. However, Ste-containing spermatid retained Lamin Dm0 for a prolonged time. Delayed Lamin Dm0 removal is associated with defective formation of the dense complex, which is composed of the bundle of microtubules and serves as a structural support for sperm nuclear morphogenesis. Defective dense complex formation in Ste-containing spermatid led to defective sperm DNA compaction. Together, the present study reveals an unexpected cellular mechanism by which a meiotic driver, Ste, sabotages sperm development.
The impact of sterile insect technique processes on the performance of tephritid flies
35190Mayren Sánchez-Rosario, Jorge Toledo, Walther Enkerlin, Insect Science, 2025-09-29 09:49:25.
The sterile insect technique (SIT) is a pest control method that has been successful in controlling various species of fruit flies of economic importance worldwide. However, SIT procedures can affect the performance of mass-reared sterile fruit flies, compromising the SIT effectiveness. This review aims to identify and analyze the adverse effects associated with each step of the SIT. Special emphasis is placed on identifying critical points in the SIT process that compromise the quality and highlighting the stages that require greater optimization to improve the effectiveness of the technique. We reviewed the main scientific findings that document the impact of domestication, mass-rearing, irradiation, handling, and release on the biology, ecology, behavior, and genetic makeup of sterile males, and how they affect the performance of sterile males under natural conditions, and the effectiveness of the SIT. Although all stages of the Sterile Insect Technique (SIT) impose some degree of compromise on insect performance, domestication and mass-rearing have the most profoundly negative impact on the field performance of sterile fruit flies. As the initial and most influential stages, they largely determine the overall quality and competitiveness of released insects, exerting a stronger impact than any subsequent SIT component.
The role of the transformer gene in sex determination and its employment in CRISPR/Cas9-based homing gene drive in the global fruit pest Drosophila suzukii
35172Dan Deng, Xueying Yi, Wen Wen, Liuqing He, Wei Peng, Insect Biochemistry and Molecular Biology, 184. 2025-09-26 14:04:36.
Sex determination of Diptera is established by the cascade genes such as transformer (tra), though the primary signals for sex determination differ among different insects. Here, we report the isolation, expression and function of tra gene in an invasive pest, Drosophila suzukii, and study the potential use of the D. suzukii tra (Dstra) gene in CRISPR/Cas9-based homing gene drive for genetic-based pest management. The Dstra gene is highly conserved in structure and has a sex-specific transcript. To test the function of this gene in sex determination, Dstra dsRNA was injected into embryos. Almost all XX embryos developed into masculinized phenotypic male adults with intersex morphology. Abnormal ovaries were revealed in XX pseudomales upon dissection. Based on the necessary role of Dstra for female development, we developed and evaluated a homing gene drive that targets Dstra in D. suzukii. The drive component consisting of multiplex Dstra single guide RNAs and Cas9 with Dsvasa promoter was introduced into the Dstra locus. Abnormal development of both the external genitalia and gonads was observed in G0 and G1 chromosomal female adults that expressed the male-specific doublesex (dsx) transcript. Interestingly, knocking out Dstra led to significantly reduced fertility in adults of corresponding sex and moderate transmission rates of the DsRed gene (63.54 %) were observed. Our results not only confirm the conserved function of the Dstra gene in sex determination, but also highlight the potential of sex conversion-based suppression gene-drive strategy targeting the Dstra gene in controlling of D. suzukii populations.
Rapid protamine evolution suppresses meiotic drive in Drosophila
35159Ching-Ho Chang, Aida Flor de la Cruz, Isabel Mejia Natividad, Alex Noyola, Harmit S. Malik, bioRxiv, 2025-09-22 10:55:08.
Many animal species replace histones with protamines during spermatogenesis. Despite their importance for sperm function, protamines rapidly evolve in many species; the biological causes behind their rapid evolution remain unknown. Here, using in vivo gene replacement, we investigated the causes and consequences underlying the rapid evolution of protamine Mst77F, which is essential for male fertility in D. melanogaster. Mst77F ortholog replacements led to defects in DNA compaction of X-chromosome-bearing sperm compared to Y-chromosome-bearing sperm during spermatogenesis, resulting in fewer X-bearing mature sperm and male-biased progeny. Unlike D. melanogaster, Mst77F is not essential for male fertility in D. yakuba but is still required to suppress sex-ratio distortion. Our results suggest that relentless pressure to suppress sex chromosomal meiotic drive drives the rapid evolution of protamines.
Fruit fly tests in Greece target invasive species threat
35161Vassilis Kyriakoulis, Phys.org, 2025-09-15 15:24:50.
In a small persimmon orchard in northern Greece, scientists carefully open paper bags to release thousands of flies, in an experiment aimed at blunting the destructive impact of invasive new species. The insects are sterile male Mediterranean fruit flies (Ceratitis capitata), a pest that annually causes significant damage to crops in Naousa, where a large proportion of Greece's prominent export, the peach, is produced. But the project is ultimately aimed at curbing an even greater threat: fruit fly species from Asia, which have begun to make their appearance in southeastern Europe as climate change increases local temperatures. The four-year, EU-funded project titled REACT brings together researchers from 12 different countries including the UK, Israel and South Africa. The program has a budget of 6.65 million euros ($7.8 million). "Our approach is to locally eradicate Mediterranean fruit fly populations and then apply this knowledge to other species of interest, such as the oriental fruit fly and the peach fruit fly," said project participant Nikos Papadopoulos, a professor of Applied Entomology at the University of Thessaly. The male flies are grown at the University of Patras and are fed a bacterial supplement that makes them more active, resilient, and competitive, said George Tsiamis, the university's Laboratory of Microbiology Systems director, during a media tour organized in Naousa by the research team.
Sequence and expression analysis of potential spermatogenesis-specific gene cognates in the Caribbean fruit fly, Anastrepha suspensa
35118Alfred M. Handler, Richard B. Furlong, Chao Chen, Daniel A. Hahn, Insect Science, 2025-09-08 08:26:08.
The sterile insect technique (SIT) is a highly effective biologically-based method for the suppression of many insect pest populations. SIT efficacy could be improved by methods of male sterilization that avoid the use of irradiation that can result in diminished fitness and mating competitiveness. Alternative sterilization methods include conditional disruption of genes for male fertility, or using their sperm-specific promoters to drive the expression of genes for lethal effectors. Testing has begun for the testis-specific β2-tubulin gene, though additional male fertility genes are required for redundancy or replacement, and for species where the β2-tubulin isoform does not exist or is not testis-specific. Here we had the goal of identifying and characterizing the sequence and transcriptional expression of two genes in the caribfly, Anastrepha suspensa, that are cognates of D. melanogaster spermatocyte-specific male fertility genes. In Drosophila, wampa encodes a coiled-coil dynein subunit required for axonemal assembly essential to microtubule-based sperm motility, while Prosα6T is a proteasome subunit gene required for spermatid individualization and nuclear maturation. In A. suspensa a cognate to wampa exhibited testis-specific transcript expression, which was minimal in both male and female body tissue. A Prosα6T cognate was not apparent in A. suspensa, but its constitutive isoform, Prosα6, expresses in male testes, but also in male and female body tissue. Thus, for A. suspensa, wampa remains a strong candidate gene for male sterility strategies for SIT including a direct target for gene-editing knockout and use of its promoter for testis-specific toxicity or cell death in conditional expression systems.
The shibirets4 mutation causes temperature sensitive paralytic and lethal phenotypes in the Queensland fruit fly, Bactrocera tryoni
35094Anzu Okada, Mamoru Okamoto, Thu N.M. Nguyen, et al., Insect Science, 2025-09-01 19:43:43.
Bactrocera tryoni, the Queensland fruit fly, is among the most damaging insect pests to the Australian horticultural industry as larvae infest ripening fruits or vegetables prior to harvest. Genetic biocontrol using Sterile Insect Technique (SIT) programs have been used to successfully suppress populations, via mass release of factory-reared sterile males that mate with wild females. Bi-sex flies are currently used for releases, although the efficiency of these control programs could be improved through using genetic sexing strains that eliminate females early during development, as they are not required for SIT. Here we used CRISPR/Cas9 mutagenesis to modify two nucleotides in the B. tryoni gene shibire, which created a proline to serine amino acid substitution and produced a temperature sensitive phenotype. Shibire is an essential GTPase required in endocytosis and synaptic vesicle recycling, and classical mutagenic screens in the vinegar fly Drosophila melanogaster previously identified temperature sensitive alleles including shits4 that results in adult paralysis. In B. tryoni, the shits4 mutant strain exhibited similar adult paralytic phenotypes when exposed to high temperatures, as well as temperature dependent lethality at egg, larval and pupal stages when subjected to heat treatment above standard rearing temperatures. These temperature sensitive phenotypes could be adapted to develop a SIT genetic sexing strain for conditional elimination of females prior to sterile releases, to improve efficiency and reduce costs.
Novel stressors and trait variation determine X-linked meiotic drive frequency
35021Fisher Adam M., White Nicola, Bonsall Michael B., Price Tom AR. and Knell Robert J., Proc. R. Soc. B., 292. 2025-08-13 16:09:01.
Sex ratio meiotic drive alleles bias their transmission by impairing the viability of non-drive gametes, leading to skewed population sex ratios. Despite theoretical predictions that drive alleles should reach fixation causing population extinction, meiotic drive persists at intermediate frequencies in wild populations, though the reasons for this are unclear. Here, we investigate how novel environmental stress and genotype-specific fitness costs contribute to drive frequency. Using a suppression-free X-linked meiotic drive system in Drosophila pseudoobscura, we exposed flies to varying doses of the pesticide permethrin and measured mortality and fecundity across genotypes. We found that drive-bearing males (SR) and drive-homozygous females (SRSR) exhibited heightened mortality, both in the presence and absence of pesticide, while heterozygous (SRST) females exhibited superior fecundity. Using a mathematical model parametrized with our empirical findings, we explored the long-term population dynamics of meiotic drive under different conditions. Our model predicts that drive frequency has a concave relationship with pesticide dose and is strongly modulated by genotype-specific female fecundity. These results suggest that novel environmental stressors and drive-induced fitness effects play key roles in determining meiotic drive frequencies. Our findings improve our understanding of drive frequencies in the wild and have direct implications for drive-based pest control.
Drive, suppression, and escape from suppression of a selfish chromosome
35016Jackson Taylor Ridges, Jackson Bladen, Robert L. Unckless, Nitin Phadnis, bioRxiv, 2025-08-11 14:46:50.
Meiotic drivers are selfish chromosomes that are predicted to spark a rapid intragenomic arms-race with their suppressors. However, the long-term persistence of unsuppressed selfish chromosomes in natural populations violates these theoretical expectations. The Drosophila pseudoobscura Sex-Ratio (SR) chromosome exemplifies this problem, sometimes referred to as the ancient gene drive paradox. Here, we reconstruct the evolutionary history of this SR chromosome and show that its genetic architecture and complexity has been shaped by a history of drive, suppression, and escape from suppression. Our results indicate that the current lack of resistance to the SR chromosome represents a transient condition awaiting the emergence of new suppressors.
Suppression of sex-ratio drive in Drosophila subobscura
35233Sophie Lyth, Tom Gill, Andri Manser, et al., Evolution, 2025-07-30 15:46:21.
Selfish genetic elements enjoy an evolutionary advantage by enhancing their own transmission to offspring, and their genetic suppressors are favored when they re-establish fair inheritance patterns. Here, we study an X-linked sex ratio drive system (SR) in Drosophila subobscura, which kills Y-bearing sperm of SR males, resulting in the over-transmission of the SR chromosome and a strong female bias in their offspring. We surveyed D. subobscura populations in North Africa, which naturally harbor SR, and found that suppression occurs in ∼13.5% of wild-derived lines. We characterize this suppression phenotype through a series of crossing experiments, including multigenerational introgression of SR chromosomes into a suppressing genetic background. We show that introgression can restore normal offspring sex ratios or, in some cases, result in an excess of male offspring. This suppression appears to be a multilocus trait, involving autosomes and the Y chromosomes. Suppression of SR fails to ameliorate all costs of drive, with fully suppressed SR-carrying males having depressed fertility and low offspring egg hatch rates. Further examination of internal male reproductive organs using microscopy suggests that suppressed SR males also have abnormal testes. These factors may explain why the suppression fails to reach high frequencies, despite the strong advantage of suppressing SR.
Intrinsically weak sex chromosome drive through sequential asymmetric meiosis
34889Xuefeng Meng, Yukiko M. Yamashita, Science Advances, 11. 2025-06-02 19:06:59.
Meiotic drivers are selfish genetic elements that bias their own transmission, violating Mendel’s Law of Equal Segregation. It has long been recognized that sex chromosome–linked drivers present a paradox: Their success in transmission can severely distort populations’ sex ratio and lead to extinction. This paradox is typically solved by the presence of suppressors or fitness costs associated with the driver, limiting the propagation of the driver. Here, we show that Stellate (Ste) in Drosophila melanogaster represents a novel class of X chromosome–linked driver that operates with an inherent mechanism that weakens its drive strength. Ste protein asymmetrically segregates into Y-bearing cells during meiosis I, subsequently causing their death. Unexpectedly, Ste segregates asymmetrically again during meiosis II, sparing half of the Y-bearing spermatids from Ste-induced defects, thereby weakening the drive strength. Our findings reveal a mechanism by which sex chromosome drivers avoid suicidal success.
A selfish supergene causes meiotic drive through both sexes in Drosophila
34805G.L. Keais,C.M. Saad-Roy,E. Gonzalez-Sqalli, et al., Proceedings of the National Academy of Sciences, 122. 2025-04-25 12:15:11.
Meiotic drivers are selfish genetic elements that bias their own transmission during meiosis or gamete formation. Due to the fundamental differences between male and female meiosis in animals and plants, meiotic drivers operate through distinct mechanisms in the two sexes: In females, they exploit the asymmetry of meiosis to ensure their inclusion in the egg, whereas in males, they eliminate competing gametes after symmetric meiosis. Meiotic drive is commonly reported in males, where it strongly influences the evolution of spermatogenesis, while the few known cases in females have highlighted its crucial role in centromere evolution. Despite a growing number of examples in a wide range of organisms, meiotic drive has so far only been observed in one sex or the other since its discovery nearly 100 y ago. Here, we show that a selfish X chromosome known to cause meiotic drive in male Drosophila testacea flies also causes meiotic drive in females. We find that this X chromosome has supergene architecture, harboring extensive structural rearrangements that suppress recombination between the two X chromosomes. This has contributed to a substantial expansion of its size compared to the wild-type chromosome, partly due to the accumulation of species-specific repetitive elements. Our findings suggest that female meiotic drive may play an important role in the evolutionary dynamics of polymorphic structural variants that suppress recombination, including inversions, translocations, and supergenes.
Applications and status of gene drive in plants
34771Hay BA, PLOS Biology, 23. 2025-04-18 10:06:07.
Globalization—the movement of humans, plants, animals, and microbes—together with climate change, place numerous plant and animal species under novel stresses. For plants, threats include global warming, invasive species, weeds, animal pests, and vectors of disease. Harms can be mitigated or prevented through population-scale genetic alterations that introduce beneficial traits such as disease resistance or drought tolerance (population modification), or that eliminate a harmful population (population suppression). Gene drive is a possible tool for achieving these goals. DNA mediating gene drive comprises one or more genes (the drive element) that promote their own inheritance—and any linked cargo—at rates exceeding (>50%) those of other genes. This can lead to an increase in drive element frequency even if its presence results in a fitness cost to carriers. Gene drive is attractive because it is self-amplifying and self-sustaining. One class of gene drive utilizes a Toxin-Antidote (TA) element. In nature, these often consist of two tightly linked protein-encoding genes. One encodes a toxin that is inherited by all gametes and/or progeny of a carrier; the second is an antidote that protects carriers from death. The TA element-bearing chromosome gains a relative transmission advantage by causing death of those who fail to inherit it. The first synthetic gene drive was engineered using TA logic, in Drosophila melanogaster in 2007. Recently, TA logic was also used to create the first synthetic gene drive elements in plants, in Arabidopsis thaliana. These use a Cleave and Rescue mechanism (ClvR) adapted from earlier work in Drosophila. ClvR uses DNA cleavage mediated by Cas9 and guide RNAs (gRNAs), followed by inaccurate repair, to create loss-of-function (LOF) alleles (the toxin) of endogenous versions of an essential gene. ClvR also includes a Rescue version of the essential gene recoded to prevent gene disruption (the antidote), which guarantees survival of carriers. In Drosophila, ClvR spreads because LOF alleles created in parents cause the death of progeny who lack essential gene function. In Arabidopsis this strategy was used to create gamete killers. A naturally occurring male gamete killer from rice, DUYAO-JIEYAO, consists of a two-gene protein–protein TA cassette. Modeling suggests that gamete killers such as these can bring about population modification or suppression. Interestingly, the DUYAO-JIEYAO element has undergone a substantial increase in frequency in Japonica rice populations in China over the last 50 years, demonstrating the power of such elements in nature.
An innovation in host responses to escalating genomic conflicts
34753Martí, Emiliano et al., Trends in Genetics, 2025-04-07 12:54:24.
Conflicts between selfish elements and their hosts can trigger rapid structural and regulatory changes in genomes. Chen et al. discovered a novel species-specific innovation in response to a meiotic driver in Drosophila melanogaster. Their discovery highlights a new dimension in adaptive responses to selfish elements, with broad evolutionary consequences.
Small RNA-mediated suppression of sex chromosome meiotic conflicts during Drosophila male gametogenesis
34613Vedanayagam, J., Biochemical Society Transactions, 53:281-291. 2025-02-06 11:14:24.
Meiosis is an evolutionarily conserved process in eukaryotes that ensures equal segregation of alleles and chromosomes during reproduction. Although parity in allelic transmission is the norm, selfish genes such as meiotic drivers can violate Mendel’s first law of segregation. Sex chromosome drive is a form of meiotic drive that leads to unequal segregation of sex chromosomes, resulting in sex-ratio distortion and/or sterility in the offspring. Adverse fitness effects due to sex chromosome drive trigger the evolution of suppressors to restore Mendelian segregation. However, the molecular mechanisms by which suppressors emerge and counteract meiotic drive genes remain unclear. Recent studies from Drosophila have shed light on the critical roles of small RNA-mediated post-transcriptional silencing in mitigating sex chromosome meiotic conflicts. This review highlights the recruitment of two distinct small RNA pathways to combat intragenomic conflicts during male gametogenesis and seeks to reveal the impact of molecular arms races between meiotic drivers and their suppressors in shaping genome and sex chromosome evolution.
Dissecting The Sterility Phenotype Of Drosophila Suzukii Males
34489Evrim Ağacı, The Pinnacle Gazette, 2025-02-04 17:43:46.
Groundbreaking findings on gene-edited males provide insights for pest management strategies. Researchers have made significant strides in controlling the invasive fruit pest Drosophila suzukii, commonly known as the spotted wing drosophila, utilizing innovative genetic engineering techniques to generate sterile males. This development could offer growers much-needed relief as traditional pest control methods face increasing challenges. Drosophila suzukii, native to East Asia, poses substantial threats to soft fruits, including strawberries and blueberries, by laying their eggs directly within the fruits, leading to damage and economic losses for farmers. With insecticide resistance on the rise and grower reliance on chemical management becoming less sustainable, there is urgent demand for novel pest control strategies. One promising approach is the precision-guided Sterile-Insect Technique (pgSIT), which employs CRISPR-based technology to develop sterile males efficiently. Unlike traditional Sterile-Insect Techniques, which involve labor-intensive processes like sex sorting and radiation to sterilize males, pgSIT simplifies the method and reduces costs by creating sterile males without offspring. The recent study, published on February 1, 2025, by researchers affiliated with Agragene Inc., aimed to dissect the sterility phenotype of these genetically modified males. It was found through multiple experiments and rigorous testing processes, including mating trials with wildtype females, determining the absence of mature sperm and the lack of genetic material transfer during mating.
Selfish Genetic Elements and Meiotic Drive in Drosophila
34367Nature Research Intelligence, 2025-01-28 14:04:45.
Selfish genetic elements are segments of DNA that can enhance their own transmission to the next generation, often at a cost to the organism's overall fitness. In Drosophila, or fruit flies, these elements can lead to a phenomenon known as meiotic drive, where certain alleles are preferentially passed on during reproduction, violating Mendel's law of equal segregation. Recent research has focused on understanding the mechanisms behind these selfish elements, their evolutionary implications, and how they can affect the fitness and reproductive success of their hosts.
Genetically Engineered Male Insects Shorten Their Mates’ Lifespans
34253Sneha Khedkar, The Scientist, 2025-01-13 15:13:56.
On a still night, as the air is thick with silence, the sharp, whining buzz of a mosquito shatters the calm. These blood-sucking insects that disturb people’s deep slumber are also responsible for spreading diseases such as dengue, chikungunya, malaria and Zika fever, which affect millions of people each year worldwide. Given the harmful effects of pesticides on the environment, combined with the emergence of mosquitoes resistant to pesticides, scientists are looking for alternative environment-friendly approaches for pest management. Now, researchers have developed a new population control method where male insects carrying toxic proteins can poison disease-spreading females during mating. The results, published in Nature Communications, describe a genetic biocontrol method that offers a fast and effective solution to managing pests. Such approaches are not entirely new. In the 1950s, when researchers mated female insects with radiologically sterilized males, they did not produce offsprings, reducing the next generation’s population. More recently, scientists propagated transgenes in insects that lower the fitness of future generations, resulting in decreased insect population. Although such methods are promising, they require at least one generation to take effect: Female insects may not produce offsprings, but they can continue transmitting infections. “As we’ve learned from COVID-19, reducing the spread of these diseases as quickly as possible is important to prevent epidemics,” said study author Samuel Beach, a graduate student in biologist Maciej Maselko’s lab at Macquarie University, in a press release.
Escalation of genome defense capacity enables control of an expanding meiotic driver
34251P. Chen, K.C. Pan, E.H. Park, et al., Proceedings of the National Academy of Sciences, 122. 2025-01-13 15:02:27.
From RNA interference to chromatin silencing, diverse genome defense pathways silence selfish genetic elements to safeguard genome integrity. Despite their diversity, different defense pathways share a modular organization, where numerous specificity factors identify diverse targets and common effectors silence them. In the PIWI-interacting RNA (piRNA) pathway, target RNAs are first identified by complementary base pairing with piRNAs and then silenced by PIWI-clade nucleases. Such a binary architecture allows the defense systems to be readily adaptable, where new targets can be captured via innovation of specificity factors. Thus, our current understanding of genome defense against lineage-specific selfish genes has been largely limited to specificity factor innovations, while it remains poorly understood whether other types of innovations are required. Here, we describe a new type of innovation, which escalates the genome defense capacity to control a recently expanded selfish gene in Drosophila melanogaster. Through a targeted RNAi screen for repressors of Stellate—a recently evolved meiotic driver—we identified a defense factor, Trailblazer. Trailblazer is a transcription factor that promotes the expression of two PIWI-clade nucleases, Aub and AGO3, to match Stellate in abundance. Recent innovation in the DNA-binding domain of Trailblazer enabled it to elevate Aub and AGO3 expression, thereby escalating the silencing capacity of piRNA pathway to tame expanded Stellate and safeguard fertility. As copy-number expansion is a recurrent feature of diverse selfish genes across the tree of life, we envision that augmenting the defense capacity to quantitatively match selfish genes is a repeatedly employed defense strategy in evolution.
Meiotic Drive and Speciation
34057Jeremy B. Searle and Fernando Pardo-Manuel de Villena, Annual Review of Genetics, 58:341-363. 2024-12-16 15:22:27.
Meiotic drive is the biased transmission of alleles from heterozygotes, contrary to Mendel's laws, and reflects intragenomic conflict rather than organism-level Darwinian selection. Theory has been developed as to how centromeric properties can promote female meiotic drive and how conflict between the X and Y chromosomes in males can promote male meiotic drive. There are empirical data that fit both the centromere drive and sex chromosome drive models. Sex chromosome drive may have relevance to speciation through the buildup of Dobzhansky-Muller incompatibilities involving drive and suppressor systems, studied particularly in Drosophila. Centromere drive may promote fixation of chromosomal rearrangements involving the centromere, and those fixed rearrangements may contribute to reproductive isolation, studied particularly in the house mouse. Genome-wide tests suggest that meiotic drive promotes allele fixation with regularity, and those studying the genomics of speciation need to be aware of the potential impact of such fixations on reproductive isolation. New species can originate in many different ways (including multiple factors acting together), and a substantial body of work on meiotic drive point to it being one of the processes involved.
The Meiotic Drive: Intragenomic Competition and Selection
33610I. A. Zakharov, Russian Journal of Genetics, 60:1311-1318. 2024-11-12 12:02:24.
The article considers the distribution and mechanisms of the meiotic drive as a phenomenon manifested in unequal transmission of gene alleles and/or homologous chromosomes into gametes during meiosis. The meiotic drive has been studied in the most detail in Drosophila, mice, corn, and ascomycete fungi of the genera Neurospora and Podospora. The consequence of the meiotic drive is a shift in the frequencies of alleles in the gene pool and the maintenance of nonadaptive traits in the population.
Biotechnology-enhanced genetic controls of the global pest Drosophila suzukii
33392Ying Yan, Hassan M.M. Ahmed, Ernst A. Wimmer, et al., Trends in Biotechnology, 2024-11-04 17:35:39.
Genetic control is a biological control method that introduces traits that sterilize, kill, or modify the population via intraspecific mating. Therefore, it is regarded as a species-specific and environmentally friendly management option for pest species. Spotted wing Drosophila (SWD) is an ideal insect model for studying genetic control strategies due to its pest status, laboratory-friendly biology, and close relationship to Drosophila melanogaster, which has abundant genetic resources. Different biotechnology-enhanced genetic control strategies of SWD are featured. The working schematics, control efficacies, some resistance mechanisms, and possible future development of these strategies are described. The designs and experience from these studies aid in the sustainable control of SWD and serve as essential references to other insect pests of economic or public health importance.
Improving the suppressive power of homing gene drive by co-targeting a distant-site female fertility gene
33386Faber, N.R., Xu, X., Chen, J. et al., Nature Communications, 15. 2024-11-04 17:07:21.
Gene drive technology has the potential to address major biological challenges. Well-studied homing suppression drives have been shown to be highly efficient in Anopheles mosquitoes, but for other organisms, lower rates of drive conversion prevent elimination of the target population. To tackle this issue, we propose a gene drive design that has two targets: a drive homing site where drive conversion takes place, and a distant site where cleavage induces population suppression. We model this design and find that the two-target system allows suppression to occur over a much wider range of drive conversion efficiency. Specifically, the cutting efficiency now determines the suppressive power of the drive, rather than the conversion efficiency as in standard suppression drives. We construct a two-target drive in Drosophila melanogaster and show that both components of the gene drive function successfully. However, cleavage in the embryo from maternal deposition as well as fitness costs in female drive heterozygotes both remain significant challenges for both two-target and standard suppression drives. Overall, our improved gene drive design has the potential to ease problems associated with homing suppression gene drives for many species where drive conversion is less efficient.
Pest control gets the CRISPR treatment
33376Seydel, C., Nature Biotechnology, 2024-11-04 13:45:02.
In June 2024, the St. Louis–based pest control company Agragene released genetically modified fruit flies on berry farms in California and Oregon, moving the technology out of the laboratory and into contained field testing. The trial marked a milestone for a next-generation biocontrol technology called the precision-guided sterile insect technique, or pgSIT. “The spotted wing drosophila (SWD) is the number 1 problem for any kind of strawberry, blueberry, raspberry, blackberry grower,” said Bryan Witherbee, president and CEO of Agragene. The flies have developed resistance to conventional chemical pesticides, and fruit growers suffer enormous economic losses due to the pest. “Growers are crying out for new tools,” Witherbee said. Hope is on the horizon, not only for farmers battling SWD and other agricultural pests but also for public health agencies struggling to control disease vectors. Several companies, including Agragene, are bringing biological pest control into the CRISPR era with pgSIT and other molecular tools that can specifically target the pest without killing beneficial insects, polluting the water or blanketing communities with toxic airborne chemicals. San Diego–based Synvect is applying pgSIT to disease-causing mosquitoes. Meanwhile, Oxitec, which has already successfully commercialized its “Friendly” genetic modification platform in mosquitoes, is turning its attention to crop pests.
Fluorescent-based sex-separation technique in major invasive crop pest, Drosophila suzukii
32544Junru Liu, Danny Rayes, Minzhe Yang, Omar S. Akbari, bioRxiv, 2024-10-09 12:30:05.
Insect population biocontrol methods such as the sterile insect technique (SIT), represent promising alternatives to traditional pesticide-based control applications. To use these strategies efficiently requires scalable sex separation techniques which are currently lacking in Drosophila suzukii, a prominent crop pest species. Having previously characterized a fluorescence-based sex-sorting technique in other pests, termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter), here we explore its potential applicability to Drosophila suzukii. Here, we engineer several strains of Drosophila suzukii encoding SEPARATOR constructs that allow for efficient sex selection in early larval stages.
Exploration of the potential of a boosted sterile insect technique to control fruit flies in mango orchards
30856Esther Gnilane Diouf, Thierry Brévault, Saliou Ndiaye, Cyril Piou, Pest Management Science, 2024-06-28 15:39:38.
An innovative version of the sterile insect technique (SIT) for pest control, called boosted SIT, relies on the use of sterile males coated with a biocide to control a target wild pest population of the same species. The objective of the present study was to assess the relevance of such technology to control the fruit fly Bactrocera dorsalis and fruit losses in mango orchards using. An agent-based simulation model named BOOSTIT was used to explore the reduction of fruit losses thank to sterile male fruit flies control and economic benefits according to different strategies of sterile male release. The simulation considered a landscape of 30.25 ha made up of four mango orchards. The SIT and the boosted SIT reduced fruit losses when releases were made before the mango fruiting period. According to model simulations, releases should be performed at least seven times at 2-week intervals and with a sterile/wild male ratio of at least 10:1. Considering the benefit/cost ratio (BCR), few releases should be done with a late start date. The BCR showed economic gains from the two control methods, the number of saved fruits and BCR being higher for SIT. Our simulations showed that SIT would have better results than the boosted SIT to contribute to an effective control of Bactrocera dorsalis at the scale of a small landscape. We highlight the need for laboratory studies of other types of pathogen to find a suitable one with higher incubation time and lower cost. © 2024 Society of Chemical Industry.
Transformation of meiotic drive into hybrid sterility in Drosophila
30352Jackson Bladen, Hyuck-Jin Nam, Nitin Phadnis, bioRxiv, 2024-05-21 19:05:25.
Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. Here, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies.
Comparative analysis of Wolbachia maternal transmission and localization in host ovaries
29029Michael T.J. Hague, Timothy B. Wheeler, Brandon S. Cooper, bioRxiv, 2024-03-19 13:26:24.
Acetylcholine esterase of Drosophila melanogaster: a laboratory model to explore insecticide susceptibility gene drives
28938Hernandes, N., Qi, X.M., Bhide, S., Brown, C., Camm, B.J., Baxter, S.W. and Robin, C., Pest Management Science, 2024-02-27 18:08:08.
One of the proposed applications of gene drives has been to revert pesticide resistant mutations back to the ancestral susceptible state. Insecticides that have become ineffective because of the rise of resistance could have reinvigorated utility and be used to suppress pest populations again, perhaps at lower application doses. We have created a laboratory model for susceptibility gene drives that replaces field-selected resistant variants of the acetylcholine esterase (Ace) locus of Drosophila melanogaster with ancestral susceptible variants. We constructed a CRISPR/Cas9 homing drive and found that homing occurred in many genetic backgrounds with varying efficiencies. While the drive itself could not be homozygosed, it converted resistant alleles into susceptible ones and produced recessive lethal alleles that could suppress populations. Our studies provided evidence for two distinct classes of Gene Drive Resistance (GDR): rather than being mediated by the conventional Non-Homologous End-joining (NHEJ) pathway, one seemed to involve short homologous repair and the other was defined by genetic background. Additionally, we used simulations to explore a distinct application of susceptibility drives; the use of chemicals to prevent the spread of synthetic gene drives into protected areas. Insecticide susceptibility gene drives could be useful tools to control pest insects however problems with particularities of target loci and GDR will need to be overcome for them to be effective. Furthermore, realistic patterns of pest dispersal and high insecticide exposure rates would be required if susceptibility were to be useful as a ‘safety-switch’ to prevent the unwanted spread of gene drives.
Deep orange gene editing triggers temperature-sensitive lethal phenotypes in Ceratitis capitata
28906Sollazzo, G., Nikolouli, K., Gouvi, G. et al., BMC Biotechnology, 24. 2024-02-20 15:24:38.
The Mediterranean fruit fly, Ceratitis capitata, is a significant agricultural pest managed through area-wide integrated pest management (AW-IPM) including a sterile insect technique (SIT) component. Male-only releases increase the efficiency and cost-effectiveness of SIT programs, which can be achieved through the development of genetic sexing strains (GSS). The most successful GSS developed to date is the C. capitata VIENNA 8 GSS, constructed using classical genetic approaches and an irradiation-induced translocation with two selectable markers: the white pupae (wp) and temperature-sensitive lethal (tsl) genes. However, currently used methods for selecting suitable markers and inducing translocations are stochastic and non-specific, resulting in a laborious and time-consuming process. Recent efforts have focused on identifying the gene(s) and the causal mutation(s) for suitable phenotypes, such as wp and tsl, which could be used as selectable markers for developing a generic approach for constructing GSS. The wp gene was recently identified, and efforts have been initiated to identify the tsl gene. This study investigates Ceratitis capitata deep orange (Ccdor) as a tsl candidate gene and its potential to induce tsl phenotypes. An integrated approach based on cytogenetics, genomics, bioinformatics, and gene editing was used to characterize the Ccdor. Its location was confirmed on the right arm of chromosome 5 in the putative tsl genomic region. Knock-out of Ccdor using CRISPR/Cas9-NHEJ and targeting the fourth exon resulted in lethality at mid- and late-pupal stage, while the successful application of CRISPR HDR introducing a point mutation on the sixth exon resulted in the establishment of the desired strain and two additional strains (dor 12del and dor 51dup), all of them expressing tsl phenotypes and presenting no (or minimal) fitness cost when reared at 25 °C. One of the strains exhibited complete lethality when embryos were exposed at 36 °C. Gene editing of the deep orange gene in Ceratitis capitata resulted in the establishment of temperature-sensitive lethal mutant strains. The induced mutations did not significantly affect the rearing efficiency of the strains. As deep orange is a highly conserved gene, these data suggest that it can be considered a target for the development of tsl mutations which could potentially be used to develop novel genetic sexing strains in insect pests and disease vectors.
Revolutionary Gene Drive Could Provide Solution for Agricultural Pest Control
28877María Alejandra Trujillo, Breaking News Network, 2024-02-13 17:35:22.
The crux of the gene drive hinges on the process of sex determination in medflies. The drive effectively converts genetic females into fertile XX males, which, unlike their female counterparts, are harmless to crops. This innovative approach presents a possibility for a more environmentally friendly and cost-effective strategy to control agricultural pests—particularly those within the same group as medflies. The study was helmed by Dr. Nikolai Windbichler and Dr. Angela Meccariello of Imperial's Department of Life Sciences. Their work adds to the progressive field of gene drives, a concept that has demonstrated efficacy in laboratory settings, especially with regards to controlling populations of malaria-carrying mosquitoes. However, no gene drives have yet been released into the wild. The success of this proof-of-concept study stands as a testament to the potential of gene drives as a tool to manage agricultural pests. Dr. Meccariello, co-leader of the research, emphasized the untapped potential of gene drives in tackling pest problems in agriculture. She believes that this breakthrough could open the door to a more sustainable and economical approach to pest control.
