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.
Variable effects of transient Wolbachia infections on alphaviruses in Aedes aegypti
33429Brittany L. Dodson, Sujit Pujhari, et al., PLoS Neglected Tropical Diseases, 2024-11-05 11:32:58.
Wolbachia pipientis (= Wolbachia) has promise as a tool to suppress virus transmission by Aedes aegypti mosquitoes. However, Wolbachia can have variable effects on mosquito-borne viruses. This variation remains poorly characterized, yet the multimodal effects of Wolbachia on diverse pathogens could have important implications for public health. Here, we examine the effects of transient somatic infection with two strains of Wolbachia (wAlbB and wMel) on the alphaviruses Sindbis virus (SINV), O’nyong-nyong virus (ONNV), and Mayaro virus (MAYV) in Ae. aegypti. We found variable effects of Wolbachia including enhancement and suppression of viral infections, with some effects depending on Wolbachia strain. Both wAlbB- and wMel-infected mosquitoes showed enhancement of SINV infection rates one week post-infection, with wAlbB-infected mosquitoes also having higher viral titers than controls. Infection rates with ONNV were low across all treatments and no significant effects of Wolbachia were observed. The effects of Wolbachia on MAYV infections were strikingly strain-specific; wMel strongly blocked MAYV infections and suppressed viral titers, while wAlbB had more modest effects. The variable effects of Wolbachia on vector competence underscore the importance of further research into how this bacterium impacts the virome of wild mosquitoes including the emergent human pathogens they transmit.
Biotechnology-enhanced genetic controls of the global pest Drosophila suzukii
33392Ying Yan, Hassan M.M. Ahmed, Ernst A. Wimmer, et al., Trends in Biotechnology, 2024-11-04 17:35:39.
Genetic control is a biological control method that introduces traits that sterilize, kill, or modify the population via intraspecific mating. Therefore, it is regarded as a species-specific and environmentally friendly management option for pest species. Spotted wing Drosophila (SWD) is an ideal insect model for studying genetic control strategies due to its pest status, laboratory-friendly biology, and close relationship to Drosophila melanogaster, which has abundant genetic resources. Different biotechnology-enhanced genetic control strategies of SWD are featured. The working schematics, control efficacies, some resistance mechanisms, and possible future development of these strategies are described. The designs and experience from these studies aid in the sustainable control of SWD and serve as essential references to other insect pests of economic or public health importance.
Improving the suppressive power of homing gene drive by co-targeting a distant-site female fertility gene
33386Faber, N.R., Xu, X., Chen, J. et al., Nature Communications, 15. 2024-11-04 17:07:21.
Gene drive technology has the potential to address major biological challenges. Well-studied homing suppression drives have been shown to be highly efficient in Anopheles mosquitoes, but for other organisms, lower rates of drive conversion prevent elimination of the target population. To tackle this issue, we propose a gene drive design that has two targets: a drive homing site where drive conversion takes place, and a distant site where cleavage induces population suppression. We model this design and find that the two-target system allows suppression to occur over a much wider range of drive conversion efficiency. Specifically, the cutting efficiency now determines the suppressive power of the drive, rather than the conversion efficiency as in standard suppression drives. We construct a two-target drive in Drosophila melanogaster and show that both components of the gene drive function successfully. However, cleavage in the embryo from maternal deposition as well as fitness costs in female drive heterozygotes both remain significant challenges for both two-target and standard suppression drives. Overall, our improved gene drive design has the potential to ease problems associated with homing suppression gene drives for many species where drive conversion is less efficient.
Navigating biosafety regulatory frameworks for genetic engineering in Africa: a focus on genome editing and gene drive technologies
33383Tilahun Rabuma, Felix Moronta-Barrios, Wendy Craig, Frontiers in Bioengineering and Biotechnology, 12. 2024-11-04 16:05:02.
