Scholarly Literature
This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives). The latest are shown here.
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Use of Insect Promoters in Genetic Engineering to Control Mosquito-Borne Diseases
24584V. Bottino-Rojas and A. A. James, Biomolecules, 13. 2022-12-22 10:33:51.
Mosquito transgenesis and gene-drive technologies provide the basis for developing promising new tools for vector-borne disease prevention by either suppressing wild mosquito populations or reducing their capacity from transmitting pathogens. Many studies of the regulatory DNA and promoters of genes with robust sex-, tissue- and stage-specific expression profiles have supported the development of new tools and strategies that could bring mosquito-borne diseases under control. Although the list of regulatory elements available is significant, only a limited set of those can reliably drive spatial-temporal expression. Here, we review the advances in our ability to express beneficial and other genes in mosquitoes, and highlight the information needed for the development of new mosquito-control and anti-disease strategies.
Genes drive organisms and slippery slopes
24322D. B. Resnik, R. F. Medina, F. Gould, G. Church and J. Kuzma, Pathog Glob Health, 2022-12-22 08:58:12.
The bioethical debate about using gene drives to alter or eradicate wild populations has focused mostly on issues concerning short-term risk assessment and management, governance and oversight, and public and community engagement, but has not examined big-picture- 'where is this going?'-questions in great depth. In other areas of bioethical controversy, big-picture questions often enter the public forum via slippery slope arguments. Given the incredible potential of gene drive organisms to alter the Earth's biota, it is somewhat surprising that slippery slope arguments have not played a more prominent role in ethical and policy debates about these emerging technologies. In this article, we examine a type of slippery slope argument against using gene drives to alter or suppress wild pest populations and consider whether it has a role to play in ethical and policy debates. Although we conclude that this argument does not provide compelling reasons for banning the use of gene drives in wild pest populations, we believe that it still has value as a morally instructive cautionary narrative that can motivate scientists, ethicists, and members of the public to think more clearly about appropriate vs. inappropriate uses of gene drive technologies, the long-term and cumulative and emergent risks of using gene drives in wild populations, and steps that can be taken to manage these risks, such as protecting wilderness areas where people can enjoy life forms that have not been genetically engineered.
P-element invasions in Drosophila erecta; shed light on the establishment of host control over a transposable element
24320D. Selvaraju, F. Wierzbicki and R. Kofler, bioRxiv, 2022.12.22.521571. 2022-12-22 08:52:45.
To prevent the spread of transposable elements (TEs) hosts have developed sophisticated defence mechanisms. In mammals and invertebrates this defence mechanism operates through piRNAs. It is unclear how piRNA-based defences are established against invading TEs. According to the trap model, a TE insertion into a piRNA cluster, i.e. a distinct genomic locus, activates the host defence. Alternatively, siRNAs, generated by cleavage of dsRNA, may be the trigger for host control. To investigate this we introduced the P-element, one of the most widely studied eukaryotic transposons, into naïve lines of Drosophila erecta. We monitored the invasion in 3 replicates for more than 50 generations by sequencing the genomic DNA (using short and long-reads), the small RNAs and the transcriptome at regular intervals. A piRNA based host defence was rapidly established in 2 replicates but not in the third, where P-element copy numbers kept increasing for over 50 generations. We found that siRNAs emerged prior to piRNAs, supporting the view that siRNAs initiate host defence. However, neither insertions in piRNA clusters nor the formation of siRNAs were sufficient to stop the P-element. Instead the activation of the ping-pong cycle was shown to be crucial. We introduce a novel model, the crank-up model, which emphasizes activation of the ping-pong cycle as a critical event in establishing host control over a TE.Competing Interest StatementThe authors have declared no competing interest.
Gene drive-mediated population elimination for biodiversity conservation. When you come to a fork in the road, take it
24281B. A. Hay and M. Guo, Proceedings of the National Academy of Sciences, 119:e2218020119. 2022-12-20 14:19:44.
How can the ability of t w2 to spread at super-Mendelian frequencies be utilized even if it is unable to directly drive the population to an unfit state? Gierus, Birand, and colleagues proposed placing Cas9 and a gRNA at a neutral position within the t haplotype. In this hybrid gene drive element, which they refer to as tCRISPR, Cas9 and the gRNA cleave and (hopefully) create loss-of-function (LOF) alleles in the male germ line of the prolactin (Prl) gene, which is required for female fertility. The goal with tCRISPR is for t-based segregation distortion in males to pump the Cas9/gRNAs cassette to high frequency within the population. The latter, through cleavage followed by inaccurate repair in males, will continuously produce LOF alleles at the independently segregating Prl locus. The hope is that the combination of t-based drive and accumulation of Prl LOF alleles will drive the population to an unfit state that contains a high frequency of infertile homozygous Prl mutant females along with some frequency of infertile homozygous t males. The combination of these two effects, they propose, could eliminate populations under a wider range of parameters than with t w2 alone
Gene editing and agrifood systems
24291FAO, FAO, 2022-12-20 09:22:56.