Gene driver flies and quantum finance: News from Imperial
28872Bryony Ravate, Hayley Dunning, Imperial College London, 2024-02-13 16:54:58.
Researchers have created the first gene drive for the Mediterranean fruit fly (medfly), a global agricultural pest affecting food production. The team was led by Dr Nikolai Windbichler and Dr Angela Meccariello at Imperial's Department of Life Sciences, and included researchers from the University of East Anglia and the Hebrew University of Jerusalem. Gene drives are genetic modifications that preferentially spread throughout a species, and which are designed to reduce the population. No gene drives have been released in the wild yet, but versions in malaria-carrying mosquitos have been shown to be highly effective in the lab. This success prompted the researchers to look at other pest species that could be susceptible to similar interventions. The team were able to target the process of sex determination in medflies, creating a gene drive that transforms genetic females into fertile but harmless XX males. The proof-of-concept demonstrates how gene drives can be applied to insect pests in the same group as medflies. Dr Meccariello said: “Our results demonstrate the untapped potential for gene drives to tackle agricultural pests in an environmentally friendly and economical way.”
The haplolethal gene wupA of Drosophila exhibits potential as a target for an X-poisoning gene drive
28845Clancy D. Lawler, Ana Karla Parra Nuñez, Natalia Hernandes, Soumitra Bhide, Isabelle Lohrey, Simon Baxter, Charles Robin, bioRxiv, 2024-01-28 12:54:44.
A synthetic gene drive that targets haplolethal genes on the X-chromosome can skew the sex ratio towards males. Like an ‘X-shredder’ it does not involve ‘homing’ and that has advantages including the reduction of gene drive resistance allele formation. We examine this ‘X-poisoning’ strategy by targeting four of the 11 known X-linked haplolethal/haplosterile genes of Drosophila melanogaster with CRISPR/Cas9. We find that targeting the wupA gene during spermatogenesis skews the sex ratio so fewer than 14% of progeny are daughters. That is unless we cross the mutagenic males to X^XY female flies that bear attached-X chromosomes, which reverses the inheritance of the poisoned X chromosome so that sons inherit it from their father; in which case only 2% of the progeny are sons. These sex ratio biases suggests that most of the CRISPR/Cas9 mutants we induced in the wupA gene are haplolethal but some are recessive lethal. The males generating wupA mutants do not suffer from reduced fertility rather the haplolethal mutants arrest development in the late stages of embryogenesis well after fertilized eggs have been laid. This provides a distinct advantage over genetic manipulation strategies involving sterility which can be countered by the remating of females. We also find that wupA mutants that destroy the nuclear localization signal of shorter isoforms are not haplolethal as long as the open reading frame remains intact. Like D. melanogaster wupA orthologs of D. suzukii and Anopheles mosquitos are found on X chromosomes making wupA a viable X-poisoning target in multiple species.
Wolbachia infection negatively impacts Drosophila simulans heat tolerance in a strain- and trait-specific manner
28736Liam F Ferguson, Perran A Ross, Belinda van Heerwaarden, bioRxiv, 2023-12-19 16:09:01.
The susceptibility of insects to rising temperatures has largely been measured by their ability to survive thermal extremes. However, until recently, the capacity for maternally inherited endosymbionts to influence insect heat tolerance has been overlooked. Further, the impact of heat on traits like fertility, which can decline at temperatures below the lethal thermal limit has largely been ignored. Here, we assess the impact of three Wolbachia strains (wRi, wAu, and wNo) on the survival and fertility of Drosophila simulans exposed to heat stress during development or as adults. The impact of Wolbachia infection on heat tolerance was generally small and trait/strain specific. Only the wNo infection significantly reduced survival and fertility of adult males after a heat shock. When exposed to a fluctuating heat stress during development, the wRi and wAu strains reduced egg-to-adult survival but only the wNo infection reduced male fertility. Wolbachia densities of all three strains decreased under developmental heat stress, but reductions occurred at temperatures above those that reduced fertility of the host. These findings reveal the complexity of endosymbiont-host-environment interactions and emphasise the necessity to account for endosymbionts and their effect on both survival and fertility when investigating the vulnerability of insects to climate change.
Population suppression with dominant female-lethal alleles is boosted by homing gene drive
28685Jinyu Zhu, Jingheng Chen, Yiran Liu, Xuejiao Xu, Jackson Champer, bioRxiv, 2023-12-07 10:24:25.
Methods to suppress pest insect populations using genetic constructs and repeated releases of male homozygotes have recently been shown to be an attractive alternative to older sterile insect technique based on radiation. Female-specific lethal alleles have substantially increased power, but still require large, sustained transgenic insect releases. Gene drive alleles bias their own inheritance to spread throughout populations, potentially allowing population suppression with a single, small-size release. However, suppression drives often suffer from efficiency issues, and the most well-studied type, homing drives, tend to spread without limit. In this study, we show that coupling female-specific lethal alleles with homing gene drive allowed substantial improvement in efficiency while still retaining the self-limiting nature (and thus confinement) of a lethal allele strategy. Using a mosquito model, we show the required releases sizes for population elimination in a variety of scenarios, including different density growth curves, with comparisons to other systems. Resistance alleles reduced the power of this method, but these could be overcome by targeting an essential gene with the drive while also providing rescue. A proof-of-principle demonstration of this system in Drosophila melanogaster was effective in both basing its inheritance and achieving high lethality among females that inherit the construct in the absence of antibiotic. Overall, our study shows that substantial improvements can be achieved in female-specific lethal systems for population suppression by combining them with a gene drive.
Food for thought: Assessing the consumer welfare impacts of deploying irreversible, landscape-scale biotechnologies
28628Michael S. Jones, Zachary S. Brown, Food Policy, 121. 2023-12-04 10:24:17.
Genetically engineered insects have gained attention as regionally deployed pest control technologies, with substantial applications in agriculture for combatting intractable crop pests and diseases. One potential tool is a ‘gene drive’, using CRISPR-based gene editing. In gene drive, preferentially inherited, engineered traits are spread throughout a geographic area to reduce pest populations or inhibit disease transmission, while also potentially reducing pesticide use and crop prices. But the self-perpetuating nature of gene drives presents a consequence, in that consumers could eventually be limited to only host crops grown in the presence of these genetically engineered insects. In this study, we analyze potential consumer welfare impacts of these technologies using discrete choice experiment data from a representative sample of U.S. adults, examining preferences regarding gene drive use to control spotted wing drosophila in blueberries and Asian citrus psyllid in orange juice (OJ) production. We find smaller average discounts for gene drives versus increased conventional pesticide use or genetically modified crops. Only 27% and 25% of blueberry and OJ consumers, respectively, are estimated to derive disutility from gene drives. However, gene drive disutility for these consumers is so large that elimination of non-drive options from their choice sets results in negative (blueberries) or neutral (OJ) effects to aggregate consumer welfare when weighed against gains to other consumers from reduced prices. Positive welfare effects are recovered by retaining availability of non-gene-drive products. We argue that this type of analysis will be increasingly important as landscape-level biotechnologies are deployed to address challenges to agricultural sustainability.
Use of Drosophila Transgenics to Identify Functions for Symbiont Effectors
28574Cortez, C.T., Murphy, R.O., Owens, I.M., Beckmann, J.F., Methods in Molecular Biology, 2739. 2023-11-29 14:35:56.
Wolbachia, one of the most successful and studied insect symbionts, and Drosophila, one of the most understood model insects, can be exploited as complementary tools to unravel mechanisms of insect symbiosis. Although Wolbachia itself cannot be grown axenically as clonal isolates or genetically manipulated by standard methods, its reproductive phenotypes, including cytoplasmic incompatibility (CI), have been elucidated using well-developed molecular tools and precise transgenic manipulations available for Drosophila melanogaster. Current research only scratches the surface of how Drosophila can provide a tool for understanding Wolbachia’s evolutionary success and the molecular roles of its genetic elements. Here, we briefly outline basic methodologies inherent to transgenic Drosophila systems that have already contributed significant advances in understanding CI, but may be unfamiliar to those who lack experience in Drosophila genetics. In the future, these approaches will continue providing significant insights into Wolbachia that undoubtedly will be extended to other insect symbionts and their biological capabilities.
Wolbachia endosymbionts manipulate the self-renewal and differentiation of germline stem cells to reinforce fertility of their fruit fly host
28215S. L. Russell, J. R. Castillo and W. T. Sullivan, PLOS Biology, 21:e3002335. 2023-10-24 14:41:16.
The alphaproteobacterium Wolbachia pipientis infects arthropod and nematode species worldwide, making it a key target for host biological control. Wolbachia-driven host reproductive manipulations, such as cytoplasmic incompatibility (CI), are credited for catapulting these intracellular bacteria to high frequencies in host populations. Positive, perhaps mutualistic, reproductive manipulations also increase infection frequencies, but are not well understood. Here, we identify molecular and cellular mechanisms by which Wolbachia influences the molecularly distinct processes of germline stem cell (GSC) self-renewal and differentiation. We demonstrate that wMel infection rescues the fertility of flies lacking the translational regulator mei-P26and is sufficient to sustain infertile homozygous mei-P26knockdown stocks indefinitely. Cytology revealed that wMel mitigates the impact of mei-P26 loss through restoring proper pMad, Bam, Sxl, and Orb expression. In Oregon R files with wild-type fertility, wMel infection elevates lifetime egg hatch rates. Exploring these phenotypes through dual-RNAseq quantification of eukaryotic and bacterial transcripts revealed that wMel infection rescues and offsets many gene expression changes induced by meiP26loss at the mRNA level. Overall, we show that wMel infection beneficially reinforces host fertility at mRNA, protein, and phenotypic levels, and these mechanisms may promote the emergence of mutualism and the breakdown of host reproductive manipulations.
How mosquito-controlling bacteria might also enhance insect fertility
28212Public Library of Science, Phys Org, 2023-10-24 13:51:56.
A new study reveals biological mechanisms by which a specific strain of bacteria in the Wolbachia genus might enhance the fertility of the insects it infects—with potentially important implications for mosquito-control strategies. Shelbi Russell of the University of California Santa Cruz, US, and colleagues reported these findings in the open access journal PLOS Biology on October 24th. Different strains of Wolbachia bacteria naturally infect a number of different animals worldwide, such as mosquitos, butterflies, and fruit flies. Wolbachia can manipulate the fertility of their hosts through a specific biological mechanism that aids the spread of Wolbachia within host populations. In recent years, people have harnessed that mechanism in strategies to deliberately infect mosquitos with a specific Wolbachia strain, reducing targeted mosquito populations and thereby potentially reducing the spread of human viruses carried by mosquitos, such as dengue or Zika.
Wolbachia enhances the survival ofDrosophila infected with fungal pathogens
28218J. Perlmutter, I., A. Atadurdyyeva, M. Schedl, E. and R. Unckless, L., bioRxiv, 2023.09.30.560320. 2023-10-11 14:49:32.
Wolbachia bacteria of arthropods are at the forefront of basic and translational research on multipartite host-symbiont-pathogen interactions. These microbes are vertically inherited from mother to offspring via the cytoplasm. They are the most widespread endosymbionts on the planet due to their infamous ability to manipulate the reproduction of their hosts to spread themselves in a population, and to provide a variety of fitness benefits to their hosts. Importantly, some strains of Wolbachia can inhibit viral pathogenesis within and between arthropod hosts. Mosquitoes carrying the wMel Wolbachia strain of Drosophila melanogaster have a greatly reduced capacity to spread viruses like dengue and Zika to humans. Therefore, Wolbachia are the basis of several global vector control initiatives. While significant research efforts have focused on viruses, relatively little attention has been given to Wolbachia-fungal interactions despite the ubiquity of fungal entomopathogens in nature. Here, we demonstrate that Wolbachia increase the longevity of their Drosophila melanogaster hosts when challenged with a spectrum of yeast and filamentous fungal pathogens. We find that this pattern can vary based on host genotype, sex, and fungal species. Further, Wolbachia correlates with higher fertility and reduced pathogen titers during initial fungal infection, indicating a significant fitness benefit. This study demonstrates Wolbachia’s role in diverse fungal pathogen interactions and determines that the phenotype is broad, but with several variables that influence both the presence and strength of the phenotype. These results enhance our knowledge of the strategies Wolbachia uses that likely contribute to such a high global symbiont prevalence.Importance Wolbachia bacteria of arthropods are at the forefront of global initiatives to fight arthropod-borne viruses. Despite great success in using the symbiont to fight viruses, little research has focused on Wolbachia-fungal interactions. Here, we find that Wolbachia of Drosophila melanogaster, the same strain widely used in antiviral initiatives, can also increase the longevity of flies systemically infected with a panel of yeast and filamentous fungal pathogens. The symbiont also partially increases host fertility and reduces fungal titers during early infection, indicating a significant fitness benefit. This represents a major step forward in Wolbachia research since its pathogen blocking abilities can now be extended to a broad diversity of another major branch of microbial life. This discovery may inform basic research on pathogen blocking and has potential translational applications in areas including biocontrol in agriculture.Competing Interest StatementThe authors have declared no competing interest.
Next-generation genetic sexing strain establishment in the agricultural pest Ceratitis capitata
27972S. Davydova, J. Liu, N. Kandul, P., W. E. Braswell, O. Akbari, S. and A. Meccariello, bioRxiv, 2023.09.29.560088. 2023-10-01 07:32:11.
Tephritid fruit fly pests pose an increasing threat to the agricultural industry due to their global dispersion and a highly invasive nature. Here we showcase the feasibility of an early-detection SEPARATOR sex sorting approach through using the non-model Tephritid pest, Ceratitis capitata. This system relies on female-only fluorescent marker expression, accomplished through the use of a sex-specific intron of the highly-conserved transformer gene from C. capitata and Anastrepha ludens. The herein characterized strains have 100% desired phenotype outcomes, allowing accurate male-female separation during early development. Overall, we describe an antibiotic and temperature-independent sex-sorting system in C. capitata, which, moving forward, may be implemented in other non-model Tephritid pest species. This strategy can facilitate the establishment of genetic sexing systems with endogenous elements exclusively, which, on a wider scale, can improve pest population control strategies like sterile insect technique.Competing Interest StatementO.S.A is a founder of Agragene, Inc. and Synvect, Inc. with equity interest. N.P.K is a founder of Synvect, Inc. with equity interest. The terms of this arrangement have been reviewed and approved by the University of California, San Diego in accordance with its conflict-of-interest policies. All other authors declare no competing interests
Testing a candidate meiotic drive locus identified by pool sequencing
27983D. A. Barbash, B. Jin, K. H. C. Wei and A.-M. Dion-Côté, G3 Genes|Genomes|Genetics, 2023-09-28 07:56:24.
Meiotic drive biases the transmission of alleles in heterozygous individuals, such that Mendel’s law of equal segregation is violated. Most examples of meiotic drive have been discovered over the past century based on causing sex-ratio distortion or the biased transmission of easily scoreable genetic markers that were linked to drive alleles. More recently, several approaches have been developed that attempt to identify distortions of Mendelian segregation genome-wide. Here we test a candidate female meiotic drive locus in Drosophila melanogaster, identified previously as causing a ∼54:46 distortion ratio using sequencing of large pools of backcross progeny. We inserted fluorescent visible markers near the candidate locus and scored transmission in thousands of individual progeny. We observed a small but significant deviation from the Mendelian expectation, however it was in the opposite direction to that predicted based on the original experiments. We discuss several possible causes of the discrepancy between the two approaches, noting that subtle viability effects are particularly challenging to disentangle from potential small-effect meiotic drive loci. We conclude that pool sequencing approaches remain a powerful method to identify candidate meiotic drive loci, but that genotyping of individual progeny at early developmental stages may be required for robust confirmation.
Wolbachia Induces Structural Defects Harmful to Drosophila simulans Riverside Spermiogenesis.
28142M. G. Riparbelli, A. Pratelli and G. Callaini, Cells, 12. 2023-09-21 10:31:00.
The relationship between cytoplasmic incompatibility and the obligate intracellular alphaproteobacteria Wolbachia has for a long time been reported. Although the molecular mechanisms responsible for this reproductive alteration are beginning to be understood, the effects of Wolbachia on germ cell structure and dynamics have not yet been fully investigated. We report here that the presence of Wolbachia in infected cysts of elongating spermatids is associated with major structural defects that become more evident in mature sperm. We find mitochondrial defects, an improper axoneme structure, reduced sperm numbers, and individualization failures. The large heterogeneous variety of the ultrastructural defects found in elongating spermatids and mature sperm provide the first cytological evidence for the reduced fertility associated with Wolbachia infection in Drosophila simulans males. The observed abnormalities could be the result of the mechanical stress induced by the high bacteria numbers during the process of spermatid elongation, rather than the result of the released factors affecting the proper morphogenesis of the germ cells. Moreover, high Wolbachia densities in male germ cells may not be appropriate for causing cytoplasmic incompatibility as the bacteria are harmful for spermatid differentiation, leading to abnormal sperm that is unlikely to be functional.
Female meiotic drive shapes the distribution of rare inversion polymorphisms in Drosophila melanogaster
27674S. A. Koury, Genetics, 2023-08-24 07:04:55.
In all species, new chromosomal inversions are constantly being formed by spontaneous rearrangement and then stochastically eliminated from natural populations. In Drosophila, when new chromosomal inversions overlap with a pre-existing inversion in the population, their rate of elimination becomes a function of the relative size, position, and linkage phase of the gene rearrangements. These altered dynamics result from complex meiotic behavior wherein overlapping inversions generate asymmetric dyads that cause both meiotic drive/drag and segmental aneuploidy. In this context, patterns in rare inversion polymorphisms of a natural population can be modeled from the fundamental genetic processes of forming asymmetric dyads via crossing-over in meiosis I and preferential segregation from asymmetric dyads in meiosis II. Here, a mathematical model of crossover-dependent female meiotic drive is developed and parameterized with published experimental data from Drosophila melanogaster laboratory constructs. This mechanism is demonstrated to favor smaller, distal inversions and accelerate the elimination of larger, proximal inversions. Simulated sampling experiments indicate that the paracentric inversions directly observed in natural population surveys of Drosophila melanogaster are a biased subset that both maximizes meiotic drive and minimizes the frequency of lethal zygotes caused by this cytogenetic mechanism. Incorporating this form of selection into a population genetic model accurately predicts the shift in relative size, position, and linkage phase for rare inversions found in this species. The model and analysis presented here suggest that this weak form of female meiotic drive is an important process influencing the genomic distribution of rare inversion polymorphisms.
Wolbachia has subtle effects on thermal preference in highly inbred Drosophila melanogaster which vary with life stage and environmental conditions
27676A. Strunov, C. Schoenherr and M. Kapun, Scientific Reports, 13:13792. 2023-08-23 07:09:52.
Temperature fluctuations are challenging for ectotherms which are not able to regulate body temperature by physiological means and thus have to adjust their thermal environment via behavior. However, little is yet known about whether microbial symbionts influence thermal preference (Tp) in ectotherms by modulating their physiology. Several recent studies have demonstrated substantial effects of Wolbachia infections on host Tp in different Drosophila species. These data indicate that the direction and strength of thermal preference variation is strongly dependent on host and symbiont genotypes and highly variable among studies. By employing highly controlled experiments, we investigated the impact of several environmental factors including humidity, food quality, light exposure, and experimental setup that may influence Tp measurements in adult Drosophila melanogaster flies. Additionally, we assessed the effects of Wolbachia infection on Tp of Drosophila at different developmental stages, which has not been done before. We find only subtle effects of Wolbachia on host Tp which are strongly affected by experimental variation in adult, but not during juvenile life stages. Our in-depth analyses show that environmental variation has a substantial influence on Tp which demonstrates the necessity of careful experimental design and cautious interpretations of Tp measurements together with a thorough description of the methods and equipment used to conduct behavioral studies.
Effect of the Sterile Insect Technique and Augmentative Parasitoid Releases in a Fruit Fly Suppression Program in Mango-Producing Areas of Southeast Mexico
27989J. Cancino, P. Montoya, F. O. Gálvez, C. Gálvez and P. Liedo, Insects, 14. 2023-08-22 08:09:28.
The Sterile Insect Technique (SIT), by means of sterile male releases of Anastrepha ludens (Loew), coupled with Augmentative Biological Control (ABC), by releasing the parasitoid Diachasmimorpha longicaudata (Ashmead), was evaluated in a commercial mango production area for one year. The obtained results were compared with mean fruit fly population values from two previous years without the combined use of both techniques. The treatments were: SIT + ABC, SIT, ABC, and Control, and each treatment was established in blocks of 5000 Ha separated by distances of 5–10 km. The evaluations were carried out through fruit sampling to assess percent parasitism and trapping of adult flies to obtain Flies per Trap per Day (FTD) values. The mean percentage of parasitism increased from 0.59% in the control treatment to 19.38% in the block with ABC. The FTD values decreased from ~0.129 and ~0.012 in the control block to 0.0021 in the block with SIT and ABC, representing a 98% suppression. The difference between the two periods in the control block was not significant. We conclude that the integration of both techniques resulted in an additive suppression of the pest population, supporting the use of both control techniques in an area-wide pest management context.
Wolbachia infection at least partially rescues the fertility and ovary defects of several new Drosophila melanogaster bag of marbles protein-coding mutants
27701W. Miwa and F. A. Charles, bioRxiv, 2023.03.20.532813. 2023-08-16 09:19:09.
The D. melanogaster protein coding gene bag of marbles (bam) plays a key role in early male and female reproduction by forming complexes with partner proteins to promote differentiation in gametogenesis. Like another germline gene, Sex lethal, bam genetically interacts with the endosymbiont Wolbachia, as Wolbachia rescues the reduced fertility of a bam hypomorphic mutant. Here, we explored the specificity of the bam-Wolbachia interaction by generating 22 new bam mutants, with ten mutants displaying fertility defects. Nine of these mutants trend towards rescue by the wMel Wolbachia variant, with eight statistically significant at the fertility and/or cytological level. In some cases, fertility was increased a striking 20-fold. There is no specificity between the rescue and the known binding regions of bam, suggesting wMel does not interact with one singular bam partner to rescue the reproductive phenotype. We further tested if wMel interacts with bam in a non-specific way, by increasing bam transcript levels or acting upstream in germline stem cells. A fertility assessment of a bam RNAi knockdown mutant reveals that wMel rescue is specific to functionally mutant bam alleles and we find no obvious evidence of wMel interaction with germline stem cells in bam mutants.Author Summary Reproduction in the Drosophila melanogaster fruit fly is dependent on the bag of marbles (bam) gene, which acts early in the process of generating eggs and sperm. Mutations to this gene negatively impact the fertility of the fly, causing it to be sterile or have fewer progeny. Interestingly, we find that the bacteria Wolbachia, which resides within reproductive cells across a wide range of insects, partially restores the fertility and ovary phenotype of several bam mutants of which the resultant Bam protein is altered from wildtype. The protein function of Bam is further suggested to be important by the lack of rescue for a fly that has a fertility defect due to low expression of a non-mutated bam gene. Previous work makes similar conclusions about Wolbachia with another reproductive gene, Sex lethal (Sxl), highlighting the potential for rescue of fertility mutants to occur in a similar way across different genes. An understanding of the ways in which Wolbachia can affect host reproduction provides us with context with which to frame Wolbachia’s impact on host genes, such as bam and Sxl, and consider the evolutionary implications of Wolbachia’s infection in D. melanogaster fruit flies.Competing Interest StatementThe authors have declared no competing interest.
Population suppression by release of insects carrying a dominant sterile homing gene drive targeting doublesex in Drosophila
26903C. Weizhe, G. Jialiang, L. Yiran and C. Jackson, bioRxiv, 2023.07.17.549342. 2023-07-17 11:00:13.
Gene drive alleles, which bias their own inheritance and increase in frequency, show great promise for blocking disease transmission or directly suppressing pest populations. The most common engineered drive system is the CRISPR homing drive, which converts wild-type alleles to drive alleles in the germline of drive heterozygotes by homology-directed repair after CRISPR cleavage. One successful homing drive example targets a female-specific exon in doublesex in Anopheles mosquitos, suppressing the population by inducing recessive sterility in female drive homozygotes. We found that in Drosophila melanogaster, a 3-gRNA drive disrupting the doublesex female exon resulted in a masculine phenotype and dominant female sterility. Resistance alleles formed by end-joining repair were also dominant sterile. This was likely caused by expression of male-specific transcripts in females with drive and resistance alleles, disrupting sex development. Based on this construct, we proposed a new pest suppression system called Release of Insects carrying a Dominant-sterile Drive (RIDD). This entails continuously releasing drive heterozygous males, with drive and resistance alleles causing sterility in females. The drive remains at high frequency longer than currently used dominant female-lethal alleles (RIDL) due to drive conversion in males, and drive alleles also cause sterility based on resistance, both substantial advantages. With weekly releases of drive males into a cage population with overlapping generations, our RIDD system targeting dsx reached 100% prevalence within 27 weeks, progressively reducing egg production and eventually causing total population collapse. RIDD combines the merits of homing gene drive and RIDL. It is powerful but self-limiting, unlike unconfined standard homing drives, allowing for targeted population suppression.Competing Interest StatementThe authors have declared no competing interest.
New germline Cas9 promoters show improved performance for homing gene drive
26623D. Jie, C. Weizhe, J. Xihua, X. Xuejiao, Y. Emily, Z. Ruizhi, Z. Yuqi, M. Matt, W. M. Philipp and C. Jackson, bioRxiv, 2023.07.16.549205. 2023-07-16 08:48:12.
Gene drive systems could be a viable strategy to prevent pathogen transmission or suppress vector populations by propagating drive alleles with super-Mendelian inheritance. CRISPR-based homing gene drives, perhaps the most powerful gene drive strategy, convert wild type alleles into drive alleles in heterozygotes with the help of Cas9 and gRNA. However, achieving successful outcomes with these drives often requires high performance. Specifically, it is desirable to identify Cas9 promoters that yield high drive conversion rates, minimize the formation rate of resistance alleles in both the germline and the early embryo, and limit somatic Cas9 expression. Thus far, high-performance promoters have only been discovered in Anopheles species. In Drosophila, the nanos promoter avoids leaky somatic expression, but at the cost of high embryo resistance from maternally deposited Cas9. To improve drive efficiency, we tested eleven Drosophila melanogaster germline promoters in several configurations. Some of the new promoters achieved higher drive conversion efficiency with minimal embryo resistance, but none could completely avoid somatic expression like nanos. However, such somatic expression often did not carry detectable fitness costs when the promoter-Cas9 elements supported a rescue homing drive targeting a haplolethal gene, suggesting somatic drive conversion. Based on our findings, we selected two Cas9 promoter lines for cage experiments with a 4-gRNA suppression drive. While one promoter exhibited substantial somatic effects, leading to a low drive equilibrium frequency, the other outperformed nanos, resulting in the successful suppression of the cage population. Overall, these novel Cas9 promoters hold potential advantages for homing drives in Drosophila species and may also possess valuable homologs in other organisms.Competing Interest StatementThe authors have declared no competing interest.
The evolutionary history of Drosophila simulans Y chromosomes reveals molecular signatures of resistance to sex ratio meiotic drive
26469C. Courret, D. Ogereau, C. Gilbert, A. M. Larracuente and C. Montchamp-Moreau, Mol Biol Evol, 2023-07-04 07:54:47.
The recent evolutionary history of the Y chromosome in Drosophila simulans, a worldwide species of Afrotropical origin, is closely linked to that of X-linked meiotic drivers (Paris system). The spread of the Paris drivers in natural populations has elicited the selection of drive resistant Y chromosomes. To infer the evolutionary history of the Y chromosome in relation to the Paris drive, we sequenced 21 iso-Y lines, each carrying a Y chromosome from a different location. Among them, 13 lines carry a Y chromosome that is able to counteract the effect of the drivers. Despite their very different geographical origins, all sensitive Y's are highly similar, suggesting that they share a recent common ancestor. The resistant Y chromosomes are more divergent and segregate in four distinct clusters. The phylogeny of the Y chromosome confirms that the resistant lineage predates the emergence of Paris drive. The ancestry of the resistant lineage is further supported by the examination of Y-linked sequences in the sister species of D. simulans, D. sechellia, and D. mauritiana. We also characterized the variation in repeat content among Y chromosomes and identified multiple simple satellites associated with resistance. Altogether, the molecular polymorphism allows us to infer the demographic and evolutionary history of the Y chromosome and provides new insights on the genetic basis of resistance.
Scientists are Gene-Editing Flies to Fight Crop Damage
26310E. Mullin, WIRED, 2023-06-28 07:28:35.
In greenhouses in Oregon last month, researchers with the US Department of Agriculture began testing one such approach: sterilized male flies. The gene-edited bugs, made by St. Louis–based biotech company Agragene, are meant to suppress wild fly populations. The idea is that if they were to be released into the environment, the sterilized males would mate with wild females, resulting in a fertility dead end. “We see this technology as being able to provide healthier fruit and vegetables without doing a lot of harm to the environment,” says Agragene CEO Bryan Witherbee. Scientists at the company used the DNA editing tool Crispr to knock out two essential genes in fly embryos—one involved in male reproduction and another with female development. As a result, only sterile males hatch while the females die. “You don’t want to release females into the population, because those are the ones that are doing the damage,” says Stephanie Gamez, director of research and development at Agragene.
Regulatory logic of endogenous RNAi in silencing de novo genomic conflicts
26252J. Vedanayagam, C. J. Lin, R. Papareddy, M. Nodine, A. S. Flynt, J. Wen and E. C. Lai, PLOS Genetics, 19:e1010787. 2023-06-21 07:57:17.
Although the biological utilities of endogenous RNAi (endo-RNAi) have been largely elusive, recent studies reveal its critical role in the non-model fruitfly Drosophila simulans to suppress selfish genes, whose unchecked activities can severely impair spermatogenesis. In particular, hairpin RNA (hpRNA) loci generate endo-siRNAs that suppress evolutionary novel, X-linked, meiotic drive loci. The consequences of deleting even a single hpRNA (Nmy) in males are profound, as such individuals are nearly incapable of siring male progeny. Here, comparative genomic analyses of D. simulans and D. melanogaster mutants of the core RNAi factor dcr-2 reveal a substantially expanded network of recently-emerged hpRNA-target interactions in the former species. The de novo hpRNA regulatory network in D. simulans provides insight into molecular strategies that underlie hpRNA emergence and their potential roles in sex chromosome conflict. In particular, our data support the existence of ongoing rapid evolution of Nmy/Dox-related networks, and recurrent targeting of testis HMG Box loci by hpRNAs. Importantly, the impact of the endo-RNAi network on gene expression flips the convention for regulatory networks, since we observe strong derepression of targets of the youngest hpRNAs, but only mild effects on the targets of the oldest hpRNAs. These data suggest that endo-RNAi are especially critical during incipient stages of intrinsic sex chromosome conflicts, and that continual cycles of distortion and resolution may contribute to speciation.
CRISPR/Cas9-based split homing gene drive targeting doublesex for population suppression of the global fruit pest Drosophila suzukii
25710A. K. Yadav, C. Butler, A. Yamamoto, A. A. Patil, A. L. Lloyd and M. J. Scott, Proc Natl Acad Sci U S A, 120:e2301525120. 2023-06-13 10:38:33.
Genetic-based methods offer environmentally friendly species-specific approaches for control of insect pests. One method, CRISPR homing gene drive that target genes essential for development, could provide very efficient and cost-effective control. While significant progress has been made in developing homing gene drives for mosquito disease vectors, little progress has been made with agricultural insect pests. Here, we report the development and evaluation of split homing drives that target the doublesex (dsx) gene in Drosophila suzukii, an invasive pest of soft-skinned fruits. The drive component, consisting of dsx single guide RNA and DsRed genes, was introduced into the female-specific exon of dsx, which is essential for function in females but not males. However, in most strains, hemizygous females were sterile and produced the male dsx transcript. With a modified homing drive that included an optimal splice acceptor site, hemizygous females from each of the four independent lines were fertile. High transmission rates of the DsRed gene (94 to 99%) were observed with a line that expressed Cas9 with two nuclear localization sequences from the D. suzukii nanos promoter. Mutant alleles of dsx with small in-frame deletions near the Cas9 cut site were not functional and thus would not provide resistance to drive. Finally, mathematical modeling showed that the strains could be used for suppression of lab cage populations of D. suzukii with repeated releases at relatively low release ratios (1:4). Our results indicate that the split CRISPR homing gene drive strains could potentially provide an effective means for control of D. suzukii populations.
To fight berry-busting fruit flies, researchers focus on sterilizing the bugs
25719M. Walling, KTAL News.com, 2023-06-13 09:42:56.
Paul Nelson is used to doing battle with an invasive fruit fly called the spotted wing drosophila, a pest that one year ruined more than half the berries on the Minnesota farm he and his team run. In recent years, they’ve cut their losses closer to 5%, but it’s been labor-intensive and expensive. “It’s a pest that if you’re not willing to stick the time into it, it’s going to take over your farm,” said Nelson, the head grower at Untiedt’s, a vegetable and fruit operation about an hour west of Minneapolis. Nelson and other growers may someday get a new tool as a result of research at North Carolina State University into the insects, which ruin the berries by laying their eggs in them and have been estimated to cost growers hundreds of millions of dollars annually. The researchers, using a concept called “gene drive,” manipulated the insects’ DNA so that the female offspring would be sterile, and the method they used to achieve it significantly reduced the chance that a population could rebound.
CRISPR/Cas9-based gene drive could suppress agricultural pests
25706North Carolina State University, Phys Org, 2023-06-12 10:22:37.
Researchers have developed a "homing gene drive system" based on CRISPR/Cas9 that could be used to suppress populations of Drosophila suzukii vinegar flies—so-called "spotted-wing Drosophila" that devastate soft-skinned fruit in North America, Europe and parts of South America—according to new research from North Carolina State University. The NC State researchers developed dual CRISPR gene drive systems that targeted a specific D. suzukii gene called doublesex, which is important for sexual development in the flies. CRISPR stands for "clustered regularly interspaced short palindromic repeats" and Cas9 is an enzyme that performs like molecular scissors to cut DNA. CRISPR systems are derived from bacterial immune systems that recognize and destroy viruses and other invaders, and are being developed as solutions to problems in human, plant and animal health, among other uses. Targeting the doublesex gene resulted in female sterility in numerous experiments as females were unable to lay eggs, says Max Scott, an NC State entomologist who is the corresponding author of a paper in Proceedings of the National Academy of Sciences that describes the research. "This is the first so-called homing gene drive in an agricultural pest that potentially could be used for suppression," Scott said. Gene drives can preferentially select, change or delete particular traits or characteristics and "drive" those edits through future generations, resulting in a sometimes far greater than 50% chance of passing those changes to progeny.
How aggressive interactions with biomimetic agents optimize reproductive performances in mass-reared males of the Mediterranean fruit fly
25553D. Romano, G. Benelli and C. Stefanini, Biological Cybernetics, 2023-06-09 08:59:21.
