Scholarly Literature

This is an aggregation of scholarly literature from peer-reviewed journals,  bioRxiv , medRxiv and arXiv preprint servers focused on natural and engineered selfish genetic elements and genetic biocontrol. New citations are added as they appear. This content is intended for anyone interested in the scholarly literature on gene drive and genetic biocontrol.

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Cell-based analysis reveals that sex-determining gene signals in Ostrinia are pivotally changed by male-killing Wolbachia

24288
B. Herran, T. N. Sugimoto, K. Watanabe, S. Imanishi, T. Tsuchida, T. Matsuo, Y. Ishikawa and D. Kageyama,  PNAS Nexus,  pgac293. 2022-12-13 08:59:49. Journal
Wolbachia, a maternally transmitted bacterium, shows male-killing, an adaptive phenotype for cytoplasmic elements, in various arthropod species during the early developmental stages. In lepidopteran insects, lethality of males is accounted for by improper dosage compensation in sex-linked genes owing to Wolbachia-induced feminization. Herein, we established Ostrinia scapulalis cell lines that retained sex specificity per the splicing pattern of the sex-determining gene doublesex (Osdsx). We found that Wolbachia transinfection in male cell lines enhanced the female-specific splice variant of Osdsx (OsdsxF) while suppressing the male-specific variant (OsdsxM), indicating that Wolbachia affects sex-determining gene signals even in vitro. Comparative transcriptome analysis isolated only two genes that behave differently upon Wolbachia infection. The two genes were respectively homologous to Masculinizer (BmMasc) and zinc finger-2 (Bmznf-2), male-specifically expressed sex-determining genes of the silkworm Bombyx mori that encode CCCH-type zinc finger motif proteins. By using cultured cells and organismal samples, OsMasc and Osznf-2 were found to be sex-determining genes of O. scapulalis that are subjected to sex-specific alternative splicing depending upon the chromosomal sex, developmental stage, and infection status. Overall, our findings expound the cellular autonomy in insect sex determination and the mechanism through which sex is manipulated by intracellular selfish microbes.

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Cryptic recessive lethality of a supergene controlling social organization in ants

24183
P. Blacher, O. De Gasperin, G. Grasso, S. Sarton-Lohéac, R. Allemann and M. Chapuisat,  Molecular Ecology,  2022-12-11 11:15:44. Journal
Supergenes are clusters of linked loci that control complex phenotypes, such as alternate forms of social organization in ants. Explaining the long-term maintenance of supergenes is challenging, particularly when the derived haplotype lacks homozygous lethality and causes gene drive. In the Alpine silver ant, Formica selysi, a large and ancient social supergene with two haplotypes, M and P, controls colony social organization. Single-queen colonies only contain MM females, while multi-queen colonies contain MP and PP females. The derived P haplotype, found only in multi-queen colonies, selfishly enhances its transmission through maternal effect killing, which could have led to its fixation. A population genetic model showed that a stable social polymorphism can only be maintained under a narrow set of conditions, which includes partial assortative mating by social form (which is known to occur in the wild), and low fitness of PP queens. With a combination of field and laboratory experiments, we show that the P haplotype has deleterious effects on female fitness. The survival rate of PP queens and workers was around half the one of other genotypes. Moreover, P-carrying queens had lower fertility and fecundity compared to other queens. We discuss how cryptic lethal effects of the P haplotype help stabilize this ancient polymorphism.

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S. pombe wtf drivers use dual transcriptional regulation and selective protein exclusion from spores to cause meiotic drive

24158
N. L. Nuckolls, A. Nidamangala Srinivasa, A. C. Mok, R. M. Helston, M. A. Bravo Núñez, J. J. Lange, T. J. Gallagher, C. W. Seidel and S. E. Zanders,  PLOS Genetics,  18:e1009847. 2022-12-07 07:23:14. Journal
Author summary Genomes are often considered a collection of ‘good’ genes that provide beneficial functions for the organism. From this perspective, disease is thought to arise due to disfunction of ‘good’ genes. For example, infertility can be caused by the failure of a gene that normally helps fertility. This view is incomplete as ‘parasitic’ genes that provide no benefit to the organism also exist. These genes can also contribute to disease, often as a result of the mechanisms they use to ensure their transmission to the next generation. For example, killer meiotic drivers are found throughout eukaryotes and contribute to infertility by actively destroying the gametes (e.g., egg and sperm) that do not inherit them. In this work we study the transcriptional regulation of wtf4, a model killer meiotic driver found in fission yeast to understand mechanisms of drive. The wtf4 gene encodes both a poison and an antidote protein on largely overlapping coding sequences. We found that different promoters and differential localization properties of the poison and antidote proteins both facilitate killer meiotic drive. We also found that the expression of the poison protein relies on a key transcription factor essential for gametogenesis. The use of this transcription factor likely complicates suppressing wtf4 without compromising gametogenesis. This feature likely contributes to the evolutionary success of the wtf drivers, which are found in many copies in fission yeast genomes.

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Bioinformatic and literature assessment of toxicity and allergenicity of a CRISPR-Cas9 engineered gene drive to control the human malaria mosquito vector Anopheles gambiae

24161
A. Qureshi and J. B. Connolly,  Malaria Journal,  2022-12-06 07:52:06. Journal
Population suppression gene drive is currently being evaluated, including via environmental risk assessment (ERA), for malaria vector control. One such gene drive involves the dsxFCRISPRh transgene encoding (i) hCas9 endonuclease, (i) T1 guide RNA (gRNA) targeting the doublesex locus, and (iii) DsRed fluorescent marker protein, in genetically modified mosquitoes (GMMs). Problem formulation, the first stage of ERA, for environmental releases of dsxFCRISPRh previously identified nine potential harms to the environment or health that could occur, should expressed products of the transgene cause allergenicity or toxicity. Amino acid sequences of hCas9 and DsRed were interrogated against those of toxins or allergens from NCBI, UniProt, COMPARE and AllergenOnline bioinformatic databases and the gRNA was compared with microRNAs from the miRBase database for potential impacts on gene expression associated with toxicity or allergenicity. PubMed was also searched for any evidence of toxicity or allergenicity of Cas9 or DsRed, or of the donor organisms from which these products were originally derive While Cas9 nuclease activity can be toxic to some cell types in vitro and hCas9 was found to share homology with the prokaryotic toxin VapC, there was no evidence of a risk of toxicity to humans and other animals from hCas9. Although hCas9 did contain an 8-mer epitope found in the latex allergen Hev b 9, the full amino acid sequence of hCas9 was not homologous to any known allergens. Combined with a lack of evidence in the literature of Cas9 allergenicity, this indicated negligible risk to humans of allergenicity from hCas9. No matches were found between the gRNA and microRNAs from either Anopheles or humans. Moreover, potential exposure to dsxFCRISPRh transgenic proteins from environmental releases was assessed as negligible.Bioinformatic and literature assessments found no convincing evidence to suggest that transgenic products expressed from dsxFCRISPRh were allergens or toxins, indicating that environmental releases of this population suppression gene drive for malaria vector control should not result in any increased allergenicity or toxicity in humans or animals. These results should also inform evaluations of other GMMs being developed for vector control and in vivo clinical applications of CRISPR-Cas9.

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Tolerance-conferring defensive symbionts and the evolution of parasite virulence

24126
C. A. Smith and B. Ashby,  bioRxiv,  2022-12-05 09:03:54. Journal
Defensive symbionts in the host microbiome can confer protection from infection or reduce the harms of being infected by a parasite. Defensive symbionts are therefore promising agents of biocontrol that could be used to control or ameliorate the impact of infectious diseases. Previous theory has shown how symbionts can evolve along the parasitism-mutualism continuum to confer greater or lesser protection to their hosts, and in turn how hosts may coevolve with their symbionts to potentially form a mutualistic relationship. However, the consequences of introducing a defensive symbiont for parasite evolution and how the symbiont may coevolve with the parasite have yet to be explored theoretically. Here, we investigate the ecological and evolutionary implications of introducing a tolerance-conferring defensive symbiont into an established host-parasite system. We show that while the defensive symbiont may initially have a positive impact on the host population, parasite and symbiont evolution tend to have a net negative effect on the host population in the long-term. This is because the introduction of the defensive symbiont always selects for an increase in parasite virulence and may cause diversification into high- and low-virulence strains. Even if the symbiont experiences selection for greater host protection, this simply increases selection for virulence in the parasite, resulting in a net negative effect on the host population. Our results therefore suggest that tolerance-conferring defensive symbionts may be poor biocontrol agents for population-level infectious disease control.Competing Interest StatementThe authors have declared no competing interest.