Genome editing and gene drive technologies are increasingly gaining attraction in Africa, with researchers exploring their potential applications in agriculture, health and the environment. Acknowledging that robust regulatory frameworks are crucial in facilitating the development and utilization of these technologies, informed decision-making is, however, being impeded by the fragmented information availability and readiness of regulatory authorities on the continent. This study investigates the regulatory frameworks governing genome editing and gene drive technologies in African countries, identifies common regulatory challenges and proposes actionable solutions. Primary data were collected through questionnaires and complemented by analyzing existing biosafety regulations from online databases and scientific literature. Our findings suggest that while a few African countries have recently updated their regulatory frameworks, many are still under discussion. Challenges to development and implementation include limited resources, expertise, awareness, and public resistance. The findings underscore the urgent need for further development in regulatory capacities. By shedding light on these challenges, our study could provide African regulators with valuable insights to guide the formulation of effective regulatory frameworks. Such frameworks are essential for harnessing the potential of genome editing and gene drive technologies while safeguarding human health and the environment in Africa.
Engineering Resilient Gene Drives Towards Sustainable Malaria Control: Predicting, Testing and Overcoming Target Site Resistance
33379Ioanna Morianou, Lee Phillimore, Bhavin S. Khatri,, bioRxiv, 2024-11-04 13:56:24.
CRISPR-based gene drives are selfish genetic elements with the potential to spread through entire insect populations for sustainable vector control. Gene drives designed to disrupt the reproductive capacity of females can suppress laboratory populations of the malaria mosquito. However, any suppressive intervention will inevitably exert an evolutionary pressure for resistance. Here, we present a pipeline for the accelerated discovery, engineering, and testing of both natural and drive-induced variants that could reverse gene drive spread. We applied our method to stress-test a highly effective gene drive that has evaded resistance in all laboratory-contained releases to date, known as Ag(QFS)1. We showed that previously undetected resistant alleles can arise at low frequency, and discovered novel, partially resistant alleles that can perturb drive-invasion dynamics. We then engineered next-generation gene drives that can actively remove resistant alleles by targeting several highly conserved and non-overlapping sites in the female-specific exon of the doublesex gene. Our models predict that such gene drive designs could suppress large, natural populations of the malaria mosquito in the field.
Pest control gets the CRISPR treatment
33376Seydel, C., Nature Biotechnology, 2024-11-04 13:45:02.
In June 2024, the St. Louis–based pest control company Agragene released genetically modified fruit flies on berry farms in California and Oregon, moving the technology out of the laboratory and into contained field testing. The trial marked a milestone for a next-generation biocontrol technology called the precision-guided sterile insect technique, or pgSIT. “The spotted wing drosophila (SWD) is the number 1 problem for any kind of strawberry, blueberry, raspberry, blackberry grower,” said Bryan Witherbee, president and CEO of Agragene. The flies have developed resistance to conventional chemical pesticides, and fruit growers suffer enormous economic losses due to the pest. “Growers are crying out for new tools,” Witherbee said. Hope is on the horizon, not only for farmers battling SWD and other agricultural pests but also for public health agencies struggling to control disease vectors. Several companies, including Agragene, are bringing biological pest control into the CRISPR era with pgSIT and other molecular tools that can specifically target the pest without killing beneficial insects, polluting the water or blanketing communities with toxic airborne chemicals. San Diego–based Synvect is applying pgSIT to disease-causing mosquitoes. Meanwhile, Oxitec, which has already successfully commercialized its “Friendly” genetic modification platform in mosquitoes, is turning its attention to crop pests.
Parental-effect gene-drive elements under partial selfing, or why do Caenorhabditis genomes have hyperdivergent regions?
33170Matthew V Rockman, Genetics, 2024-10-31 08:57:53.