Mass-rearing procedures of insect species, often used in biological control and Sterile Insect Technique, can reduce the insects competitiveness in foraging, dispersal, and mating. The evocation of certain behaviours responsible to induce specific neuroendocrine products may restore or improve the competitiveness of mass-reared individuals. Herein, we used a mass-reared strain of Ceratitis capitata as model organism. C. capitata is a polyphagous pest exhibiting territorial displays that are closely related to its reproductive performance. We tested if the behaviour of C. capitata males could be altered by hybrid aggressive interactions with a conspecific-mimicking robotic fly, leading to more competitive individuals in subsequent mating events. Aggressive interactions with the robotic fly had a notable effect on subsequent courtship and mating sequences of males that performed longer courtship displays compared to naïve individuals. Furthermore, previous interactions with the robotic fly produced a higher mating success of males. Reproductive performances of C. capitata males may be improved by specific octopaminergic neurones activated during previous aggressive interactions with the robotic fly. This study adds fundamental knowledge on the potential role of specific neuro-behavioural processes in the ecology of tephritid species and paves the way to innovative biotechnological control methods based on robotics and bionics.
Essential and recurrent roles for hairpin RNAs in silencing de novo sex chromosome conflict in Drosophila simulans
25708J. Vedanayagam, M. Herbette, H. Mudgett, C. J. Lin, C. M. Lai, C. McDonough-Goldstein, S. Dorus, B. Loppin, C. Meiklejohn, R. Dubruille and E. C. Lai, PLoS Biol, 21:e3002136. 2023-06-08 10:27:14.
Meiotic drive loci distort the normally equal segregation of alleles, which benefits their own transmission even in the face of severe fitness costs to their host organism. However, relatively little is known about the molecular identity of meiotic drivers, their strategies of action, and mechanisms that can suppress their activity. Here, we present data from the fruitfly Drosophila simulans that address these questions. We show that a family of de novo, protamine-derived X-linked selfish genes (the Dox gene family) is silenced by a pair of newly emerged hairpin RNA (hpRNA) small interfering RNA (siRNA)-class loci, Nmy and Tmy. In the w[XD1] genetic background, knockout of nmy derepresses Dox and MDox in testes and depletes male progeny, whereas knockout of tmy causes misexpression of PDox genes and renders males sterile. Importantly, genetic interactions between nmy and tmy mutant alleles reveal that Tmy also specifically maintains male progeny for normal sex ratio. We show the Dox loci are functionally polymorphic within D. simulans, such that both nmy-associated sex ratio bias and tmy-associated sterility can be rescued by wild-type X chromosomes bearing natural deletions in different Dox family genes. Finally, using tagged transgenes of Dox and PDox2, we provide the first experimental evidence Dox family genes encode proteins that are strongly derepressed in cognate hpRNA mutants. Altogether, these studies support a model in which protamine-derived drivers and hpRNA suppressors drive repeated cycles of sex chromosome conflict and resolution that shape genome evolution and the genetic control of male gametogenesis.
Cell biology: Selfish B chromosomes unleashed by a dysfunctional chromosome segregation system
25563P. Ferree, Current Biology, 33:R431-R434. 2023-06-05 09:18:59.
A study in the fruit fly Drosophila melanogaster shows that a defective chromosome segregation system allows non-essential B chromosomes to transmit at higher-than-Mendelian frequencies.
Wolbachia protects Drosophila melanogaster against two naturally occurring and virulent viral pathogens
25211G. Bruner-Montero and F. M. Jiggins, Scientific Reports, 13:8518. 2023-05-25 13:38:46.
Wolbachia is a common endosymbiont that can protect insects against viral pathogens. However, whether the antiviral effects of Wolbachia have a significant effect on fitness remains unclear. We have investigated the interaction between Drosophila melanogaster, Wolbachia and two viruses that we recently isolated from wild flies, La Jolla virus (LJV; Iflaviridae) and Newfield virus (NFV; Permutotetraviridae). Flies infected with these viruses have increased mortality rates, and NFV partially sterilizes females. These effects on fitness were reduced in Wolbachia-infected flies, and this was associated with reduced viral titres. However, Wolbachia alone also reduces survival, and under our experimental conditions these costs of the symbiont can outweigh the benefits of antiviral protection. In contrast, protection against the sterilizing effect of NFV leads to a net benefit of Wolbachia infection after exposure to the virus. These results support the hypothesis that Wolbachia is an important defense against the natural pathogens of D. melanogaster. Furthermore, by reducing the cost of Wolbachia infection, the antiviral effects of Wolbachia may aid its invasion into populations and help explain why it is so common in nature.
Wolbachia genetically interacts with the bag of marbles germline stem cell gene in male D. melanogaster
26548M. Wenzel and C. F. Aquadro, MicroPubl Biol, 2023-05-25 08:57:31.
The bacterial endosymbiont Wolbachia manipulates reproduction of its arthropod hosts to promote its own maternal vertical transmission. In female D. melanogaster , Wolbachia has been shown to genetically interact with three key reproductive genes ( bag of marbles ( bam ) , Sex-lethal, and mei-P26) , as it rescues the reduced female fertility or fecundity phenotype seen in partial loss-of-function mutants of these genes . Here, we show that Wolbachia also partially rescues male fertility in D. melanogaster carrying a new, largely sterile bam allele when in a bam null genetic background. This finding shows that the molecular mechanism of Wolbachia 's influence on its hosts' reproduction involves interaction with genes in males as well as females, at least in D. melanogaster .
Combined actions of bacteriophage-encoded genes in Wolbachia-induced male lethality
25420H. Arai, H. Anbutsu, Y. Nishikawa, M. Kogawa, K. Ishii, M. Hosokawa, S. R. Lin, M. Ueda, M. Nakai, Y. Kunimi, T. Harumoto, D. Kageyama, H. Takeyama and M. N. Inoue, iScience, 26:106842. 2023-05-10 08:02:36.
Some Wolbachia endosymbionts induce male killing, whereby male offspring of infected females are killed during development; however, the origin and diversity of the underlying mechanisms remain unclear. In this study, we identified a 76 kbp prophage region specific to male-killing Wolbachia hosted by the moth Homona magnanima. The prophage encoded a homolog of the male-killing gene oscar in Ostrinia moths and the wmk gene that induces various toxicities in Drosophila melanogaster. Upon overexpressing these genes in D. melanogaster, wmk-1 and wmk-3 killed all males and most females, whereas Hm-oscar, wmk-2, and wmk-4 had no impact on insect survival. Strikingly, co-expression of tandemly arrayed wmk-3 and wmk-4 killed 90% of males and restored 70% of females, suggesting their conjugated functions for male-specific lethality. While the male-killing gene in the native host remains unknown, our findings highlight the role of bacteriophages in male-killing evolution and differences in male-killing mechanisms among insects.
B chromosomes reveal a female meiotic drive suppression system in Drosophila melanogaster
25112S. L. Hanlon and R. S. Hawley, Current Biology, 2023-04-27 10:03:45.
Selfish genetic elements use a myriad of mechanisms to drive their inheritance and ensure their survival into the next generation, often at a fitness cost to its host.(1)(,)(2) Although the catalog of selfish genetic elements is rapidly growing, our understanding of host drive suppression systems that counteract self-seeking behavior is lacking. Here, we demonstrate that the biased transmission of the non-essential, non-driving B chromosomes in Drosophila melanogaster can be achieved in a specific genetic background. Combining a null mutant of matrimony, a gene that encodes a female-specific meiotic regulator of Polo kinase,(3)(,)(4) with the TM3 balancer chromosome creates a driving genotype that is permissive for the biased transmission of the B chromosomes. This drive is female-specific, and both genetic components are necessary, but not individually sufficient, for permitting a strong drive of the B chromosomes. Examination of metaphase I oocytes reveals that B chromosome localization within the DNA mass is mostly abnormal when drive is the strongest, indicating a failure of the mechanism(s) responsible for the proper distribution of B chromosomes. We propose that some proteins important for proper chromosome segregation during meiosis, like Matrimony, may have an essential role as part of a meiotic drive suppression system that modulates chromosome segregation to prevent genetic elements from exploiting the inherent asymmetry of female meiosis.
Additive Effect of Releasing Sterile Insects Plus Biocontrol Agents against Fruit Fly Pests (Diptera: Tephritidae) under Confined Conditions
24928P. Montoya, E. Flores-Sarmiento, P. López, A. Ayala and J. Cancino, Insects, 14. 2023-03-30 13:54:53.
Pest control models integrating the use of the sterile insect technique (SIT) and augmentative biological control (ABC) have postulated that it is possible to obtain a synergistic effect from the joint use of these technologies. This synergistic effect is attributed to the simultaneous attack on two different biological stages of the pest (immature and adult flies), which would produce higher suppression on the pest populations. Here we evaluated the effect of the joint application of sterile males of A. ludens of the genetic sexing strain Tap-7 along with two parasitoid species at the field cage level. The parasitoids D. longicaudata and C. haywardi were used separately to determine their effect on the suppression of the fly populations. Our results showed that egg hatching percentage was different between treatments, with the highest percentage in the control treatment and a gradual reduction in the treatments with only parasitoids or only sterile males. The greatest induction of sterility (i.e., the lowest egg hatching percentage) occurred with the joint use of ABC and SIT, demonstrating that the earlier parasitism caused by each parasitoid species was important reaching high levels of sterility. Gross fertility rate decreased up to 15 and 6 times when sterile flies were combined with D. longicaudata and C. haywardi, respectively. The higher parasitism by D. longicaudata was determinant in the decrease of this parameter and had a stronger effect when combined with the SIT. We conclude that the joint use of ABC and SIT on the A. ludens population had a direct additive effect, but a synergistic effect was observed in the parameters of population dynamics throughout the periodic releases of both types of insects. This effect can be of crucial importance in the suppression or eradication of fruit fly populations, with the added advantage of the low ecological impact that characterizes both techniques.
The Wolbachia WalE1 effector alters Drosophila endocytosis
24855M. Martin and I. L. G. Newton, bioRxiv, 2023-03-27 15:30:37.
The most common intracellular bacterial infection is Wolbachia pipientis , a microbe that manipulates host reproduction and is used in control of insect vectors. Phenotypes induced by Wolbachia have been studied for decades and range from sperm-egg incompatibility to male killing. How Wolbachia alters host biology is less well understood. Previously, we characterized the first Wolbachia effector â€" WalE1, which encodes a synuclein domain at the N terminus. Purified WalE1 sediments with and bundles actin and when heterologously expressed in flies, increases Wolbachia titer in the developing oocyte. In this work, we first identify the native expression WalE1 by Wolbachia infecting both fly cells and whole animals. WalE1 appears as aggregates, separate from Wolbachia cells. We next show that WalE1 co-immunoprecipitates with the host protein Past1 and that WalE1 manipulates host endocytosis. Yeast expressing WalE1 show deficiency in uptake of FM4-64 dye, and flies harboring mutations in Past1 or overexpressing WalE1 are sensitive to AgNO (3) , a hallmark of endocytosis defects. Finally, we also show that Past1 null flies harbor more Wolbachia overall and in late egg chambers. Our results identify interactions between a Wolbachia secreted effector and a host protein and point to yet another important host cell process impinged upon by Wolbachia .
A male-killing Wolbachia endosymbiont is concealed by another endosymbiont and a nuclear suppressor
24920K. M. Richardson, P. A. Ross, B. S. Cooper, W. R. Conner, T. Schmidt and A. A. Hoffmann, PLoS Biol, 21:e3001879. 2023-03-22 13:30:17.
Bacteria that live inside the cells of insect hosts (endosymbionts) can alter the reproduction of their hosts, including the killing of male offspring (male killing, MK). MK has only been described in a few insects, but this may reflect challenges in detecting MK rather than its rarity. Here, we identify MK Wolbachia at a low frequency (around 4%) in natural populations of Drosophila pseudotakahashii. MK Wolbachia had a stable density and maternal transmission during laboratory culture, but the MK phenotype which manifested mainly at the larval stage was lost rapidly. MK Wolbachia occurred alongside a second Wolbachia strain expressing a different reproductive manipulation, cytoplasmic incompatibility (CI). A genomic analysis highlighted Wolbachia regions diverged between the 2 strains involving 17 genes, and homologs of the wmk and cif genes implicated in MK and CI were identified in the Wolbachia assembly. Doubly infected males induced CI with uninfected females but not females singly infected with CI-causing Wolbachia. A rapidly spreading dominant nuclear suppressor genetic element affecting MK was identified through backcrossing and subsequent analysis with ddRAD SNPs of the D. pseudotakahashii genome. These findings highlight the complexity of nuclear and microbial components affecting MK endosymbiont detection and dynamics in populations and the challenges of making connections between endosymbionts and the host phenotypes affected by them.
Distinct Wolbachia localization patterns in oocytes of diverse host species reveal multiple strategies of maternal transmission
24853Y. A. Radousky, M. T. J. Hague, S. Fowler, E. Paneru, A. Codina, C. Rugamas, G. Hartzog, B. S. Cooper and W. Sullivan, Genetics, 2023-03-13 15:24:48.
A broad array of endosymbionts radiate through host populations via vertical transmission, yet much remains unknown concerning the cellular basis, diversity and routes underlying this transmission strategy. Here we address these issues, by examining the cellular distributions of Wolbachia strains that diverged up to 50 million years ago in the oocytes of 18 divergent Drosophila species. This analysis revealed three Wolbachia distribution patterns: 1) a tight clustering at the posterior pole plasm (the site of germline formation); 2) a concentration at the posterior pole plasm, but with a significant bacteria population distributed throughout the oocyte; 3) and a distribution throughout the oocyte, with none or very few located at the posterior pole plasm. Examination of this latter class indicates Wolbachia accesses the posterior pole plasm during the interval between late oogenesis and the blastoderm formation. We also find that one Wolbachia strain in this class concentrates in the posterior somatic follicle cells that encompass the pole plasm of the developing oocyte. In contrast, strains in which Wolbachia concentrate at the posterior pole plasm generally exhibit no or few Wolbachia in the follicle cells associated with the pole plasm. Taken together, these studies suggest that for some Drosophila species, Wolbachia invade the germline from neighboring somatic follicle cells. Phylogenomic analysis indicates that closely related Wolbachia strains tend to exhibit similar patterns of posterior localization, suggesting that specific localization strategies are a function of Wolbachia-associated factors. Previous studies revealed that endosymbionts rely on one of two distinct routes of vertical transmission: continuous maintenance in the germline (germline-to-germline) or a more circuitous route via the soma (germline-to-soma-to-germline). Here we provide compelling evidence that Wolbachia strains infecting Drosophila species maintain the diverse arrays of cellular mechanisms necessary for both of these distinct transmission routes. This characteristic may account for its ability to infect and spread globally through a vast range of host insect species.
Assessing the hybridization potential between a hypothetical gene drive-modified Drosophila suzukii strain and non-target Drosophila species
24990J. Romeis, S. Wolf, J. Collatz, J. Enkerli and F. Widmer, IOBC-WPRS Bulletin, 163:108. 2023-03-13 14:49:23.
Genetically engineered gene drives (GD) are a potentially powerful tool to control pest insects by population suppression or even elimination. Before living GD modified insects can be released into the environment, they must pass an environmental risk assessment (ERA). A key question to be addressed is the potential acquisition of functional GD elements by nontarget species as this may lead to the loss of those species and to a disruption of the ecosystem services they provide. The main route for gene flow is through hybridization between the GD insect strain and closely related species that co-occur in the area of release. Using the invasive Drosophila suzukii as a case study, we demonstrate how the potential for hybridization can be assessed.
A male-killing gene encoded by a symbiotic virus of Drosophila
24838D. Kageyama, T. Harumoto, K. Nagamine, A. Fujiwara, T. N. Sugimoto, A. Jouraku, M. Tamura, T. K. Katoh and M. Watada, Nature Communications, 14:1357. 2023-03-13 08:49:35.
In most eukaryotes, biparentally inherited nuclear genomes and maternally inherited cytoplasmic genomes have different evolutionary interests. Strongly female-biased sex ratios that are repeatedly observed in various arthropods often result from the male-specific lethality (male-killing) induced by maternally inherited symbiotic bacteria such as Spiroplasma and Wolbachia. However, despite some plausible case reports wherein viruses are raised as male-killers, it is not well understood how viruses, having much smaller genomes than bacteria, are capable of inducing male-killing. Here we show that a maternally inherited double-stranded RNA (dsRNA) virus belonging to the family Partitiviridae (designated DbMKPV1) induces male-killing in Drosophila. DbMKPV1 localizes in the cytoplasm and possesses only four genes, i.e., one gene in each of the four genomic segments (dsRNA1−dsRNA4), in contrast to ca. 1000 or more genes possessed by Spiroplasma or Wolbachia. We also show that a protein (designated PVMKp1; 330 amino acids in size), encoded by a gene on the dsRNA4 segment, is necessary and sufficient for inducing male-killing. Our results imply that male-killing genes can be easily acquired by symbiotic viruses through reassortment and that symbiotic viruses are hidden players in arthropod evolution. We anticipate that host-manipulating genes possessed by symbiotic viruses can be utilized for controlling arthropods.
Genomic and cytogenetic analysis of the Ceratitis capitata temperature-sensitive lethal region
25470G. Sollazzo, G. Gouvi, K. Nikolouli, R. A. Aumann, H. Djambazian, M. A. Whitehead, P. Berube, S.-H. Chen, G. Tsiamis, A. C. Darby, J. Ragoussis, M. F. Schetelig and K. Bourtzis, G3-Genes Genomes Genetics, 13. 2023-03-03 08:40:56.
Genetic sexing strains (GSS) are an important tool in support of sterile insect technique (SIT) applications against insect pests and disease vectors. The yet unknown temperature-sensitive lethal (tsl) gene and the recently identified white pupae (wp) gene have been used as selectable markers in the most successful GSS developed so far, the Ceratitis capitata (medfly) VIENNA 8 GSS. The molecular identification of the tsl gene may open the way for its use as a marker for the development of GSS in other insect pests and disease vectors of SIT importance. Prior studies have already shown that the tsl gene is located on the right arm of chromosome 5, between the wp and Zw loci (tsl genomic region). In the present study, we used genomic, transcriptomic, bioinformatic, and cytogenetic approaches to characterize and analyze this genomic region in wild-type and tsl mutant medfly strains. Our results suggested the presence of 561 genes, with 322 of them carrying SNPs and/or insertion–deletion (indel) mutations in the tsl genomic region. Furthermore, comparative transcriptomic analysis indicated the presence of 32 differentially expressed genes, and bioinformatic analysis revealed the presence of 33 orthologs with a described heat-sensitive phenotype of Drosophila melanogaster in this region. These data can be used in functional genetic studies to identify the tsl gene(s) and the causal mutation(s) responsible for the temperature-sensitive lethal phenotype in medfly, and potentially additional genes causing a similar phenotype.
Effects of Wolbachia on Transposable Element Expression Vary Between Drosophila melanogaster Host Genotypes
24871A. T. Eugénio, M. S. P. Marialva and P. Beldade, Genome Biology Evolution, 15. 2023-03-03 08:07:31.
Transposable elements (TEs) are repetitive DNA sequences capable of changing position in host genomes, thereby causing mutations. TE insertions typically have deleterious effects but they can also be beneficial. Increasing evidence of the contribution of TEs to adaptive evolution further raises interest in understanding what factors impact TE activity. Based on previous studies associating the bacterial endosymbiont Wolbachia with changes in the abundance of piRNAs, a mechanism for TE repression, and to transposition of specific TEs, we hypothesized that Wolbachia infection would interfere with TE activity. We tested this hypothesis by studying the expression of 14 TEs in a panel of 25 Drosophila melanogaster host genotypes, naturally infected with Wolbachia and annotated for TE insertions. The host genotypes differed significantly in Wolbachia titers inside individual flies, with broad-sense heritability around 20%, and in the number of TE insertions, which depended greatly on TE identity. By removing Wolbachia from the target host genotypes, we generated a panel of 25 pairs of Wolbachia-positive and Wolbachia-negative lines in which we quantified transcription levels for our target TEs. We found variation in TE expression that was dependent on Wolbachia status, TE identity, and host genotype. Comparing between pairs of Wolbachia-positive and Wolbachia-negative flies, we found that Wolbachia removal affected TE expression in 21.1% of the TE-genotype combinations tested, with up to 2.3 times differences in the median level of transcript. Our data show that Wolbachia can impact TE activity in host genomes, underscoring the importance this endosymbiont can have in the generation of genetic novelty in hosts.
Ovarian Transcriptional Response to Wolbachia Infection in D. melanogaster in the Context of Between-Genotype Variation in Gene Expression
24807S. I. Frantz, C. M. Small, W. A. Cresko and N. D. Singh, G3-Genes Genomes Genetics, 2023-03-01 08:37:16.
Wolbachia is a maternally-transmitted endosymbiotic bacteria that infects a wide variety of arthropod and nematode hosts. The effects of Wolbachia on host biology are far-reaching and include changes in host gene expression. However, previous work on the host transcriptional response has generally been investigated in the context of a single host genotype. Thus, the relative effect of Wolbachia infection versus host genotype on gene expression is unknown. Here we explicitly test the relative roles of Wolbachia infection and host genotype on host gene expression by comparing the ovarian transcriptomes of four strains of D. melanogaster infected and uninfected with Wolbachia. Our data suggest that infection explains a small amount of transcriptional variation, particularly in comparison to variation in gene expression among strains. However, infection specifically affects genes related to cell cycle, translation, and metabolism. We also find enrichment of cell division and recombination processes among genes with infection-associated differential expression. Broadly, the transcriptomic changes identified in this study provide novel understanding of the relative magnitude of the effect of Wolbachia infection on gene expression in the context of host genetic variation, and also point to genes that are consistently differentially expressed in response to infection among multiple genotypes.
Next-generation CRISPR gene-drive systems using Cas12a nuclease
24783S. Sanz Juste, E. M. Okamoto, X. Feng and V. L. Del Amo, bioRxiv, 2023.02.20.529271. 2023-02-20 09:40:53.
One method for reducing the impact of vector-borne diseases is through the use of CRISPR-based gene drives, which manipulate insect populations due to their ability to rapidly propagate desired genetic traits into a target population. However, all current gene drives employ a Cas9 nuclease that is constitutively active, impeding our control over their propagation abilities and limiting the generation of novel gene drive arrangements. Yet, other nucleases such as the temperature-sensitive Cas12a have not been explored for gene drive designs. To address this, we herein present a proof-of-concept gene-drive system driven by Cas12a that can be regulated via temperature modulation. Furthermore, we combined Cas9 and Cas12a to build double gene drives capable of simultaneously spreading two independent engineered alleles. The development of Cas12a-mediated gene drives provides an innovative option for designing next-generation vector control strategies to combat disease vectors and agricultural pests.Competing Interest StatementAll authors declare no competing interests.
Expansion and loss of sperm nuclear basic protein genes in Drosophila correspond with genetic conflicts between sex chromosomes
24732C.-H. Chang, I. Mejia Natividad and H. S. Malik, eLife, 12:e85249. 2023-02-10 09:47:51.
Many animal species employ sperm nuclear basic proteins (SNBPs) or protamines to package sperm genomes tightly. SNBPs vary across animal lineages and evolve rapidly in mammals. We used a phylogenomic approach to investigate SNBP diversification in Drosophila species. We found that most SNBP genes in Drosophila melanogaster evolve under positive selection except for genes essential for male fertility. Unexpectedly, evolutionarily young SNBP genes are more likely to be critical for fertility than ancient, conserved SNBP genes. For example, CG30056 is dispensable for male fertility despite being one of three SNBP genes universally retained in Drosophila species. We found 19 independent SNBP gene amplification events that occurred preferentially on sex chromosomes. Conversely, the montium group of Drosophila species lost otherwise-conserved SNBP genes, coincident with an X-Y chromosomal fusion. Furthermore, SNBP genes that became linked to sex chromosomes via chromosomal fusions were more likely to degenerate or relocate back to autosomes. We hypothesize that autosomal SNBP genes suppress meiotic drive, whereas sex-chromosomal SNBP expansions lead to meiotic drive. X-Y fusions in the montium group render autosomal SNBPs dispensable by making X-versus-Y meiotic drive obsolete or costly. Thus, genetic conflicts between sex chromosomes may drive SNBP rapid evolution during spermatogenesis in Drosophila species.
A selfish genetic element and its suppressor causes gross damage to testes in a fly
24697S. Lyth, A. Manser, G. Hurst, T. Price and R. Verspoor, bioRxiv, 2023.02.06.527273. 2023-02-06 12:34:06.
Selfish genetic elements (SGEs), specifically X-chromosome meiotic drive (XCMD), create huge conflicts within a hosts genome and can have profound effects on fertility. Suppressors are a common evolutionary response to XCMD to negate its costs. However, whether suppressors themselves can cause negative non-target effects remains understudied. Here, we examine whether the intragenomic conflicts created by XCMD and its suppressor affects gonad morphology in Drosophila subobscura. We found significant differences in testes, seminal vesicle, and accessory gland size depending on whether a male carried a non-driving X chromosome, an XCMD, and if the XCMD was suppressed. We also found the first evidence of extreme whole-organ damage to testes that is specifically associated with a suppressor of XCMD. Unlike other studies, our evidence suggests that XCMD in D. subobscura inflicts extreme damage on male gonads. This damage is most severe if both XCMD and its suppressor are both present. While costs of suppression have importance in theoretical models, they have largely been ignored in empirical XCMD systems. Overall, this study highlights that genetic conflict, created by SGEs and their suppressors, is a potent evolutionary force that can have major impacts on gonad development and gametogenesis.Competing Interest StatementThe authors have declared no competing interest.
Assessing potential hybridization between a hypothetical gene drive-modified Drosophila suzukii and nontarget Drosophila species
24610S. Wolf, J. Collatz, J. Enkerli, F. Widmer and J. Romeis, Risk Analysis, 2023-01-24 09:02:35.
Genetically engineered gene drives (geGD) are potentially powerful tools for suppressing or even eradicating populations of pest insects. Before living geGD insects can be released into the environment, they must pass an environmental risk assessment to ensure that their release will not cause unacceptable harm to non-targeted entities of the environment. A key research question concerns the likelihood that nontarget species will acquire the functional GD elements; such acquisition could lead to reduced abundance or loss of those species and to a disruption of the ecosystem services they provide. The main route for gene flow is through hybridization between the geGD insect strain and closely related species that co-occur in the area of release and its expected dispersal. Using the invasive spotted-wing drosophila, Drosophila suzukii, as a case study, we provide a generally applicable strategy on how a combination of interspecific hybridization experiments, behavioral observations, and molecular genetic analyses can be used to assess the potential for hybridization.
Wolbachia Promotes Its Own Uptake by Host Cells
24576L. B. Nevalainen, E. M. Layton and I. L. G. Newton, Infection and Immunity, e0055722. 2023-01-17 08:49:38.
Wolbachia pipientis is an incredibly widespread bacterial symbiont of insects, present in an estimated 25 to 52% of species worldwide. Wolbachia is faithfully maternally transmitted both in a laboratory setting and in the wild. In an established infection, Wolbachia is primarily intracellular, residing within host-derived vacuoles that are associated with the endoplasmic reticulum. However, Wolbachia also frequently transfers between host species, requiring an extracellular stage to its life cycle. Indeed, Wolbachia has been moved between insect species for the precise goal of controlling populations. The use of Wolbachia in this application requires that we better understand how it initiates and establishes new infections. Here, we designed a novel method for live tracking Wolbachia cells during infection using a combination of stains and microscopy. We show that live Wolbachia cells are taken up by host cells at a much faster rate than dead Wolbachia cells, indicating that Wolbachia bacteria play a role in their own uptake and that Wolbachia colonization is not just a passive process. We also show that the host actin cytoskeleton must be intact for this to occur and that drugs that disrupt the actin cytoskeleton effectively abrogate Wolbachia uptake. The development of this live infection assay will assist in future efforts to characterize Wolbachia factors used during host infection.
Single-cell transcriptome sequencing reveals Wolbachia-mediated modification in early stages of Drosophila spermatogenesis
24466W. Dou, B. Sun, Y. Miao, D. Huang and J. Xiao, Proceedings of the Royal Society B: Biological Sciences, 290:20221963. 2023-01-11 08:36:44.
Wolbachia are the most widely distributed intracellular bacteria, and their most common effect on host phenotype is cytoplasmic incompatibility (CI). A variety of models have been proposed to decipher the molecular mechanism of CI, among which the host modification (HM) model predicts that Wolbachia effectors play an important role in sperm modification. However, owing to the complexity of spermatogenesis and testicular cell-type heterogeneity, whether Wolbachia have different effects on cells at different stages of spermatogenesis or whether these effects are linked with CI remains unknown. Therefore, we used single-cell RNA sequencing to analyse gene expression profiles in adult male Drosophila testes that were infected or uninfected by Wolbachia. We found that Wolbachia significantly affected the proportion of different types of germ cells and affected multiple metabolic pathways in germ cells. Most importantly, Wolbachia had the greatest impact on germline stem cells, resulting in dysregulated expression of genes related to DNA compaction, and Wolbachia infection also influenced the histone-to-protamine transition in the late stage of sperm development. These results support the HM model and suggest that future studies on Wolbachia-induced CI should focus on cells in the early stages of spermatogenesis.
Wolbachia endosymbionts manipulate GSC self-renewal and differentiation to enhance host fertility
24270S. L. Russell, J. R. Castillo and W. T. Sullivan, bioRxiv, 2022.12.15.520626. 2022-12-17 14:03:40.
The alphaproteobacterium Wolbachia pipientis infects thousands of arthropod and nematode species worldwide, making it a key target for host biological control. Wolbachia-driven host reproductive manipulations, such as cytoplasmic incompatibility (CI), are often credited for catapulting these intracellular bacteria to high frequencies in their host populations. Positive, perhaps mutualistic, reproductive manipulations may also increase infection frequencies, but they are not well understood on molecular, cellular, or organismal levels. Previous studies demonstrated that Wolbachia is capable of partially rescuing sex-lethal, a gene required for germline stem cell (GSC) self renewal and bag-of-marbles, a gene required for GSC differentiation. Here, we identify molecular and cellular mechanisms by which Wolbachia is able to influence molecularly distinct processes of GSC self renewal and differentiation through our discovery that the wMel strain rescues meiotic-P26 mutants. Mei-P26 is an essential translational regulator and is required for both GSC self-renewal and differentiation. We demonstrate that wMel rescues the fertility of flies lacking adequate mei-P26 dosage and function, and is sufficient to sustain infertile homozygous mei-P26 hypomorphic stocks indefinitely. Cytology revealed that wMel infection mitigates the impact of mei-P26 loss on both germline stem cell maintenance and cyst differentiation through restoring proper pMad, Bam, Sxl, and Orb expression. Rescue in males, amplification of dominant negative effects, and multiallelic rescue suggest that wMel either directly or indirectly replaces Mei-P26 function. Even in wild-type individuals, wMel infection elevates lifetime egg lay and hatch rates. Over time, the beneficial fertility reinforcement mechanisms described here may promote the emergence of mutualism and the breakdown of CI.HighlightsThe wMel strain of Wolbachia restores fertility in females and males deficient for the essential translational regulator meiotic-P26Mei-P26’s germline maintenance and oocyte cyst differentiation functions are genetically rescued by wMel infectionPerturbed pMad, Sxl, Bam, and Orb expression are mitigated by wMel infectionwMel infection elevates lifetime egg lay and hatch rates in wild-type fliesCompeting Interest StatementThe authors have declared no competing interest.
Deregulation of Y-linked protamine-like genes in sex chromosome-biased spermatid demise
24124J. I. Park, G. W. Bell and Y. M. Yamashita, bioRxiv, 2022-12-05 08:57:46.
Meiotic drive is a phenomenon wherein a genetic element achieves a higher rate of transmission than dictated by Mendelian segregation (1-3). One proposed mechanism for meiotic drivers to achieve biased transmission is by sabotaging essential processes of gametogenesis (e.g. spermatogenesis), leading to demise of gametes that contain their opponents (1). Studies in D. simulans have recently found that a set of meiotic driver genes contain a sequence homologous to protamines (4, 5), critical proteins that package sperm chromatin (6-8). However, the underlying mechanisms of drive and the relevance of protamine-like sequences in meiotic drive remain unknown. While studying the function of Modulo, the homolog of Nucleolin in Drosophila melanogaster (9, 10), we unexpectedly discovered Y-linked protamine genes function as a meiotic driver: we found that modulo mutant's known sterility is caused by deregulation of the autosomal protamine-like gene (Mst77F) and its Y chromosome-linked homolog (Mst77Y). Modulo regulates these genes at the step of polyadenylation of the transcripts. We show that Mst77Y likely acts as a dominant-negative form of Mst77F, interfering with the process of histone-to-protamine transition, leading to nuclear decompaction. Overexpression of Mst77Y in a wild-type background is sufficient to cause nuclear decompaction and results in the biased demise of X chromosome-bearing sperm. We propose that dominant-negative protamine variants may be a common strategy found in male meiotic drive and may explain known rapid divergence of protamine genes.Competing Interest StatementThe authors have declared no competing interest.
Modeling-informed Engineered Genetic Incompatibility strategies to overcome resistance in the invasive Drosophila suzukii
28350A. Sychla, N. R. Feltman, W. D. Hutchison and M. J. Smanski, Frontiers in Insect Science, 2. 2022-11-22 10:46:03.
Engineered Genetic Incompatibility (EGI) is an engineered extreme underdominance genetic system wherein hybrid animals are not viable, functioning as a synthetic speciation event. There are several strategies in which EGI could be leveraged for genetic biocontrol of pest populations. We used an agent-based model of Drosophila suzukii (Spotted Wing Drosophila) to determine how EGI would fare with high rates of endemic genetic resistance alleles. We discovered a surprising failure mode wherein field-generated females convert an incompatible male release program into a population replacement gene drive. Local suppression could still be attained in two seasons by tailoring the release strategy to take advantage of this effect, or alternatively in one season by altering the genetic design of release agents. We show in this work that data from modeling can be utilized to recognize unexpected emergent phenomena and a priori inform genetic biocontrol treatment design to increase efficacy.
Hidden endosymbionts: A male-killer concealed by another endosymbiont and a nuclear suppressor
23793K. M. Richardson, P. A. Ross, B. S. Cooper, W. R. Conner, T. Schmidt and A. A. Hoffmann, bioRxiv, 2022.10.19.512817. 2022-10-22 06:41:08.
Maternally transmitted endosymbiotic bacteria that cause male killing (MK) have only been described from a few insects, but this may reflect challenges in their detection rather than a rarity of MK. Here we identify MK Wolbachia in populations of Drosophila pseudotakahashii, present at a low frequency (around 4%) in natural populations and previously undetected due to a different fixed Wolbachia strain in this species expressing a different reproductive manipulation, cytoplasmic incompatibility (CI). The MK phenotype was eliminated after tetracycline treatment that removed Wolbachia. Molecular analyses indicated the MK phenotype to be expressed when a second Wolbachia strain was present alongside the CI Wolbachia. A genomic analysis highlighted Wolbachia regions diverged between the strains involving 17 genes and also identified the Wolbachia as representing an outgroup to a clade of Wolbachia infecting melanogaster-group species, including wRi-like and wMel-like strains. Doubly infected males induced CI with uninfected females but not females singly infected with CI-causing Wolbachia. The MK phenotype manifested at the larval stage and was transmitted maternally at a high fidelity but with occasional loss of the MK Wolbachia strain. A rapidly spreading dominant nuclear suppressor genetic element affecting MK was identified through backcrossing and subsequent analysis with ddRAD SNPs of the D. pseudotakahashii genome. These findings highlight the complexity of nuclear and microbial components affecting MK endosymbiont detection and dynamics in populations, and the challenges of making connections between endosymbionts and the host phenotypes affected by them.Competing Interest StatementThe authors have declared no competing interest.
Mitotic exchange in female germline stem cells is the major source of Sex Ratio chromosome recombination in Drosophila pseudoobscura
23719S. Koury, G3 Genes|Genomes|Genetics, 2022-10-04 06:48:20.