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Deregulation of Y-linked protamine-like genes in sex chromosome-biased spermatid demise

24124
J. I. Park, G. W. Bell and Y. M. Yamashita,  bioRxiv,  2022-12-05 08:57:46. Journal
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.

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A mass rearing cost calculator for the control of Culex quinquefasciatus in Hawaiʻi using the incompatible insect technique

24332
A. E. Vorsino and Z. Xi,  Parasites and Vectors,  15:453. 2022-12-05 08:32:07. Journal
Hawaiʻi’s native forest avifauna is experiencing drastic declines due to climate change-induced increases in temperature encroaching on their upper-elevation montane rainforest refugia. Higher temperatures support greater avian malaria infection rates due to greater densities of its primary vector, the southern house mosquito Culex quinquefasciatus, and enhance development of the avian malaria parasite Plasmodium relictum. Here we propose the use of the incompatible insect technique (IIT) or the combined IIT/sterile insect technique (SIT) for the landscape-scale (i.e., area-wide) control of Cx. quinquefasciatus, and have developed a calculator to estimate the costs of IIT and IIT/SIT applications at various sites in Hawaiʻi.

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Meiotic transmission patterns of additional genomic elements in Brachionus asplanchnoidis, a rotifer with intraspecific genome size variation

24116
J. Blommaert and C.-P. Stelzer,  Scientific Reports,  12:20900. 2022-12-03 09:37:14. Journal
Intraspecific genome size (GS) variation in Eukaryotes is often mediated by additional, nonessential genomic elements. Physically, such additional elements may be represented by supernumerary (B-)chromosomes or by large heterozygous insertions into the regular chromosome set. Here we analyze meiotic transmission patterns of Megabase-sized, independently segregating genomic elements (ISEs) in Brachionus asplanchnoidis, a planktonic rotifer that displays an up to two-fold intraspecific GS variation due to variation in size and number of these elements. To gain insights into the meiotic transmission patterns of ISEs, we measured GS distributions of haploid males produced by individual mother clones using flow cytometry and compared these distributions to theoretical distributions expected under a range of scenarios. These scenarios considered transmission biases resembling (meiotic) drive, or cosegregation biases, e.g., if pairs of ISEs preferentially migrated towards the same pole during meiosis. We found that the inferred transmission patterns were diverse and ranged from positive biases (suggesting drive) to negative biases (suggesting drag), depending on rotifer clone and its ISE composition. Additionally, we obtained evidence for a negative cosegregation bias in some of the rotifer clones, i.e., pairs of ISEs exhibited an increased probability of migrating towards opposite poles during meiosis. Strikingly, these transmission and segregation patterns were more similar among members of a genetically homogeneous inbred line than among outbred members of the population. Comparisons between early and late stages of haploid male embryonic development (e.g., young synchronized male eggs vs. hatched males) showed very similar GS distributions, suggesting that transmission biases occur very early in male development, or even during meiosis. Very large genome size was associated with reduced male embryonic survival, suggesting that excessive amounts of ISEs might be detrimental to male fitness. Altogether, our results indicate considerable functional diversity of ISEs in B. asplanchnoidis, with consequences on meiotic transmission and embryonic survival.

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Determining the landscape of resistance to gene drives in the malaria mosquito

27631
I. Morianou,  Imperial College London,  2022-12-01 10:17:51. Journal
Gene drives are engineered selfish genetic elements with the potential to spread throughout entire insect populations for sustainable vector control. Recently, a gene drive was shown to eliminate caged populations of the malaria mosquito by targeting the highly conserved female-specific exon of the doublesex gene. This caused females, homozygous for the gene drive, to develop as sterile intersex individuals, leading to the observed population crash. However, target site resistant alleles that block gene drive activity, whilst encoding a functional copy of the target gene, may halt gene drive spread in the wild. These may be naturally occurring or generated by the gene drive itself. This thesis presents a pipeline for the discovery, genetic engineering, and testing of putative drive-resistant variants. First, to investigate the potential for natural resistance, existing population genomics data were interrogated for the presence of natural single nucleotide polymorphisms (SNPs) at the highly conserved gene drive target region. To investigate the potential for drive-induced resistance, a high-throughput assay was designed to generate a high volume of mutations at the gene drive target site and screen them for their ability to restore dsx function. These methods yielded three putatively resistant SNPs: one natural polymorphism and two rare Cas9-induced mutations. These were engineered in the mosquito genome for testing, using a novel method termed CRISPR-mediated cassette exchange (CriMCE). It was confirmed that all three polymorphisms are functional and offer full, partial or no resistance to gene drive. Importantly, partial resistance to gene drive is being demonstrated for the first time. To mitigate observed resistance, gene drive systems targeting multiple sites simultaneously were developed. These showed improved drive dynamics and caused rapid elimination of caged mosquito populations within 7-8 generations. The experimental pipeline described here can be applied to pre-empt and mitigate resistance against any gene drive strategy, prior to field testing.

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A comprehensive overview of the existing microbial symbionts in mosquito vectors: An important tool for impairing pathogentransmission

24088
V. Vandana, M. P. Kona, J. Kumar, O. P. Singh and K. C. Pandey,  Experimental Parasitology,  243. 2022-11-30 09:06:12. Journal
The emergence of drug-resistant parasites and/or insecticide-resistant mosquito vectors necessitates developing alternative tools that either supplement or replace the conventional malaria control strategies. Trans-infecting the mosquito vector with symbionts that can either compete with a targeted pathogen or manipulate the host biology by reducing its vectorial capacity could be a promising and innovative biological approach for the control of infectious diseases This idea could be utilized to develop a novel and efficient vector control strategy; symbionts are dispersed into vector populations to reduce their ability to transmit human pathogens. Here, we reported the natural existence of Microsporidian (an obligate fungus) in the field-collected An. stephensi mosquito. However, laboratory-reared An. stephensi and An. culicifacies did not exhibit microsporidian infection. Similarly, 16s rRNA PCR identified -1kb amplicons in laboratory-reared An. stephensi and An. culicifacies, indicating the presence of naturally residing different bacterial species. DNA sequencing of these amplicons revealed the identities of different bacteria which are not well-characterized in terms of plasmodia-interaction activity in the Indian malaria vector. This article summarizes an overview of the previously studied microbial symbionts for their role in Plasmodium transmission along with a list of new or unexplored symbionts in the disease transmitting mosquito vectors. The summarized information could be utilized to explore such microbial symbionts for their role in Plasmodium-transmission biology in-depth and implementation in the malaria control interventions globally.

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Meiotic drive adaptive testes enlargement during early development in the stalk-eyed fly

24087
S. L. Bradshaw, L. Meade, J. Tarlton-Weatherall and A. Pomiankowski,  Biology Letters,  18:20220352. 2022-11-30 09:02:09. Journal
The sex ratio (SR) X-linked meiotic drive system in stalk-eyed flies destroys Y-bearing sperm. Unlike other SR systems, drive males do not suffer fertility loss. They have greatly enlarged testes which compensate for gamete killing. We predicted that enlarged testes arise from extended development with resources re-allocated from the accessory glands, as these tend to be smaller in drive males. To test this, we tracked the growth of the testes and accessory glands of wild-type and drive males over 5-6 weeks post-eclosion before males attained sexual maturity. Neither of the original predictions is supported by these data. Instead, we found that the drive male testes were enlarged at eclosion, reflecting a greater allocation of resources to the testes during pupation. Testes grow at a higher rate during early adult development in drive males, but there was no evidence that this retards the growth of the accessory glands. Further experiments are proposed to investigate whether smaller accessory glands only arise in drive males post-copulation or when flies are subjected to nutritional stress. Our experimental findings support the idea that enlarged testes in drive males arise as an adaptive allocation of resources to traits that enhance male reproductive success.

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Does severe hypoxia during irradiation of Aedes aegypti pupae improve sterile male performance?