Self-fertile Caenorhabditis nematodes carry a surprising number of Medea elements, alleles that act in heterozygous mothers and cause death or developmental delay in offspring that don’t inherit them. At some loci, both alleles in a cross operate as independent Medeas, affecting all the homozygous progeny of a selfing heterozygote. The genomic coincidence of Medea elements and ancient, deeply coalescing haplotypes, which pepper the otherwise homogeneous genomes of these animals, raises questions about how these apparent gene-drive elements persist for long periods of time. Here I investigate how mating system affects the evolution of Medeas, and their paternal-effect counterparts, peels. Despite an intuition that antagonistic alleles should induce balancing selection by killing homozygotes, models show that, under partial selfing, antagonistic elements experience positive frequency dependence: the common allele drives the rare one extinct, even if the rare one is more penetrant. Analytical results for the threshold frequency required for one allele to invade a population show that a very weakly penetrant allele, one whose effects would escape laboratory detection, could nevertheless prevent a much more penetrant allele from invading under high rates of selfing. Ubiquitous weak antagonistic Medeas and peels could then act as localized barriers to gene flow between populations, generating genomic islands of deep coalescence. Analysis of gene expression data, however, suggest that this cannot be the whole story. A complementary explanation is that ordinary ecological balancing selection generates ancient haplotypes on which Medeas can evolve, while high homozygosity in these selfers minimizes the role of gene drive in their evolution.
Exploring The Dynamics of Gene Drive Mosquitoes Within Wild Populations Using an Agent-Based Simulation
34602S. Wickramasooriya, I. Mahmood, A. Calinescu, M. Wooldridge and G. Lanzaro, 2024 Annual Modeling and Simulation Conference, Washington, D.C.:1-14. 2024-10-29 10:38:49.
Gene drive technology is emerging as a potentially powerful tool in combating vector-borne diseases – notably malaria. This study introduces an agent-based model (ABM) focused on the deployment of genetically engineered mosquitoes with gene drive (GEM) in Príncipe Island, Republic of São Tomé and Príncipe, an island nation in the Gulf of Guinea, West Africa. Grounded in empirical data from laboratory and field studies, our model forecasts the dynamics of mosquito populations central to devising efficacious GEM release strategies. The core objective is to evaluate the time required for GEMs to constitute 90% of the mosquito population and to elucidate their dispersal throughout the island. This research is instrumental in understanding GEM potential in controlling malaria vectors.
Stalk-eyed flies carrying a driving X chromosome compensate by increasing fight intensity
32712Kimberly A. Paczolt, Macy E. Pritchard, Gabrielle T. Welsh, et al., Frontiers in Ethology, 3. 2024-10-22 17:39:40.
Exaggerated ornaments provide opportunities to understand how selection can operate at different levels to shape the evolution of a trait. While these features aid their bearer in attracting mates or fending off competitors, they can also be costly and influenced by the environment and genetic variation. The eyestalks of the stalk-eyed fly, Teleopsis dalmanni, are of interest because eyestalk length is the target of both intra- and intersexual selection and is also reduced by loci on a highly-divergent sex ratio X chromosome (XSR), a meiotic driver accounting for up to 30% of wild X chromosomes. Male stalk-eyed flies fight to control access to females and over food using a combination of low-intensity displays and high-intensity physical fights. We staged, filmed, and scored contests between pairs of eyespan-matched males to evaluate whether X chromosome type impacts the behavior and outcome of aggressive interactions. While our results broadly match expectations from previous studies, we found that XSR males used more high-intensity behaviors than males carrying a non-driving, standard X chromosome (XST), particularly when their eyestalks were of similar size or smaller than their opponents. Additionally, we found that when XSR males use high-intensity behaviors, they win more bouts than when they use low-intensity behaviors. Taken together, these results suggest that XSR impacts male aggressive behavior to compensate for the shorter eyestalks of XSR males and may help to explain how this selfish chromosome is maintained.
Wolbachia Invasion in Mosquitoes with Incomplete CI, Imperfect Maternal Transmission and Maturation Delay
32710Ma X, Su Y, Bulletin of Mathematical Biology, 2024-10-22 17:32:46.