Sex Ratio chromosomes in Drosophila pseudoobscura are selfish X chromosome variants associated with three non-overlapping inversions. In the male germline, Sex Ratio chromosomes distort segregation of X and Y chromosomes (99:1), thereby skewing progeny sex ratio. In the female germline, segregation of Sex Ratio chromosomes is mendelian (50:50), but non-overlapping inversions strongly suppress recombination establishing a 26 Megabase haplotype (constituting ∼20% of the haploid genome). Rare crossover events located between non-overlapping inversions can disrupt this haplotype, and recombinants have sometimes been found in natural populations. We recently reported on the first lab-generated Sex Ratio recombinants occurring at a rate of 0.0012 crossovers per female meiosis. An improved experimental design presented here reveals these recombination events were at least 4-fold more frequent than previously estimated. Furthermore, recombination events were strongly clustered, indicating the majority arose from mitotic exchange in female germline stem cells and not from meiotic crossing-over in primary oocytes. Finally, asymmetric recovery of complementary recombinants was consistent with unequal exchange causing the recombination-induced viability defects. Incorporating these experimental results into population models for Sex Ratio chromosome evolution provided a substantially better fit to natural population frequencies and allowed maintenance of the highly differentiated 26 Megabase Sex Ratio haplotype without invoking strong epistatic selection. This study provides the first estimate of spontaneous mitotic exchange for naturally-occurring chromosomes in Drosophila female germline stem cells, reveals a much higher Sex Ratio chromosome recombination rate, and develops a mathematical model that accurately predicts the rarity of recombinant Sex Ratio chromosomes in natural populations.
Wolbachia action in the sperm produces developmentally deferred chromosome segregation defects during the Drosophila mid-blastula transition
23615B. Warecki, S. W. A. Titen, M. S. Alam, G. Vega, N. Lemseffer, K. Hug, et al., eLife, 11:e81292. 2022-09-23 09:36:01.
Wolbachia, a vertically transmitted endosymbiont infecting many insects, spreads rapidly through uninfected populations by a mechanism known as cytoplasmic incompatibility (CI). In CI, a paternally delivered modification of the sperm leads to chromatin defects and lethality during and after the first mitosis of embryonic development in multiple species. However, whether CI-induced defects in later stage embryos are a consequence of the first division errors or caused by independent defects remains unresolved. To address this question, we focused on ~1/3 of embryos from CI crosses in Drosophila simulans that develop apparently normally through the first and subsequent pre-blastoderm divisions before exhibiting mitotic errors during the mid-blastula transition and gastrulation. We performed single embryo PCR and whole genome sequencing to find a large percentage of these developed CI-derived embryos bypass the first division defect. Using fluorescence in situ hybridization, we find increased chromosome segregation errors in gastrulating CI-derived embryos that had avoided the first division defect. Thus, Wolbachia action in the sperm induces developmentally deferred defects that are not a consequence of the first division errors. Like the immediate defect, the delayed defect is rescued through crosses to infected females. These studies inform current models on the molecular and cellular basis of CI.
Fitness effects of CRISPR endonucleases in Drosophila melanogaster populations
23673A. M. Langmüller, J. Champer, S. Lapinska, L. Xie, M. Metzloff, S. E. Champer, J. Liu, Y. Xu, J. Du, A. G. Clark and P. W. Messer, eLife, 11:e71809. 2022-09-22 08:22:04.
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 provides a highly efficient and flexible genome editing technology with numerous potential applications ranging from gene therapy to population control. Some proposed applications involve the integration of CRISPR/Cas9 endonucleases into an organism’s genome, which raises questions about potentially harmful effects to the transgenic individuals. One example for which this is particularly relevant are CRISPR-based gene drives conceived for the genetic alteration of entire populations. The performance of such drives can strongly depend on fitness costs experienced by drive carriers, yet relatively little is known about the magnitude and causes of these costs. Here, we assess the fitness effects of genomic CRISPR/Cas9 expression in Drosophila melanogaster cage populations by tracking allele frequencies of four different transgenic constructs that allow us to disentangle ‘direct’ fitness costs due to the integration, expression, and target-site activity of Cas9, from fitness costs due to potential off-target cleavage. Using a maximum likelihood framework, we find that a model with no direct fitness costs but moderate costs due to off-target effects fits our cage data best. Consistent with this, we do not observe fitness costs for a construct with Cas9HF1, a high-fidelity version of Cas9. We further demonstrate that using Cas9HF1 instead of standard Cas9 in a homing drive achieves similar drive conversion efficiency. These results suggest that gene drives should be designed with high-fidelity endonucleases and may have implications for other applications that involve genomic integration of CRISPR endonucleases.
Quality control traceability during the packing and release process of Ceratitis capitata for sterile insect technique
23621Y. Contreras-Navarro, H. Luis-Alvarez, G. García-Coapio, R. Hernández, S. Flores and P. Montoya, Journal of Applied Entomology, 2022-09-13 14:29:43.
Abstract In programmes applying the sterile insect technique (SIT), the quality of insects deployed in the field determines the success in preventing, suppressing, containing or eradicating the pest population. In the fruit fly emergence and release facility (ERF) of the Moscamed Program in Mexico, irradiated pupae of Ceratitis capitata are packed in Mexico-type towers, and key adult quality parameters, such as emergence, fliers and survival, are determined throughout the packing, handling and release process. However, different methodologies are used to estimate the percentage of fliers in the different stages of the process, raising doubts of whether observed differences are due to the effect of each stage or to the methodology used. With this in mind, we developed an alternative called ?Adult Flier device? (=AF-device) to evaluate the adult flier parameter following a critical evaluation path of five steps: (1) upon arrival at ERF, (2) post-packing, (3) post-holding, (4) post-chilling and (5) post-release, where adult fliers and survival under stress were evaluated. We also compared the current methodologies for the estimation of ?absolute fliers? available in different operating manuals. Our results suggest that the AF-device allows reliable traceability of sterile insect quality parameters throughout the packing and release process, since no significant differences were observed with the control treatments. In the chilling stage, the five methodologies tested were equivalent, but the AF-device was less time-consuming and required less manpower and biological material than the other methodological options. Our results demonstrate that the use of the AF-device can be a feasible, versatile, innovative and efficient alternative to evaluate quality control parameters throughout the process of packing and releasing sterile insects, providing reliable results in a timely manner with less hand labour using minimal biological material.
Hoisted with his own petard: How sex-ratio meiotic drive in Drosophila affinis creates resistance alleles that limit its spread
23471W. J. Ma, E. M. Knoles, K. B. Patch, M. M. Shoaib and R. L. Unckless, J Evol Biol, 2022-08-23 07:13:52.
Meiotic drivers are selfish genetic elements that tinker with gametogenesis to bias their own transmission into the next generation of offspring. Such tinkering can have significant consequences on gametogenesis and end up hampering the spread of the driver. In Drosophila affinis, sex-ratio meiotic drive is caused by an X-linked complex that, when in males with a susceptible Y chromosome, results in broods that are typically more than 95% female. Interestingly, D. affinis males lacking a Y chromosome (XO) are fertile and males with the meiotic drive X and no Y produce only sons-effectively reversing the sex-ratio effect. Here, we show that meiotic drive dramatically increases the rate of nondisjunction of the Y chromosome (at least 750X), meaning that the driver is creating resistant alleles through the process of driving. We then model how the O might influence the spread, dynamics and equilibrium of the sex-ratio X chromosome. We find that the O can prevent the spread or reduce the equilibrium frequency of the sex-ratio X chromosome, and it can even lead to oscillations in frequency. Finally, with reasonable parameters, the O is unlikely to lead to the loss of the Y chromosome, but we discuss how it might lead to sex-chromosome turnover indirectly.
CRISPR, an eco-friendly technology, may detect crop pests
23460W. Adam, list23, 2022-08-22 09:16:51.
Drosophila suzukii, an invading insect pest, is a threat to agricultural yields, especially to the production of fruits such as strawberries, cherries, plums, and grapes in western countries. Until now, control measures to stop the spread of D. suzukii have been inadequate. A research published in GEN Biotechnology (Precision Guided Sterile Males Suppress Populations of an Invasive Crop Pest) describes the development of a programmable CRISPR-based technique that might, if implemented at large in the wild, eliminate fertile male D. suzukii, effectively, specifically, and safely controlling this pest population. The team at the University of California, San Diego (UCSD) implemented a temperature-inducible, precision-guided, sterile insect technique (pgSIT), described by the team in an earlier investigation, to breed infertile but fit D. suzukii males with modest shorter lifespans. Through empirical experimentation and mathematical modeling, the researchers demonstrated that repeated release of sterilized males can rapidly and successfully eliminate D. suzukii populations.
Comparative Ubiquitome Analysis Reveals Deubiquitinating Effects Induced by Wolbachia Infection in Drosophila melanogaster
23489Q. Zong, B. Mao, H. B. Zhang, B. Wang, W. J. Yu, Z. W. Wang and Y. F. Wang, International Journal Molecular Science, 23. 2022-08-21 07:14:27.
The endosymbiotic Wolbachia bacteria frequently cause cytoplasmic incompatibility (CI) in their insect hosts, where Wolbachia-infected males cross with uninfected females, leading to no or fewer progenies, indicating a paternal modification by Wolbachia. Recent studies have identified a Wolbachia protein, CidB, containing a DUB (deubiquitylating enzyme) domain, which can be loaded into host sperm nuclei and involved in CI, though the DUB activity is not necessary for CI in Drosophila melanogaster. To investigate whether and how Wolbachia affect protein ubiquitination in testes of male hosts and are thus involved in male fertility, we compared the protein and ubiquitinated protein expressions in D. melanogaster testes with and without Wolbachia. A total of 643 differentially expressed proteins (DEPs) and 309 differentially expressed ubiquitinated proteins (DEUPs) were identified to have at least a 1.5-fold change with a p-value of <0.05. Many DEPs were enriched in metabolic pathway, ribosome, RNA transport, and post-translational protein modification pathways. Many DEUPs were involved in metabolism, ribosome, and proteasome pathways. Notably, 98.1% DEUPs were downregulated in the presence of Wolbachia. Four genes coding for DEUPs in ubiquitin proteasome pathways were knocked down, respectively, in Wolbachia-free fly testes. Among them, Rpn6 and Rpn7 knockdown caused male sterility, with no mature sperm in seminal vesicles. These results reveal deubiquitylating effects induced by Wolbachia infection, suggesting that Wolbachia can widely deubiquitinate proteins that have crucial functions in male fertility of their hosts, but are not involved in CI. Our data provide new insights into the regulatory mechanisms of endosymbiont/host interactions and male fertility.
Precision Guided Sterile Males Suppress Populations of an Invasive Crop Pest
23453N. P. Kandul, J. Liu, A. Buchman, I. C. Shriner, R. M. Corder, N. Warsinger-Pepe, T. Yang, A. K. Yadav, M. J. Scott, J. M. Marshall and O. S. Akbari, GEN Biotechnology, 1:372-385. 2022-08-18 10:24:32.
The Drosophila suzukii invasion of western countries has created an immense agricultural and economic threat to crop production. Despite many attempts to suppress its population, D. suzukii continues to destroy soft-flesh fruits. Precision guided sterile insect technique (pgSIT) utilizes the accuracy of programmable CRISPR gene targeting to generate sterilized males that can be deployed to suppress populations. Here, we generate pgSIT in D. suzukii and empirically and mathematically demonstrate that sterilized males are fit, competitive, and can eliminate populations of D. suzukii. Altogether, we describe an efficient way to generate sterile D. suzukii for release and safe effective population suppression.
CRISPR-based technology targets global crop pest
23449University of California - San Diego, Phys Org, 2022-08-18 10:05:07.
Applying new CRISPR-based technology to a broad agricultural need, researchers at the University of California San Diego have set their aims on a worldwide pest known to decimate valuable food crops. Nikolay Kandul, Omar Akbari and their colleagues first demonstrated the precision-guided sterile insect technique, or pgSIT, in Drosophila melanogaster, the common fruit fly, in 2019. The technology, later adapted to mosquitoes, uses programmable CRISPR techniques to edit key genes that control sex determination and fertility. Under the new system, pgSIT-developed insect eggs are deployed into a targeted population and only sterile males hatch, resulting in a fertility dead end for that species. Kandul, Akbari and their colleagues have now adapted the technology for use in Drosophila suzukii, an invasive fruit fly (also known as the spotted-wing drosophila) responsible for millions of dollars in crop damage. The advancement is described in the journal GEN Biotechnology.
Effect of Wolbachia Infection and Adult Food on the Sexual Signaling of Males of the Mediterranean Fruit Fly Ceratitis capitata
23487G. A. Kyritsis, P. Koskinioti, K. Bourtzis and N. T. Papadopoulos, Insects, 13. 2022-08-17 07:10:32.
Sexual signaling is a fundamental component of sexual behavior of Ceratitis capitata that highly determines males' mating success. Nutritional status and age are dominant factors known to affect males' signaling performance and define the female decision to accept a male as a sexual partner. Wolbachia pipientis, a widespread endosymbiotic bacterium of insects and other arthropods, exerts several biological effects on its hosts. However, the effects of Wolbachia infection on the sexual behavior of medfly and the interaction between Wolbachia infection and adult food remain unexplored. This study was conducted to determine the effects of Wolbachia on sexual signaling of protein-fed and protein-deprived males. Our findings demonstrate that: (a) Wolbachia infection reduced male sexual signaling rates in both food regimes; (b) the negative effect of Wolbachia infection was more pronounced on protein-fed than protein-deprived males, and it was higher at younger ages, indicating that the bacterium regulates male sexual maturity; (c) Wolbachia infection alters the daily pattern of sexual signaling; and (d) protein deprivation bears significant descent on sexual signaling frequency of the uninfected males, whereas no difference was observed for the Wolbachia-infected males. The impact of our findings on the implementation of Incompatible Insect Technique (IIT) or the combined SIT/IIT towards controlling insect pests is discussed.
“Selfish Genetic Elements” – Supergene Wreaks Havoc in a Genome
23302University of Rochester, SciTechDaily, 2022-07-25 07:37:40.
“Selfish genetic elements” litter the human genome. They do not seem to benefit their hosts but instead seek only to propagate themselves. These selfish genetic elements can wreak havoc. For example, they can distort sex ratios, impair fertility, cause harmful mutations, and even potentially cause population extinction. Biologists have for the first time used population genomics to shed light on the evolution and consequences of a selfish genetic element known as Segregation Distorter (SD). These researchers at the University of Rochester, include Amanda Larracuente, an associate professor of biology, and Daven Presgraves, a University Dean’s Professor of Biology. In a paper published recently in the journal eLife, the scientists report that SD has caused dramatic changes in chromosome organization and genetic diversity.
What can we learn from selfish loci that break Mendel’s law?
23349S. E. Zanders, PLOS Biology, 20:e3001700. 2022-07-19 07:31:24.
Mendel’s law of segregation provides a critical foundation for genetic inquiry It is not, however, without exceptions Historically, 2 such exceptions (sex chromosome linkage and chromosome missegregation in meiosis) were used by Drosophila geneticists to help demonstrate that genes are carried on chromosomes Looking forward, modern geneticists interested in understanding the mechanisms of heredity have much to learn from additional exceptions to Mendel’s law In particular, selfish genes that break Mendel’s law of segregation to gain a transmission advantage into the next generation are likely to be oversized contributors to shaping the process of sexual reproduction These selfish genes exploit reproduction such that a given selfish locus is transmitted to more than half of the offspring produced by an organism There are a variety of selfish DNAs, but here I will focus on transposable elements and drive loci as examples Transposable elements can generate novel copies of themselves using copy and paste or cut and paste mechanisms Importantly, transposable elements are selected to mobilize in the germline as that allows new copies to be passed on to subsequent generations Drive loci preferentially bias their own transmission such that a driver+ /driver− heterozygote will pass the driver+ allele to more than half of its viable progeny Drivers are diverse and can act during meiosis, gametogenesis, or post-fertilization Both transposable elements and drivers are found throughout eukaryotes, including humans
Hoisted with his own petard: how sex-ratio meiotic drive in <em>Drosophila affinis</em> creates resistance alleles that limit its spread
23231W.-J. Ma, E. M. Knoles, K. B. Patch, M. M. Shoaib and R. L. Unckless, bioRxiv, 2022.02.14.480432. 2022-06-19 06:28:31.
Meiotic drivers are selfish genetic elements that tinker with gametogenesis to bias their own transmission into the next generation of offspring. Such tinkering can have significant consequences on gametogenesis and end up hampering the spread of the driver. In Drosophila affinis, sex-ratio meiotic drive is caused by an X-linked complex that, when in males with a susceptible Y chromosome, results in broods that are typically more than 95% female. Interestingly, D. affinis males lacking a Y chromosome (XO) are fertile and males with the meiotic drive X and no Y produce only sons - effectively reversing the sex-ratio effect. Here, we show that meiotic drive dramatically increases the rate of nondisjunction of the Y chromosome (at least 750X), meaning that the driver is creating resistant alleles through the process of driving. We then model how the O might influence the spread, dynamics and equilibrium of the sex-ratio X chromosome. We find that the O can prevent the spread or reduce the equilibrium frequency of the sex-ratio X chromosome and it can even lead to oscillations in frequency. Finally, with reasonable parameters, the O is unlikely to lead to the loss of the Y chromosome, but we discuss how it might lead to sex-chromosome turnover indirectly.Competing Interest StatementThe authors have declared no competing interest.
Male-killing-associated bacteriophage WO identified from comparisons of Wolbachia endosymbionts of Homona magnanima
22901H. Arai, H. Anbutsu, Y. Nishikawa, M. Kogawa, K. Ishii, M. Hosokawa, S.-R. Lin, M. Ueda, M. Nakai, Y. Kunimi, T. Harumoto, D. Kageyama, H. Takeyama and M. N. Inoue, bioRxiv, 2022-06-13 06:22:33.
The origin and mechanism of male-killing, an advantageous strategy employed by maternally transmitted symbionts such as Wolbachia, remain unclear. We compared genomes of four Wolbachia strains derived from Homona magnanima, a male-killing strain wHm-t (1.5 Mb), and three non-male-killing strains, wHm-a (1.1 Mb), wHm-b (1.3 Mb), and wHm-c (1.4 Mb). A wHm-t-specific 76-kbp prophage region harboured two tandemly arrayed WO-mediated killing (wmk) gene homologs (wmk-1/wmk-2 and wmk-3/wmk-4). Of these, wmk-1 or wmk-3 killed almost all Drosophila melanogaster individuals when transgenically overexpressed. Dual expression of wmk-3 and wmk-4 killed all males and rescued females. We propose a novel hypothesis wherein horizontally transmitted proto-Wolbachia with a single wmk killed both sexes, and tandem duplication of wmk allowed an evolutionary transition to a vertically transmitted symbiont, causing male-killing. Our study highlights the bacteriophage as a critical driver of the evolution of male-killing and argues for a conserved male-killing mechanism in diverse insects.Competing Interest StatementThe authors have declared no competing interest.
A nickase Cas9 gene-drive system promotes super-Mendelian inheritance in Drosophila
22584V. L. Del Amo, S. S. Juste and V. M. Gantz, Cell Rep, 39:110843. 2022-05-24 09:32:51.
CRISPR-based gene-drives have been proposed for managing insect populations, including disease-transmitting mosquitoes, due to their ability to bias their inheritance toward super-Mendelian rates (>50%). Current technologies use a Cas9 that introduces DNA double-strand breaks into the opposing wild-type allele to replace it with a copy of the gene-drive allele via DNA homology-directed repair. However, the use of different Cas9 versions is unexplored, and alternative approaches could increase the available toolkit for gene-drive designs. Here, we report a gene-drive that relies on Cas9 nickases that generate staggered paired nicks in DNA to propagate the engineered gene-drive cassette. We show that generating 5' overhangs in the system yields efficient allelic conversion. The nickase gene-drive arrangement produces large, stereotyped deletions that are advantageous to eliminate viable animals carrying small mutations when targeting essential genes. Our nickase approach should expand the repertoire for gene-drive arrangements aimed at applications in mosquitoes and beyond.
Intronic gRNAs for the Construction of Minimal Gene Drive Systems
22478A. Nash, P. Capriotti, A. Hoermann, P. A. Papathanos and N. Windbichler, Frontiers in Bioengineering and Biotechnology, 10. 2022-05-12 07:00:08.
Gene drives are promising tools for the genetic control of insect vector or pest populations. CRISPR-based gene drives are generally highly complex synthetic constructs consisting of multiple transgenes and their respective regulatory elements. This complicates the generation of new gene drives and the testing of the behavior of their constituent functional modules. Here, we explored the minimal genetic components needed to constitute autonomous gene drives in Drosophila melanogaster. We first designed intronic gRNAs that can be located directly within coding transgene sequences and tested their functions in cell lines. We then integrated a Cas9 open reading frame hosting such an intronic gRNA within the Drosophila rcd-1r locus that drives the expression in the male and female germlines. We showed that upon removal of the fluorescent transformation marker, the rcd-1rd allele supports efficient gene drive. We assessed the propensity of this driver, designed to be neutral with regards to fitness and host gene function, to propagate in caged fly populations. Because of their simplicity, such integral gene drives could enable the modularization of drive and effector functions. We also discussed the possible biosafety implications of minimal and possibly recoded gene drives.
The fate of a suppressed X-linked meiotic driver: experimental evolution in Drosophila simulans
22676H. Bastide, D. Ogereau, C. Montchamp-Moreau and P. R. Gérard, Chromosome Research, 2022-04-30 07:53:46.
Sex-ratio (SR) meiotic drivers are X-linked selfish genetic elements that promote their own transmission by preventing the production of Y-bearing sperm, which usually lowers male fertility. The spread of SR drivers in populations is expected to trigger the evolution of unlinked drive suppressors, a theoretically predicted co-evolution that has been observed in nature. Once completely suppressed, the drivers are expected either to decline if they still affect the fitness of their carriers, or to evolve randomly and possibly get fixed if the suppressors eliminate their deleterious effects. To explore this issue, we used the Paris sex-ratio system of Drosophila simulans in which drive results from the joint effect of two elements on the X chromosome: a segmental duplication and a deficient allele of the HP1D2 gene. We set up six experimental populations starting with 2/3 of X chromosomes carrying both elements (X(SR)) in a fully suppressing background. We let them evolve independently during almost a hundred generations under strong sexual competition, a condition known to cause the rapid disappearance of unsuppressed Paris X(SR) in previous experimental populations. In our study, the fate of X(SR) chromosomes varied among populations, from extinction to their maintenance at a frequency close to the starting one. While the reasons for these variable outcomes are still to be explored, our results show that complete suppression can prevent the demise of an otherwise deleterious X(SR) chromosome, turning a genetic conflict into cooperation between unlinked loci. Observations in natural populations suggest a contrasting fate of the two elements: disappearance of the duplication and maintenance of deficient HP1D2 alleles.
A homing suppression gene drive with multiplexed gRNAs maintains high drive conversion efficiency and avoids functional resistance alleles
22572E. Yang, M. Metzloff, A. M. Langmuller, X. J. Xu, A. G. Clark, P. W. Messer and J. Champer, G3-Genes Genomes Genetics, 13. 2022-04-08 09:02:04.
Gene drives are engineered alleles that can bias inheritance in their favor, allowing them to spread throughout a population. They could potentially be used to modify or suppress pest populations, such as mosquitoes that spread diseases. CRISPR/Cas9 homing drives, which copy themselves by homology-directed repair in drive/wild-type heterozygotes, are a powerful form of gene drive, but they are vulnerable to resistance alleles that preserve the function of their target gene. Such resistance alleles can prevent successful population suppression. Here, we constructed a homing suppression drive in Drosophila melanogaster that utilized multiplexed gRNAs to inhibit the formation of functional resistance alleles in its female fertility target gene. The selected gRNA target sites were close together, preventing reduction in drive conversion efficiency. The construct reached a moderate equilibrium frequency in cage populations without apparent formation of resistance alleles. However, a moderate fitness cost prevented elimination of the cage population, showing the importance of using highly efficient drives in a suppression strategy, even if resistance can be addressed. Nevertheless, our results experimentally demonstrate the viability of the multiplexed gRNAs strategy in homing suppression gene drives.
Field Suppression of Spotted Wing Drosophila (SWD) (Drosophila suzukii Matsumura) Using the Sterile Insect Technique (SIT)
21241R. A. Homem, Z. Mateos-Fierro, R. Jones, D. Gilbert, A. R. McKemey, G. Slade and M. T. Fountain, Insects, 13. 2022-03-26 06:14:15.
Drosophila suzukii (spotted wing drosophila—SWD) is an economically important pest of soft and stone fruit worldwide. Control relies on broad-spectrum insecticides, which are neither fully effective nor environmentally sustainable. The sterile insect technique (SIT) is a proven, effective and environmentally friendly pest-management tool. Here, we investigated, for the first time, the potential of using SIT to control D. suzukii in field conditions without physical barriers that limit insect invasion. A proprietary method of rearing and irradiation with X-rays was used to obtain males that were 99% sterile. Sterile males were released twice per week from April to October 2021 on a site in Kent, UK, where everbearing strawberries were grown in open polytunnels. The infestation of wild female D. suzukii was monitored weekly using red sticky traps with dry lure at the treated site and at two similar control sites that did not receive sterile male releases. Releases of sterile males suppressed the wild female D. suzukii population by up to 91% in comparison with the control sites. We thus demonstrated the feasibility of SIT to achieve season-long control of D. suzukii using early, sustained and dynamically targeted releases of sterile males. This provides a promising environmentally friendly method to control this important pest.
Evaluation of Additional Drosophila suzukii Male-Only Strains Generated Through Remobilization of an FL19 Transgene
25425A. Yamamoto, A. K. Yadav and M. J. Scott, Frontiers in Bioengineering and Biotechnology, 10. 2022-03-15 08:27:00.
Drosophila suzukii (D. suzukii) (Matsumura, 1931; Diptera: Drosophilidae), also known as spotted wing Drosophila, is a worldwide pest of fruits with soft skins such as blueberries and cherries. Originally from Asia, D. suzukii is now present in the Americas and Europe and has become a significant economic pest. Growers largely rely on insecticides for the control of D. suzukii. Genetic strategies offer a species-specific environmentally friendly way for suppression of D. suzukii populations. We previously developed a transgenic strain of D. suzukii that produced only males on a diet that did not contain tetracycline. The strain carried a single copy of the FL19 construct on chromosome 3. Repeated releases of an excess of FL19 males led to suppression of D. suzukii populations in laboratory cage trials. Females died as a consequence of overexpression of the tetracycline transactivator (tTA) and tTA-activated expression of the head involution defective proapoptotic gene. The aim of this study was to generate additional male-only strains that carried two copies of the FL19 transgene through crossing the original line with a piggyBac jumpstarter strain. Males that carried either two chromosome 3 or a singleX-linked transgene were identified through stronger expression of the red fluorescent protein marker gene. The brighter fluorescence of the X-linked lines was likely due to dosage compensation of the red fluorescent protein gene. In total, four X-linked lines and eleven lines with two copies on chromosome 3 were obtained, of which five were further examined. All but one of the strains produced only males on a diet without tetracycline. When crossed with wild type virgin females, all of the five two copy autosomal strains examined produced only males. However, the single copy X-linked lines did not show dominant female lethality. Five of the autosomal lines were further evaluated for productivity (egg to adult) and male competition. Based on these results, the most promising lines have been selected for future population suppression experiments with strains from different geographical locations.
No Sting in the Tail for Sterile Bisex Queensland Fruit Fly (Bactrocera tryoni Froggatt) Release Programs
20589O. L. Reynolds, D. Collins, B. C. Dominiak and T. Osborne, Insects, 2022-03-09 11:29:49.
Global markets do not tolerate the presence of fruit fly (Tephritidae) in horticultural produce. A key method of control for tephritidae pests, is the sterile insect technique (SIT). Several countries release a bisex strain, i.e., males and females, however the sterile male is the only sex which contributes to wild population declines when released en masse. In commercial orchards, there are concerns that sterile females released as part of bisex strains, may oviposit, i.e., ‘sting’ and cause damage to fruit, rendering it unmarketable. Australia has released a bisex strain of sterile Queensland fruit fly, Bactrocera tryoni Froggatt, for several decades to suppress wild pest populations, particularly in peri-urban and urban environments. Here, we assessed fruit damage in two commercially grown stone fruit orchards where bisex sterile B. tryoni were released, and in an orchard that did not receive sterile flies. The number of detected stings were higher in only one SIT release orchard, compared with the control; however, there was no difference between SIT and control orchards in the number of larvae detected. We showed that there is no evidence that sterile female B. tryoni released in large numbers caused stings, or damage that led to downgraded or unsaleable fruit. The bisex strain of sterile B. tryoni is recommended for use in commercial stone-fruit orchards, under the conditions in which this trial was conducted.
Hoisted with his own petard: how sex-ratio meiotic drive in Drosophila affnis creates resistance alleles that limit its spread
20440W.-J. Ma, K. B. Patch, E. M. Knoles, M. M. Shoaib and R. L. Unckless, bioRxiv, 2022.02.14.480432. 2022-02-16 09:24:56.
Meiotic drivers are selfish genetic elements that tinker with gameto-genesis to bias their own transmission into the next generation of off-spring. Such tinkering can have significant consequences on gameto-genesis and end up hampering the spread of the driver. In Drosophila affrnis, sex-ratio meiotic drive is caused by an X-linked complex that, when in males with a susceptible Y chromosome, results in broods that are more than 95% female. Interestingly, D. affrnis males lacking a Y chromosome (XO) are fertile and males with the meiotic drive X and no Y produce only sons - effectively reversing the sex-ratio effect. Here, we show that meiotic drive dramatically increases the rate of nondisjunction of the Y chromosome (at least 50X), meaning that the driver is creating resistant alleles through the process of driving. We then model how the O might influence the spread, dynamics and equilibrium of the sex-ratio X chromosome. We find that the O can prevent the spread or reduce the equilibrium frequency of the sex-ratio X chromosome and it can even lead to oscillations in frequency. Finally, with reasonable parameters, the O is unlikely to lead to the loss of the Y chromosome, but we discuss how it might lead to sex-chromosome turnover indirectly.Competing Interest StatementThe authors have declared no competing interest.
Endosymbionts moderate constrained sex allocation in a haplodiploid thrips species in a temperature-sensitive way
20394A. Katlav, D. T. Nguyen, J. L. Morrow, R. N. Spooner-Hart and M. Riegler, Heredity, 9. 2022-02-03 09:32:33.
Maternally inherited bacterial endosymbionts that affect host fitness are common in nature. Some endosymbionts colonise host populations by reproductive manipulations (such as cytoplasmic incompatibility; CI) that increase the reproductive fitness of infected over uninfected females. Theory predicts that CI-inducing endosymbionts in haplodiploid hosts may also influence sex allocation, including in compatible crosses, however, empirical evidence for this is scarce. We examined the role of two common CI-inducing endosymbionts, Cardinium and Wolbachia, in the sex allocation of Pezothrips kellyanus, a haplodiploid thrips species with a split sex ratio. In this species, irrespective of infection status, some mated females are constrained to produce extremely male-biased broods, whereas other females produce extremely female-biased broods. We analysed brood sex ratio of females mated with males of the same infection status at two temperatures. We found that at 20 degrees C the frequency of constrained sex allocation in coinfected pairs was reduced by 27% when compared to uninfected pairs. However, at 25 degrees C the constrained sex allocation frequency increased and became similar between coinfected and uninfected pairs, resulting in more male-biased population sex ratios at the higher temperature. This temperature-dependent pattern occurred without changes in endosymbiont densities and compatibility. Our findings indicate that endosymbionts affect sex ratios of haplodiploid hosts beyond the commonly recognised reproductive manipulations by causing female-biased sex allocation in a temperature-dependent fashion. This may contribute to a higher transmission efficiency of CI-inducing endosymbionts and is consistent with previous models that predict that CI by itself is less efficient in driving endosymbiont invasions in haplodiploid hosts.
Could Crispr Flip the Switch on Insects’ Resistance to Pesticides?
20288E. Mullin, WIRED, 2022-02-02 11:53:17.
WHILE THE COVID-19 pandemic raged across the world in 2020, another disease was quietly infecting more than 220 million people on the continent of Africa: malaria. That year, the disease led to more than 600,000 deaths, most of them children. Caused by the parasite Plasmodium, the illness is spread through the bites of infected female Anopheles mosquitoes. Insecticide-treated bed nets and indoor spraying have long been some of the most effective strategies for combating the disease. But decades of using these chemicals has lessened their potency. It happens like this: Insecticides kill off most of the mosquitoes in an area. But a small number may survive because something about their genetic makeup makes them unaffected by the pesticide. Mosquitoes within that small population mate with each other and pass on their genes to their offspring, breeding more resistant mosquitoes. In some cases, resistance has built up just a few years after the introduction of an insecticide. It makes fighting deadly mosquitoes a constant game of whack-a-mole. Insecticides remain the frontline in fighting malaria, because interventions like building mosquito-resistant housing are still experimental, and the effort to develop a vaccine has taken decades. Last summer the World Health Organization recommended Mosquirix, the first anti-parasitic vaccine, for African children under age 5, but it is only 30 percent effective at preventing serious disease, and will take many years to achieve approval and distribution among individual nations.
Genetically engineered insects with sex-selection and genetic incompatibility enable population suppression
20286A. Upadhyay, N. R. Feltman, A. Sychla, A. Janzen, S. R. Das, M. Maselko and M. Smanski, eLife, 11. 2022-02-02 11:49:30.
Engineered Genetic Incompatibility (EGI) is a method to create species-like barriers to sexual reproduction. It has applications in pest control that mimic Sterile Insect Technique when only EGI males are released. This can be facilitated by introducing conditional female-lethality to EGI strains to generate a sex-sorting incompatible male system (SSIMS). Here, we demonstrate a proof of concept by combining tetracycline-controlled female lethality constructs with a pyramus-targeting EGI line in the model insect Drosophila melanogaster. We show that both functions (incompatibility and sex-sorting) are robustly maintained in the SSIMS line and that this approach is effective for population suppression in cage experiments. Further we show that SSIMS males remain competitive with wild-type males for reproduction with wild-type females, including at the level of sperm competition.
Paternal transmission of the Wolbachia CidB toxin underlies cytoplasmic incompatibility
20434B. Horard, K. Terretaz, A. S. Gosselin-Grenet, H. Sobry, M. Sicard, F. Landmann and B. Loppin, Current Biology, 2022-02-01 08:53:36.
Wolbachia are widespread endosymbiotic bacteria that manipulate the reproduction of arthropods through a diversity of cellular mechanisms. In cytoplasmic incompatibility (CI), a sterility syndrome originally discovered in the mosquito Culex pipiens, uninfected eggs fertilized by sperm from infected males are selectively killed during embryo development following the abortive segregation of paternal chromosomes in the zygote. Despite the recent discovery of Wolbachia CI factor (cif) genes, the mechanism by which they control the fate of paternal chromosomes at fertilization remains unknown. Here, we have analyzed the cytological distribution and cellular impact of CidA and CidB, a pair of Cif proteins from the Culex-infecting Wolbachia strain wPip. We show that expression of CidB in Drosophila S2R+ cells induces apoptosis unless CidA is co-expressed and associated with its partner. In transgenic Drosophila testes, both effectors colocalize in germ cells until the histone-to-protamine transition in which only CidB is retained in maturing spermatid nuclei. We further show that CidB is similarly targeted to maturing sperm of naturally infected Culex mosquitoes. At fertilization, CidB associates with paternal DNA regions exhibiting DNA replication stress, as a likely cause of incomplete replication of paternal chromosomes at the onset of the first mitosis. Importantly, we demonstrate that inactivation of the deubiquitylase activity of CidB does not abolish its cell toxicity or its ability to induce CI in Drosophila. Our study thus demonstrates that CI functions as a transgenerational toxin-antidote system and suggests that CidB acts by poisoning paternal DNA replication in incompatible crosses.