24069
D. A. Tussey, K. J. Linthicum and D. A. Hahn,  Parasites and Vectors,  15:446. 2022-11-28 10:25:24. Journal
The yellow fever mosquito, Aedes aegypti, vectors several pathogens responsible for human diseases. As a result, this mosquito species is a priority for control by mosquito control districts in Florida. With insecticide resistance development becoming a concern, alternative control strategies are needed for Ae. aegypti. Sterile insect technique (SIT) is an increasingly popular option that is being explored as a practical area-wide control method. However, questions about sterile male performance persist. The objectives of this study were to determine the extent to which hypoxia exposure prior to and during irradiation effects the longevity, activity and mating competitiveness of sterile male Ae. aegypti.

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Engineering stringent genetic biocontainment of yeast with a protein stability switch

24034
S. A. Hoffmann and Y. Cai,  bioRxiv,  2022.11.24.517818. 2022-11-24 09:51:15. Journal
Synthetic biology holds immense promise to tackle key problems we are facing, for instance in resource use, environmental health, and human health care. However, comprehensive safety measures are needed to deploy genetically engineered microorganisms in open-environment applications. Here, we describe a genetic biocontainment system based on conditional stability of essential proteins. We used a yeast-adapted destabilizing domain degron, which can be stabilized by estradiol addition (ERdd). Leveraging the yeast GFP collection and lab automation platforms, we ERdd-tagged 775 essential genes and screened for strains with estradiol dependent growth. Three genes, SPC110, DIS3 and RRP46, were found to be particularly suitable. Respective strains showed no growth defect in the presence of estradiol and strong growth inhibition in its absence. Of these, SPC110-ERdd offered the most stringent containment, with an escape frequency of 7.0x10-8, and full growth restoration at 100 nM estradiol. By systematically analysing the containment escapees, we identified the non- essential C-terminal region of SPC110 as target for escape mutations. Its removal decreased the escape frequency with a single ERdd tag further to 4.3x10-9. Combining SPC110-ERdd with a second ERdd tag on either DIS3 or RRP46 resulted in escape frequencies below the detection limit of the used assay (<2x10-10). Being based on conditional protein stability, this approach is mechanistically orthogonal to previously reported intrinsic biocontainment systems. It thus can be readily combined with other systems, for instance ones based on transcriptional or translational control of essential gene expression, to achieve multiplexed, extremely stringent control over the survival of engineered organisms.Competing Interest StatementThe authors have declared no competing interest.

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Developing radiation-based sterile insect technique (SIT) for controlling Aedes aegypti: identification of a sterilizing dose

24028
C. Chen, R. L. Aldridge, S. Gibson, J. Kline, V. Aryaprema, W. Qualls, R.-d. Xue, L. Boardman, K. J. Linthicum and D. A. Hahn,  Pest Management Science,  2022-11-24 09:37:31. Journal
Abstract Background The sterile insect technique (SIT) is emerging as a tool to supplement traditional pesticide-based control of Aedes aegypti, a prominent mosquito vector of microbes that have increased the global burden of human morbidity and mortality over the past 50?years. SIT relies on rearing, sterilizing, and releasing large numbers of male mosquitoes that will mate with fertile wild females, thus reducing production of offspring from the target population. In this study, we investigated the effects of ionizing radiation (gamma) on male and female survival, longevity, mating behavior, and sterility of Ae. aegypti in a dose-response design. This work is a first step towards developing an operational SIT field suppression program against Ae. aegypti in St. Augustine, Florida, USA. Results Exposing late-stage pupae to 50 Gy of radiation yielded 99% male sterility while maintaining similar survival of pupae to adult emergence, adult longevity, and male mating competitiveness compared to unirradiated males. Females were completely sterilized at 30 Gy, and when females were dosed with 50 Gy, they had a lower incidence of blood feeding than unirradiated females. Conclusion Our work suggests that an ionizing radiation dose of 50 Gy should be used for future development of operational SIT in our program area because at this dose males are 99% sterile while maintaining mating competitiveness against unirradiated males. Furthermore, females that might be accidentally released with sterile males due to errors in sex sorting are also sterile and less likely to blood feed than unirradiated females at our 50 Gy dose.

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Modeling-informed Engineered Genetic Incompatibility strategies to overcome resistance in the invasive Drosophila suzukii

28350
A. Sychla, N. R. Feltman, W. D. Hutchison and M. J. Smanski,  Frontiers in Insect Science,  2. 2022-11-22 10:46:03. Journal
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.

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A CRISPR endonuclease gene drive reveals distinct mechanisms of inheritance bias

24021
S. A. N. Verkuijl, E. Gonzalez, M. Li, J. X. D. Ang, N. P. Kandul, M. A. E. Anderson, O. S. Akbari, M. B. Bonsall and L. Alphey,  Nature Communications,  13:7145. 2022-11-21 09:45:13. Journal
CRISPR/Cas gene drives can bias transgene inheritance through different mechanisms. Homing drives are designed to replace a wild-type allele with a copy of a drive element on the homologous chromosome. In Aedes aegypti, the sex-determining locus is closely linked to the white gene, which was previously used as a target for a homing drive element (wGDe). Here, through an analysis using this linkage we show that in males inheritance bias of wGDe did not occur by homing, rather through increased propagation of the donor drive element. We test the same wGDe drive element with transgenes expressing Cas9 with germline regulatory elements sds3, bgcn, and nup50. We only find inheritance bias through homing, even with the identical nup50-Cas9 transgene. We propose that DNA repair outcomes may be more context dependent than anticipated and that other previously reported homing drives may, in fact, bias their inheritance through other mechanisms.

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The effect of mating complexity on gene drive dynamics

23967
P. Verma, R. G. Reeves, S. Simon, M. Otto and C. S. Gokhale,  The American Naturalist,  2022-11-15 12:33:47. Journal
Gene drive technology promises to deliver on some of the global challenges humanity faces today in health care, agriculture, and conservation. However, there is a limited understanding of the consequences of releasing self-perpetuating transgenic organisms into wild populations under complex ecological conditions. In this study, we analyze the impact of three such complexities—mate choice, mating systems, and spatial mating network—on the population dynamics for two distinct classes of modification gene drive systems. All three factors had a high impact on the modeling outcome. First, we demonstrate that distortion-based gene drives appear to be more robust against mate choice than viability-based gene drives. Second, we find that gene drive spread is much faster for higher degrees of polygamy. Including a fitness cost, the drive is fastest for intermediate levels of polygamy. Finally, the spread of a gene drive is faster and more effective when the individuals have fewer connections in a spatial mating network. Our results highlight the need to include mating complexities when modeling the properties of gene drives, such as release thresholds, timescales, and population-level consequences. This inclusion will enable a more confident prediction of the dynamics of engineered gene drives and possibly even inform about the origin and evolution of natural gene drives.

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Driving lessons: a brief (personal) history of centromere drive

24030
H. S. Malik,  Genetics,  2022-11-15 09:41:41. Journal
Meiosis is an important specialized cell division in many eukaryotic species, including fungi, plants, and animals. Meiosis results in the production of haploid gametes starting from a diploid cell via 1 round of replication and 2 rounds of cell division. In an influential article published in 1957, Sandler and Novitski first pointed out that meiosis is also an intense battleground, in which gametes vie for evolutionary supremacy with each other, often poisoning their competition to gain a fratricidal advantage (Sandler and Novitski 1957). This competition, which they termed “meiotic drive,” operates as an evolutionary force that can cause an increase in frequency of the allele that is favored during meiotic transmission. Unlike alleles that rise in frequency because they confer a fitness advantage to their carriers, meiotic drivers can rise in frequency even while conferring significant fitness disadvantages on their carriers. Thus, meiotic drivers can be viewed as the quintessential selfish genes; it is the best interest of the rest of the genome to counteract their action to restore organismal fitness.

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CRISPR-Mediated Cassette Exchange (CriMCE): A Method to Introduce and Isolate Precise Marker-Less Edits

24026
I. Morianou, A. Crisanti, T. Nolan and A. M. Hammond,  The CRISPR Journal,  2022-11-15 09:33:31. Journal
The introduction of small unmarked edits to the genome of insects is essential to study the molecular underpinnings of important biological traits, such as resistance to insecticides and genetic control strategies. Advances in CRISPR genome engineering have made this possible, but prohibitively laborious for most laboratories due to low rates of editing and the lack of a selectable marker. To facilitate the generation and isolation of precise marker-less edits we have developed a two-step method based on CRISPR-mediated cassette exchange (CriMCE) of a marked placeholder for a variant of interest. This strategy can be used to introduce a wider range of potential edits compared with previous approaches while consolidating the workflow. We present proof-of-principle that CriMCE is a powerful tool by engineering three single nucleotide polymorphism variants into the genome of Anopheles gambiae, with 5?41???higher rates of editing than homology-directed repair or prime editing.