The mechanism of cytoplasmic incompatibility (CI) is important in the study of Wolbachia invasion in wild mosquitoes. Su et al. (Bull Math Biol 84(9):95, 2022) proposed a delay differential equation model by relating the CI effect to maturation delay. In this paper, we investigate the dynamics of this model by allowing the same density-dependent death rate and distinct density-independent death rates. Through analyzing the existence and stability of equilibria, we obtain the parameter conditions for Wolbachia successful invasion if the maternal transmission is perfect. While if the maternal transmission is imperfect, we give the ranges of parameters to ensure failure invasion, successful invasion and partially suppressing, respectively. Meanwhile, numerical simulations indicate that the system may exhibit monostable and bistable dynamics when parameters vary. Particularly, in the bistable situation an unstable separatrix, like a line, exists when choosing constant functions as initial values; and the maturation delay affects this separatrix in an interesting way.
Wolbachia-based emerging strategies for control of vector-transmitted disease
32708Diego Montenegro, Gerardo Cortés-Cortés, María Guadalupe Balbuena-Alonso, et al., Acta Tropica, 260. 2024-10-22 17:28:54.
Dengue fever is a mosquito-transmitted disease of great public health importance. Dengue lacks adequate vaccine protection and insecticide-based methods of mosquito control are proving increasingly ineffective. Here we review the emerging use of mosquitoes transinfected with the obligate intracellular bacterium Wolbachia pipientis for vector control. Wolbachia often induces cytoplasmic incompatibility in its mosquito hosts, resulting in infertile progeny between an infected male and an uninfected female. Wolbachia infection also suppresses the replication of pathogens in the mosquito, a process known as “pathogen blocking”. Two strategies have emerged. The first one releases Wolbachia carriers (both male and female) to replace the wild mosquito population, a process driven by cytoplasmic incompatibility and that becomes irreversible once a threshold is reached. This suppresses disease transmission mainly by pathogen blocking and frequently requires a single intervention. The second strategy floods the field population with an exclusively male population of Wolbachia-carrying mosquitoes to generate infertile hybrid progeny. In this case, transmission suppression depends largely on decreasing the population density of mosquitoes driven by infertility and requires continued mosquito release. The efficacy of both Wolbachia-based approaches has been conclusively demonstrated by randomized and non-randomized studies of deployments across the world. However, results conducted in one setting cannot be directly or easily extrapolated to other settings because dengue incidence is highly affected by the conditions into which the mosquitoes are released. Compared to traditional vector control methods, Wolbachia-based approaches are much more environmentally friendly and can be effective in the medium/long term. On the flip side, they are much more complex and cost-intensive operations, requiring a substantial investment, infrastructure, trained personnel, coordination between agencies, and community engagement. Finally, we discuss recent evidence suggesting that the release of Wolbachia-transinfected mosquitoes has a moderate potential risk of spreading potentially dangerous genes in the environment.
The potential of gene drives in malaria vector species to control malaria in African environments
32702Hancock, P.A., North, A., Leach, A.W. et al., Nature Communications, 15. 2024-10-22 14:44:25.
Gene drives are a promising means of malaria control with the potential to cause sustained reductions in transmission. In real environments, however, their impacts will depend on local ecological and epidemiological factors. We develop a data-driven model to investigate the impacts of gene drives that causes vector population suppression. We simulate gene drive releases in sixteen ~ 12,000 km2 areas of west Africa that span variation in vector ecology and malaria prevalence, and estimate reductions in vector abundance, malaria prevalence and clinical cases. Average reductions in vector abundance ranged from 71.6–98.4% across areas, while impacts on malaria depended strongly on which vector species were targeted. When other new interventions including RTS,S vaccination and pyrethroid-PBO bednets were in place, at least 60% more clinical cases were averted when gene drives were added, demonstrating the benefits of integrated interventions. Our results show that different strategies for gene drive implementation may be required across different African settings.
Practical Application of a Relationship-Based Model to Engagement for Gene-Drive Vector Control Programs
32533Ana Kormos, Lodney Nazaré, Adionilde Aguiar dos Santos, and Gregory C. Lanzaro, The American Journal of Tropical Medicine and Hygiene, 111:341-360. 2024-10-15 12:04:35.