Genetic Strategy Reverses Insecticide Resistance
20108H. Tasoff, The Current, 2022-01-18 17:08:09.
University of California biologists have now developed a method that reverses insecticide resistance using CRISPR/Cas9 technology. A team including UC Santa Barbara researchers Craig Montell(link is external) and Menglin Li(link is external), UC San Diego researchers Bhagyashree Kaduskar, Raja Kushwah and Professor Ethan Bier of UCSD’s Tata Institute for Genetics and Society (TIGS) used the genetic editing tool to replace an insecticide-resistant gene in fruit flies with the normal insecticide-susceptible form. Their achievement, described in Nature Communications(link is external), could significantly reduce the amount of insecticides used. “This strategy could be used to reverse the resistance of mosquito disease vectors that spread devastating diseases that impact hundreds of millions of people each year,” said Craig Montell, a professor of molecular, cellular and developmental Biology at UC Santa Barbara.
Stakeholder engagement to inform the risk assessment and governance of gene drive technology to manage spotted-wing drosophila
20212A. E. Kokotovich, S. K. Barnhill-Dilling, J. E. Elsensohn, R. Li, J. A. Delborne and H. Burrack, Journal of Environmental Management, 307:114480. 2022-01-04 15:32:08.
Emerging biotechnologies, such as gene drive technology, are increasingly being proposed to manage a variety of pests and invasive species. As one method of genetic biocontrol, gene drive technology is currently being developed to manage the invasive agricultural pest spotted-wing drosophila (Drosophila suzukii, SWD). While there have been calls for stakeholder engagement on gene drive technology, there has been a lack of empirical work, especially concerning stakeholder engagement to inform risk assessment. To help address this gap and inform future risk assessments and governance decisions for SWD gene drive technology, we conducted a survey of 184 SWD stakeholders to explore how they define and prioritize potential benefits and potential adverse effects from proposed SWD gene drive technology. We found that stakeholders considered the most important potential benefits of SWD gene drive technology to be: 1) Decrease in the quantity or toxicity of pesticides used, and 2) Decrease in SWD populations. Stakeholders were most concerned about the potential adverse effects of: 1) Decrease in beneficial insects, 2) Increase in non-SWD secondary pest infestations, and 3) Decrease in grower profits. Notably, we found that even stakeholders who expressed support for the use of SWD gene drive technology expressed concerns about potential adverse effects from the technology, emphasizing the need to move past simplistic, dichotomous views of what it means to support or oppose a technology. These findings suggest that instead of focusing on the binary question of whether stakeholders support or oppose SWD gene drive technology, it is more important to identify and assess the factors that are consequential to stakeholder decision making – including, for example, exploring whether and under what conditions key potential adverse effects and potential benefits would result from the use of SWD gene drive technology.
Genetic conversion of a split-drive into a full-drive element
19540G. Terradas, J. B. Bennett, Z. Li, J. M. Marshall and E. Bier, bioRxiv, 2021.12.05.471291. 2021-12-06 20:21:27.
Gene-drive systems offer an important new avenue for spreading beneficial traits into wild populations. Their core components, Cas9 and guide RNA (gRNA), can either be linked within a single cassette (full gene drive, fGD) or provided in two separate elements (split gene drive, sGD) wherein the gRNA-bearing element drives in the presence of an independent static source of Cas9. We previously designed a system engineered to turn split into full gene drives. Here, we provide experimental proof-of-principle for such a convertible system inserted at the spo11 locus, which is recoded to restore gene function. In multigenerational cage studies, the reconstituted spo11 fGD cassette initially drives with slower kinetics than the unlinked sGD element (using the same Mendelian vasa-Cas9 source), but eventually reaches a similar level of final introgression. Different kinetic behaviors may result from transient fitness costs associated with individuals co-inheriting Cas9 and gRNA transgenes during the drive process.
Nuclear transport genes recurrently duplicate by means of RNA intermediates in Drosophila but not in other insects
19591A. Mirsalehi, D. N. Markova, M. Eslamieh and E. Betrán, BMC Genomics, 22:876. 2021-12-06 17:52:07.
We find that most of the nuclear transport duplications in Drosophila are of a few classes of nuclear transport genes, RNA mediated and fast evolving. We also retrieve many pseudogenes for the Ran gene. Some of the duplicates are relatively young and likely contributing to the turnover expected for genes under strong but changing selective pressures. These duplications are potentially revealing what features of nuclear transport are under selection. Unlike in flies, we find only a few duplications when we study the Drosophila duplicated nuclear transport genes in dipteran species outside of Drosophila, and none in other insects.
Rapid evolutionary dynamics of an expanding family of meiotic drive factors and their hpRNA suppressors
19515J. Vedanayagam, C. J. Lin and E. C. Lai, Nature Ecology and Evolution, 2021-12-03 17:20:42.
Meiotic drivers are a class of selfish genetic elements whose existence is frequently hidden due to concomitant suppressor systems. Accordingly, we know little of their evolutionary breadth and molecular mechanisms. Here, we trace the evolution of the Dox meiotic drive system in Drosophila simulans, which affects male-female balance (sex ratio). Dox emerged via stepwise mobilization and acquisition of multiple D. melanogaster gene segments including from protamine, which mediates compaction of sperm chromatin. Moreover, we reveal novel Dox homologs and massive amplification of Dox superfamily genes on X chromosomes of its closest sisters D. mauritiana and D. sechellia. Emergence of Dox loci is tightly associated with 359-class satellite repeats that flank de novo genomic copies. In concert, we find coordinated diversification of autosomal hairpin RNA-class siRNA loci that target subsets of Dox superfamily genes. Overall, we reveal fierce genetic arms races between meiotic drive factors and siRNA suppressors associated with recent speciation.
CRISPR gene-drive systems based on Cas9 nickases promote super-Mendelian inheritance in Drosophila
19471V. Lopez del Amo, S. Sanz Juste and V. M. Gantz, bioRxiv, 2021.12.01.470847. 2021-12-02 15:07:14.
CRISPR-based gene drive systems can be used to modify entire wild populations due to their ability to bias their own inheritance towards super-Mendelian rates (>100%). Current gene drives contain a Cas9 and a gRNA gene inserted at the location targeted by the gRNA. These gene products are able to cut the opposing wildtype allele, and lead to its replacement with a copy of the gene drive through the homology-directed DNA repair pathway. When this allelic conversion occurs in the germline it leads to the preferential inheritance of the engineered allele; a property that has been proposed to disseminate engineered traits for managing disease-transmitting mosquito populations. Here, we report a novel gene-drive strategy relying on Cas9 nickases which operates by generating staggered paired-nicks in the DNA to promote propagation of the gene drive allele. We show that only when 5' overhangs are generated, the system efficiently leads to allelic conversion. Further, the nickase gene-drive arrangement produces large stereotyped deletions, providing potential advantages for targeting essential genes. Indeed, the nickase-gene-drive design should expand the options available for gene drive designs aimed at applications in mosquitoes and beyond.
Gene drive that results in addiction to a temperature-sensitive version of an essential gene triggers population collapse in Drosophila
19441G. Oberhofer, T. Ivy and B. A. Hay, Proceedings of the National Academy of Sciences, 118:e2107413118. 2021-12-01 20:58:01.
One strategy for population suppression seeks to use gene drive to spread genes that confer conditional lethality or sterility, providing a way of combining population modification with suppression. Stimuli of potential interest could be introduced by humans, such as an otherwise benign virus or chemical, or occur naturally on a seasonal basis, such as a change in temperature. Cleave and Rescue (ClvR) selfish genetic elements use Cas9 and guide RNAs (gRNAs) to disrupt endogenous versions of an essential gene while also including a Rescue version of the essential gene resistant to disruption. ClvR spreads by creating loss-of-function alleles of the essential gene that select against those lacking it, resulting in populations in which the Rescue provides the only source of essential gene function. As a consequence, if function of the Rescue, a kind of Trojan horse now omnipresent in a population, is condition dependent, so too will be the survival of that population. To test this idea, we created a ClvR in Drosophila in which Rescue activity of an essential gene, dribble, requires splicing of a temperature-sensitive intein (TS-ClvRdbe). This element spreads to transgene fixation at 23 °C, but when populations now dependent on Ts-ClvRdbe are shifted to 29 °C, death and sterility result in a rapid population crash. These results show that conditional population elimination can be achieved. A similar logic, in which Rescue activity is conditional, could also be used in homing-based drive and to bring about suppression and/or killing of specific individuals in response to other stimuli.
Area-wide management of fruit flies in a tropical mango growing area integrating the sterile insect technique and biological control: From a research to an operational programme
19391Liedo, P., Montoya, P. , and Toledo, J., AREA-WIDE INTEGRATED PEST MANAGEMENT: Development and Field Application, 2021-11-29 17:29:33.
The Sterile Insect Technique (SIT) has been successfully used for the control of fruit flies in a number of places in the world. One requirement for its successful application is that wild populations should be at low densities to achieve effective sterile to wild fly overflooding ratios. This has been an important reason that has limited its integration in fruit fly management in tropical fruit growing areas, where climate conditions and the availability of hosts all year-round results in high population densities. Here we report the results of a project where SIT integration into fruit fly management was evaluated under the tropical conditions of the mango growing area in the Soconusco region of Chiapas, Mexico. The basis for the area-wide integrated pest management (AW-IPM) approach was the knowledge of the population dynamics of the pest fruit flies in the region and of the fruit phenology. The main commercial mango growing areas are in the lowlands, where fruit fly populations are very low outside of the mango production season. Population densities are higher in the midlands and highlands, where alternate hosts are common in backyards and as part of the natural vegetation. We call these refuge areas, and the AW-IPM approach aimed at establishing a biological barrier with releases of parasitoids and sterile male fruit flies to suppress the fruit fly populations and prevent or minimize the dispersal of wild flies from the refuge areas to the mango orchards. In 2014, after two years of releases, fruit fly population densities were suppressed more than 70% in the release area and 65% in the entire area, including the lowlands with the mango orchards. With the support of fruit growers, state and federal governments, this project was continued and established as an operational AW-IPM programme. In 2016, after 4 years of programme implementation, the detection of wild flies was significantly reduced, and the number of batches of fruit that were rejected at the packing houses due to the detection of infested fruits was the lowest in the past 12 years, since the recording of these data was initiated. These indicators declined even further in 2017. The results obtained demonstrate that AW-IPM integrating the SIT can be applied successfully against fruit flies under tropical conditions with naturally high pest densities, providing there is adequate knowledge on the population dynamics of the fruit fly species present in the region.
Area-wide management of mediterranean fruit fly with the sterile insect technique in South Africa: New production and management techniques pay dividends
19358Venter, J. H., Baard, C. W. L., and Barnes, B. N., AREA-WIDE INTEGRATED PEST MANAGEMENT: Development and Field Application, 2021-11-29 16:27:01.
A mass-rearing facility to produce sterile male Mediterranean fruit flies, Ceratitis capitata (Wiedemann), for a Sterile Insect Technique (SIT) programme in the Hex River Valley in the Western Cape Province started in the late 1990s. The programme was initially underfunded and could only produce about 5 million sterile male flies per week. The resultant aerial release rate of 500 sterile males/ha/week reduced wild Mediterranean fruit fly populations substantially, but not to sufficiently low levels. Due to financial considerations, in 2003 aerial releases were replaced with ground releases targeting all gardens, other hotspots and neglected host plants. It was clear that with more funding, fruit fly mass-rearing facility and field operations could be improved, better quality control could be implemented, and more and better quality male sterile flies could be produced and released. Increased government support in 2001 resulted in a larger mass-rearing facility, and further improvements included the implementation of a quality control management system and the introduction of a new genetic sexing strain (VIENNA 8). The resultant increase in the production of sterile Mediterranean fruit flies of better quality enabled the SIT programme to be systematically introduced to additional fruit production areas. The Mediterranean fruit fly SIT programme was privatised in 2003 and is now operated by FruitFly Africa (Pty) Ltd. In 2009 a new approach to funding was adopted with a renewable Memorandum of Understanding (MoU) between the Department of Agriculture, Forestry and Fisheries (DAFF) and the deciduous fruit and table grape industry. Under the MoU, the DAFF provides 50% of the necessary funding, while 50% is collected from growers through statutory levies. In 2010 a new state of the art mass-rearing facility became operational and subsequent improvements in production processes and facility maintenance resulted in improved fruit fly production and quality. By 2016 sterile male production had increased to 56 million flies per week. After 12 years of ground releases of sterile Mediterranean fruit flies, aerial releases were resumed in three main production areas, and, at the time of writing, include approximately 15 000 ha of commercial deciduous fruit and table grapes. As a result of this well-funded area-wide integrated pest management (AW-IPM) programme, average wild Mediterranean fruit fly populations in the SIT areas have decreased by as much as 73%. The South African Mediterranean fruit fly SIT programme now aims to manage some of the fruit production areas as areas of low pest prevalence. Increased funding and a stable income stream also enabled FruitFly Africa to apply early detection and rapid response programmes for invasive pests such as Bactrocera dorsalis in relevant areas.
Wolbachia reduces virus infection in a natural population of Drosophila
19437R. Cogni, S. D. Ding, A. C. Pimentel, J. P. Day and F. M. Jiggins, Communications Biology, 4:1327. 2021-11-25 20:42:30.
Wolbachia is a maternally transmitted bacterial symbiont that is estimated to infect approximately half of arthropod species. In the laboratory it can increase the resistance of insects to viral infection, but its effect on viruses in nature is unknown. Here we report that in a natural population of Drosophila melanogaster, individuals that are infected with Wolbachia are less likely to be infected by viruses. By characterising the virome by metagenomic sequencing and then testing individual flies for infection, we found the protective effect of Wolbachia was virus-specific, with the prevalence of infection being up to 15% greater in Wolbachia-free flies. The antiviral effects of Wolbachia may contribute to its extraordinary ecological success, and in nature the symbiont may be an important component of the antiviral defences of insects.
Temperature-Inducible Precision-Guided Sterile Insect Technique
19268N. P. Kandul, J. R. Liu and O. S. Akbari, CRISPR Journal, 14. 2021-11-03 16:11:04.
Releases of sterile males are the gold standard for many insect population control programs, and precise sex sorting to remove females prior to male releases is essential to the success of these operations. To advance traditional methods for scaling the generation of sterile males, we previously described a CRISPR-mediated precision-guided sterile insect technique (pgSIT), in which Cas9 and gRNA strains are genetically crossed to generate sterile males for mass release. While effective at generating F-1 sterile males, pgSIT requires a genetic cross between the two parental strains, which requires maintenance and sexing of two strains in a factory. Therefore, to advance pgSIT further by removing this crossing step, here we describe a next-generation temperature-inducible pgSIT (TI-pgSIT) technology and demonstrate its proof-of-concept in Drosophila melanogaster. Importantly, we were able to develop a true breeding strain for TI-pgSIT that eliminates the requirement for sex sorting-a feature that may help further automate production at scale.
Centromere function in asymmetric cell division in Drosophila female and male germline stem cells
19322A. M. Kochendoerfer, F. Modafferi and E. M. Dunleavy, Open Biology, 11:210107. 2021-11-03 14:14:53.
The centromere is the constricted chromosomal region required for the correct separation of the genetic material at cell division. The kinetochore protein complex assembles at the centromere and captures microtubules emanating from the centrosome to orchestrate chromosome segregation in mitosis and meiosis. Asymmetric cell division (ACD) is a special type of mitosis that generates two daughter cells with different fates. Epigenetic mechanisms operating at the centromere have been proposed to contribute to ACD. Recent studies have shown that an asymmetric distribution of CENP-A—the centromere-specific histone H3 variant—between sister chromatids can bias chromosome segregation in ACD. In stem cells, this leads to non-random sister chromatid segregation, which can affect cell fate. These findings support the ‘silent sister' hypothesis, according to which the mechanisms of ACD are epigenetically regulated through centromeres. Here, we review the recent data implicating centromeres in ACDs and cell fate in Drosophila melanogaster female and male germline stem cells.
RNA virome diversity and Wolbachia infection in individual Drosophila simulans flies
19073A. S. Ortiz-Baez, M. Shi, A. A. Hoffmann and E. C. Holmes, Journal of General Virology, 102. 2021-10-28 20:29:18.
The endosymbiont bacteria of the genus Wolbachia are associated with multiple mutualistic effects on insect biology, including nutritional and antiviral properties. Members of the genus Wolbachia naturally occur in fly species of the genus Drosophila, providing an operational model host for studying how virome composition may be affected by its presence. Drosophila simulans populations can carry a variety of strains of members of the genus Wolbachia, with the wAu strain associated with strong antiviral protection under experimental conditions. We used D. simulans sampled from the Perth Hills, Western Australia, to investigate the potential virus protective effect of the wAu strain of Wolbachia on individual wild-caught flies. Our data revealed no appreciable variation in virus composition and abundance between individuals infected or uninfected with Wolbachia associated with the presence or absence of wAu. However, it remains unclear whether wAu might affect viral infection and host survival by increasing tolerance rather than inducing complete resistance. These data also provide new insights into the natural virome diversity of D. simulans. Despite the small number of individuals sampled, we identified a repertoire of RNA viruses, including nora virus, galbut virus, thika virus and La Jolla virus, that have been identified in other species of the genus Drosophila. Chaq virus-like sequences associated with galbut virus were also detected. In addition, we identified five novel viruses from the families Reoviridae, Tombusviridae, Mitoviridae and Bunyaviridae. Overall, this study highlights the complex interaction between Wolbachia and RNA virus infections and provides a baseline description of the natural virome of D. simulans.
Ecological vulnerability analysis for suppression of Drosophila suzukii by gene drives
19082C. R. Lalyer, L. Sigsgaard and B. Giese, Global Ecology and Conservation, 32:e01883. 2021-10-17 20:44:52.
Synthetic gene drives are transgenic constructs that aim to bias heredity and thereby influence the characteristics and fate of populations regarding abundance and evolution. Aside from irreversible effects in ecosystems that could be triggered by the release of a gene drive, research on confinable drives or even the reversibility of gene drives is underway and shows first success under laboratory conditions. However, their effectiveness under realistic conditions is not entirely clear unless first test releases have taken place. Since a potentially irreversible intervention into ecosystems is created, a prospective assessment is needed. We present an approach of prospective ecological vulnerability analysis for the proposed control of the invasive pest Drosophila suzukii by using gene drives. The analysis considers the accidental spread of the gene drive to the native habitat of Drosophila suzukii, with a focus on Japan. It contains a mapping of potential impacts as a consequence of the suppression of the insect. Multiple cascading effects were identified including the potential spread of the gene drive in geographic range or potential hybridization with non-target species. Determining the vulnerability of an ecosystem requires information regarding specific characteristics at different organizational levels. The vulnerability analysis of an affected ecosystem will initially serve to identify gaps in knowledge. Reducing complexity and breaking down the potential events that might arise from a gene drive population suppression enables to better understand endpoints i.e. concrete effects. Three potential effects have been selected for a specific analysis of the vulnerability of populations and species. A high vulnerability was obtained for the suppression of non-target (native) populations of Drosophila suzukii as well as for a decrease in specialized parasitoid abundance. The paper proposes the outline of a comprehensive prospective approach to understand the susceptibility of an ecosystem to unintended and irreversible harm.
Sexual selection can partly explain low frequencies of Segregation Distorter alleles
18815T. A. Keaney, T. M. Jones and L. Holman, Proceedings of the Royal Society B: Biological Sciences, 288:20211190. 2021-09-29 15:21:33.
The Segregation Distorter (SD) allele found in Drosophila melanogaster distorts Mendelian inheritance in heterozygous males by causing developmental failure of non-SD spermatids, such that greater than 90% of the surviving sperm carry SD. This within-individual advantage should cause SD to fix, and yet SD is typically rare in wild populations. Here, we explore whether this paradox can be resolved by sexual selection, by testing if males carrying three different variants of SD suffer reduced pre- or post-copulatory reproductive success. We find that males carrying the SD allele are just as successful at securing matings as control males, but that one SD variant (SD-5) reduces sperm competitive ability and increases the likelihood of female remating. We then used these results to inform a theoretical model; we found that sexual selection could limit SD to natural frequencies when sperm competitive ability and female remating rate equalled the values observed for SD-5. However, sexual selection was unable to explain natural frequencies of the SD allele when the model was parameterized with the values found for two other SD variants, indicating that sexual selection alone is unlikely to explain the rarity of SD.
Wolbachia-Conferred Antiviral Protection Is Determined by Developmental Temperature
18357E. Chrostek, N. Martins, M. S. Marialva and L. Teixeira, mBio, e0292320. 2021-09-08 14:13:12.
Overall, we show that Wolbachia-conferred antiviral protection is temperature dependent, being present or absent depending on the environmental conditions. This interaction likely impacts Wolbachia-host interactions in nature and, as a result, frequencies of host and symbionts in different climates. Dependence of Wolbachia-mediated pathogen blocking on developmental temperature could be used to dissect the mechanistic bases of protection and influence the deployment of Wolbachia to prevent transmission of arboviruses. IMPORTANCE Insects are often infected with beneficial intracellular bacteria. The bacterium Wolbachia is extremely common in insects and can protect them from pathogenic viruses. This effect is being used to prevent transmission of dengue and Zika viruses by Wolbachia-infected mosquitoes. To understand the biology of insects in the wild, we need to discover which factors affect Wolbachia-conferred antiviral protection. Here, we show that the temperature at which insects develop from eggs to adults can determine the presence or absence of antiviral protection. The environment, therefore, strongly influences this insect-bacterium interaction. Our work may help to provide insights into the mechanism of viral blocking by Wolbachia, deepen our understanding of the geographical distribution of host and symbiont, and incentivize further research on the temperature dependence of Wolbachia-conferred protection for control of mosquito-borne disease.
Diverse wMel variants of Wolbachia pipientis differentially rescue fertility and cytological defects of the bag of marbles partial loss of function mutation in Drosophila melanogaster
18817J. E. Bubnell, P. Fernandez-Begne, C. K. S. Ulbing and C. F. Aquadro, G3 Genes|Genomes|Genetics, 2021-09-07 15:29:22.
In Drosophila melanogaster, the maternally inherited endosymbiont Wolbachia pipientis interacts with germline stem cell genes during oogenesis. One such gene, bag of marbles (bam) is the key switch for differentiation and also shows signals of adaptive evolution for protein diversification. These observations have led us to hypothesize that W. pipientis could be driving the adaptive evolution of bam for control of oogenesis. To test this hypothesis, we must understand the specificity of the genetic interaction between bam and W. pipientis. Previously, we documented that the W. pipientis variant, wMel, rescued the fertility of the bamBW hypomorphic mutant as a transheterozygote over a bam null. However, bamBW was generated more than 20 years ago in an uncontrolled genetic background and maintained over a balancer chromosome. Consequently, the chromosome carrying bamBW accumulated mutations that have prevented controlled experiments to further assess the interaction. Here, we used CRISPR/Cas9 to engineer the same single amino acid bam hypomorphic mutation (bamL255F) and a new bam null disruption mutation into the w1118 isogenic background. We assess the fertility of wildtype bam, bamL255F/bamnull hypomorphic, and bamL255F/bamL255F mutant females, each infected individually with 10 W. pipientis wMel variants representing three phylogenetic clades. Overall, we find that all of the W. pipientis variants tested here rescue bam hypomorphic fertility defects with wMelCS-like variants exhibiting the strongest rescue effects. In addition, these variants did not increase wildtype bam female fertility. Therefore, both bam and W. pipientis interact in genotype-specific ways to modulate female fertility, a critical fitness phenotype.
Satellite DNA-mediated diversification of a sex-ratio meiotic drive gene family in Drosophila
18354C. A. Muirhead and D. C. Presgraves, Nature Ecology & Evolution, 2021-09-06 14:01:24.
Sex chromosomes are susceptible to the evolution of selfish meiotic drive elements that bias transmission and distort progeny sex ratios. Conflict between such sex-ratio drivers and the rest of the genome can trigger evolutionary arms races resulting in genetically suppressed ‘cryptic’ drive systems. The Winters cryptic sex-ratio drive system of Drosophila simulans comprises a driver, Distorter on the X (Dox) and an autosomal suppressor, Not much yang, a retroduplicate of Dox that suppresses via production of endogenous small interfering RNAs (esiRNAs). Here we report that over 22 Dox-like (Dxl) sequences originated, amplified and diversified over the ~250,000-year history of the three closely related species, D. simulans, D. mauritiana and D. sechellia. The Dxl sequences encode a rapidly evolving family of protamines. Dxl copy numbers amplified by ectopic exchange among euchromatic islands of satellite DNAs on the X chromosome and separately spawned four esiRNA-producing suppressors on the autosomes. Our results reveal the genomic consequences of evolutionary arms races and highlight complex interactions among different classes of selfish DNAs.
A Monte Carlo study to investigate the feasibility to use the Moroccan panoramic irradiator in sterile insect technique programs
18159A. Aknouch, Y. El-ouardi, L. Hamroud, R. Sebihi, M. Mouhib, M. Yjjou, A. Didi and A. Choukri, Radiation and Environmental Biophysics, 2021-08-14 18:10:19.
Mediterranean fly pest (Ceratitis) is one of the most destructive pests of fruit species in Morocco. The sterile insect technique (SIT) is an environmentally friendly strategy that uses ionizing radiation to sterilize adult insects. Morocco has a panoramic gamma irradiator used to irradiate agri-food products. This irradiator is not dedicated to SIT programs due to its geometry that does not allow to obtain a dose uniformity ratio (DUR) recommended for such applications. This article presents a Monte Carlo study to investigate the feasibility of using the panoramic gamma irradiator at the National Institute for Agronomic Research (NIAR) of Tangier, Morocco, to setting up SIT methods and contributing to Ceratitis control programs. The Monte Carlo method was used to simulate the concrete bunker in which the panoramic gamma irradiator is installed. To obtain a recommended DUR required for SIT programs, two cells similar of the Gammacell-220 irradiator, which is mainly used in the SIT programs around the world, were simulated inside the concrete bunker. The simulation and calculations were performed using the MCNPX-2.7e Monte Carlo simulation code. It is demonstrated that at both investigated positions, the spatial distribution of dose rates in the two modeled irradiation cells, which were similar to a gammacell-220 irradiator cell, are uniform enough that the cells can be used for SIT programs. It is concluded that the panoramic irradiator at NIAR can be used to contribute to the control of Mediterranean fly pest and other insect pests in Morocco.
Red queen’s race: rapid evolutionary dynamics of an expanding family of meiotic drive factors and their hpRNA suppressors
17957J. Vedanayagam, C.-J. Lin and E. C. Lai, bioRxiv, 2021.08.05.454923. 2021-08-06 16:51:10.
Meiotic drivers are a class of selfish genetic elements that are widespread across eukaryotes. Their activities are often detrimental to organismal fitness and thus trigger drive suppression to ensure fair segregation during meiosis. Accordingly, their existence is frequently hidden in genomes, and their molecular functions are little known. Here, we trace evolutionary steps that generated the Dox meiotic drive system in Drosophila simulans (Dsim), which distorts male:female balance (sex-ratio) by depleting male progeny. We show that Dox emerged via stepwise mobilization and acquisition of portions of multiple D. melanogaster genes, including the sperm chromatin packaging gene protamine. Moreover, we reveal novel Dox homologs in Dsim and massive, recent, amplification of Dox superfamily genes specifically on X chromosomes of its closest sister species D. mauritiana (Dmau) and D. sechellia (Dsech). The emergence of Dox superfamily genes is tightly associated with 1.688 family satellite repeats that flank de novo genomic copies. In concert, we find coordinated emergence and diversification of autosomal hairpin RNA/siRNAs loci that target subsets of Dox superfamily genes across simulans clade species. Finally, an independent set of protamine amplifications the Y chromosome of D. melanogaster indicates that protamine genes are frequent and recurrent players in sex chromosome dynamics. Overall, we reveal fierce genetic arms races between meiotic drive factors and siRNA suppressors associated with recent speciation.Competing Interest StatementThe authors have declared no competing interest.
Comparative response to post-production process of two Anastrepha ludens strains: Application in the sterile insect technique
17725J. Arredondo, J. F. Aguirre-Medina, J. S. Meza, J. Cancino and F. Diaz-Fleischer, Journal of Applied Entomology, 11. 2021-07-07 14:54:23.
The new desiccation-resistant (DR) strain of Anastrepha ludens Loew differs in its life-history traits from the non-selected strain (NS). Given the innate resistance of DR flies to stressors, it is necessary to determine the packing and shipment conditions for their use in the sterile insect technique (SIT). First, we used pupae to evaluate the interaction of hypoxia period (12, 24 and 36 hr) and temperature (15.3 (+/- 0.9), 19.5 (+/- 1.0), 25.5 (+/- 0.6) and 30.1 (+/- 0.5) C-o). Second, adults were exposed to densities of 1.0, 1.3 and 1.5 flies/cm(2) and chilling periods of 0, 3 and 5 hr. We observed a negative relationship of emergence and flight ability with hypoxia period and temperature in both strains especially when flies were exposed to 36 hr of hypoxia and 30celcius. Interestingly, knock-down time decreased as male density increased, but when chilling time increased, recovery time also increased. Both chilling time and male density had negative effects on male weight. Chilling time reduced male survival when exposed to desiccation, while both chilling time and male density decreased male survival under starvation conditions. Negative effects on number of matings were observed only on the first day after chilling but not on the following days. We found that DR flies survive approximately twice as long as flies from the NS strain when exposed to starvation or desiccation stressors. We discuss our results on the basis of the potential use of DR flies in SIT programmes.
Distinct spermiogenic phenotypes underlie sperm elimination in the Segregation Distorter meiotic drive system
17832M. Herbette, X. L. Wei, C. H. Chang, A. M. Larracuente, B. Loppin and R. Dubruille, PLOS Genetics, 17:26. 2021-07-06 13:14:02.
Here we show that SD/SD+ males of different genotypes but with similarly strong degrees of distortion have distinct spermiogenic phenotypes. In some genotypes, SD+ spermatids fail to fully incorporate protamines after the removal of histones, and degenerate during the individualization stage of spermiogenesis. In contrast, in other SD/SD+ genotypes, protamine incorporation appears less disturbed, yet spermatid nuclei are abnormally compacted, and mature sperm nuclei are eventually released in the seminal vesicle. Our analyses of different SD+ chromosomes suggest that the severity of the spermiogenic defects associates with the copy number of the Rsp satellite. We propose that when Rsp copy number is very high (> 2000), spermatid nuclear compaction defects reach a threshold that triggers a checkpoint controlling sperm chromatin quality to eliminate abnormal spermatids during individualization. Author summary In diploid organisms, both alleles of the same gene have an equal chance to be transmitted to the progeny. However, in many species including mammals, insects and plants, selfish genetic elements perturb gametogenesis in a way that favors their own transmission to the detriment of the homologous chromosome that does not carry them. In Drosophila melanogaster, Segregation Distorter (Sd) is a well-characterized selfish locus that induces, by still-unclear mechanisms, the elimination of sperm cells which contain the homologous second chromosome when this carries a large heterochromatic block of repetitive DNA called Rsp. Here, we show that in Sd males, the replacement of histones by sperm specific protamine-like proteins is perturbed in the differentiating Rsp sperm cells, which are then eliminated before their release in the seminal vesicle. However, in some genetic backgrounds, many spermatids Rsp tend to escape this elimination and defective sperm nuclei are found in the seminal vesicle. We show that these phenotypes are partly linked to the number of repeats in the Rsp block and can be modulated by suppressors present in the genetic background. Our work thus helps to understand how selfish loci exploit gametogenesis to favor their own transmission and highlights the essential role of heterochromatin in spermiogenesis progression.
Effect of the timing of pupal irradiation on the quality and sterility of oriental fruit flies (Diptera: Tephritidae) for use in Sterile Insect Technique
17781T. J. Fezza, P. A. Follett and T. E. Shelly, Applied Entomology and Zoology, 8. 2021-07-05 17:37:25.
The Sterile Insect Technique (SIT) is a target-specific, biologically based method used to control pestiferous tephritids entailing the release of mass-reared, sterilized males of the target species to achieve sterile male x wild female matings. As documented for several tephritid species, sterilizing irradiation may have adverse effects on various biological parameters, including life span, flight ability, and mating competitiveness. To minimize these impacts and ensure sterility, released flies must be irradiated at a precise dose at a specific and uniform age. The objective of the present study was to determine the impact of pupal age at the time of irradiation on flight ability, male survival, fertility, and mating competitiveness for the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) irradiated at 100 Gy. We concluded that flies irradiated as pupae 4 days before emergence were significantly compromised with respect to flight ability and male survival when compared to flies irradiated 1 or 2 days before emergence. Additionally, we determined that crosses between males irradiated 1 day before emergence with non-irradiated females yielded significantly more pupae than the same cross with males irradiated at 2, 3, and 4 days before emergence. Although rare, the occurrence of pupae and emerged adults suggested low levels of fertility for flies irradiated as pupae 1 day before emergence, but complete sterility at 2, 3, and 4 days before emergence. These findings suggest that SIT programs can potentially irradiate pupae at 2 or 3 days before emergence without compromising the quality of the released flies, which would permit the distribution of flies over greater distances.
Remating in Ceratitis capitata sterile males: Implications in sterile insect technique programmes
17827M. Catala-Oltra, E. Llacer, O. Dembilio, I. Pla, A. Urbaneja and M. Perez-Hedo, Journal of Applied Entomology, 8. 2021-07-02 14:57:45.
Sterile insect technique (SIT) is used, among other biological control tools, as a sustainable measure for the management of Ceratitis capitata Wiedemann (Diptera: Tephritidae) in many agricultural regions where this pest can trigger severe economic impacts. The tendency of wild females to remate multiple times has been deeply studied; it has been a common point of controversy when evaluating SIT programmes. Nevertheless, the remating potential of the released sterile males remains unknown. Here, under laboratory conditions, the remating capability of mass-reared sterile males was determined. Wild-type virgin females were offered to sterile males (Vienna-8 strain), which had the opportunity to mate up to four consecutive times. The remating assays were carried out at 24 hr, 48 hr, 4 days and 7 days after the first mating. At the end of each tested time period, males were divided according to their mating response, mated or unmated, and subsequently reused for the next round of mating assays. The frequency of successful remating in each tested time period was obtained. Insemination was confirmed by determining the sperm transfer in mated female spermathecae by quantitative real-time PCR. Our results demonstrate that 73% of the mass-reared sterile males were able to remate 24 hr after the first mating, 55% of which remated again the day after. Close to 25% of the V8 sterile males tended to copulate in all of the four mating opportunities. The qPCR analysis of the spermathecae contents verified an effective transfer of V8 sperm to wild females with every mating; 99% of copulations resulted in sperm transfer. These findings shed light on the remating potential of V8 sterile males, an aspect until now underestimated in many SIT programmes.
A transgenic female killing system for the genetic control of Drosophila suzukii
17506M. F. Schetelig, J. Schwirz and Y. Yan, Scientific Reports, 11:12938. 2021-06-24 14:13:24.