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A Wolbachia factor for male killing in lepidopteran insects

24016
S. Katsuma, K. Hirota, N. Matsuda-Imai, T. Fukui, T. Muro, K. Nishino, H. Kosako, K. Shoji, H. Takanashi, T. Fujii, S.-i. Arimura and T. Kiuchi,  Nature Communications,  13:6764. 2022-11-14 12:59:35. Journal
Bacterial symbionts, such as Wolbachia species, can manipulate the sexual development and reproduction of their insect hosts. For example, Wolbachia infection induces male-specific death in the Asian corn borer Ostrinia furnacalis by targeting the host factor Masculinizer (Masc), an essential protein for masculinization and dosage compensation in lepidopteran insects. Here we identify a Wolbachia protein, designated Oscar, which interacts with Masc via its ankyrin repeats. Embryonic expression of Oscar inhibits Masc-induced masculinization and leads to male killing in two lepidopteran insects, O. furnacalis and the silkworm Bombyx mori. Our study identifies a mechanism by which Wolbachia induce male killing of host progeny.

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Independent evaluation of Wolbachia infected male mosquito releases for control of Aedes aegypti in Harris County, Texas, using a Bayesian abundance estimator

23969
S. Lozano, K. Pritts, D. Duguma, C. Fredregill and R. Connelly,  PLOS Neglected Tropical Diseases,  16:e0010907. 2022-11-14 12:37:36. Journal
Among disease vectors, Aedes aegypti (L.) (Diptera: Culicidae) is one of the most insidious species in the world. The disease burden created by this species has dramatically increased in the past 50 years, and during this time countries have relied on pesticides for control and prevention of viruses borne by Ae. aegypti. The small number of available insecticides with different modes of action had led to increases in insecticide resistance, thus, strategies, like the “Incompatible Insect Technique” using Wolbachia’s cytoplasmic incompatibility are desirable. We evaluated the effect of releases of Wolbachia infected Ae. aegypti males on populations of wild Ae. aegypti in the metropolitan area of Houston, TX. Releases were conducted by the company MosquitoMate, Inc. To estimate mosquito population reduction, we used a mosquito abundance Bayesian hierarchical estimator that accounted for inefficient trapping. MosquitoMate previously reported a reduction of 78% for an intervention conducted in Miami, FL. In this experiment we found a reduction of 93% with 95% credibility intervals of 86% and 96% after six weeks of continual releases. A similar result was reported by Verily Life Sciences, 96% [94%, 97%], in releases made in Fresno, CA.

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Centromere drive: chromatin conflict in meiosis

23856
P. Talbert and S. Henikoff,  Current Opinion in Genetics and Development,  77:102005. 2022-11-11 10:41:54. Journal
Centromeres are essential loci in eukaryotes that are necessary for the faithful segregation of chromosomes in mitosis and meiosis. Centromeres organize the kinetochore, the protein machine that attaches sister chromatids or homologous chromosomes to spindle microtubules and regulates their disjunction. Centromeres have both genetic and epigenetic determinants, which can come into conflict in asymmetric female meiosis in seed plants and animals. The centromere drive model was proposed to describe this conflict and explain how it leads to the rapid evolution of both centromeres and kinetochores. Recent studies confirm key aspects of the centromere drive model, clarify its mechanisms, and implicate rapid centromere/kinetochore evolution in hybrid inviability between species.

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Influence of public hesitancy and receptivity on reactive behaviours towards releases of male Wolbachia-Aedes mosquitoes for dengue control

23860
M. O. Lwin, Z. Ong, C. Panchapakesan, A. Sheldenkar, L. T. Soh, I. Chen, X. Li, W. Niah, K. Vasquez, S. Sim and L.-C. Ng,  PLOS Neglected Tropical Diseases,  16:e0010910. 2022-11-11 10:06:20. Journal
Singapore, a highly urbanized Asian tropical country that experiences periodic dengue outbreaks, is piloting field releases of male Wolbachia-carrying Aedes aegyptimosquitoes with the aim of suppressing urban populations of the primary dengue vector Aedes aegypti. This study proposes and assesses a model to explain the roles of hesitancy and receptivity towards Project Wolbachia–Singapore in influencing reactive mosquito prevention behaviors (reactive behaviors) towards the release of Wolbachia-Aedes mosquitoes for residents living in the release sites. Interestingly, both hesitancy and receptivity predicted greater instances of reactive behaviors. The model also examines the roles of general knowledge about Wolbachia technology, perceived severity of mosquito bites, perceived density of mosquitoes, and social responsibility as predictors of hesitancy, receptivity, and reactive behaviors towards the release of Wolbachia-Aedes mosquitoes. Hesitancy towards the project mediated the effects of general knowledge, perceived severity of mosquito bites, and perceived density of mosquitoes on reactive behaviors towards the releases, although receptivity towards the project did not. Having less knowledge about Project Wolbachia–Singapore was associated with higher hesitancy towards the project and higher likelihood of performing reactive behaviors towards the releases. Individuals who perceive mosquito bites to be more severe and think that there are more mosquitoes in their living environments were also more likely to be hesitant about the project and practice reactive behaviors. However, both hesitancy and receptivity towards the project mediated the effect of social responsibility on reactive behaviors. Receptivity towards the project was driven by social responsibility, which was also associated with reduced hesitancy towards the project. Our findings suggest that, to address the hesitancy reported by a minority of participants, future outreach efforts should focus on strengthening the public’s sense of social responsibility

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Wolbachia inhibits ovarian formation and increases blood feeding rate in female Aedes aegypti

23858
M.-J. Lau, P. A. Ross, N. M. Endersby-Harshman, Q. Yang and A. A. Hoffmann,  PLOS Neglected Tropical Diseases,  16:e0010913. 2022-11-11 09:59:48. Journal
Author summary Wolbachia bacteria reduce the transmission of dengue and other arboviruses transmitted by their mosquito hosts once they have invaded host populations. This invasion process is being undertaken in Aedes aegypti mosquito populations throughout the world but can be slowed by deleterious fitness costs that the Wolbachia bacteria have on their mosquito hosts. Here we investigate in detail a recently identified cost where one of the Wolbachia strains being used in invasions causes infertility in females when the females develop from eggs that have been stored for a period. We show that slowed larval development (through food reduction) can cause the same phenomenon and that the emerged females lack functional ovaries. These infertile females also take blood meals more often. The results have implications for the successful invasion of Wolbachia under ecological circumstances where the mosquito eggs have to persist in the absence of water for a period and where larval food is limiting.

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Leveraging a natural murine meiotic drive to suppress invasive populations

23835
L. Gierus, A. Birand, M. D. Bunting, G. I. Godahewa, S. G. Piltz, K. P. Oh, A. J. Piaggio, D. W. Threadgill, J. Godwin, O. Edwards, P. Cassey, J. V. Ross, T. A. A. Prowse and P. Q. Thomas,  Proceedings of the National Academy of Sciences,  119:e2213308119. 2022-11-08 09:36:13. Journal
Invasive rodents are a major cause of environmental damage and biodiversity loss, particularly on islands. Unlike insects, genetic biocontrol strategies including population-suppressing gene drives with biased inheritance have not been developed in mice. Here, we demonstrate a gene drive strategy (t(CRISPR)) that leverages super-Mendelian transmission of the t haplotype to spread inactivating mutations in a haplosufficient female fertility gene (Prl). Using spatially explicit individual-based in silico modeling, we show that t(CRISPR) can eradicate island populations under a range of realistic field-based parameter values. We also engineer transgenic t(CRISPR) mice that, crucially, exhibit biased transmission of the modified t haplotype and Prl mutations at levels our modeling predicts would be sufficient for eradication. This is an example of a feasible gene drive system for invasive alien rodent population control.