Engagement is an important component in the advancement of gene-drive vector control research programs as developers look to transition the technology from the laboratory to the field. As research advances and engagement surrounding this novel technology is put into practice, knowledge can be gained from practical experiences and applications in the field. A relationship-based model (RBM) provides a framework for end-user development of engagement programs and strategies. The model places end users at the center of the engagement decision-making processes rather than as recipients of predetermined strategies, methods, and definitions. Successful RBM application for healthcare delivery has previously been demonstrated, and the University of California Malaria Initiative (UCMI) has applied this model to its gene-drive program in the Democratic Republic of São Tomé and Príncipe. The model emphasizes the importance of local leadership in the planning, development, and implementation of all phases of project engagement. The primary aim of this paper is to translate the model from paper to practice and provide a transparent description, using practical examples, of the UCMI program implementation of RBM at its field site. End-user development of the UCMI engagement program provides a unique approach to the development of ethical, transparent, and effective engagement strategies for malaria control programs. This paper may also serve as a reference and example for projects looking to establish an engagement program model that integrates end-user groups in the decision-making processes surrounding engagement.
Identification of novel genes responsible for a pollen killer present in local natural populations of Arabidopsis thaliana
32527Anthony Ricou, Matthieu Simon, et al., bioRxiv, 2024-10-15 11:51:17.
Certain genetic elements are qualified as selfish because they favor their transmission to the progeny during reproduction to the detriment of gametes that do not carry them. These elements are widespread in fungi as well as in plants or in animals, and they are made up of two or even three components, which are specific to each species. Therefore, they must be studied on a case-by-case basis. Moreover, understanding how they appear and propagate in local population remains a major issue in evolutionary biology. Here we have characterized, in the model plant Arabidopsis, the three genes involved in such an element, called a pollen killer. This pollen killer targets the mitochondria to cause the death of pollen grains that do not carry it. We investigated the three genes in several hundred genotypes collected worldwide, giving us a global view of their diversity at the species level. We also found that some French local populations contain both sensitive and killer plants, which constitutes an invaluable resource for studying the evolution of a pollen killer in the wild.
Evolutionary modes of wtf meiotic driver genes in Schizosaccharomyces pombe
32524Yan-Hui Xu, Fang Suo, Xiao-Ran Zhang, et al., Genome Biology and Evolution, 2024-10-15 11:46:16.
Killer meiotic drivers (KMDs) are a class of selfish genetic elements that bias inheritance in their favor by destroying meiotic progeny that do not carry them. How KMDs evolve is not well understood. In the fission yeast Schizosaccharomyces pombe, the largest gene family, known as the wtf genes, is a KMD family that causes intraspecific hybrid sterility. Here, we investigate how wtf genes evolve using long-read-based genome assemblies of 31 distinct S. pombe natural isolates, which encompass the known genetic diversity of S. pombe. Our analysis, involving nearly 1,000 wtf genes in these isolates, yields a comprehensive portrayal of the intraspecific diversity of wtf genes. Leveraging single-nucleotide polymorphisms in adjacent unique sequences, we pinpoint wtf-gene-containing loci that have recently undergone gene conversion events and infer their pre-gene-conversion state. These events include the revival of wtf pseudogenes, lending support to the notion that gene conversion plays a role in preserving this gene family from extinction. Moreover, our investigation reveals that solo long terminal repeats (LTRs) of retrotransposons, frequently found near wtf genes, can act as recombination arms, influencing the upstream regulatory sequences of wtf genes. Additionally, our exploration of the outer boundaries of wtf genes uncovers a previously unrecognized type of directly oriented repeats flanking wtf genes. These repeats may have facilitated the early expansion of the wtf gene family in S. pombe. Our findings enhance the understanding of the mechanisms influencing the evolution of this KMD gene family.
Fluorescent-based sex-separation technique in major invasive crop pest, Drosophila suzukii
32544Junru Liu, Danny Rayes, Minzhe Yang, Omar S. Akbari, bioRxiv, 2024-10-09 12:30:05.