Gene-editing technologies represent a promising new tool for plant and animal breeding in low- and middle-income countries. They enhance precision and efficiency over current breeding methods and could lead to rapid development of improved plant varieties and animal breeds. However, as for any new technology, they have their merits and demerits. There is, as yet, no international consensus regarding if and how gene-edited organisms should be regulated, and whether their release would fall under the regulatory framework of the Cartagena Protocol on Biosafety to the Convention on Biological Diversity. This science- and evidence-based Issue Paper on gene editing and agrifood systems presents a balanced discussion of the most pertinent aspects of gene editing, including the consequences for human hunger, human health, food safety, effects on the environment, animal welfare, socioeconomic impact and distribution of benefits. Intrinsic ethical concerns and issues of governance and regulation are addressed, and the roles of the public and private sectors, alone and in partnership, are summarized. Various scenarios are also presented for how gene editing might be used in the future to help transform agrifood systems.
A Natural Fungal Gene Drive Enacts Killing via DNA Disruption
24286A. S. Urquhart and D. M. Gardiner, mBio, e0317322. 2022-12-20 08:53:56.
Fungal spore killers are a class of selfish genetic elements that positively bias their own inheritance by killing non-inheriting gametes following meiosis. As killing takes place specifically within the developing fungal ascus, a tissue which is experimentally difficult to isolate, our understanding of the mechanisms underlying spore killers are limited. In particular, how these loci kill other spores within the fungal ascus is largely unknown. Here, we overcome these experimental barriers by developing model systems in 2 evolutionary distant organisms, Escherichia coli (bacterium) and Saccharomyces cerevisiae (yeast), similar to previous approaches taken to examine the wtf spore killers. Using these systems, we show that the Podospora anserina spore killer protein SPOK1 enacts killing through targeting DNA. IMPORTANCE Natural gene drives have shaped the genomes of many eukaryotes and recently have been considered for applications to control undesirable species. In fungi, these loci are called spore killers. Despite their importance in evolutionary processes and possible applications, our understanding of how they enact killing is limited. We show that the spore killer protein Spok1, which has homologues throughout the fungal tree of life, acts via DNA disruption. Spok1 is only the second spore killer locus in which the cellular target of killing has been identified and is the first known to target DNA. We also show that the DNA disrupting activity of Spok1 is functional in both bacteria and yeast suggesting a highly conserved mode of action.
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.
Assessing the efficacy of male Wolbachia-infected mosquito deployments to reduce dengue incidence in Singapore: study protocol for a cluster-randomized controlled trial
24268J. Ong, S. H. Ho, S. X. H. Soh, Y. Wong, Y. Ng, K. Vasquez, Y. L. Lai, Y. X. Setoh, C. S. Chong, V. Lee, J. C. C. Wong, C. H. Tan, S. Sim, L. C. Ng and J. T. Lim, Trials, 23:1023. 2022-12-17 13:57:59.
The study is designed as a parallel, two-arm, non-blinded cluster-randomized (CR) controlled trial to be conducted in high-rise public housing estates in Singapore, an equatorial city-state. The aim is to determine whether large-scale deployment of male Wolbachia-infected Ae. aegypti mosquitoes can significantly reduce dengue incidence in intervention clusters. We will use the CR design, with the study area comprising 15 clusters with a total area of 10.9 km(2), covering approximately 722,204 residents in 1713 apartment blocks. Eight clusters will be randomly selected to receive the intervention, while the other seven will serve as non-intervention clusters. Intervention efficacy will be estimated through two primary endpoints:
Exploring the value of a global gene drive project registry
24279R. I. Taitingfong, C. Triplett, V. N. Vásquez, R. M. Rajagopalan, R. Raban, A. Roberts, G. Terradas, B. Baumgartner, C. Emerson, F. Gould, F. Okumu, C. E. Schairer, H. C. Bossin, L. Buchman, K. J. Campbell, A. Clark, J. Delborne, K. Esvelt, J. Fisher, R., Nature Biotechnology, 2022-12-15 14:15:40.