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Gene drive technologies: navigating the ethical landscape

24074
N. d. Graeff,  Utrecht University,  2022-11-04 10:41:56. Journal
Gene drives are technologies that modify a particular genetic element in animals or insects so that this genetic element does not follow the typical rules of heredity, and is passed onto future generations with an increased likelihood. Gene drive technologies could be used to tackle intractable problems such as vector-borne diseases like malaria or the biodiversity impact of invasive species. At the same time, the development and governance of gene drives raise a range of ethical questions and concerns that warrant proactive ethical evaluation. In the PhD thesis ?Gene drive technologies: navigating the ethical landscape?, Nienke de Graeff analyzes these questions and concerns. In Part I, she outlines the ?ethical landscape? of gene drive technologies by identifying the associated ethical challenges through literature review and empirical ethical research. Important challenges concern how the uncertainty and risks of these technologies should be navigated, whether it is morally permissible to intervene in nature in this way, and how the development, governance, and potential deployment of gene drive technologies should be guided. In Part II, De Graeff normatively analyzes various of these challenges and provides guidance to navigate them. In Part III, she stipulates recommendations for researchers and policymakers in the gene drive field as well as lessons learned for ethics parallel research as an approach for early ethical guidance of new and emerging technologies more generally.

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Making waves: Comparative analysis of gene drive spread characteristics in a continuous space model

23816
M. Pan and J. Champer,  bioRxiv,  2022.11.01.514650. 2022-11-02 10:23:47. Journal
With their ability to rapidly increase in frequency, gene drives can be used to modify or suppress target populations after an initial release of drive-containing individuals. Recent advances in this field have revealed many possibilities for different types of drives, and several of these have been realized in experimental demonstrations. These drives all have unique advantages and disadvantages related to their ease of construction, confinement, and capacity to act as a modification or suppression system. While many properties of these drives have been explored in modelling studies, assessment of these drives in continuous space environments has been limited, often focusing on outcomes rather than fundamental properties. Here, we conduct a comparative analysis of many different gene drive types that have the capacity to form a wave of advance against wild-type alleles in one-dimensional continuous space. We evaluate the drive wave speed as a function of drive performance and ecological parameters, which reveals substantial differences between drive performance in panmictic versus spatial environments. In particular, we find that suppression drive waves are uniquely vulnerable to fitness costs and undesired CRISPR cleavage activity that can form resistance alleles in embryos by maternal deposition. Some drives, though, retain robust characteristics even with widely varying performance characteristics. To gain a better understanding of drive waves, we compare panmictic performance of drives across the full range of drive frequencies. We find that rates of wild-type allele removal in panmictic setting is correlated with drive wave speed, though this is also affected by a range of other factors. Overall, our results provide a useful resource for understanding the performance of drives in continuous spatial environments, which may be most representative of potential drive deployment in many relevant scenarios.Competing Interest StatementThe authors have declared no competing interest.

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Asymmetric Inheritance: The Diversity and Evolution of Non-Mendelian Reproductive Strategies

L. Ross, A. J. Mongue, C. N. Hodson and T. Schwander,  Annual Review of Ecology, Evolution, and Systematics,  53:1-23. 2022-11-02 08:36:15. Journal
The ability to reproduce is the key trait that distinguishes living organisms from inorganic matter, and the strategies used to achieve successful reproduction are almost as diverse as the organisms themselves. In animals, the most widespread form of reproduction involves separate male and female sexes: Each sex produces haploid gametes via meiosis, and two gametes fuse to form a new diploid organism. In some cases, both parents contribute equally to the nuclear and cytoplasmic genomes of their offspring. However, such fully symmetric reproduction of both parents represents the extreme end of a continuum toward complete asymmetry, where offspring inherit their nuclear and cytoplasmic genomes from only one of the two parents. Asymmetries also occur with respect to the fate of maternally and paternally inherited genomes and which sex is affected by non-Mendelian inheritance. In this review, we describe the diversity of animal reproductive systems along different axes with a symmetry?asymmetry continuum and suggest evolutionary routes that may have led to increased levels of asymmetry.

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GMOs in Africa: Status, adoption and public acceptance

27490
L. A. Gbadegesin, E. A. Ayeni, C. K. Tettey, V. A. Uyanga, O. O. Aluko, J. K. Ahiakpa, C. O. Okoye, J. I. Mbadianya, M. A. Adekoya, R. O. Aminu, F. P. Oyawole and P. Odufuwa,  Food Control,  141:109193. 2022-11-01 13:46:04. Journal
Globally, genetically modified (GM) crops contribute to food security by increasing crop yield, quality and shelf-life. The commercialisation and adoption of GM crops in many developed countries raised hope of improving food security and livelihood. Africa, a developing continent facing malnutrition, food crises and inadequate food production technologies has been slow to accept GM crops. The hesitancy to accept GM crops emanates from unfavourable policies shaped by public opinion, despite its potential for achieving the zero-hunger agenda. Impeding factors hampering the adoption of GM technology necessitate biosecurity regulations on GM crops to monitor the crop biosafety, environmental and health concerns. Herein, we reviewed GM crops status and adoption in Africa and possible constraints to their acceptance amidst some commercialised GM crops in African countries. Efforts aimed at improving GM adoption in Africa should include the provision of adequate monitoring and surveillance system, science-based policies, political will and a robust public education on GM technology.

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A sterile insect technique pilot trial on Captiva Island: defining mosquito population parameters for sterile male releases using mark–release–recapture

23818
D. O. Carvalho, R. Morreale, S. Stenhouse, D. A. Hahn, M. Gomez, A. Lloyd and D. Hoel,  Parasites and Vectors,  15:405. 2022-11-01 10:41:32. Journal
The sterile insect technique (SIT), which involves area-wide inundative releases of sterile insects to suppress the reproduction of a target species, has proven to be an effective pest control method. The technique demands the continuous release of sterilized insects in quantities thatThe sterile insect technique (SIT), which involves area-wide inundative releases of sterile insects to suppress the reproduction of a target species, has proven to be an effective pest control method. The technique demands the continuous release of sterilized insects in quantities that ensure a high sterile male:wild male ratio for the suppression of the wild population over succeeding generations. Over the course of seven mark-release-recapture studies using single- and multiple-point releases, 190,504 sterile marked males were released, for which the recapture rate was 1.5% over a mean period of 12 days. The mean distance traveled by sterile males of the local strain of Ae. aegypti that has colonized Captiva Island was 201.7 m from the release point, with an observed maximum traveled distance of 404.5 m. The released sterile mosquitoes had a probability of daily survival of 0.67 and an average life expectancy of ~ 2.46 days.s These data together with the population size estimate and sterile:wild ratio provide a solid basis for planning the SIT operational phase which is aimed at mosquito population suppression. ensure a high sterile male:wild male ratio for the suppression of the wild population over succeeding generations.

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Modeling the efficacy of CRISPR gene drive for snail immunity on schistosomiasis control

23810
R. E. Grewelle, J. Perez-Saez, J. Tycko, E. K. O. Namigai, C. G. Rickards and G. A. De Leo,  PLOS Neglected Tropical Diseases,  16:e0010894. 2022-10-31 09:02:03. Journal
CRISPR gene drives could revolutionize the control of infectious diseases by accelerating the spread of engineered traits that limit parasite transmission in wild populations. Gene drive technology in mollusks has received little attention despite the role of freshwater snails as hosts of parasitic flukes causing 200 million annual cases of schistosomiasis. A successful drive in snails must overcome self-fertilization, a common feature of host snails which could prevents a drive's spread. Here we developed a novel population genetic model accounting for snails' mixed mating and population dynamics, susceptibility to parasite infection regulated by multiple alleles, fitness differences between genotypes, and a range of drive characteristics. We integrated this model with an epidemiological model of schistosomiasis transmission to show that a snail population modification drive targeting immunity to infection can be hindered by a variety of biological and ecological factors; yet under a range of conditions, disease reduction achieved by chemotherapy treatment of the human population can be maintained with a drive. Alone a drive modifying snail immunity could achieve significant disease reduction in humans several years after release. These results indicate that gene drives, in coordination with existing public health measures, may become a useful tool to reduce schistosomiasis burden in selected transmission settings with effective CRISPR construct design and evaluation of the genetic and ecological landscape.