The spotted wing Drosophila (Drosophila suzukii) is an invasive pest of soft-skinned fruit crops. It is rapidly transmitted in Europe and North America, causing widespread agricultural losses. Genetic control strategies such as the sterile insect technique (SIT) have been proposed as environment-friendly and species-restricted approaches for this pest. However, females are inefficient agents in SIT programs. Here we report a conditional female-killing (FK) strategy based on the tetracycline-off system. We assembled sixteen genetic constructs for testing in vitro and in vivo. Twenty-four independent transgenic strains of D. suzukii were generated and tested for female-specific lethality. The strongest FK effect in the absence of tetracycline was achieved by the construct containing D. suzukii nullo promoter for early gene expression, D. suzukii pro-apoptotic gene hidAla4 for lethality, and the transformer gene intron from the Mediterranean fruit fly Ceratitis capitata for female-specific splicing. One strain carrying this construct eliminated 100% of the female offspring during embryogenesis and produced only males. However, homozygous females from these FK strains were not viable on a tetracycline-supplemented diet, possibly due to the basal expression of hidAla4. Potential improvements to the gene constructs and the use of such FK strains in an SIT program are discussed.
Experimental demonstration of tethered gene drive systems for confined population modification or suppression
17153M. Metzloff, E. Yang, S. Dhole, A. G. Clark, P. W. Messer and J. Champer, bioRxiv, 2021.05.29.446308. 2021-05-30 10:50:23.
Tethered drive systems, in which a locally confined gene drive provides the CRISPR nuclease needed for a homing drive, could provide a solution to this problem, offering the power of a homing drive and confinement of the supporting drive. Here, we demonstrate the engineering of a tethered drive system in Drosophila, using a TARE drive to support modification and suppression homing drives. Each drive was able to bias inheritance in its favor, and the TARE drive was shown to spread only when released above a threshold frequency in experimental cage populations. After the TARE drive had established in the population, it facilitated the spread of a subsequently released split homing modification drive (to all individuals in the cage) and of a homing suppression drive (to its equilibrium frequency). Our results show that the tethered drive strategy is a viable and easily engineered option for providing confinement of homing drives to target populations. Competing Interest StatementThe authors have declared no competing interest.
A Novel Genetic Sexing Strain of Anastrepha Ludens for Cost-Effective Sterile Insect Technique Applications: Improved Genetic Stability and Rearing Efficiency
17125E. Ramírez-Santos, P. Rendon, G. Gouvi, A. Zacharopoulou, K. Bourtzis, C. Cáceres and K. Bloem, Insects, 12. 2021-05-27 19:00:07.
Anastrepha ludens (Loew) is one of the most destructive insect pests damaging several fruits of economic importance. The sterile insect technique (SIT) is used under an area-wide integrated pest management approach, to suppress these pest populations. Mass rearing facilities were initially established to produce sterile males of bi-sexual strains in support of SIT. The first genetic sexing strain (GSS) for A. ludens, Tapachula-7, based on pupal color dimorphism, was a key development since the release of males-only significantly increases the SIT efficiency. In this study, we document the development of a novel pupal color-based GSS. Twelve radiation-induced translocation lines were assessed as potential GSS in terms of recombination rates and rearing efficiency at a small scale. The best one, GUA10, was cytogenetically characterized: it was shown to carry a single translocation between the Y chromosome and chromosome 2, which is known to carry the black pupae marker. This GSS was further evaluated at medium and large scales regarding its genetic stability, productivity and quality versus Tapachula-7. GUA10 presented better genetic stability, fecundity, fertility, production efficiency, flying ability, and male mating, clear indicators that GUA10 GSS can significantly improve the efficacy and cost-effectiveness of SIT applications against this pest species.
Pest reduction with female killers and sterile males
17114L. Mertz, Good Fruit Grower, 2021-05-25 18:40:52.
New ways to fight spotted wing drosophila are in the works, thanks to new genetic engineering tools. These transgenic methods introduce new reproduction-hampering genes into male SWD, so that when they mate with females, the females either don’t have any young, or their female young die early in their development. The approach falls under the umbrella of sterile insect technique (SIT), which has traditionally been done with radiation to sterilize males that are then released to reduce pest reproduction. “SITs are thought of as green technologies, because they are species-specific, they have the advantage that the control agent is the insect itself, and they reduce the dependence on insecticides,” said Max Scott, a professor of entomology at North Carolina State University who is developing one of these approaches. He and his research group have incorporated a female-killing gene into male SWD. In a different approach, the San Diego company Agragene is advancing technology first developed by University of California, San Diego researchers. Here, the project makes use of an advanced gene-editing tool — called CRISPR — to add genes that both kill females and sterilize males. “We really do believe that our technology will bring a sea change to what’s going on out there,” said Gordon Alton, president and CEO of Agragene Inc. If all goes well, he anticipates growers will have access to the technology within two to three years
New genetic copycatchers detect efficient and precise CRISPR editing in a living organism
17013UNIVERSITY OF CALIFORNIA - SAN DIEGO, UNIVERSITY OF CALIFORNIA - SAN DIEGO, 2021-05-11 12:55:38.
Researchers at the University of California San Diego have laid the groundwork for a potential new type of gene therapy using novel CRISPR-based techniques. Working in fruit flies and human cells, research led by UC San Diego Postdoctoral Scholar Zhiqian Li in Division of Biological Sciences Professor Ethan Bier's laboratory demonstrates that new DNA repair mechanisms could be designed to address the effects of debilitating diseases and damaged cell conditions. The scientists developed a novel genetic sensor called a "CopyCatcher," which capitalizes on CRISPR-based gene drive technology, to detect instances in which a genetic element is copied precisely from one chromosome to another throughout cells in the body of a fruit fly.
CopyCatchers are versatile active genetic elements that detect and quantify inter-homolog somatic gene conversion
17008Z. Li, N. Marcel, S. Devkota, A. Auradkar, S. M. Hedrick, V. M. Gantz and E. Bier, Nature Communications, 12:2625. 2021-05-11 12:45:39.
CRISPR-based active genetic elements, or gene-drives, copied via homology-directed repair (HDR) in the germline, are transmitted to progeny at super-Mendelian frequencies. Active genetic elements also can generate widespread somatic mutations, but the genetic basis for such phenotypes remains uncertain. It is generally assumed that such somatic mutations are generated by non-homologous end-joining (NHEJ), the predominant double stranded break repair pathway active in somatic cells. Here, we develop CopyCatcher systems in Drosophila to detect and quantify somatic gene conversion (SGC) events. CopyCatchers inserted into two independent genetic loci reveal unexpectedly high rates of SGC in the Drosophila eye and thoracic epidermis. Focused RNAi-based genetic screens identify several unanticipated loci altering SGC efficiency, one of which (c-MYC), when downregulated, promotes SGC mediated by both plasmid and homologous chromosome-templates in human HEK293T cells. Collectively, these studies suggest that CopyCatchers can serve as effective discovery platforms to inform potential gene therapy strategies.
Sterile Insect Technique Programme against Mediterranean Fruit Fly in the Valencian Community (Spain)
16965I. Plá, J. García de Oteyza, C. Tur, M. Á. Martínez, M. C. Laurín, E. Alonso, M. Martínez, Á. Martín, R. Sanchis, M. C. Navarro, M. T. Navarro, R. Argilés, M. Briasco, Ó. Dembilio and V. Dalmau, Insects, 12. 2021-05-04 15:09:26.
The Mediterranean fruit fly, Ceratitis capitata (Wied.), is an endemic pest in fruit-growing areas of the Spanish Mediterranean coast. In the Valencian Community, it represents a serious problem in the cultivation of citrus and numerous species of fruit, such as peach, cherry, apricot, persimmon, etc. For over 50 years, the Department of Agriculture of Valencia has led, promoted, and carried out a C. capitata control programme to protect crops, especially citrus fruits, because this community is the largest national producer and the leading region for fresh citrus exports in the world. Traditionally, pest control has been based on the use of insecticides. However, a reduction of more than 90% of a target wild population was achieved in the frame of a pilot integrated pest management (IPM) project based on the sterile insect technique (SIT), which was implemented from 2003 to 2006. Based on this successful result, in 2007 the Department of Agriculture of Valencia initiated an area-wide integrated pest management (AW-IPM) programme for the suppression of C. capitata, using the SIT as the primary control method. Complementary activities are implemented periodically in hotspots and during different time periods depending on the pest population dynamics. As a result, there has been a reduction of more than 90% in the use of insecticides by aerial means to control C. capitata, as well as a growth trend in exports of citrus and fresh fruits from the Valencian Community in recent years. This paper provides a historical review of the Valencian programme and briefly describes how technological innovations and decision-making tools have contributed to programme efficiency.
Major fly pest genetically modified in lab to produce more males
16835H. Dunning, Imperial College London, 2021-04-23 14:29:07.
It has been predicted that the world's population will increase to over nine billion people by 2050, and that global food production will need to increase by around 70 percent to match this rate of change. Lead researcher Dr Angela Meccariello, from the Department of Life Sciences at Imperial, said: “Currently, medfly infestations are estimated to contribute towards a loss of up $298 US million annually due to crop damage across a wide geographic area and in over 250 different species of fruits and vegetables. “Due to factors such as climate change, the spread of invasive species and pesticide resistance, there is potential for the negative impact of the medfly on global agriculture to increase if left unchecked. We therefore need new technologies to fight these pests, and our modification could be one such tool.” The team’s modification works by using a DNA-cutting enzyme to destroy the X chromosome during the production of sperm, leading to predominantly male offspring, as females require two Xs. In their experiments, they managed to produce populations of the flies that were 80% male.
Engineered sex ratio distortion by X-shredding in the global agricultural pest Ceratitis capitata
16837A. Meccariello, F. Krsticevic, R. Colonna, G. Del Corsano, B. Fasulo, P. A. Papathanos and N. Windbichler, BMC Biology, 19:78. 2021-04-16 14:29:21.
Genetic sex ratio distorters are systems aimed at effecting a bias in the reproductive sex ratio of a population and could be applied for the area-wide control of sexually reproducing insects that vector disease or disrupt agricultural production. One example of such a system leading to male bias is X-shredding, an approach that interferes with the transmission of the X-chromosome by inducing multiple DNA double-strand breaks during male meiosis. Endonucleases targeting the X-chromosome and whose activity is restricted to male gametogenesis have recently been pioneered as a means to engineer such traits.
Introduction of a cold sensitivity-conferring mutation into the RTA-Bddsx hybrid system of Bactrocera dorsalis for establishment of a thermally controllable homozygous line
17327S. M. Dai, C. Y. Huang and C. Chang, Pest Management Science, 7. 2021-04-10 14:40:01.
BACKGROUND For efficient control of the economically important fruit pest Bactrocera dorsalis, a hybrid system combining ricin toxicity and sex-related alternative splicing of the doublesex gene has been developed. This system exhibits the expected female-specific lethal effect; however, the transgenic females do not survive, making it difficult to raise stable homozygous lines. Since modification of ricin toxin A chain (RTA) through a single-residue change (Gly(212) > Arg(212)) leads to cold-sensitive posttranslational repression of its toxicity, we utilized this unique property to obtain RTA-Bddsx females that survive at low temperature for line maintenance. RESULTS In transient expression experiments using embryonic injection, two groups treated with RTAcs-derived DNA (LERQcs and RTAcs) exhibited temperature-dependent effects. The toxicity was higher at 29 degrees C than at 18 degrees C. The proportion of males was close to 50% at 18 degrees C in all the tested groups except LERQcs-treated flies, which exhibited a high proportion of males (over 70%) at 29 degrees C. The results indicate the cold-sensitive responses of RTA and further suggest a female-specific lethal effect. Subsequently, 14 putative RTAcs-Bddsx transgenic Ds-Red(+) G(1) males were identified, and female-specific lethal effects were observed in Ds-Red(+) G(2) and G(3) lines under cultivation at 29 degrees C but not at 18 degrees C. The male ratio can be increased to up to 95% in G(3) line 001, indicating that RTAcs functions well in B. dorsalis. CONCLUSION The improved RTAcs-Bddsx system with conditional toxicity represents a novel and promising step toward the practical control of B. dorsalis.
Determining the Sterilization Doses under Hypoxia for the Novel Black Pupae Genetic Sexing Strain of Anastrepha fraterculus (Diptera, Tephritidae)
16672P. D. Giustina, T. Mastrangelo, S. Ahmad, G. Mascarin and C. Caceres, Insects, 12. 2021-03-30 13:38:24.
Our study reports for the first time the dose-sterility response under hypoxia for two different A. fraterculus strains. The pupae were derived from a bisexual strain (a Brazilian-1 population) and a recently developed genetic sexing strain (GSS-89). Two hours prior to irradiation, pupae were transferred to sealed glass bottles and irradiated when oxygen concentration was below 3%. Four types of crosses with nonirradiated flies of the bisexual strain were set to assess sterility for each radiation dose. For males from both strains, Weibull dose–response curves between radiation doses and the proportion of egg hatch, egg-to-pupa recovery, and recovery of adults were determined. The GSS males revealed high sterility/mortality levels compared to males from the bisexual strain at doses < 40 Gy, but a dose of 74 Gy reduced egg hatch by 99% regardless of the male strain and was considered the sterilizing dose. The fertility of irradiated females was severely affected even at low doses under hypoxia.
Genetically Encoded CRISPR components Yield Efficient Gene Editing in the Invasive Pest, Drosophila suzukii
16602N. P. Kandul, E. J. Belikoff, J. Liu, A. Buchman, F. Li, A. Yamamoto, T. Yang, I. Shriner, M. J. Scott and O. Akbari, bioRxiv, 2021.03.15.435483. 2021-03-16 18:28:51.
Here we have developed transgenic strains that encode three different terminators and four different promoters to express Cas9 in both the soma and/or germline of SWD. The Cas9 lines were evaluated through genetic crossing to transgenic lines that encode single guide RNAs targeting the conserved X-linked yellow body and white eye genes. We find that several Cas9/gRNA lines display very high editing capacity. Going forward, these tools will be instrumental for evaluating gene function in SWD and may provide tools useful for the development of new genetic strategies for control of this invasive species.
A confinable home and rescue gene drive for population modification
16579N. P. Kandul, J. Liu, J. B. Bennett, J. M. Marshall and O. S. Akbari, eLife, 10:e65939. 2021-03-05 16:30:16.
Homing based gene drives, engineered using CRISPR/Cas9, have been proposed to spread desirable genes throughout populations. However, invasion of such drives can be hindered by the accumulation of resistant alleles. To limit this obstacle, we engineer a confinable population modification Home-and-Rescue (HomeR) drive in Drosophila targeting an essential gene. In our experiments, resistant alleles that disrupt the target gene function were recessive lethal, and therefore disadvantaged. We demonstrate that HomeR can achieve an increase in frequency in population cage experiments, but that fitness costs due to the Cas9 insertion limit drive efficacy.
Improving the Phenotypic Properties of the Ceratitis capitata (Diptera: Tephritidae) Temperature-Sensitive Lethal Genetic Sexing Strain in Support of Sterile Insect Technique Applications
16226M. F. Porras, J. S. Meza, E. G. Rajotte, K. Bourtzis and C. Caceres, Journal of Economic Entomology, 113:2688-2694. 2021-01-31 16:33:01.
We present the first evidence that this slower development is due to a different gene, here namely slow development (sd), which is closely linked to the tsl gene. Taking advantage of recombination phenomena between the two loci, we report the isolation of a novel temperature sensitivity lethal strain using the wp mutation as a morphological marker, which showed faster development (wp tsl FD) during the larval stage and increased in its temperature sensitivity compared with the normal tsl strain. Moreover, the introgression of this novel wp tsl FD combined trait into the Vienna 8(D53-) GSS, resulted in a novel Vienna 8(D53-) FD GSS, where females showed differences in the thermal sensibility, larval development speed, and productivity profiles. The modification of these traits and their impact on the mass rearing of the GSS for sterile insect technique applications are discussed.
White pupae phenotype of tephritids is caused by parallel mutations of a MFS transporter
16691C. M. Ward, R. A. Aumann, M. A. Whitehead, K. Nikolouli, G. Leveque, G. Gouvi, E. Fung, S. J. Reiling, H. Djambazian, M. A. Hughes, S. Whiteford, C. Caceres-Barrios, T. N. M. Nguyen, A. Choo, P. Crisp, S. B. Sim, S. M. Geib, F. Marec, I. Hacker, J. Ragous, Nature Communications, 12. 2021-01-21 15:50:54.
Here, we use classical and modern genetic approaches to identify and functionally characterize causal wp(-) mutations in these distantly related fruit fly species. We find that the wp phenotype is produced by parallel mutations in a single, conserved gene. CRISPR/Cas9-mediated knockout of the wp gene leads to the rapid generation of white pupae strains in C. capitata and B. tryoni. The conserved phenotype and independent nature of wp(-) mutations suggest this technique can provide a generic approach to produce sexing strains in other major medical and agricultural insect pests. The white pupae (wp) phenotype has been used for decades to selectively remove females of tephritid species in genetic sexing, but the determining gene is unknown. Here, the authors show that wp phenotype is produced by parallel mutations in a Major Facilitator Superfamily domain containing gene across multiple species.
Manipulation of Gut Symbionts for Improving the Sterile Insect Technique: Quality Parameters of Bactrocera dorsalis (Diptera: Tephritidae) Genetic Sexing Strain Males After Feeding on Bacteria-Enriched Diets
17222Q. Zhang, P. Cai, B. Wang, X. Liu, J. Lin, R. Hua, H. Zhang, C. Yi, X. Song, Q. Ji, J. Yang and S. Chen, Journal of Economic Entomology, 114:560-570. 2021-01-18 16:16:41.
One environmentally friendly method used to manage Bactrocera dorsalis (Hendel), a key agricultural pest of substantial economic importance, is the sterile insect technique (SIT). Nevertheless, several deficiencies related to this strategy impair the success of the SIT, including the inferior performance of released sterile males compared with wild males, which could be partly solved by the utilization of gut symbionts as probiotic dietary components. In this study, a culture-dependent method was used to isolate and characterize gut-associated bacterial species in adult B. dorsalis genetic sexing strain (GSS) males. In addition, three bacterial isolates from the Enterobacteriaceae family, namely, Enterobacter sp., Morganella morganii, and Moellerella wisconsensis, were used as supplements in larval and adult diets to assess their effects on the life-history traits of irradiated males. Consistent with many previous studies, Enterobacter spp. was shown to be beneficial, with some quality control indices, such as adult size, pupal weight, survival rate under stress and nutritionally rich conditions, and mating competitiveness, being significantly increased, while slight nonsignificant increases in emergence rate and flight ability were observed. Conversely, the M. morganii and M. wisconsensis strains both had negative effects on irradiated male fitness and mating competitiveness. Our results, in combination with those of earlier studies, can contribute to improving the effectiveness of SIT application by enhancing the different aspects of augmentative rearing and biological traits of pests under laboratory rearing conditions.
Edit, undo: Temporary gene editing could help solve the mosquito problem
15900L. Dormehl, digitaltrends, 2020-12-31 14:22:29.
But if SyFy original movies have taught us anything, it’s that genetically tweaking organisms and then releasing them can… well, not go quite according to plan.With that in mind, a new Texas A&M AgriLife Research project seeks to test out genetic modifications of mosquitos that would delete themselves from the genetic code after a certain period. This means that “test runs” of genetic changes could be made, knowing that everything will reset to normal after a designated period like one year (which equates to around 20 generations of mosquito).
Precise single base substitution in the shibire gene by CRISPR/Cas9-mediated homology directed repair in Bactrocera tryoni
16693A. Choo, E. Fung, I. Y. Chen, R. Saint, P. Crisp and S. W. Baxter, BMC Genetics, 21. 2020-12-18 15:58:10.
Here we introduce a known Drosophila melanogaster temperature sensitive embryonic lethal mutation into Bactrocera tryoni, a serious horticultural pest in Australia. A non-synonymous point mutation in the D. melanogaster gene shibire causes embryonic lethality at 29 degrees C and we successfully used CRISPR/Cas9 technology to recreate the orthologous shibire temperature sensitive-1 (shi(ts1)) mutation in B. tryoni. Genotypic analyses over three generations revealed that a high fitness cost was associated with the shi(ts1) mutant allele and shi(ts1) homozygotes were not viable at 21 degrees C, which is a more severe phenotype than that documented in D. melanogaster.ConclusionsWe have demonstrated the first successful use of CRISPR/Cas9 to introduce precise single base substitutions in an endogenous gene via homology-directed repair in an agricultural pest insect and this technology can be used to trial other conditional mutations for the ultimate aim of generating genetic sexing strains for SIT.
‘A plague to be reckoned with’: UMN research creates a buzz with invasive fruit fly research
15238B. Most, The Minnesota Daily, 2020-11-18 13:26:31.
n early November, assistant professor Mike Smanski published an article about a new breakthrough in this research, demonstrating for the first time this kind of genetic engineering was possible in the common fruit fly. This shows that researchers could engineer this work into spotted wing drosophila in the future. The University’s Smanski Lab has also studied this technique in mosquitoes, zebra fish and carp, but never with this type of fruit fly, he said. “These are all a new class of genetic pesticide, basically, that allow you to engineer the pest organism itself and convert that pest organism into the pesticide,” Smanski said. Through this work the researchers can create a pest that is biologically the same, but when the females mate with these genetically modified males, they will not produce viable offspring, he said. This sterile insect technique can be helpful not only in reducing the population of insects, but in reducing the impacts of insecticides on surrounding species and nearby ecosystems, said Feltman, a second-year biochemistry, molecular biology and biophysics graduate student.
The Sterile Insect Technique: Success and Perspectives in the Neotropics
15185D. Perez-Staples, F. Diaz-Fleischer and P. Montoya, Neotropical Entomology, 14. 2020-10-28 15:12:56.
Here, we review SIT in the Neotropics and focus on particular recent successful cases of eradication of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), as well as effective programs used against the Mexican fruit fly Anastrepha ludens (Loew), the New World screwworm fly Cochliomyia hominivorax (Coquerel)), and the Cactus moth Cactoblastis cactorum (Berg). We examine when SIT does not work and innovations that have made SIT more efficient and also highlight complimentary techniques that can be used in conjunction. We address potential candidate species that could be controlled through SIT, for example Philornis downsi Dodge & Aitken. Finally, we consider the impact of climate change in the context of the use of the SIT against these pests. Given the recent dramatic decline in insect biodiversity, investing in environmentally friendly means of pest control should be a priority. We conclude that SIT should be promoted in the region, and leadership and political will is needed for continued success of SIT in the Neotropics.
Selfish genetic elements and male fertility
15183R. L. Verspoor, T. A. R. Price and N. Wedell, Philosophical Transactions of the Royal Society B-Biological Sciences, 375:7. 2020-10-20 14:40:03.
Selfish genetic elements (SGEs) are diverse and near ubiquitous in Eukaryotes and can be potent drivers of evolution. Here, we discuss SGEs that specifically act on sperm to gain a transmission advantage to the next generation. The diverse SGEs that affect sperm often impose costs on carrier males, including damaging ejaculates, skewing offspring sex ratios and in particular reducing sperm-competitive success of SGE-carrying males. How males and females tolerate and mitigate against these costs is a dynamic and expanding area of research. The intense intra-genomic conflict that these selfish elements generate could also have implications for male fertility and spermatogenesis more widely. This article is part of the theme issue 'Fifty years of sperm competition'.
Fruit fly breakthrough puts killer mozzies on notice
14812V. Tressider, The Lighthouse, 2020-10-19 15:34:08.
A new designer fruit fly paves the way for scientists to replace disease-carrying mosquitoes with harmless, genetically modified versions, says Macquarie University researcher Dr Maciej Maselko.
Inherently confinable split-drive systems in Drosophila
14294G. Terradas, A. B. Buchman, J. B. Bennett, I. Shriner, J. M. Marshall, O. S. Akbari and E. Bier, bioRxiv, 2020.09.03.282079. 2020-09-03 14:16:46.
Here, we test split gene-drive (sGD) systems in Drosophila melanogaster that were inserted into essential genes required for viability (rab5, rab11, prosalpha2) or fertility (spo11). I
A home and rescue gene drive forces its inheritance stably persisting in populations
14006N. P. Kandul, J. Liu, J. B. Bennett, J. M. Marshall and O. Akbari, bioRxiv, 2020.08.21.261610. 2020-08-23 17:46:58.
We demonstrate that HomeR can achieve nearly ~100% transmission enabling it to persist at genotypic fixation in several multi-generational population cage experiments, underscoring its long term stability.
Engineered Reproductively Isolated Species Drive Reversible Population Replacement
13837A. Buchman, I. Shriner, T. Yang, J. Liu, I. Antoshechkin, J. M. Marshall, M. W. Perry and O. S. Akbari, bioRxiv, 2020.08.09.242982. 2020-08-10 15:42:26.
Engineered reproductive species barriers are useful for impeding gene flow and driving desirable genes into wild populations in a reversible threshold-dependent manner. We engineer multiple reproductively isolated SPECIES and demonstrate their threshold-dependent gene drive capabilities in D. melanogaster.
CRISPR gene drives could eliminate many vector-driven pests and diseases, but challenges remain
13631J. Champer, Genetic Literacy Project, 2020-08-06 14:11:01.
A functioning gene drive system could fundamentally change our strategies for the control of vector-borne diseases by facilitating rapid dissemination of transgenes that prevent pathogen transmission or reduce vector capacity. CRISPR/Cas9 gene drive promises such a mechanism, which works by converting cells that are heterozygous for the drive construct into homozygotes, thereby enabling super-Mendelian inheritance.
Extensive Recombination Suppression and Epistatic Selection Causes Chromosome-Wide Differentiation of a Selfish Sex Chromosome in Drosophila pseudoobscura
14296Z. L. Fuller, S. A. Koury, C. J. Leonard, R. E. Young, K. Ikegami, J. Westlake, S. Richards, S. W. Schaeffer and N. Phadnis, Genetics, 216:205. 2020-07-30 14:22:50.
Here, we conduct a multifaceted study of the multiply inverted Drosophila pseudoobscura SR chromosome to understand the evolutionary history, genetic architecture, and present-day dynamics that shape this enigmatic selfish chromosome.
Chemical controllable gene drive in Drosophila
13773D. Chae, J. Lee, N. Lee, K. Park, S. J. Moon and H. H. Kim, ACS Synthetic Biology, in press. 2020-07-30 12:48:10.
Here, we report a chemical-induced control of gene drive. We prepared a CRISPR-based gene drive system that can be removed by a site-specific recombinase, Rippase, the expression of which is induced by the chemical RU486 in fruit flies. Exposure of fruit flies to RU486 resulted in 7-12% removal of gene drive elements at each generation, leading to a significant reduction in gene drive-fly propagation.
Nix alone is sufficient to convert female Aedes aegypti into fertile males and myo-sex is needed for male flight
13780A. Aryan, M. A. E. Anderson, J. K. Biedler, Y. M. Qi, J. M. Overcash, A. N. Naumenko, M. V. Sharakhova, C. H. Mao, Z. N. Adelman and Z. J. Tu, Proceedings of the National Academy of Sciences of the United States of America, 117:17702-17709. 2020-07-28 13:17:04.
Here, we report the generation of multiple transgenic lines that express Nix under the control of its own promoter. Genetic and molecular analyses of these lines provided insights unattainable from previous transient experiments. We show that the Nix transgene alone, in the absence of the M-locus, was sufficient to convert females into males with all male-specific sexually dimorphic features and male-like gene expression.
Analysis of a Strong Suppressor of Segregation Distorter inDrosophila melanogaster
14264R. G. Temin, Genetics, 215:1085-1105. 2020-06-19 14:59:33.
These studies highlight the polygenic nature of distortion and its dependence on a constellation of positive and negative modifiers, provide insight into the stability of Mendelian transmission in natural populations even when a drive system arises, and pave the way for molecular characterization ofSu(SD)whose identity should reveal new information about the mechanism of distortion.
Recessive Z-linked lethals and the retention of haplotype diversity in a captive butterfly population
11972I. J. Saccheri, S. Whiteford, C. J. Yung and A. E. van't Hof, Heredity, 2020-05-13 18:21:56.
Sex chromosomes are predicted to harbour elevated levels of sexually antagonistic variation due to asymmetries in the heritability of recessive traits in the homogametic versus heterogametic sex.
Development and testing of a novel killer–rescue self-limiting gene drive system in Drosophila melanogaster
11214S. H. Webster, M. R. Vella and M. J. Scott, Proceedings of the Royal Society B: Biological Sciences, 287:20192994. 2020-04-15 15:04:49.
Here we report the development and testing of a novel self-limiting gene drive system, Killer–Rescue (K–R), in Drosophila melanogaster. This system is composed of an autoregulated Gal4 Killer (K) and a Gal4-activated Gal80 Rescue (R). Overexpression of Gal4 is lethal, but in the presence of R activation of Gal80 leads to much lower levels of Gal4 and rescue of lethality. We demonstrate that with a single 2 : 1 engineered to wild-type release, K drives R through the population and after nine generations, more than 98% of the population carry R and less than 2% of the population are wild-type flies. We discuss how this simple K–R gene drive system may be readily adapted for population replacement in a human health pest, Aedes aegypti, or for population suppression in an agricultural pest, Drosophila suzukii.
Engineering multiple species-like genetic incompatibilities in insects
12543M. Maselko, N. Feltman, A. Upadhyay, A. Hayward, S. Das, N. Myslicki, A. J. Peterson, M. B. O’Connor and M. J. Smanski, bioRxiv, 2020-04-05 17:32:23.
Speciation constrains the flow of genetic information between populations of sexually reproducing organisms. Gaining control over mechanisms of speciation would enable new strategies to manage wild populations of disease vectors, agricultural pests, and invasive species. Additionally, such control would provide safe biocontainment of transgenes and gene drives. Natural speciation can be driven by pre-zygotic barriers that prevent fertilization or by post-zygotic genetic incompatibilities that render the hybrid progeny inviable or sterile. Here we demonstrate a general approach to create engineered genetic incompatibilities (EGIs) in the model insect Drosophila melanogaster. Our system couples a dominant lethal transgene with a recessive resistance allele. EGI strains that are homozygous for both elements are fertile and fecund when they mate with similarly engineered strains, but incompatible with wild-type strains that lack resistant alleles. We show that EGI genotypes can be tuned to cause hybrid lethality at different developmental life-stages. Further, we demonstrate that multiple orthogonal EGI strains of D. melanogaster can be engineered to be mutually incompatible with wild-type and with each other. Our approach to create EGI organisms is simple, robust, and functional in multiple sexually reproducing organisms.
Engineering a minimal gene drive system for integral replacement in Drosophila melanogaster
25648A. Nash, Imperial College London, 2020-04-01 07:48:50.
Gene drives represent a powerful tool for the control of vector-borne diseases. By suppressing or replacing vector populations, laboratory studies have highlighted the potential for this group of tools to make a powerful impact on the burden of zoonotic disease. Current genetic drive systems have a number of limitations, namely their complexity, susceptibility to genetic resistance, and a high regulatory threshold. Here we suggest a novel design paradigm for the creation of replacement gene drives, which we have termed ‘Integral Replacement’. By splitting drive constructs, and integrating components into endogenous loci, we have aimed to engineer a minimal drive system, with low fitness cost, higher resilience to resistance alleles, and with greater flexibility for field testing. In so doing we have generated a model that illustrates increases in efficacy versus existing drive systems, and expanded on work performed on intronic gRNA cassettes. We subsequently were able to build prototype Integral Gene Drive (IGD) components, and demonstrate their efficacy using the model organism Drosophila melanogaster, providing evidence for an initial proof-of-principle for this novel design paradigm.
A fly model establishes distinct mechanisms for synthetic CRISPR/Cas9 sex distorters
7973B. Fasulo, A. Meccariello, M. Morgan, C. Borufka, P. A. Papathanos and N. Windbichler, PLOS Genetics, 16:e1008647. 2020-03-13 15:02:19.
Author summary Harmful insect populations can be eliminated for a lack of females if they are made to produce mostly male offspring. There are genes that occur naturally that make males produce mostly sons and, although we don’t know exactly how they work, this appears to coincide with damage to the X-chromosome during the production of sperm. Recently, we showed in a mosquito species that such sex-biasing genes could also be constructed artificially from first principles. To better understand if this works in other species too, we designed and built male-biasing genes of two types in the fruit fly and determined what is needed to for a shift towards males. We show how different ways of cutting the X-chromosome DNA at different times with CRISPR, results in distinct outcomes and started to ask what cellular processes are involved in this. These models will help us to design such genes for the control of insect species that transmit disease or threaten crops.
Genetic Variation and Potential for Resistance Development to the tTA Overexpression Lethal System in Insects
7939K. E. Knudsen, W. R. Reid, T. M. Barbour, L. M. Bowes, J. Duncan, E. Philpott, S. Potter and M. J. Scott, G3: Genes|Genomes|Genetics, Early Online:g3.400990.2020. 2020-02-05 20:27:28.
Release of insect pests carrying the dominant lethal tetracycline transactivator (tTA) overexpression system has been proposed as a means for population suppression. High levels of the tTA transcription factor are thought to be toxic due to either transcriptional squelching or interference with protein ubiquitination. Here we utilized the Drosophila melanogaster Genetic Reference Panel (DGRP) to examine the influence of genetic variation on the efficacy of a female-specific tTA overexpression system. The level of female lethality between DGRP lines varied from 11 to 97% with a broad sense heritability of 0.89. A genome-wide association analysis identified 192 allelic variants associated with high or low lethality (p<10-5), although none were significant when corrected for multiple testing. 151 of the variants fell within 108 genes that were associated with several biological processes including transcription and protein ubiquitination. In four lines with high female lethality, tTA RNA levels were similar or higher than in the parental tTA overexpression strain. In two lines with low lethality, tTA levels were 2-fold lower than in the parental strain. However, in two other lines with low lethality, tTA levels were only 0-30% lower. RNAseq analysis identified genes that were up or downregulated in the low female lethal lines compared to the four high lethal lines. For example, genes associated with RNA processing and rRNA maturation were significantly upregulated in low lethal lines. Our data suggest that standing genetic variation in an insect population could provide multiple mechanisms for resistance to the tTA overexpression system.
Autosomal suppression and fitness costs of an old driving X chromosome in Drosophila testacea
7363G. Keais, S. Lu and S. Perlman, Journal of Evolutionary Biology, 2020-01-28 21:58:18.
Driving X chromosomes (XDs) are meiotic drivers that bias their own transmission through males by killing Y-bearing gametes. These chromosomes can in theory spread rapidly in populations and cause extinction, but many are found as balanced polymorphisms or as ?cryptic? XDs shut down by drive suppressors. The relative likelihood of these outcomes, as well as the evolutionary pathways through which they come about, are not well-understood. An XD was recently discovered in the mycophagous fly, Drosophila testacea, presenting the opportunity to compare this XD with the well-studied XD of its sister species, Drosophila neotestacea. Comparing features of independently evolved XDs in young sister species is a promising avenue towards understanding how XDs and their counteracting forces change over time. In contrast to the XD of D. neotestacea, we find that the XD of D. testacea is old, with its origin predating the radiation of three species: D. testacea, D. neotestacea, and their shared sister species, Drosophila orientacea. Motivated by the suggestion that older XDs should be more deleterious to carriers, we assessed the effect of the XD on both male and female fertility. Unlike what is known from D. neotestacea, we found a strong fitness cost in females homozygous for the XD in D. testacea: a large proportion of homozygous females failed to produce offspring after being housed with males for several days. Our male fertility experiments show that while XD male fertility is lower under sperm depleting conditions, XD males have comparable fertility to males carrying a standard X chromosome under a free mating regime, which may better approximate conditions in wild populations of D. testacea. Lastly, we demonstrate the presence of autosomal suppression of X chromosome drive. Our results provide support for a model of XD evolution where the dynamics of young XDs are governed by fitness consequences in males, whereas in older XD systems, both suppression and fitness consequences in females likely supersede male fitness costs.