Recent calls to establish a global project registry before releasing any gene-drive-modified organisms (GDOs) have suggested a registry could be valuable to coordinate research, collect data to monitor and evaluate potential ecological impacts, and facilitate transparent communication with community stakeholders and the general public. Here, we report the results of a multidisciplinary expert workshop on GDO registries convened on 8–9 December 2020 involving 70 participants from 14 countries. Participants had expertise in gene drive design, conservation and population modeling, social science, stakeholder engagement, governance and regulation, international policy, and vector control; they represented 45 organizations, spanning national and local governmental agencies, international organizations, nonprofit organizations, universities, and district offices overseeing local vector control. The workshop aimed to gather perspectives on a central question: “In what ways could a gene-drive project registry both contribute to and detract from the fair development, testing and use of GDOs?” We specifically queried the perceived purpose of a registry, the information that would need to be included, and the perceived value of a registry. Three primary findings emerged from the discussion: first, many participants agreed a registry could serve a coordinating function for multidisciplinary and multisector work activities; second, doing so may require different design elements, depending on the target end-user group and intended purpose for that group; and third, these different information requirements lead to concerns about information sharing via a registry, suggesting potential obstacles to achieving transparency through such a mechanism. We conclude that any development of a gene-drive project registry requires careful and inclusive deliberation, including with potential end-users, to ensure that registry design is optimal.
Performance characteristics allow for confinement of a CRISPR toxin-antidote gene drive designed for population suppression
24272S. Zhang and J. Champer, bioRxiv, 2022.12.13.520356. 2022-12-15 14:08:18.
Gene drives alleles that can bias their own inheritance are a promising way to engineer populations for control of disease vectors, invasive species, and agricultural pests. Recent advancements in the field have yielded successful examples of powerful suppression type drives and confined modification type drives, but developing confined suppression drives has proven more difficult. This is because the necessary power for strong suppression is often incompatible with the characteristics needed for drive confinement. However, one type of CRISPR toxin-antidote drive may be strong enough and confined, the TADE (Toxin-Antidote Dominant Embryo) suppression drive. By disrupting a haplolethal target gene and a haplosufficient female fertility gene, this drive quickly eliminates wild-type alleles and eventually induces population suppression. It has been shown to perform effectively in panmictic populations. However, confinement in spatial scenarios may be substantially different. Here, we use a reaction-diffusion model to assess the performance of TADE suppression drive in continuous space. We measure the drive wave advance speed while varying several performance parameters and find that moderate fitness costs or embryo cutting (from maternally deposited nuclease) can eliminate the drive’s ability to form a wave of advance. We assess the release size required for the drive to propagate, and finally, we investigate migration corridor scenarios. Depending on the corridor size and dispersal, it is often possible for the drive to suppress one population and then persist in the corridor without invading the second population. This prevents re-invasion by wild-type, which may be a particularly desirable outcome in some scenarios. Thus, even imperfect variants of TADE suppression drive may be excellent candidates for confined population suppression.Competing Interest StatementThe authors have declared no competing interest.
Cell-based analysis reveals that sex-determining gene signals in Ostrinia are pivotally changed by male-killing Wolbachia
24288B. 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.
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.
Cryptic recessive lethality of a supergene controlling social organization in ants
24183P. Blacher, O. De Gasperin, G. Grasso, S. Sarton-Lohéac, R. Allemann and M. Chapuisat, Molecular Ecology, 2022-12-11 11:15:44.
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.
S. pombe wtf drivers use dual transcriptional regulation and selective protein exclusion from spores to cause meiotic drive
24158N. 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.
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.
Bioinformatic and literature assessment of toxicity and allergenicity of a CRISPR-Cas9 engineered gene drive to control the human malaria mosquito vector Anopheles gambiae
24161A. Qureshi and J. B. Connolly, Malaria Journal, 2022-12-06 07:52:06.
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.
Tolerance-conferring defensive symbionts and the evolution of parasite virulence
24126C. A. Smith and B. Ashby, bioRxiv, 2022-12-05 09:03:54.
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.
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.
A mass rearing cost calculator for the control of Culex quinquefasciatus in Hawaiʻi using the incompatible insect technique
24332A. E. Vorsino and Z. Xi, Parasites and Vectors, 15:453. 2022-12-05 08:32:07.
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.
Meiotic transmission patterns of additional genomic elements in Brachionus asplanchnoidis, a rotifer with intraspecific genome size variation
24116J. Blommaert and C.-P. Stelzer, Scientific Reports, 12:20900. 2022-12-03 09:37:14.
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.
Determining the landscape of resistance to gene drives in the malaria mosquito
27631I. Morianou, Imperial College London, 2022-12-01 10:17:51.
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.
A comprehensive overview of the existing microbial symbionts in mosquito vectors: An important tool for impairing pathogentransmission
24088V. Vandana, M. P. Kona, J. Kumar, O. P. Singh and K. C. Pandey, Experimental Parasitology, 243. 2022-11-30 09:06:12.
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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