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Gene drive by Fusarium SKC1 is dependent on its competing allele

23833
J. M. Lohmar, N. A. Rhoades, T. M. Hammond and D. W. Brown,  Fungal Genetics and Biology,  163:103749. 2022-10-29 09:19:43. Journal
The Fusarium verticillioides SKC1 gene driver is transmitted to offspring in a biased manner through spore killing. The mechanism that allows SKC1 to kill non-SKC1 offspring while sparing others is poorly understood. Here we report that gene drive by SKC1 is dependent on SKC1's competing allele. We propose that SKC1's competing allele influences the ability of a genome defense process to detect SKC1, and we provide evidence that this genome defense process is meiotic silencing by unpaired DNA (MSUD). Our findings suggest that the successful deployment of gene drivers to control pathogenic fungi will require researchers to consider how competing alleles influence the ability of gene drivers to be detected by genome defense processes.

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Expression of mosquito miRNAs in entomopathogenic fungus induces pathogen-mediated host RNA interference and increases fungal efficacy

23853
C. Cui, Y. Wang, Y. Li, P. Sun, J. Jiang, H. Zhou, J. Liu and S. Wang,  Cell Reports,  41:111527. 2022-10-25 10:15:50. Journal
Summary The growing threat of insecticide resistance prompts the urgent need to develop additional tools for mosquito control. Entomopathogenic fungi provide an eco-friendly alternative to chemical insecticides. One limitation to the use of mycoinsecticides is their relatively low virulence. Here, we report an approach for suppressing mosquito immunity and increasing fungal virulence. We engineered Beauveria bassiana to express Aedes immunosuppressive microRNAs (miRNAs) to induce host RNA interference (RNAi) immune responses. We show that engineered strains can produce and deliver the miRNAs into host cells to activate cross-kingdom RNAi during infection and suppress mosquito immunity by targeting multiple host genes, thereby dramatically increasing fungal virulence against Aedes aegypti and Galleria mellonella larvae. Importantly, expressing host miRNAs also significantly increases fungal virulence against insecticide-resistant mosquitoes, creating potential for insecticide-resistance management. This pathogen-mediated RNAi (pmRNAi)-based approach provides an innovative strategy to enhance the efficacy of fungal insecticides and eliminate the likelihood of resistance development.

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Cross-kingdom RNAi to enhance the efficacy of insect pathogens

23851
S. Asgari,  Trends in Parasitology,  2022-10-25 10:11:07. Journal
Insect pathogens play significant roles in the biocontrol of medical and agricultural pests. Cui et al. demonstrated that genetically modified (GM) fungi expressing host mosquito miRNAs could enhance the efficacy of the fungus by suppressing the host immune response. This opens avenues for utilisation of cross-kingdom RNAi in biocontrol.

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Monotonicity properties arising in a simple model of Wolbachia invasion for wild mosquito populations

24568
D. Vicencio, O. Vasilieva and P. Gajardo,  Mathematical Biosciences and Engineering,  20:1148-1175. 2022-10-25 08:23:57. Journal
Using tools borrowed from monotone dynamical system theory, in the proposed model, we prove the existence of an invariant threshold manifold that allows us to provide practical recommendations for performing single and periodic releases of Wolbachia-carrying mosquitoes, seeking the eventual elimination of wild insects that are capable of transmitting infections to humans. We illustrate these findings with numerical simulations using parameter values corresponding to the wMelPop strain of Wolbachia that is considered the best virus blocker but induces fitness loss in its carriers. In these tests, we considered multiple scenarios contrasting a periodic release strategy against a strategy with a single inundative release, comparing their effectiveness. Our study is presented as an expository and mathematically accessible tool to study the use of Wolbachia-based biocontrol versus more complex models.

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Pulled, pushed or failed: the demographic impact of a gene drive can change the nature of its spatial spread

23805
L. Kläy, L. Girardin, V. Calvez and F. Débarre,  arXiv,  2022-10-25 07:50:10. Journal
Understanding the temporal spread of gene drive alleles -- alleles that bias their own transmission -- through modeling is essential before any field experiments. In this paper, we present a deterministic reaction-diffusion model describing the interplay between demographic and allelic dynamics, in a one-dimensional spatial context. We focused on the traveling wave solutions, and more specifically, on the speed of gene drive invasion (if successful). We considered various timings of gene conversion (in the zygote or in the germline) and different probabilities of gene conversion (instead of assuming 100% conversion as done in a previous work). We compared the types of propagation when the intrinsic growth rate of the population takes extreme values, either very large or very low. When it is infinitely large, the wave can be either successful or not, and, if successful, it can be either pulled or pushed, in agreement with previous studies (extended here to the case of partial conversion). In contrast, it cannot be pushed when the intrinsic growth rate is vanishing. In this case, analytical results are obtained through an insightful connection with an epidemiological SI model. We conducted extensive numerical simulations to bridge the gap between the two regimes of large and low growth rate. We conjecture that, if it is pulled in the two extreme regimes, then the wave is always pulled, and the wave speed is independent of the growth rate. This occurs for instance when the fitness cost is small enough, or when there is stable coexistence of the drive and the wild-type in the population after successful drive invasion. Our model helps delineate the conditions under which demographic dynamics can affect the spread of a gene drive.

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New self-sexing Aedes aegypti strain eliminates barriers to scalable and sustainable vector control for governments and communities in dengue-prone environments

23796
S. A. M. Spinner, Z. H. Barnes, A. M. Puinean, P. Gray, T. Dafa’alla, C. E. Phillips, C. Nascimento de Souza, T. F. Frazon, K. Ercit, A. Collado, N. Naish, E. Sulston, G. C. Ll. Phillips, K. K. Greene, M. Poletto, B. D. Sperry, S. A. Warner, N. R. Rose, G,  Frontiers in Bioengineering and Biotechnology,  10. 2022-10-25 07:35:02. Journal
For more than 60 years, efforts to develop mating-based mosquito control technologies have largely failed to produce solutions that are both effective and scalable, keeping them out of reach of most governments and communities in disease-impacted regions globally. High pest suppression levels in trials have yet to fully translate into broad and effective Aedes aegypti control solutions. Two primary challenges to date–the need for complex sex-sorting to prevent female releases, and cumbersome processes for rearing and releasing male adult mosquitoes–present significant barriers for existing methods. As the host range of Aedes aegypti continues to advance into new geographies due to increasing globalisation and climate change, traditional chemical-based approaches are under mounting pressure from both more stringent regulatory processes and the ongoing development of insecticide resistance. It is no exaggeration to state that new tools, which are equal parts effective and scalable, are needed now more than ever. This paper describes the development and field evaluation of a new self-sexing strain of Aedes aegypti that has been designed to combine targeted vector suppression, operational simplicity, and cost-effectiveness for use in disease-prone regions. This conditional, self-limiting trait uses the sex-determination gene doublesex linked to the tetracycline-off genetic switch to cause complete female lethality in early larval development. With no female progeny survival, sex sorting is no longer required, eliminating the need for large-scale mosquito production facilities or physical sex-separation. In deployment operations, this translates to the ability to generate multiple generations of suppression for each mosquito released, while being entirely self-limiting. To evaluate these potential benefits, a field trial was carried out in densely-populated urban, dengue-prone neighbourhoods in Brazil, wherein the strain was able to suppress wild mosquito populations by up to 96%, demonstrating the utility of this self-sexing approach for biological vector control. In doing so, it has shown that such strains offer the critical components necessary to make these tools highly accessible, and thus they harbour the potential to transition mating-based approaches to effective and sustainable vector control tools that are within reach of governments and at-risk communities who may have only limited resources.

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Combining transgenesis with paratransgenesis to fight malaria

23802
W. Huang, J. Vega-Rodriguez, C. Kizito, S.-J. Cha and M. Jacobs-Lorena,  eLife,  11:e77584. 2022-10-25 06:30:55. Journal
Malaria is among the deadliest infectious diseases, and Plasmodium, the causative agent, needs to complete a complex development cycle in its vector mosquito for transmission to occur. Two promising strategies to curb transmission are transgenesis, consisting of genetically engineering mosquitoes to express antimalarial effector molecules, and paratransgenesis, consisting of introducing into the mosquito commensal bacteria engineered to express antimalarial effector molecules. Although both approaches restrict parasite development in the mosquito, it is not known how their effectiveness compares. Here we provide an in-depth assessment of transgenesis and paratransgenesis and evaluate the combination of the two approaches. Using the Q-system to drive gene expression, we engineered mosquitoes to produce and secrete two effectors – scorpine and the MP2 peptide – into the mosquito gut and salivary glands. We also engineered Serratia, a commensal bacterium capable of spreading through mosquito populations to secrete effectors into the mosquito gut. Whereas both mosquito-based and bacteria-based approaches strongly reduced the oocyst and sporozoite intensity, a substantially stronger reduction of Plasmodium falciparum development was achieved when transgenesis and paratransgenesis were combined. Most importantly, transmission of Plasmodium berghei from infected to naïve mice was maximally inhibited by the combination of the two approaches. Combining these two strategies promises to become a powerful approach to combat malaria.