A selfish genetic element linked to increased lifespan impacts metabolism in female house mice
5652Lopes, P. C. and A. K. Lindholm, The Journal of Experimental Biology, 2019:212704. 2019-12-17 18:01:15.
Gene drive systems can lead to the evolution of traits that further enhance the transmission of the driving element. In gene drive, one allele is transmitted to offspring at a higher frequency than the homologous allele. This has a range of consequences, which generally include a reduction in fitness of the carrier of the driving allele, making such systems “selfish”. The t haplotype is one such driver, found in house mice. It is linked to a reduction in litter size in matings among heterozygous animals, but also to increased lifespan in wild females that carry it. Here, we tested whether carrying the t haplotype was associated with altered resting metabolic rate (RMR). We show that females carrying the t haplotype decrease RMR as they increase in size, compared to wildtype females or males of either genotype. Our study elucidates a plausible mechanism by which a selfish genetic element increases lifespan.
Gene drive and resilience through renewal with next generation Cleave and Rescue selfish genetic elements
5602Oberhofer, G., T. Ivy and B. A. Hay, bioRxiv, 2019:2019.2012.2013.876169. 2019-12-17 16:01:29.
Gene drive-based strategies for modifying populations face the problem that genes encoding cargo and the drive mechanism are subject to separation, mutational inactivation, and loss of efficacy. Resilience, an ability to respond to these eventualities in ways that restore population modification with functional genes is needed for long-term success. Here we show that resilience can be achieved through cycles of population modification with Cleave and Rescue (ClvR) selfish genetic elements. ClvR comprises a DNA sequence-modifying enzyme such as Cas9/gRNAs that disrupts endogenous versions of an essential gene, and a recoded version of the essential gene resistant to cleavage. ClvR spreads by creating conditions in which those lacking ClvR die because they lack functional versions of the essential gene. Cycles of modification can in principal be carried out if two ClvR elements targeting different essential genes are located at the same genomic position, and one of them, ClvRn+1, carries a Rescue transgene from an earlier element, ClvRn. ClvRn+1 should spread within a population of ClvRn, while also bringing about a decrease in its frequency. To test this hypothesis we first show that multiple ClvRs, each targeting a different essential gene, function when located at a common chromosomal position in Drosophila. We then show that when several of these also carry the Rescue from a different ClvR, they spread to transgene fixation in populations fixed for the latter, and at its expense. Therefore, genetic modifications of populations can be overwritten with new content, providing an ongoing point of control.
Mass-Rearing of Drosophila suzukii for Sterile Insect Technique Application: Evaluation of Two Oviposition Systems
17766F. Sassù, K. Nikolouli, S. Caravantes, G. Taret, R. Pereira, M. J. B. Vreysen, C. Stauffer and C. Cáceres, Insects, 10. 2019-12-12 15:07:36.
Drosophila suzukii (Diptera: Drosophilidae) is an invasive pest of a wide range of commercial soft-skinned fruits. To date, most management tactics are based on spraying of conventional and/or organic insecticides, baited traps, and netting exclusion. Interest has been expressed in using the sterile insect technique (SIT) as part of area-wide integrated pest management (AW-IPM) programs to control D. suzukii infestations. Mass-rearing protocols are one of the prerequisites for successful implementation of the SIT. To establish mass-rearing methods for this species, two different egg-collection systems were developed and compared with respect to the number of eggs produced, egg viability, pupa and adult recovery, adult emergence rate, and flight ability. Female flies kept in cages equipped with a wax panel produced significantly more eggs with higher viability and adult emergence rate, as compared to the netted oviposition system. The wax panel system was also more practical and less laborious regarding the collection of eggs. Furthermore, the wax panel oviposition system can be adapted to any size or design of an adult cage. In conclusion, this system bears great promise as an effective system for the mass production of D. suzukii for SIT.
Does meiotic drive alter male mate preference?
7960S. R. Finnegan, L. Nitsche, M. Mondani, M. F. Camus, K. Fowler and A. Pomiankowski, Behavioral Ecology, 13:194-201. 2019-10-20 14:14:20.
Male mate preferences have been demonstrated across a range of species, including the Malaysian stalk-eyed fly, Teleopsis dalmanni. This species is subject to sex-ratio (SR), an X-linked male meiotic driver, which causes the dysfunction of Y-sperm and the production of all-female broods. While there has been work considering female avoidance of meiotic drive males, the mating decisions of drive-bearing males have not been considered previously. Drive males may be less able to bear the cost of choice as SR is associated with a low-frequency inversion that causes reduced organismal fitness. Drive males may also experience weaker selection for preference maintenance if they are avoided by females. Using binary choice trials, across two experiments, we confirmed male preference for large (fecund) females but found no evidence that the strength of male preference differs between drive and standard males. We showed that large eyespan males displayed strong preference for large females, whereas small eyespan males showed no preference. Taken together, these results suggest that, even though meiotic drive is associated with lower genetic quality, it does not directly interfere with male mate preference among available females. However, as drive males tend to have smaller eyespan (albeit only similar to 5% on average), this will to a minor extent weaken their strength of preference.
Sex-ratio meiotic drive shapes the evolution of the Y chromosome in Drosophila simulans
6174Q. Helleu, C. Courret, D. Ogereau, K. L. Burnham, N. Chaminade, M. Chakir, S. Aulard and C. Montchamp-Moreau, Molecular Biology and Evolution, 36:2668-2681. 2019-07-10 18:50:56.
The recent emergence and spread of X-linked segregation distorters-called "Paris" system-in the worldwide species Drosophila simulans has elicited the selection of drive-resistant Y chromosomes. Here, we investigate the evolutionary history of 386 Y chromosomes originating from 29 population samples collected over a period of 20 years, showing a wide continuum of phenotypes when tested against the Paris distorters, from high sensitivity to complete resistance (males sire similar to 95% to similar to 40% female progeny). Analyzing around 13 kb of Y-linked gene sequences in a representative subset of nine Y chromosomes, we identified only three polymorphic sites resulting in three haplotypes. Remarkably, one of the haplotypes is associated with resistance. This haplotype is fixed in all samples from Sub-Saharan Africa, the region of origin of the drivers. Exceptionally, with the spread of the drivers in Egypt and Morocco, we were able to record the replacement of the sensitive lineage by the resistant haplotype in real time, within only a few years. In addition, we performed in situ hybridization, using satellite DNA probes, on a subset of 21 Y chromosomes from six locations. In contrast to the low molecular polymorphism, this revealed extensive structural variation suggestive of rapid evolution, either neutral or adaptive. Moreover, our results show that intragenomic conflicts can drive astonishingly rapid replacement of Y chromosomes and suggest that the emergence of Paris segregation distorters in East Africa occurred less than half a century ago.
CRISPR gene drive efficiency and resistance rate is highly heritable with no common genetic loci of large effect
3901Champer, JW, Z. X.; Luthra, A.; Reeves, R.; Chung, J.; Liu, C.; Lee, Y. L.; Liu, J. X.; Yang, E.; Messer, P. W.; Clark, A. G., Genetics, 212:333-341. 2019-01-19 00:00:00.
Gene drives could allow for control of vector-borne diseases by directly suppressing vector populations or spreading genetic payloads designed to reduce pathogen transmission. Clustered regularly interspaced short palindromic repeat (CRISPR) homing gene drives work by cleaving wild-type alleles, which are then converted to drive alleles by homology-directed repair, increasing the frequency of the drive in a population over time. However, resistance alleles can form when end-joining repair takes place in lieu of homology-directed repair. Such alleles cannot be converted to drive alleles, which would eventually halt the spread of a drive through a population. To investigate the effects of natural genetic variation on resistance formation, we developed a CRISPR homing gene drive in Drosophila melanogaster and crossed it into the genetically diverse Drosophila Genetic Reference Panel (DGRP) lines, measuring several performance parameters. Most strikingly, resistance allele formation postfertilization in the early embryo ranged from 7 to 79% among lines and averaged 42 +/- 18%. We performed a genome-wide association study using our results in the DGRP lines, and found that the resistance and conversion rates were not explained by common alleles of large effect, but instead there were several genetic polymorphisms showing weak association. RNA interference knockdown of several genes containing these polymorphisms confirmed their effect, but the small effect sizes imply that their manipulation would likely yield only modest improvements to the efficacy of gene drives.
Controlling invasive rodents via synthetic gene drive and the role of polyandry
3927Manser, AC, S. J.; Sutter, A.; Blondel, D. V.; Serr, M.; Godwin, J.; Price, T. A. R., Proceedings of the Royal Society B-Biological Sciences, 286:9. 2019-01-05 00:00:00.
House mice are a major ecosystem pest, particularly threatening island ecosystems as a non-native invasive species. Rapid advances in synthetic biology offer new avenues to control pest species for biodiversity conservation. Recently, a synthetic sperm-killing gene drive construct called t-Sry has been proposed as a means to eradicate target mouse populations owing to a lack of females. A factor that has received little attention in the discussion surrounding such drive applications is polyandry. Previous research has demonstrated that sperm-killing drivers are extremely damaging to a male's sperm competitive ability. Here, we examine the importance of this effect on the t-Sry system using a theoretical model. We find that polyandry substantially hampers the spread of t-Sry such that release efforts have to be increased three-to sixfold for successful eradication. We discuss the implications of our finding for potential pest control programmes, the risk of drive spread beyond the target population, and the emergence of drive resistance. Our work highlights that a solid understanding of the forces that determine drive dynamics in a natural setting is key for successful drive application, and that exploring the natural diversity of gene drives may inform effective gene drive design.
Sustainability as a framework for considering gene drive mice for invasive rodent eradication
3886Barnhill-Dilling, SKS, M.; Blondel, D. V.; Godwin, J., Sustainability, 11:1334. 2019-01-04 00:00:00.
Gene drives represent a dynamic and controversial set of technologies with applications that range from mosquito control to the conservation of biological diversity on islands. Currently, gene drives are being developed in mice that may one day serve as an important tool for reducing invasive rodent pests, a key threat to island biodiversity and economies. Gene drives in mice are still in development in laboratories, and wild release of modified mice is likely a distant reality. However, technological changes outpace the existing capacity of regulatory frameworks, and thus require integrated governance frameworks. We suggest sustainability-which gives equal consideration to the environment, economy, and society-as one framework for addressing complexity and uncertainty in the governance of emerging gene drive technologies for invasive species management. We explore the impacts of rodent gene drives on island environments, including potential conservation and restoration of island biodiversity. We outline considerations for rodent gene drives on island economies, including impacts on agricultural and tourism losses, and reductions in biosecurity costs. Finally, we address the social dimension as an essential space for deliberation that will be integral to evaluating the potential deployment of gene drive rodents on islands.
Multiplexing gRNAs to Hedge Against Resistance to Gene Drive
4720Travis Van Warmerdam, IGTRCN, 2018-11-25 00:00:00.
Recently, Oberhofer et al (2018) published a paper examining the mechanisms of homing endonuclease gene drives in The Proceedings of the National Academy of Sciences. They used a novel nuclease-encoding cassette containing four multiplexed gRNAs targeting genes required for viability or female fertility in Drosophila melanogaster.
Cas9 Gene Drive, Sex-Conversion and Evolved Resistance
4721Anna Buchman, IGTRCN, 2018-09-24 00:00:00.
In a recent manuscript, KaramiNejadRanjbar et al. demonstrate the development of a proof of principle Cas9-based suppression gene drive in D. melanogaster that can be applied to pest insects, and discuss the implications of resistance allele formation for practical use of such a drive system.
Rapid comeback of males: evolution of male-killer suppression in a green lacewing population
3979Hayashi, MN, M.; Kageyama, D., Proceedings of the Royal Society B-Biological Sciences, 285:6. 2018-01-17 00:00:00.
Evolutionary theory predicts that the spread of cytoplasmic sex ratio distorters leads to the evolution of host nuclear suppressors, although there are extremely few empirical observations of this phenomenon. Here, we demonstrate that a nuclear suppressor of a cytoplasmic male killer has spread rapidly in a population of the green lacewing Mallada desjardinsi. An M. desjardinsi population, which was strongly female-biased in 2011 because of a high prevalence of the male-killing Spiroplasma endosymbiont, had a sex ratio near parity in 2016, despite a consistent Spiroplasma prevalence. Most of the offspring derived from individuals collected in 2016 had 1 : 1 sex ratios in subsequent generations. Contrastingly, all-female or female-biased broods appeared frequently from crossings of these female offspring with males derived from a laboratory line founded by individuals collected in 2011. These results suggest near-fixation of a nuclear suppressor against male killing in 2016 and reject the notion that a non-male-killing Spiroplasma variant has spread in the population. Consistently, no significant difference was detected in mitochondrial haplotype variation between 2011 and 2016. These findings, and earlier findings in the butterfly Hypolimnas bolina in Samoa, suggest that these quick events of male recovery occur more commonly than is generally appreciated.
Selfish genetic elements
3955Agren, JAC, A. G., PLOS Genetics, 14:20. 2018-01-13 00:00:00.
Selfish genetic elements (historically also referred to as selfish genes, ultra-selfish genes, selfish DNA, parasitic DNA, genomic outlaws) are genetic segments that can enhance their own transmission at the expense of other genes in the genome, even if this has no or a negative effect on organismal fitness. [1-6] Genomes have traditionally been viewed as cohesive units, with genes acting together to improve the fitness of the organism. However, when genes have some control over their own transmission, the rules can change, and so just like all social groups, genomes are vulnerable to selfish behaviour by their parts. Early observations of selfish genetic elements were made almost a century ago, but the topic did not get widespread attention until several decades later. Inspired by the gene-centred views of evolution popularized by George Williams[7] and Richard Dawkins,[8] two papers were published back-to-back in Nature in 1980-by Leslie Orgel and Francis Crick[9] and Ford Doolittle and Carmen Sapienza[10] respectively-introducing the concept of selfish genetic elements (at the time called "selfish DNA") to the wider scientific community. Both papers emphasized that genes can spread in a population regardless of their effect on organismal fitness as long as they have a transmission advantage. Selfish genetic elements have now been described in most groups of organisms, and they demonstrate a remarkable diversity in the ways by which they promote their own transmission.[11] Though long dismissed as genetic curiosities, with little relevance for evolution, they are now recognized to affect a wide swath of biological processes, ranging from genome size and architecture to speciation.[12]
Gene flow mediates the role of sex chromosome meiotic drive during complex speciation
3994Meiklejohn, CDL, Emily L.; Gordon, Kathleen E.; Rzatkiewicz, Thomas; Kingan, Sarah B.; Geneva, Anthony J.; Vedanayagam, Jeffrey P.; Muirhead, Christina A.; Garrigan, Daniel; Stern, David L.; Presgraves, Daven C., eLife, 7:e35468. 2018-01-12 00:00:00.
During speciation, sex chromosomes often accumulate interspecific genetic incompatibilities faster than the rest of the genome. The drive theory posits that sex chromosomes are susceptible to recurrent bouts of meiotic drive and suppression, causing the evolutionary build-up of divergent cryptic sex-linked drive systems and, incidentally, genetic incompatibilities. To assess the role of drive during speciation, we combine high-resolution genetic mapping of X-linked hybrid male sterility with population genomics analyses of divergence and recent gene flow between the fruitfly species, Drosophila mauritiana and D. simulans. Our findings reveal a high density of genetic incompatibilities and a corresponding dearth of gene flow on the X chromosome. Surprisingly, we find that a known drive element recently migrated between species and, rather than contributing to interspecific divergence, caused a strong reduction in local sequence divergence, undermining the evolution of hybrid sterility. Gene flow can therefore mediate the effects of selfish genetic elements during speciation.
Carrying a selfish genetic element predicts increased migration propensity in free-living wild house mice
4012Runge, J-NL, Anna K., Proceedings of the Royal Society B: Biological Sciences, 285:20181333. 2018-01-10 00:00:00.
Life is built on cooperation between genes, which makes it vulnerable to parasitism. Selfish genetic elements that exploit this cooperation can achieve large fitness gains by increasing their transmission relative to the rest of the genome. This leads to counter-adaptations that generate unique selection pressures on the selfish genetic element. This arms race is similar to host–parasite coevolution, as some multi-host parasites alter the host’s behaviour to increase the chance of transmission to the next host. Here, we ask if, similarly to these parasites, a selfish genetic element in house mice, the t haplotype, also manipulates host behaviour, specifically the host’s migration propensity. Variants of the t that manipulate migration propensity could increase in fitness in a meta-population. We show that juvenile mice carrying the t haplotype were more likely to emigrate from and were more often found as migrants within a long-term free-living house mouse population. This result may have applied relevance as the t has been proposed as a basis for artificial gene drive systems for use in population control.
Genetic conflicts: the usual suspects and beyond
4058McLaughlin, RNM, H. S., Journal of Experimental Biology, 220:6-17. 2017-01-16 00:00:00.
Selfishness is pervasive and manifests at all scales of biology, from societies, to individuals, to genetic elements within a genome. The relentless struggle to seek evolutionary advantages drives perpetual cycles of adaptation and counter-adaptation, commonly referred to as Red Queen interactions. In this review, we explore insights gleaned from molecular and genetic studies of such genetic conflicts, both extrinsic (between genomes) and intrinsic (within genomes or cells). We argue that many different characteristics of selfish genetic elements can be distilled into two types of advantages: an over-replication advantage (e.g. mobile genetic elements in genomes) and a transmission distortion advantage (e.g. meiotic drivers in populations). These two general categories may help classify disparate types of selfish genetic elements.
Sperm competition suppresses gene drive among experimentally evolving populations of house mice
4056Manser, AL, A. K.; Simmons, L. W.; Firman, R. C., Molecular Ecology, 26:5784-5792. 2017-01-14 00:00:00.
Drive genes are genetic elements that manipulate the 50% ratio of Mendelian inheritance in their own favour, allowing them to rapidly propagate through populations. The action of drive genes is often hidden, making detection and identification inherently difficult. Yet drive genes can have profound evolutionary consequences for the populations that harbour them: most known drivers are detrimental to organismal gamete development, reproduction and survival. In this study, we identified the presence of a well-known drive gene called t haplotype post hoc in eight replicate selection lines of house mice that had been evolving under enforced monandry or polyandry for 20 generations. Previous work on these selection lines reported an increase in sperm competitive ability in males evolving under polyandry. Here, we show that this evolutionary response can be partly attributed to gene drive. We demonstrate that drive-carrying males are substantially compromised in their sperm competitive ability. As a consequence, we found that t frequencies declined significantly in the polyandrous lines while remaining at stable, high levels in the monandrous lines. For the first time in a vertebrate, we thus provide direct experimental evidence that the mating system of a species can have important repercussions on the spread of drive genes over evolutionary relevant timescales. Moreover, our work highlights how the covert action of drive genes can have major, potentially unintended impact on our study systems.
Sry gene drive for rodent control: Reply to Gemmell and Tompkins
4051Kanavy, DS, M., Trends in Ecology & Evolution, 32:315-316. 2017-01-09 00:00:00.
We would like to thank Gemmell and Tompkins for their interest and comments onthe articlebyPiaggioet al. [1].Theissues raised by Gemmell and Tompkins [2] are very pertinent, and they correctly identified that the format of the article did not lend itself to a comprehensive discussion of the ideas of using gene drives in mice. The method being considered in the Piaggio et al. article is to utilize a naturally occurring t-allele transgene (Tg) to sex-bias amouse population, causing it to crash. Inserting the sex-determining region on the Y chromosome (Sry) into the Tg allows biased inheritance where the majority of the offspring born are phenotypically male.
Towards the genetic control of invasive species
4047Harvey-Samuel, TA, T.; Alphey, L., Biological Invasions, 19:1683-1703. 2017-01-05 00:00:00.
Invasive species remain one of the greatest threats to global biodiversity. Their control would be enhanced through the development of more effective and sustainable pest management strategies. Recently, a novel form of genetic pest management (GPM) has been developed in which the mating behaviour of insect pests is exploited to introduce genetically engineered DNA sequences into wild conspecific populations. These 'transgenes' work in one or more ways to reduce the damage caused by a particular pest, for example reducing its density, or its ability to vector disease. Although currently being developed for use against economically important insect pests, these technologies would be highly appropriate for application against invasive species that threaten biodiversity. Importantly, these technologies have begun to advance in scope beyond insects to vertebrates, which include some of the world's worst invasives. Here we review the current state of this rapidly progressing field and, using an established set of eradication criteria, discuss the characteristics which make GPM technologies suitable for application against invasive pests.
Concept and history of genetic control
6014Scott, M. J. and Benedict, M. Q., Genetic Control of Malaria and Dengue, 2:31-54. 2016-12-30 20:16:45.
Genetic control of insects is an established method, mainly for insects that are important crop and veterinary pests such as medflies and screwworm. Efforts to use the same technologies against insects of medical importance, especially mosquitoes, have had limited success. The successes against mosquitoes have been accomplished using forms of both conventional and modern methods, both of which are promising. In this chapter, we provide highlights of the development of genetic control of agricultural pests and describe how the development of methods against mosquitoes reflects those advances. While admiring successful genetic control programs is motivating, we suggest that much can also be learned from both past successful and failed efforts, as doing so will increase our ability to improve future activities.
Mitonuclear interactions, mtDNA-mediated thermal plasticity, and implications for the Trojan Female Technique for pest control
13745J. N. Wolff, D. M. Tompkins, N. J. Gemmell and D. K. Dowling, Scientific Reports, 6. 2016-07-21 19:45:17.
Here we test whether the male-sterilizing effects previously associated with the mt: Cyt-b mutation are consistent across three thermal and three nuclear genomic contexts. The effects of this mutation were indeed moderated by the nuclear background and thermal environment, but crucially the fertility of males carrying the mutation was invariably reduced relative to controls. This mutation thus constitutes a promising candidate for the further development of the TFT.
No evidence for female discrimination against male house mice carrying a selfish genetic element
4103Sutter, AL, A. K., Current Zoology, 62:675-685. 2016-01-21 00:00:00.
Meiotic drivers distort transmission to the next generation in their favor, with detrimental effects on the fitness of their homologues and the rest of the genome. Male carriers of meiotic drivers commonly inflict costs on their mates through genetic incompatibility, reduced fecundity, or biased brood sex ratios. Given these costs, evidence for female discrimination against male carriers is surprisingly rare. One of few examples is the t haplotype in house mice, a meiotic driver that shows strong transmission distortion in males and is typically homozygote lethal. As a consequence, mating between 2 t heterozygous (+/t) mice leads to high embryo mortality. Previous experiments showing that +/t females avoid this incompatibility cost by preferring +/+versus +/t males have inferred preference based on olfactory cues or brief social interactions. Evidence from mating contexts in laboratory settings and semi-natural populations has been inconclusive. Here, we investigated female choice from a large number of no-choice mating trials. We found no evidence for discrimination against +/t males based on mating, remating, and copulatory behavior. Further, we found no evidence for avoidance of incompatibility through selective interactions between gametes. The likelihood of mating showed significant effects of female weight and genotype, suggesting that our test paradigm enabled females to exhibit mate choice. We discuss the strengths and limitations of our approach. By explicitly considering selection at both the individual and gene level, we argue why precopulatory female discrimination by +/t females may be less evolutionarily stable than discrimination by all females based on postcopulatory mechanisms.
Cas9-triggered chain ablation of cas9 as a gene drive brake
4106Wu, BL, L. Q.; Gao, X. J. J., Nature Biotechnology, 34:137-138. 2016-01-04 00:00:00.
We designed and synthesized a transgene system that we named Cas9-triggered chain ablation (CATCHA). The CATCHA transgene encodes a guide RNA (gRNA) that is expressed ubiquitously from a U6:2 promoter. The gRNA targets a site within the DNA sequence of cas9. The guide RNA is flanked by homology arms (of 1,042 bp and 1,003 bp) that match the cas9 sequences next to the gRNA-specified cleavage site (Fig. 1a). In the presence of both CATCHA and cas9, Cas9 proteins will be guided to cleave the cas9 genomic locus from which Cas9 proteins are expressed. Upon repair of the cleaved cas9 by homology-directed repair (HDR), the cas9 locus will be converted to CATCHA. Such conversion in heterozygous offspring favors amplification of CATCHA in the cas9- carrying population
Meiotic drive changes sperm precedence patterns in house mice: potential for male alternative mating tactics?
4104Sutter, AL, A. K., BMC Evolutionary Biology, 16:15. 2016-01-02 00:00:00.
Background: With female multiple mating (polyandry), male-male competition extends to after copulation (sperm competition). Males respond to this selective pressure through physiological, morphological and behavioural adaptations. Sperm competitiveness is commonly decreased in heterozygote carriers of male meiotic drivers, selfish genetic elements that manipulate the production of gametes in males. This might give carriers an evolutionary incentive to reduce the risk of sperm competition. Here, we explore this possibility in house mice. Natural populations frequently harbour a well-characterised male driver (t haplotype), which is transmitted to 90 % of heterozygous (+/t) males' offspring. Previous research demonstrated strong detrimental effects on sperm competitiveness, and suggested that +/t males are particularly disadvantaged against wild type males when first-to-mate. Low paternity success in the first-to-mate role is expected to favour male adaptations that decrease the risk of sperm competition by preventing female remating. Genotype-specific paternity patterns (sperm precedence) could lead to genetically determined alternative reproductive tactics that can spread through gene level selection. Here, we seek confirmation that +/t males are generally disadvantaged when first-to-mate and address whether males of different genotypes differ in reproductive tactics (copulatory and morphological) to maximise individual or driver fitness. Finally, we attempt to explain the mechanistic basis for alternative sperm precedence patterns in this species. Results: We confirmed that +/t males are weak sperm competitors when first to mate. When two +/t males competed, the second-to-mate was more successful, which contrasts with first male sperm precedence when wild type males competed. However, we found no differences between male genotypes in reproductive behaviour or morphology that were consistent with alternative reproductive tactics. Sperm of +/+ and +/t males differed with respect to in vitro sperm features. Premature hypermotility in +/t males' sperm can potentially explain why +/t males are very weak sperm competitors when first-to-mate. Conclusions: Our results demonstrate that meiotic drivers can have strong effects on sperm precedence patterns, and may provide a heritable basis for alternative reproductive tactics motivated by reduced sperm competitiveness. We discuss how experimental and evolutionary constraints may help explain why male genotypes did not show the predicted differences.
Female house mice avoid fertilization by t haplotype incompatible males in a mate choice experiment
4122Manser, AK, B.; Lindholm, A. K., Journal of Evolutionary Biology, 28:54-64. 2015-01-20 00:00:00.
The t haplotype in house mice is a well-known selfish genetic element with detrimental, nonadditive fitness consequences to its carriers: recessive lethal mutations cause t/t homozygotes to perish in utero. Given the severe genetic incompatibility imposed by the t haplotype, we predict females to avoid fertilization by t haplotype incompatible males. Indeed, some of the strongest evidence for compatibility mate choice is related to the t haplotype in house mice. However, all previous evidence for compatibility mate choice in this system is based on olfactory preference. It is so far unknown how general these preferences are and whether they are relevant in an actual mating context. Here, we assess female compatibility mate choice related to t haplotypes in a setting that - for the first time - allowed females to directly interact and mate with males. This approach enabled us to analyse female behaviour during the testing period, and the resulting paternity success and fitness consequences of a given choice. We show that genetic incompatibilities arising from the t haplotype had severe indirect fitness consequences and t females avoided fertilization by t incompatible males. The results are inconclusive whether this avoidance of t fertilization by t females was caused by pre- or post-copulatory processes.
Detrimental effects of an autosomal selfish genetic element on sperm competitiveness in house mice
4126Sutter, AL, A. K., Proceedings of the Royal Society B-Biological Sciences, 282:1-8. 2015-01-04 00:00:00.
Female multiple mating (polyandry) is widespread across many animal taxa and indirect genetic benefits are a major evolutionary force favouring polyandry. An incentive for polyandry arises when multiple mating leads to sperm competition that disadvantages sperm from genetically inferior mates. A reduction in genetic quality is associated with costly selfish genetic elements (SGEs), and studies in invertebrates have shown that males bearing sex ratio distorting SGEs are worse sperm competitors than wild-type males. We used a vertebrate model species to test whether females can avoid an autosomal SGE, the t haplotype, through polyandry. The t haplotype in house mice exhibits strong drive in t heterozygous males by affecting spermatogenesis and is associated with homozygous in utero lethality. We used controlled matings to test the effect of the t haplotype on sperm competitiveness. Regardless of mating order, t heterozygous males sired only 11% of zygotes when competing against wild-type males, suggesting a very strong effect of the t haplotype on sperm quality. We provide, to our knowledge, the first substantial evidence that polyandry ameliorates the harmful effects of an autosomal SGE arising through genetic incompatibility. We discuss potential mechanisms in our study species and the broader implications for the benefits of polyandry.
Meiotic drive influences the outcome of sexually antagonistic selection at a linked locus
4152Patten, MM, Journal of Evolutionary Biology, 27:2360-2370. 2014-01-10 00:00:00.
Most meiotic drivers, such as the t-haplotype in Mus and the segregation distorter (SD) in Drosophila, act in a sex-specific manner, gaining a transmission advantage through one sex although suffering only the fitness costs associated with the driver in the other. Their inheritance is thus more likely through one of the two sexes, a property they share with sexually antagonistic alleles. Previous theory has shown that pairs of linked loci segregating for sexually antagonistic alleles are more likely to remain polymorphic and that linkage disequilibrium accrues between them. I probe this similarity between drive and sexual antagonism and examine the evolution of chromosomes experiencing these selection pressures simultaneously. Reminiscent of previous theory, I find that: the opportunity for polymorphism increases for a sexually antagonistic locus that is physically linked to a driving locus; the opportunity for polymorphism at a driving locus also increases when linked to a sexually antagonistic locus; and stable linkage disequilibrium accompanies any polymorphic equilibrium. Additionally, I find that drive at a linked locus favours the fixation of sexually antagonistic alleles that benefit the sex in which drive occurs. Further, I show that under certain conditions reduced recombination between these two loci is selectively favoured. These theoretical results provide clear, testable predictions about the nature of sexually antagonistic variation on driving chromosomes and have implications for the evolution of genomic architecture.
Requirements for effective malaria control with homing endonuclease genes
4203Deredec, AG, H. C. J.; Burt, A., Proceedings of the National Academy of Sciences of the United States of America, 108:e874-e880. 2011-01-21 00:00:00.
Malaria continues to impose a substantial burden on human health. We have previously proposed that biological approaches to control the mosquito vector of disease could be developed using homing endonuclease genes (HEGs), a class of selfish or parasitic gene that exists naturally in many microbes. Recent lab studies have demonstrated that HEGs can function in mosquitoes. We constructed and analyzed a model of mosquito population genetics and malaria epidemiology to determine how well HEGs need to function in order to have a significant effect on the burden of disease. Our model, combined with currently available data, indicates that populations of Anopheles gambiae could be eliminated by releasing 2-3 HEGs targeting female fertility genes, or a driving-Y chromosome that is transmitted to 75-96% of progeny. Combinations of fertility-targeting HEGs and Y drive may also be effective. It is possible to eliminate the disease without eliminating the vector, but the parameter space producing this outcome appears to be small. HEGs causing a quantitative reduction in adult survival can be more effective than those targeting female fertility, but the selection coefficients that need to be imposed are still large, unless many HEGs are to be released. Simulations show that HEG-based strategies can be effective over socially relevant time frames. Important limiting assumptions of the models are that there is only a single vector species, and we model a homogeneous population, not a landscape. Nevertheless, we conclude that HEG-based approaches could have a transformational effect on malaria control efforts.
Use of Genetically Engineered Fruit Fly and Pink Bollworm in APHIS Plant Pest Control Programs: Final Environmental Impact Statement—October 2008
16049USDA/APHIS, USDA/APHIS, 2008-10-01 20:18:57.
The U.S. Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), in cooperation with several States and foreign countries, is proposing further development of genetically engineered fruit fly species and pink bollworm for use in various applications of the sterile insect technique (SIT) applied to agency invasive plant pest control programs. There have been laboratory and confined field studies to test the efficacy of certain genetic engineering applications that could provide benefits to these programs, but these techniques have not been applied in agency eradication actions or preventive release program (PRP) strategies.
Wolbachia and cytoplasmic incompatibility in mosquitoes
4300Sinkins, SP, Insect Biochemistry and Molecular Biology, 34:723-729. 2004-01-18 00:00:00.
Wolbachia are maternally inherited bacteria that induce cytoplasmic incompatibility in mosquitoes, and are able to use these patterns of sterility to spread themselves through populations. For this reason they have been proposed as a gene drive system for mosquito genetic replacement, as well as for the reduction of population size or for modulating population age structure in order to reduce disease transmission. Here, recent progress in the study of mosquito Wolbachia is reviewed. We now have much more comprehensive estimates of the parameters that can affect the spread of Wolbachia through natural populations from low starting frequencies. and for waves of spread to be maintained in the face of partial barriers to gene flow. In Aedes albopictits these dynamics are extremely favourable, with very high maternal transmission fidelity and levels of incompatibility recorded. Correspondence between measurements taken in the lab and field is much better than in the Drosophila simulans model system. Important research goals are also discussed, including Wolbachia transformation, interspecific transfer and the elucidation of the mechanisms of incompatibility and rescue; all will be aided by a wealth of new Wolbachia genome information. (C) 2004 Elsevier Ltd. All rights reserved.
Transmission ratio distortion in mice
4314Lyon, MF, Annual Review of Genetics, 37:393-408. 2003-01-12 00:00:00.
The most studied example of transmission ratio distortion (TRD) in mice is that of the t-complex. This is a variant-region of Chromosome 17 which exists as a polymorphism in wild mice. Males heterozygous for a t-haplotype and a normal Chr 17 transmit-the t haplotype to >50% of their young, up to 99%.- Homozygous males are-sterile. The TRD produced by-the t-complex, is due to the action of three or more distorter genes (Tcd) on a responder. gene (Tcr). t-Haplotypes are maintained intact by crossover suppression induced by four neighboring inversions, the Tcd and by Tcr loci lying in different inversions. Sperm formation is normal in t/t males, but sperm function is impaired through gross defects in sperm motility. The responder gene has been identified as a fusion gene formed from a sperm motility kinase and a ribosomal S6 kinase. Three candidate distorter genes have also been identified as genes coding for dynein chains, and thus possibly involved in sperm flagellar function.
Site-specific selfish genes as tools for the control and genetic engineering of natural populations
4306Burt, A, Proceedings of the Royal Society B-Biological Sciences, 270:921-928. 2003-01-04 00:00:00.
Site-specific selfish genes exploit host functions to copy themselves into a defined target DNA sequence, and include homing endonuclease genes, group II introns and some LINE-like transposable elements. If such genes can be engineered to target new host sequences, then they can be used to manipulate natural populations, even if the number of individuals released is a small fraction of the entire population. For example, a genetic load sufficient to eradicate a population can be imposed in fewer than 20 generations, if the target is an essential host gene, the knockout is recessive and the selfish gene has an appropriate promoter. There will be selection for resistance, but several strategies are available for reducing the likelihood of it evolving. These genes may also be used to genetically engineer natural populations, by means of population-wide gene knockouts, gene replacements and genetic transformations. By targeting sex-linked loci just prior to meiosis one may skew the population sex ratio, and by changing the promoter one may limit the spread of the gene to neighbouring populations. The proposed constructs are evolutionarily stable in the face of the mutations most likely to arise during their spread, and strategies are also available for reversing the manipulations.
Nonrandom segregation during meiosis: the unfairness of females
4328de Villena, FPMS, C., Mammalian Genome, 12:331-339. 2001-01-06 00:00:00.