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Ethics of gene drive mosquitoes for malaria elimination

24071
A. J. Roberts,  McMaster University,  2022-10-24 10:34:04. Link
This thesis is concerned with presenting analyses regarding key ethical issues regarding and arising from the development and potential use of gene drive modified mosquitoes for the purpose of malaria elimination. Each of the chapters constituting this thesis offers a rigorously researched analysis which attempts to answer questions thus far unanswered in the academic literature. Chapter one explores whether the development and use of this technology can be fairly considered unethical in principle; concluding it cannot be. Chapter two explores the appropriate relationship between this technology and the precautionary principle, a prominent regulatory and governance principle which has been invoked as ostensible support for an indefinite global moratorium on all gene drive technology. The chapter concludes that the precautionary principle, at least as articulated by UNESCO, does not provide justification for a global moratorium on gene drive technology. In fact, the precautionary principle is likely unfit as a regulatory norm for some kinds of gene drive products and purposes. Chapter three was co-authored with Delphine Thizy, Global Stakeholder Engagement Manager for Target Malaria, one of the leading consortiums working on research and development of gene drive biotechnology for malaria control. Together we articulate the ethical principles selected to guide Target Malaria’s stakeholder engagement, as well as provide the rationale for their selection and expound upon some early lessons from their implementation. Chapter four offers an analysis with the goal of locating the ethically appropriate locus of political organization from which to seek permission for a gene drive modified organism release into the shared environment. The chapter considers the appropriateness of each of the following levels of political organization: consent of individuals, local communities, nation states, and international governance institutions. The conclusion arrived at, with some caveats, is that such a decision is most appropriately issued by a nation state.

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Hidden endosymbionts: A male-killer concealed by another endosymbiont and a nuclear suppressor

23793
K. 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. Journal
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.

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Hurdles in responsive community engagement for the development of environmental biotechnologies

25089
A. M. Normandin, L. M. Fitzgerald, J. Yip and S. W. Evans,  Synthetic Biology,  7:ysac022. 2022-10-20 06:56:55. Journal
Recent calls for engaging communities in biotechnology development do not draw enough attention to the hurdles that must be overcome for engagement strategies to effectively feed back into research design and conduct. These hurdles call into question many standard ways of operating and assessing in traditional scientific disciplines. The first steps in addressing these hurdles can be the most difficult. In reflecting on our own experiences in the early-stage development of environmental biotechnologies, we provide a set of techniques to help scientists and their collaborators learn to become more responsive to the needs and attitudes of communities with which they are engaging.Graphical Abstract

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Driving down malaria transmission with engineered gene drives

23780
W. T. Garrood, P. Cuber, K. Willis, F. Bernardini, N. M. Page and R. E. Haghighat-Khah,  Frontiers in Genetics,  13. 2022-10-19 07:08:43. Link
The last century has witnessed the introduction, establishment and expansion of mosquito-borne diseases into diverse new geographic ranges. Malaria is transmitted by female Anopheles mosquitoes. Despite making great strides over the past few decades in reducing the burden of malaria, transmission is now on the rise again, in part owing to the emergence of mosquito resistance to insecticides, antimalarial drug resistance and, more recently, the challenges of the COVID-19 pandemic, which resulted in the reduced implementation efficiency of various control programs. The utility of genetically engineered gene drive mosquitoes as tools to decrease the burden of malaria by controlling the disease-transmitting mosquitoes is being evaluated. To date, there has been remarkable progress in the development of CRISPR/Cas9-based homing endonuclease designs in malaria mosquitoes due to successful proof-of-principle and multigenerational experiments. In this review, we examine the lessons learnt from the development of current CRISPR/Cas9-based homing endonuclease gene drives, providing a framework for the development of gene drive systems for the targeted control of wild malaria-transmitting mosquito populations that overcome challenges such as with evolving drive-resistance. We also discuss the additional substantial works required to progress the development of gene drive systems from scientific discovery to further study and subsequent field application in endemic settings.

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Mosquito Gene Drives and the Malaria Eradication Agenda

23731
Editor: R. Carballar-Lejarazu,,  Jenny Stanford Publishing,  2022-10-17 06:37:46. Link
Malaria is one of most serious infectious diseases today and has afflicted humankind for thousands of years. A significant number of people still die from this mosquito-borne disease, despite the use of various malaria prevention and control methods over hundreds of years and more than a century of coordinated global control efforts using modern tools, together with research into and development of new strategies for prevention, diagnosis, and disease treatment. Genetic approaches that focus on the vector mosquitoes to prevent malaria parasite transmission have been considered for many decades. Genetic control strategies received a significant boost with the successful development of gene-drive systems, genetic methods for rapidly spreading beneficial genes and phenotypes through mosquito populations. This book reviews some concepts of gene drive systems and describes pioneering applications to control mosquito populations and prevent parasite transmission.

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Assessing single-locus CRISPR/Cas9-based gene drive variants in the mosquito Aedes aegypti via single generation crosses and modeling

23756
W. Reid, A. E. Williams, I. Sanchez-Vargas, J. Lin, R. Juncu, K. E. Olson and A. W. E. Franz,  G3 Genes|Genomes|Genetics,  2022-10-17 06:25:18. Journal
Critical to the design of a single-locus autonomous GD is that the selected genomic locus is amenable to both GD and appropriate expression of the antiviral effector. In our study, we used reverse engineering to target two intergenic genomic loci, which had previously shown to be highly permissive for antiviral effector gene expression, and we further investigated the use of three promoters (nanos, β2-tubulin, or zpg) for Cas9 expression. We then quantified the accrual of insertions or deletions (indels) after single generation crossings, measured maternal effects, and assessed fitness costs associated with the various transgenic lines to model the rate of GD fixation. Overall, MGDrivE modeling suggested that when an autonomous GD is placed into an intergenic locus, the GD system will eventually be blocked by the accrual of GD blocking resistance alleles and ultimately be lost in the population. Moreover, while genomic locus and promoter selection were critically important for the initial establishment of the autonomous GD, it was the fitness of the GD line that most strongly influenced the persistence of the GD in the simulated population. As such, we propose that when autonomous CRISPR/Cas9 based GD systems are anchored in an intergenic locus, they temporarily result in a strong population replacement effect, but as GD-blocking indels accrue, the GD becomes exhausted due to the fixation of CRISPR resistance alleles.

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Introgression of a synthetic sex ratio distortion transgene into different genetic backgrounds of Anopheles coluzzii

23760
P. Pollegioni, T. Persampieri, R. L. Minuz, A. Bucci, A. Trusso, S. Di Martino, C. Leo, M. Bruttini, M. Ciolfi, A. M. Waldvogel, F. Tripet, A. Simoni, A. Crisanti and R. Müller,  Insect Molecular Biology,  2022-10-17 06:14:10. Journal
The development of genetically modified mosquitoes (GMM) and their subsequent field release offers innovative approaches for vector control of malaria. A non-gene drive self-limiting male-bias Ag(PMB)1 strain has been developed in a 47-year-old laboratory G3 strain of Anopheles gambiae s.l. When Ag(PMB)1 males are crossed to wild-type females, expression of the endonuclease I-PpoI during spermatogenesis causes the meiotic cleavage of the X chromosome in sperm cells, leading to fertile offspring with a 95% male bias. However, WHO states that the functionality of the transgene could differ when inserted in different genetic backgrounds of An. coluzzii which is currently a predominant species in several West-African countries and thus a likely recipient for a potential release of self-limiting GMMs. In this study, we introgressed the transgene from the donor Ag(PMB)1 by six serial backcrosses into two recipient colonies of An. coluzzii that had been isolated in Mali and Burkina Faso. Scans of informative SNP markers and whole-genome sequencing analysis revealed a nearly complete introgression of chromosome 3 and X, but a remarkable genomic divergence in a large region of the chromosome 2 between the later backcrossed (BC6) transgenic offspring and the recipient paternal strains. These findings suggested to extend the backcrossing breeding strategy beyond BC6 generation and increase the introgression efficiency of critical regions that have ecological and epidemiological implications through the targeted selection of specific markers. Disregarding of differential introgression efficiency, we concluded that the phenotype of the sex ratio distorter is stabile in the BC6 introgressed An. coluzzii strains. This article is protected by copyright. All rights reserved.