Most geneticists assume that chromosome segregation during meiosis is Mendelian (i.e., each allele at each locus is represented equally in the gametes). The great majority of reports that discuss non-Mendelian transmission have focused on systems of gametic selection, such as the mouse t-haplotype and Segregation distorter in Drosophila, or on systems in which post-fertilization selection takes place, Because the segregation of chromosomes in such systems is Mendelian and unequal representation of alleles among offspring is achieved through gamete dysfunction or embryonic death, there is a common perception that true disturbances in the randomness of chromosome segregation are rare and of limited biological significance. In this review we summarize data on nonrandom segregation in a wide variety of genetic systems. Despite apparent differences between some systems, the basic requirements for nonrandom segregation can be deduced from their shared characteristics: i) asymmetrical meiotic division(s); ii) functional asymmetry of the meiotic spindle poles: and iii) functional heterozygosity at a locus that mediates attachment of a chromosome to the spindle. The frequency with which all three of these requirements al e fulfilled in natural populations is an known, but our analyses indicate that nonrandom segregation occurs with sufficient frequency during female meiosis, and in exceptional cases of male meiosis, that it has important biological, clinical, and evolutionary consequences.
Segregation distortion of mouse t-haplotypes: The molecular basis emerges
4346Schimenti, J, Trends in Genetics, 16:240-243. 2000-01-04 00:00:00.
The t haplotype is an ancestral version of proximal mouse chromosome 17 that has evolved mechanisms to persist as an intact genomic variant in mouse populations. t haplotypes contain mutations that affect embryonic development, male fertility and male transmission ratio distortion (TRD), Collectively, these mutations drive the evolutionary success of t haplotypes, a phenomenon that remains one of the longstanding mysteries of mouse genetics. Molecular genetic analysis of TRD has been confounded by inversions that arose to lock together the various elements of this complex trait. Our first molecular glimpse of the TRD mechanism has finally been revealed with the cloning of the t complex responder (Tcr) locus, a chimeric kinase with a genetically cis active effect. Whereas + sperm in a +/t male have impaired flagellar function caused by the deleterious action of trans-active, t-haplotype-encoded 'distorters,' the mutant activity of Tcr counterbalances the distorter effects, maintaining the motility and fertilizing ability of t sperm.
Physical mapping of male fertility and meiotic drive quantitative trait loci in the mouse t complex using chromosome deficiencies
4345Planchart, AY, Y.; Schimenti, J. C., Genetics, 155:803-812. 2000-01-03 00:00:00.
The t complex spans 20 cM of the proximal region of mouse chromosome 17. A variant form, the t haplotype (t), exists at significant frequencies in wild mouse populations and is characterized by the presence of inversions that suppress recombination with Mild-type (+) chromosomes. Transmission ratio distortion and sterility are associated with t and affect males only. It is hypothesized that these phenomena are caused by trans-acting distorter/sterility factors that interact with a responder locus (Tcr(t)) and that the distorter and sterility factors are the same because homozygosity of the distorters causes male sterility. One factor, Tcd1, was previously shown to be amorphic using a chromosome deletion. To overcome limitations imposed by recombination suppression, we used a series of deletions within the t complex in trans to t chromosomes to characterize the Tcd1 region. The find that the distorter activity of Tcd1 is distinct from a linked sterility factor, originally called tcs1. YACs mapped with respect to deletion breakpoints localize tcs1 to a 1.1-Mb interval flanked by D17Aus9 and Tctex1. We present evidence for the existence of multiple proximal t complex regions that exhibit distorter activity. These studies demonstrate the utility of chromosome deletions for complex trait analysis.
Segregation distortion in a deme structured population: opposing demands of gene, individual and group selection
4364van Boven, MW, F. J., Journal of Evolutionary Biology, 12:80-93. 1999-01-02 00:00:00.
The evolution of segregation distortion is governed by the interplay of selection at different levels. Despite their systematic advantage at the gamete level, none of the well-known segregation distorters spreads to fixation since they induce severe negative fitness effects at the individual level. In a deme-structured population, selection at the population level also plays a role. By means of a population genetical model, we analyse the various factors that determine the success of a segregation distorter in a metapopulation, Our focus is on the question of how the success of a distorter allele is affected by its segregation ratio and its fitness effects at the individual level. The analysis reveals that distorter alleles with high segregation ratios are the best invaders and reach the highest frequencies within single demes. However, the productivity of a deme harbouring a distorter with a high segregation ratio may be significantly reduced. As a consequence, an efficient distorter will be underrepresented in the migrant pool and, moreover, it may increase the probability of deme extinction. In other words, efficient distorters with high segregation ratios may well succumb to their own success. Therefore, distorters with intermediate segregation ratios may reach the highest frequency in the metapopulation as a result of the opposing forces of gamete, individual and group selection. We discuss the implications of this conclusion for the t complex of the house mouse.
Mariner transposition and transformation of the yellow fever mosquito, Aedes aegypti
6256C. J. Coates, N. Jasinskiene, L. Miyashiro and A. A. James, Proceedings of the National Academy of Sciences of the United States of America, 95:3748-3751. 1998-03-07 19:31:51.
The mariner transposable element is capable of interplasmid transposition in the embryonic soma of the yellow fever mosquito, Aedes aegypti. To determine if this demonstrated mobility could be utilized to genetically transform the mosquito, a modified mariner element marked with a wild type allele of the Drosophila melanogaster cinnabar gene was microinjected into embryos of a kynurenine hydroxylase-deficient, white-eyed recipient strain. Three of 69 fertile male founders resulting from the microinjected embryos produced families with colored-eyed progeny individuals, a transformation rate of 4%. The transgene-mediated complementation of eve color was observed to segregate in a Mendelian manner, although one insertion segregates with the recessive allele (female-determining) of the sex-determining locus, and a separate insertion is homozygous lethal. Molecular analysis of selected transformed families demonstrated that a single complete copy of the construct had integrated independently in each case acid that it had done so in a transposase-mediated manner. The availability of a mariner transformation system greatly enhances our ability to study and manipulate this important vector species.
Stable transformation of the yellow fever mosquito, Aedes aegypti, with the Hermes element from the housefly
6254N. Jasinskiene, C. J. Coates, M. Q. Benedict, A. J. Cornel, C. S. Rafferty, A. A. James and F. H. Collins, Proceedings of the National Academy of Sciences of the United States of America, 95:3743-3747. 1998-03-07 19:28:29.
The mosquito Aedes aegypti is the world's most important vector of yellow fever and dengue viruses, Work is currently in progress to control the transmission of these viruses by genetically altering the capacity of wild Ae, aegypti populations to support virus replication. The germ-line transformation system reported here constitutes a major advance toward the implementation of this control strategy, A modified Hermes transposon carrying a 4.7-kb fragment of genomic DNA that includes a wild-type allele of the Drosophila melanogaster cinnabar (cn) gene was used to transform a white-eyed recipient strain of Ae, aegypti. Microinfection of preblastoderm mosquito embryos with this construct resulted in 50% of the emergent G(0) adults showing some color in their eyes, Three transformed families were recovered, each resulting from an independent insertion event of the cn(+)-carrying transposon, The cn(+) gene functioned as a semidominant transgene and segregated in Mendelian ratios, Hermes shows great promise as a vector for efficient, heritable, and stable transformation of this important mosquito vector species.
Evolution of segregation distortion: Potential for a high degree of polymorphism
4377van Boven, MW, F. J., Journal of Theoretical Biology, 192:131-142. 1998-01-15 00:00:00.
By means of a population genetical model, we study the evolution of segregation distortion. Most models of segregation distortion focus on a single distorter allele. In contrast, we consider the competition between a large number of distorters. Motivated by systems as the t complex of the house mouse or the Sd complex of Drosophila melanogaster, we assume that there is some "complementation" between distorter alleles, i.e. that the fitness of individuals heterozygous for two distorter alleles is higher than the fitness of homozygous individuals. In the presence of complementation, the most efficient distorter allele with the highest segregation ratio often does not outcompete less efficient distorters. In fact, our results show that coexistence of a large number of distorter alleles is more typical than the competitive exclusion of less efficient distorters by a single superior allele. We first consider the analytically tractable system where all distorters show the same amount of complementation. In this case, all distorters with a segregation ratio higher than a certain critical value will persist, resulting in a polymorphic population where the average segregation ratio is only slightly larger than 0.5. If the degree of complementation varies, there may be more than one stable equilibrium, and the outcome of competition may depend on the initial conditions. Motivated by empirical examples, we also consider the case that the distorting ability of an allele is negatively related to its effects on individual fitness. Interestingly, the outcome of competition depends crucially on details of such a trade-off. We conclude that verbal arguments are insufficient to predict the evolution of segregation distortion. (C) 1998 Academic Press Limited.
Identification of the t complex-encoded cytoplasmic dynein light chain Tctex1 in inner arm I1 supports the involvement of flagellar dyneins in meiotic drive
4370Harrison, AO-C, P.; King, S. M., Journal of Cell Biology, 140:1137-1147. 1998-01-08 00:00:00.
The cytoplasmic dynein light chain Tctex1 is a candidate for one of the distorter products involved in the non-Mendelian transmission of mouse t haplotypes. It has been unclear, however, how the t-specific mutations in this protein, which is found associated with cytoplasmic dynein in many tissues, could result in a male germ cell-specific phenotype. Here, we demonstrate that Tctex1 is not only a cytoplasmic dynein component, but is also present both in mouse sperm and Chlamydomonas flagella. Genetic and biochemical dissection of the Chlamydomonas flagellum reveal that Tctex1 is a previously undescribed component of inner dynein arm Il. Combined with the recent identification of another putative t complex distorter, Tctex2, within the outer dynein arm, these results support the hypothesis that transmission ratio distortion (meiotic drive) of mouse t haplotypes involves dysfunction of both flagellar inner and outer dynein arms but does not require the cytoplasmic isozyme.
Putting the brake on drive: meiotic drive of t haplotypes in natural populations of mice
4365Ardlie, KG, Trends in Genetics, 14:189-193. 1998-01-03 00:00:00.
Mouse t haplotypes are a 'selfish' form of chromosome 17 that show non-mendelian transmission from heterozygous +/t males. The considerable transmission bias in favour of t haplotypes should result in very high frequencies of these chromosomes in natural populations, but they seldom occur at the high frequencies expected. Recent research on this and other meiotic drive systems has shown bow a variety of mechanisms have evolved to suppress drive, and to re-establish mendelian segregation.
Identification of a male meiosis-specific gene, Tcte2, which is differentially spliced in species that form sterile hybrids with laboratory mice and deleted in t chromosomes showing meiotic drive
4382Braidotti, GB, D. P., Developmental Biology, 186:85-99. 1997-01-20 00:00:00.
Tcte2 (t complex testes expressed 2) is a male meiosis-specific gene that maps to band 3.3 of mouse chromosome 17. Two distinct male fertility defects, hybrid sterility and transmission ratio distortion, have previously been mapped to this region. Hybrid sterility arises in crosses between different mouse species and the F1 generation males have defects in the first meiotic division and are sterile. Transmission ratio distortion is shown by males heterozygous for the t haplotype form of chromosome 17 and is a type of meiotic drive in which male gametes function unequally at fertilization. The Tcte2 gene expresses a coding mRNA and a number of putative non-ORF transcripts in meiosis I. A deletion of the 5' part of the locus abolishes Tcte2 expression on the t haplotype form of chromosome 17. Additionally, the series of putative non-ORF RNAs at the Tcte2 locus are differentially spliced in species that show hybrid sterility when crossed to laboratory mice. The identification of polymorphisms in t haplotypes and in different mouse species allows alleles of Tcte2 to be proposed as candidates for loci which contribute to both meiotic drive and hybrid sterility phenotypes. While theoretical considerations have previously been used to propose that speciation and meiotic drive involve alleles of the same genes, Tcte2 is the first cloned candidate gene to support this link at a molecular level. (C) 1997 Academic Press.
Segregation distortion in unstructured and structured populations: Competition between ‘sterile’ t haplotypes
4403VanBoven, MW, F. J., Netherlands Journal of Zoology, 46:216-226. 1996-01-21 00:00:00.
By means of two simple models we investigate the competition between sex-specific segregation distorters in unstructured and structured populations. The models are motivated by the t complex of the house mouse. Some variants at this gene complex, the t haplotypes, distort Mendelian segregation in their favour in heterozygous males. The selective advantage at the gamete level is counterbalanced by strong negative fitness effects at the individual level. A large number of t haplotypes with varying degrees of segregation distortion has been found. In order to address this phenomenon we explicitly model the competition between two t haplotypes which induce male sterility when homozygous. Surprisingly, a distorter which is inferior at the gamete level and equivalent in every other respect to a more efficient distorter may well persist in a population. We argue that rare distorters are inherently favoured, and that, as a result, fitness considerations alone are not sufficient to predict the outcome of competition. Since 'sterile' t haplotypes are not only influenced by gamete and individual selection, but also by selection at the level of the group, we furthermore study the relation between unstructured and structured populations. It is shown that the persistence of a seemingly inferior distorter is also possible in a structured population. In contrast, a single efficient distorter with high segregation ratio may not even be able to persist in a structured population. Hence, in a metapopulation with migration between local demes, the segregation ratio is an even worse predictor of the evolutionary success of a segregation distorter than in an unstructured population.
Competition between segregation distorters: Coexistence of ”superior” and ”inferior” haplotypes at the t complex
4402vanBoven, MW, F. J.; Heg, D.; Huisman, J., Evolution, 50:2488-2498. 1996-01-20 00:00:00.
By means of population genetical models, we investigate the competition between sex-specific segregation distorters. Although the models are quite general, they are motivated by a specific example, the t complex of the house mouse. Some variants at this gene complex, the t haplotypes. distort Mendelian segregation in heterozygous males in their favor. The selective advantage at the gamete level is counterbalanced by strong negative fitness effects at the individual level (male sterility or even lethality in both sexes). A plethora of different t haplotypes has been found, both in the field and in the lab. Up to now, however, models have focused on the equilibrium frequency of a single t haplotype. In contrast, we explicitly model the competition between several t haplotypes, A deterministic model for a large, well-mixed population predicts a surprisingly high degree of polymorphism. Haplotypes with seemingly inferior fitness characteristics may easily coexist with ''superior'' haplotypes. For instance, a lethal haplotype with a low segregation ratio may stably coexist with a sterile haplotype with a high segregation ratio, Stable coexistence is even possible for haplotypes with a segregation disadvantage. A simple stochastic model shows that the same principles apply in the context of a structured metapopulation. Although counterintuitive at first sight, all our results can be explained by the fact that segregation distorters have an inherent advantage when they are rare. We conclude that fitness comparisons are not sufficient to predict the outcome of competition when selective forces are acting at different levels.
The mouse t-complex-encoded protein Tctex-1 is a light chain of brain cytoplasmic dynein
4395King, SMD, J. F.; Benashski, S. E.; Lye, R. J.; PatelKing, R. S.; Pfister, K. K., Journal of Biological Chemistry, 271:32281-32287. 1996-01-13 00:00:00.
Mammalian brain cytoplasmic dynein contains three light chains of M(r) = 8,000, 14,000, add 22,000 (King, S. M., Barbarese, E., Dillman, J. F., III, Patel-King, R. S., Carson, J. H., and Pfister, K. Kr (1996) J. Biol. Chem. 271, 19358-19366). Peptide sequence data (16/16 residues correct) implicate the M(r) = 14,000 polypeptide as Tctex-1, a protein encoded within the mouse t-complex. Tctex-1 cosediments with microtubules and is eluted with ATP or salt but not with GTP as expected for a dynein subunit, The ATP-eluted protein precisely cosediments with known cytoplasmic dynein proteins in sucrose density gradients, Tctex-1 also is immunoprecipitated from brain and other tissue homogenates by a monoclonal antibody raised against the 74-kDa cytoplasmic dynein intermediate chain, Quantitative densitometry indicates that Tctex-1 is a stoichiometric component of the dynein complex, As Tctex-1 is a candidate for involvement in the transmission ratio distortion (meiotic drive) of mouse t-haplotypes, these results suggest that cytoplasmic dynein dysfunction may play an important role in non-mendelian chromosome segregation.
Low frequency of mouse t haplotypes in wild populations is not explained by modifiers of meiotic drive
4390Ardlie, KGS, L. M., Genetics, 144:1787-1797. 1996-01-08 00:00:00.
t haplotypes are naturally occurring forms of mouse chromosome 17 that show non-Mendelian transmission from heterozygous +/t males. In laboratory studies, transmission ratios of greater than or equal to 0.90 or higher are typically observed. With transmission ratios of this level, theoretical analyses predict high frequencies of t haplotypes (similar to 75%) in wild populations. In contrast, empirical frequencies of only 15-25% are typically found. This has led to the suggestion that modifiers of drive may play a role in reducing t frequencies. We have measured transmission ratio distortion (TRD) levels in wild +/t mice to examine this hypothesis. TRD was very high in both litters collected from wild-caught pregnant females, and in wild litters bred in the laboratory (mean = 0.9). Contrary to the results of other studies, we found no difference in TRD levels between semilethal and lethal t haplotypes nor between litters conceived from cycling or postpartum estrus. We found three litters with aberrantly low TRDs that were all multiply sired, although the role this might play in natural populations is unknown. These findings show a general absence of modifiers of drive in natural populations and suggest that other factors are responsible for the low observed frequencies of wild t haplotypes.
Gene transfer into the Medfly, Ceratitis capitata, using a Drosophila hydei transposable element.
6269T. G. Loukeris, I. Livadaras, B. Arca, S. Zabalou and C. Savakis, Science, 270:2002-2005. 1995-12-22 16:35:47.
Exogenous functional DNA was introduced into the germline chromosomes of the Mediterranean fruit fly (medfly) Ceratitis capitata with a germline transformation system based on the transposable element Minos from Drosophila hydei. Transformants were identified as phenotypic revertants of a white-eyed mutation carried by the recipient strain. Clusters of transformants were detected among the progeny of 390 individuals screened for germline transformation. Five independent and phenotypically active integration events were identified, in each of which a single copy of the transposon was inserted into a different site of the medfly genome. Molecular analysis indicates that they represent transposase-mediated insertions of the transposon into medfly chromosomes.
Tctex2 – a sperm tail surface protein mapping to the t-complex
4405Huw, LYG, A. S.; Willison, K.; Artzt, K., Developmental Biology, 170:183-194. 1995-01-03 00:00:00.
Transmission ratio distortion (TRD) in mouse t-haplotypes remains the most significant example of meiotic drive in vertebrates. While the underlying mechanism that fuels it is still mysterious, TRD is clearly a complex multigene phenomenon. The characterization of Tctex2 (t-complex testis expressed 2) shows it to be one of several candidates for involvement in TRD, Tctex2 maps to the t-complex and encodes a membrane-associated protein found exclusively on the sperm tail. The t-haplotype form of Tctex2 is aberrant in both the level of its expression and its primary amino acid sequence, but is nonetheless translated and transported to its normal location. The multiple amino acid changes in the t-form make it extremely unlikely that it can function normally and, since it is found on sperm tails, suggest that it may actively interfere with the development of normal gamete function in males. The possible role of Tctex2 in t-complex transmission ratio distortion and sterility is discussed. (C) 1995 Academic Press, Inc.
The evolution of lethals in the t-haplotype system of the mouse
4411Charlesworth, B, Proceedings of the Royal Society B-Biological Sciences, 258:101-107. 1994-01-09 00:00:00.
The evolution of lethal haplotypes in the t-haplotype segregation distortion system of Mus is examined by mathematical and computer models. The models assume that there is reproductive compensation for the loss of lethal embryos, such that the net reproductive success of a female is not reduced in proportion to the frequency of lethal offspring which she produces. The initial population consists of a mixture of wildtype and homozygous male-sterile t-haplotypes. The failure of sterile males to reproduce may cause a higher fitness cost to mothers heterozygous for t-haplotypes than does elimination of a recessive lethal. Under certain conditions, a recessive lethal will spread and come to a polymorphic equilibrium. Wildtype, lethal and non-lethal haplotypes are all present at this equilibrium. Ifa second lethal mutation arises on a non-lethal t-haplotype in such an equilibrium population, it will increase in frequency and eventually displace the non-lethal t-haplotypes. A third lethal t-haplotype introduced at a low frequency into an equilibrium with two lethals can sometimes be selected for, although this is less likely if compensation is strong. The theoretical predictions are compared with data on natural populations.
The peculiar journey of a selfish chromosome: Mouse t-haplotypes and meiotic drive
4428Silver, LM, Trends in Genetics, 9:250-254. 1993-01-06 00:00:00.
Mouse t haplotypes are descendents of a variant form of chromosome 17 that evolved the ability to propagate itself at the expense of the wild-type homolog from heterozygous +/t males. Although once enigmatic, these widespread selfish chromosomes have revealed many of their secrets in response to a combined assault with molecular, genetic and phylogenetic techniques. This review summarizes the current understanding of t haplotypes and their raison d'etre.
Evolution of the mouse t-haplotype – Recent and worldwide introgression to Mus musculus
4433Morita, TK, H.; Murata, K.; Nozaki, M.; Delarbre, C.; Willison, K.; Satta, Y.; Sakaizumi, M.; Takahata, N.; Gachelin, G.; Matsushiro, A., Proceedings of the National Academy of Sciences of the United States of America, 89:6851-6855. 1992-01-11 00:00:00.
Mouse t haplotypes are variants of chromosome 17, consisting of four inversions. Despite the homozygous lethality and pleiotropic effect on embryonic development, sperm production, and recombination, they have widely spread in natural populations of the house mouse (10-40% in frequency) because of the meiotic drive advantage. We sequenced 14 Tcp-1 (t-complex polypeptide 1) genes from four t haplotypes, nine wild mice, and a rat as a reference. From a comparison of intron sequences of 610 base pairs, we dated the origin of t haplotypes to 2.9 +/- 0.7 million years ago, which predates the splitting of Mus musculus subspecies (almost-equal-to 1 million years ago). However, the Tcp-1 intron sequences of t haplotypes from different M. musculus subspecies from various parts of the world show no divergence, indicating the recent introgression (no earlier than 0.8 million years ago) of a single ancestral type. Nucleotide changes in coding regions are also consistent with this conclusion. Hence, polymorphisms among t haplotypes including lethality factors have accumulated during this short time period independently in each M. musculus subspecies.
Can transposable elements be used to drive disease refractoriness genes into vector populations?
6271M. G. Kidwell and J. M. C. Ribeiro, Parasitology Today, 8:325-329. 1992-01-08 16:40:55.
A number of biological procedures are currently being considered as alternatives to insecticide-based methods for the control of insect vectors of disease. Among these are the adaptation of various genetic mechanisms to drive genes of interest, such as refractoriness to malaria in mosquitoes, into natural populations, for vector control purposes. Here, Margaret Kidwell and Jose Ribeiro develop a rationale for the possible use of transposable genetic elements, one of these potential drive mechanisms, and some of the problems being faced in seeking to determine the feasibility of such a strategy are described.
A comparative approach to the population genetics theory of segregation distortion
4440Feldman, MWO, Sarah P., American Naturalist, 137:443-456. 1991-01-18 00:00:00.
Mathematical models of four well-known naturally occurring systems of segregation distortion are compared. These include the sex-ratio chromosome of Drosophila pseudoobscura, the Segregation Distorter (SD) complex of D. melanogaster, the t locus in Mus musculus, and the sex-ratio system in Aedes aegypti. Dynamics of these models are compared with the classical one-locus multiple-allele viability system. For the SD complex and the sex-ratio model of A. aegypti, the role of recombination is reviewed. Departures from Mendelian segregation cause fascinating irregularities in the relationship between linkage and linkage disequilibrium, as well as in predictions for the evolution of recombination itself.
Meiotic drive of t-haplotypes – chromosome segregation in mice with tertiary trisomy
4435Agulnik, AIA, S. I.; Ruvinsky, A. O., Genetical Research, 57:51-54. 1991-01-13 00:00:00.
The properties of the t haplotypes, specific mutant states of the proximal region of chromosomes 17 in the house mouse, are of continuing interest. One such property is increased transmission of the t haplotype by heterozygous t/+ males to offspring. Using the reciprocal translocation T(16; 17)43H we have constructed males with tertiary trisomy of chromosome 17 (+ T43/ + +/Rb7 +) carrying the Robertsonian translocation Rb(16.17)7Bnr. Only the progeny of these males which had inherited either T43/ + or Rb7 from their male parent were viable. The segregation patterns in the offspring of t-bearing trisomics were analysed on days 16-18 of embryonic development. It was found that, when the t12 haplotype is in the normal acrocentric (males + + T43/ + t12 + /Rb7 + +), its presence in the gamete + t12 + / + + T43 does not produce meiotic drive. However, when t6 is in Rb7, meiotic drive was observed: 80% of offspring carried the t haplotype. It is concluded that the meiotic drive is probably inhibited by the presence of a normal homologue of chromosome 17 in the same sperm. Possible mechanisms for the t haplotype effect are discussed.
Meiotic drive of t haplotypes: chromosome segregation in mice with tertiary trisomy
4434Agulnik, AIA, Sergei I.; Ruvinsky, Anatoly O., Genetics Research, 57:51. 1991-01-12 00:00:00.
The properties of the / haplotypes, specific mutant states of the proximal region of chromosomes17 in the house mouse, are of continuing interest. One such property is increased transmission ofthe / haplotype by heterozygous // + males to offspring. Using the reciprocal translocationT(16; 17)43H we have constructed males with tertiary trisomy of chromosome 17( + T43/+ +/Rb7 + ) carrying the Robertsonian translocation Rb(16.17)7Bnr. Only the progeny ofthese males which had inherited either T43/ + or Rb7 from their male parent were viable. Thesegregation patterns in the offspring of /-bearing trisomics were analysed on days 16-18 ofembryonic development. It was found that, when the tn haplotype is in the normal acrocentric(c?c?+ + T43/ + //2+/Rb7 + +), its presence in the gamete +/" + /+ + T43 does not producemeiotic drive. However, when t6 is in Rb7, meiotic drive was observed: 80 % of offspring carriedthe / haplotype. It is concluded that the meiotic drive is probably inhibited by the presence of anormal homologue of chromosome 17 in the same sperm. Possible mechanisms for the t haplotypeeffect are discussed
Segregation distorters
4451Lyttle, TW, Annual Review of Genetics, 25:511-557. 1991-01-09 00:00:00.
Segregation distorters are genetic elements that exhibit the phenomenon of meiotic drive; that is, the mechanics of the meiotic divisions cause one member of a pair of heterozygous alleles or heteromorphic chromosomes to be transmitted to progeny in excess of the expected Mendelian proportion of 50% ( 1 34 , 1 36). In this review, we refer to these as genic or chromosomal drive, respectively. Genic meiotic drive is initially limited in its impact to the population dynamics of the drive locus itself and those loci fortuitiously in close linkage. Alleles at these latter loci may enjoy indirect drive through genetic hitchhiking, leading eventually to the establishment of drive haplotypes (64). The haplotype may be extended by incorporating chromosome rearrangements that reduce recombination and promote further linkage disequilibrium between the drive locus and more distant modifier loci ( 1 04 , 1 28, 1 64). In the extreme , the haplotype becomes coextensive with the chromosome, leading to a form of chromosomal meiotic drive. For a parent heterozygous for either type of drive system, the statistic k is used to denote the proportion of progeny (and by inference, successful gametes) that carry the allele or chromosome exhibiting segregation distortion. Thus , k can vary from 0 . 5 (Mendelian segregation segregation) to 1 .0 (complete segregation distortion with only one gamete class recovered in the progeny) .
The Genetic Basis of Transmission-Ratio Distortion and Male Sterility Due to the t Complex
4449Lyon, MF, American Naturalist, 137:349-358. 1991-01-07 00:00:00.
The abnormal transmission ratios observed in male mice heterozygous for a complete t haplotype have been shown by breeding studies to be due to three or more distorter genes acting on a responder gene. The action of the t form of the responder is relatively resistant to this harmful action. When the distorters are homozygous, their harmful action is more severe. The t form of the responder is then affected, and the males are sterile. The distorter and responder genes are distributed over a region occupying the proximal third of mouse chromosome 17. Crossover suppression between t and wild-type bapiotypes in this region is due to the presence of inversions and is thought to be selectively advantageous in locking the genetic factors together. The recessive lethals carried by many t haplotypes are also thought to be advantageous in removing the sterile males from the population. Transmission ratio is also affected by genetic background, and there is evidence of differences among t haplotypes either in the responder or in cis-acting effects of distorters.
Behavioral reduction in the transmission of deleterious t-haplotypes by wild house mice
4446Lenington, SH, I. L., The American Naturalist, 137:366-378. 1991-01-04 00:00:00.
About 25% of wild house mice are heterozygous (+/t) for a variable recessive haplotype of the T locus. Although t haplotypes are highly deleterious when homozygous, they are maintained in wild mouse populations because they are associated with transmission-ratio distortion in heterozygous males, which may transmit their t haplotype to 90%-100% of their progeny. In a study of factors affecting variation in male transmission ratio in matings between wild-caught +/t males and +/+ females, we found (1) that male transmission ratio is considerably lower in litters produced as a result of postpartum-estrus matings than in litters produced as a result of cycling-estrus matings, (2) that the frequency of postpartum-estrus litters is much higher when +/t males mate with females caught from the same location as themselves than when they mate with females caught elsewhere, and (3) that, as a result of findings I and 2, the male transmission ratio is considerably lower in within-population matings than in betweenpopulation matings. These data suggest that the frequency of t haplotypes within populations may be correlated with the migration rate and that t haplotypes may be found in high frequencies only in populations for which the migration rate is high.
Molecular and chromosomal studies on the origin of t-haplotypes in mice
4444Hammer, MF, American Naturalist, 137:359-365. 1991-01-02 00:00:00.
Mouse t haplotypes are variant forms of the proximal third of chromosome 17 that enhance their representation in the gene pool by means of a male-specific transmission-ratio distortion. As with other systems of meiotic drive, they are maintained as independent genetic entities by inversions that suppress recombination with their wild-type homologues. This article reviews some of the evidence for the origin of this complex system based on DNA and chromosomal comparisons. Such comparisons suggest a stepwise evolution of t haplotypes, whereby the proximal and distal inversion occurred on separate chromosomal lineages and at different times. The initial event leading to the spread of t haplotypes may have been an inversion occurring on the wild-type chromosome (nondriving) 2-4 million yr ago. An additional implication of the data is that meiotic drive gives t haplotypes the ability to traverse species boundaries and spread rapidly around the world.
Genetics-driving genes and chromosomes
4463Charlesworth, B, Nature, 332:394-395. 1988-01-21 00:00:00.
Thereare several genetic and chromosomal systems in which Mendel's first law - the equal probability of transmission of maternal and paternal alternative alleles or homologues - is violated. This phenomenon was named 'meiotic drive' in 1957 by Sandler and Novitski, who drew attention to the fact that it operates as an evolutionary force which can cause an increase in the population frequency of the allele or chromosome which is favoured in transmission, even if it confers a disadvantage on its carriers in terms of fitness at the level of the individual
Genetic-transformation of Drosophila with transposable element vectors
6252G. M. Rubin and A. C. Spradling, Science, 218:348-353. 1982-10-22 19:25:36.
Exogenous DNA sequences were introduced into the Drosophila germ line. A rosy transposon (ry1), constructed by inserting a chromosomal DNA fragment containing the wild-type rosy gene into a P transposable element, transformed germ line cells in 20 to 50 percent of the injected rosy mutant embryos. Transformants contained one or two copies of chromosomally integrated, intact ry1 that were stably inherited in subsequent generations. These transformed flies had wild-type eye color indicating that the visible genetic defect in the host strain could be fully and permanently corrected by the transferred gene. To demonstrate the generality of this approach, a DNA segment that does not confer a recognizable phenotype on recipients was also transferred into germ line chromosomes.
Genetic control of insect populations: I. Cage studies of chromosome replacement by compound autosomes in Drosophila melanogaste
6297M. Fitz-Earle, D. G. Holm and D. T. Suzuki, Genetics, 74:461-475. 1973-07-08 19:53:27.
A genetic method for insect control was evaluated using the test organism, Drosophila melanogaster. The technique involved the displacement under a system of continuous reproduction, of standard strains by those carrying compound autosomes. The eradication of the replacements could subsequently be achieved through the use of temperature-sensitive lethal mutations.—While certain compound autosome strains failed to displace standards in population cages, even at the initial release ratio of 25:1, others were highly successful. Indeed, for some strains when the ratio of compounds to standards was as low as 9:1, the population rapidly went to fixation in favor of the compound line.—Hatchability was found to be an insufficient index of fitness to estimate the initial ratios of compounds to standards that would guarantee fixation of the former. Differences in other fitness components, such as development time, were detected that could seriously modify displacement, especially with continuous overlapping generations. The importance of examining the fitness of various compound lines and selecting the most competitive in cages, prior to field tests, cannot be overemphasized.
Analysis of a general population genetic model of meiotic drive
4501Hartl, DL, Evolution, 24:538-545. 1970-01-19 00:00:00.
The purpose of this article is to present the detailed solution of a model of meiotic drive which Lewontin (1968) has suggested would be helpful in understanding the evo- lutionary dynamics of the t-alleles in the house mouse. Because mice tend to breed in small endogamous family units, however, the deterministic model is only a very rough approximation to what would be expected to occur in nature, and to gain better insight one is forced to undertake Monte Carlo simulation of small populations (Lewontin and Dunn, 1960; Lewontin, 1968).
Studies of the genetic variability in populations of wild house mice .2. Analysis of eight additional alleles at locus – T
6113L. C. Dunn, Genetics, 42:299-311. 1957-01-02 19:27:44.
1 Eight additional lethal alleles at locus T are described, each derived from a wild heterozygote in one of six different wild populations. 2. The frequency of heterozygotes appears to be high in most wild populations, possibly as high as 50 percent. 3. In two of the populations in which several heterozygotes were found, the same allele was isolated from each heterozygote of the same population. One heterozygote was found in each of two subpopulations on the same farm. These two alleles have not been shown to be different. One wild heterozygote from another population transmitted two different alleles; probably one was a new mutant, giving rise to the possibility that more than one allele may occur in the same population, although the rule at present is to find but one type of variant allele per population. 4. All wild t alleles show the “male segregation ratio peculiarity” by which male heterozygotes transmit the t allele to a great majority (about 96 percent) of the offspring. This may be due to the effects of natural selection on factors favoring high transmission ratios. 5. t alleles from the wild fall into at least three groups, one with three viable alleles, and two groups of lethals. Lethals within the same group have not formed viable compounds when combined; lethals belonging to different groups do form viable compounds by complementary interaction and are thus shown to be nonidentical. 6. Since 29 alleles have now been detected at this locus, many of which are nonidentical, the locus is assumed to contain many sites of mutation and to have great potential complexity.
Sur la reproduction des souris anoures
6057N. Dobrovolskaia-Zavadskaia and N. Kobozieff, Comptes rendus des séances de la Société de biologie et de ses filiales, 97:116-119. 1927-06-15 15:44:03.
Nous ne connaissons que deux lignees de Souris sans queue, celle de Lang (1913), et cell de Duboscq (1922). L’elevange de Lang (lignee des Souris brachyures et anoures du preparateur Alfred Nageli) a donne 199 Souris normales, pour 173 brachyures et 9 anoures. Croisses entre ells et aveec des bachyures, les Souris anoures n’ont donne aucune reproduction. Dans la lignee du P Duboscq, provenant d’une femelle anoure A et de son frere normal, et comportant 25 petis en 8 portees, il y avait 8 anoures, don’t la plupart moururent jeunes.
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