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Anopheles homing suppression drive candidates exhibit unexpected performance differences in simulations with spatial structure

23734
S. E. Champer, I. K. Kim, A. G. Clark, P. W. Messer and J. Champer,  eLife,  11:e79121. 2022-10-14 06:37:55. Journal
Recent experiments have produced several Anopheles gambiae homing gene drives that disrupt female fertility genes, thereby eventually inducing population collapse. Such drives may be highly effective tools to combat malaria. One such homing drive, based on the zpg promoter driving CRISPR/Cas9, was able to eliminate a cage population of mosquitoes. A second version, purportedly improved upon the first by incorporating an X-shredder element (which biases inheritance towards male offspring), was similarly successful. Here, we analyze experimental data from each of these gene drives to extract their characteristics and performance parameters and compare these to previous interpretations of their experimental performance. We assess each suppression drive within an individual-based simulation framework that models mosquito population dynamics in continuous space. We find that the combined homing/X-shredder drive is actually less effective at population suppression within the context of our mosquito population model. In particular, the combined drive often fails to completely suppress the population, instead resulting in an unstable equilibrium between drive and wild-type alleles. By contrast, otherwise similar drives based on the nos promoter may prove to be more promising candidates for future development than originally thought.

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Wolbachia wAlbB inhibit dengue and Zika infection in the mosquito Aedes aegypti with an Australian background

23714
L. E. Hugo, G. Rašić, A. J. Maynard, L. Ambrose, C. Liddington, C. J. E. Thomas, N. S. Nath, M. Graham, C. Winterford, B. M. C. R. Wimalasiri-Yapa, Z. Xi, N. W. Beebe and G. J. Devine,  PLOS Neglected Tropical Diseases,  16:e0010786. 2022-10-13 06:27:20. Journal
Biological control of mosquito vectors using the endosymbiotic bacteria Wolbachia is an emerging strategy for the management of human arboviral diseases. We recently described the development of a strain of Aedes aegypti infected with the Wolbachia strain wAlbB (referred to as the wAlbB2-F4 strain) through simple backcrossing of wild type Australian mosquitoes with a wAlbB infected Ae. aegypti strain from the USA. Field releases of male wAlbB2-F4 mosquitoes resulted in the successful suppression of wild populations of mosquitoes in the trial sites by exploiting the strain’s Wolbachia-induced cytoplasmic incompatibility. We now demonstrate that the strain is resistant to infection by dengue and Zika viruses and is genetically similar to endemic Queensland populations. There was a fourfold reduction in the proportion of wAlbB2-F4 mosquitoes that became infected following a blood meal containing dengue 2 virus (16.7%) compared to wild type mosquitoes (69.2%) and a 6–7 fold reduction in the proportion of wAlbB2-F4 mosquitoes producing virus in saliva following a blood meal containing an epidemic strain of Zika virus (8.7% in comparison to 58.3% in wild type mosquitoes). Restriction-site Associated DNA (RAD) sequencing revealed that wAlbB2-F4 mosquitoes have > 98% Australian ancestry, confirming the successful introduction of the wAlbB2 infection into the Australian genomic background through backcrossing. Genotypic and phenotypic analyses showed the wAlbB2-F4 strain retains the insecticide susceptible phenotype and genotype of native Australian mosquitoes. We demonstrate that the Wolbachia wAlbB2-F4, in addition to being suitable for population suppression programs, can also be effective in population replacement programs given its inhibition of virus infection in mosquitoes. The ease at which a target mosquito population can be transfected with wAlbB2, while retaining the genotypes and phenotypes of the target population, shows the utility of this strain for controlling the Ae. aegypti mosquitoes and the pathogens they transmit.

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The wtf meiotic driver gene family has unexpectedly persisted for over 100 million years

23712
M. De Carvalho, G. S. Jia, A. Nidamangala Srinivasa, R. B. Billmyre, Y. H. Xu, J. J. Lange, I. M. Sabbarini, L. L. Du and S. E. Zanders,  eLife,  11. 2022-10-13 06:23:07. Journal
Meiotic drivers are selfish elements that bias their own transmission into more than half of the viable progeny produced by a driver+/driver- heterozygote. Meiotic drivers are thought to exist for relatively short evolutionary timespans because a driver gene or gene family is often found in a single species or in a group of very closely related species. Additionally, drivers are generally considered doomed to extinction when they spread to fixation or when suppressors arise. In this study, we examine the evolutionary history of the wtf meiotic drivers first discovered in the fission yeast Schizosaccharomyces pombe. We identify homologous genes in three other fission yeast species, S. octosporus, S. osmophilus, and S. cryophilus, which are estimated to have diverged over 100 million years ago from the S. pombe lineage. Synteny evidence supports that wtf genes were present in the common ancestor of these four species. Moreover, the ancestral genes were likely drivers as wtf genes in S. octosporus cause meiotic drive. Our findings indicate that meiotic drive systems can be maintained for long evolutionary timespans.

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Risk Assessment on the Release of Wolbachia-Infected Aedes aegypti in Yogyakarta, Indonesia

23707
D. Buchori, A. Mawan, I. Nurhayati, A. Aryati, H. Kusnanto and U. K. Hadi,  Insects,  13. 2022-10-12 08:16:52. Journal
Wolbachia-infected Aedes aegypti is the latest technology that was developed to eliminate dengue fever. The Ministry of Research and Technology of the Republic of Indonesia (Kemenristekdikti) established an expert group to identify future potential risks that may occur over a period of 30 years associated with the release of Wolbachia-infected Ae. aegypti. The risk assessment consisted of identifying different hazards that may have impacts on humans and the environment. From the consensus among the experts, there were 56 hazards identified and categorized into 4 components, namely, ecological matters, efficacy in mosquito management, economic and sociocultural issues, and public health standards. There were 19 hazards in the ecological group. The overall likelihood in the ecology of the mosquito is very low (0.05), with moderate consequence (0.74), which resulted in negligible risk. For the efficacy in mosquito management group, there were 12 hazards that resulted in very low likelihood (0.11) with high consequence (0.85). The overall risk for mosquito management efficacy was very low (0.09). There were 14 hazards identified in the public health standard with very low likelihood (0.07), moderate consequence (0.50) and negligible risk (0.04). Lastly, 13 hazards were identified in the economic and sociocultural group with low likelihood (0.01) but of moderate consequence (0.5), which resulted in a very low risk (0.09). The risk severity level of the four components leading to the endpoint risk of “cause more harm” due to releasing Wolbachia-infected Ae. aegypti is negligible (0.01).

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Improvement of Resistance in Plants Against Insect-Pests Using Genome Editing Tools

25205
S. Bhat and S. Kumar,  Genome Editing: Current Technology Advances and Applications for Crop Improvement,  2022-10-09 09:31:41. Journal
During growth period plants are subjected to both biotic and abiotic stresses. Like other biotic stresses, insect-pests are the most serious challenge for the plants particularly in yield losses. Genome editing techniques are becoming an emerging technology bringing real revolution in genetic engineering and biotechnology. Editing of targeted gene provides ways to elucidate extensive ranges of aims for the improvement, protection, and increased yield of various crops. Researchers all over the world have unraveled the usage of numerous gene editing methods from endonuclease to CRISPR/Cas in various aspects of plants like plant growth and development, insect-pest control, and other biotic stresses. The key goal of this chapter is to highlight various techniques of genome editing approaches which can be used to develop resistance in plants against insect-pests. New crop-based methods that reiterate the effective utilization of these techniques in insect-pest management as well as plant in resistance against pests are highlighted. This chapter also highlights the implication of genome editing as well as framework for its specific regulation.

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