Insect population biocontrol methods such as the sterile insect technique (SIT), represent promising alternatives to traditional pesticide-based control applications. To use these strategies efficiently requires scalable sex separation techniques which are currently lacking in Drosophila suzukii, a prominent crop pest species. Having previously characterized a fluorescence-based sex-sorting technique in other pests, termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter), here we explore its potential applicability to Drosophila suzukii. Here, we engineer several strains of Drosophila suzukii encoding SEPARATOR constructs that allow for efficient sex selection in early larval stages.
Evaluation of Wolbachia infection in Aedes aegypti suggests low prevalence and highly heterogeneous distribution in Medellín, Colombia
32509rley Calle-Tobón, Raúl Rojo-Ospina, et al., Acta Tropica, 260. 2024-10-08 09:19:14.
Dengue virus, transmitted mainly by Aedes aegypti mosquitoes, is a significant public health challenge in tropical and subtropical countries, with an incidence that is growing at an alarming rate. The release of Wolbachia-carrying mosquitoes has been suggested as a strategy to reduce the incidence of multiple arboviruses. In Medellín, Colombia, large-scale releases of Wolbachia-infected Ae. aegypti mosquitoes were performed between 2017 and 2022 by the World Mosquito Program to facilitate population replacement. In this study, we evaluated the prevalence and distribution of Wolbachia-infected Ae. aegypti two years after completion of these releases. We conducted the sampling across 19 communes in Medellín, using 416 ovitraps to collect Ae. aegypti eggs from epidemiological weeks 26 to 41 in 2023. Upon hatching the collected eggs, we identified and pooled adult female Ae. aegypti for DNA extraction. Subsequently, we conducted PCR assays for the detection of Wolbachia infection in these mosquitoes. We used maximum likelihood estimation (MLE) and Bayesian methods to estimate the prevalence of Wolbachia infection, while using QGIS to analyze spatial distribution of infection in the region. A total of 774 female Ae. aegypti mosquitoes from 182 pools were evaluated. We detected Wolbachia in 33.5 % of pools, with an estimated individual minimum infection rate of 9.5 % and a maximum of 33.2 %. The prevalence varied significantly across communes, with the highest rates observed in the northeastern and southwestern areas. Spatial analysis revealed a highly heterogeneous island-like distribution of Wolbachia across Medellín with a few hotspots. The observed Wolbachia prevalence in this work was lower than previously reported. We suspect a decline in the prevalence of Wolbachia-infected Ae. aegypti mosquitoes in Medellín following the completion of their release.
Loss-of-function in testis-specific serine/threonine protein kinase triggers male infertility in an invasive moth
32506Wei, Z., Wang, Y., Zheng, K. et al., Communications Biology, 7. 2024-10-08 09:10:05.
Genetic biocontrol technologies present promising and eco-friendly strategies for the management of pest and insect-transmitted diseases. Although considerable advancements achieve in gene drive applications targeting mosquitoes, endeavors to combat agricultural pests have been somewhat restricted. Here, we identify that the testis-specific serine/threonine kinases (TSSKs) family is uniquely expressed in the testes of Cydia pomonella, a prominent global invasive species. We further generated male moths with disrupted the expression of TSSKs and those with TSSKs disrupted using RNA interference and CRISPR/Cas9 genetic editing techniques, resulting in significant disruptions in spermiogenesis, decreased sperm motility, and hindered development of eggs. Further explorations into the underlying post-transcriptional regulatory mechanisms reveales the involvement of lnc117962 as a competing endogenous RNA (ceRNA) for miR-3960, thereby regulating TSSKs. Notably, orchard trials demonstrates that the release of male strains can effectively suppress population growth. Our findings indicate that targeting TSSKs could serve as a feasible avenue for managing C. pomonella populations, offering significant insights and potential strategies for controlling invasive pests through genetic sterile insect technique (gSIT) technology.
Gene Drive and Symbiont Technologies for Control of Mosquito-Borne Diseases
32504Guan-Hong Wang, Ary Hoffmann, and Jackson Champer, Annual Review of Entomology, 70. 2024-10-08 09:05:08.
Mosquito-borne diseases, such as dengue and malaria, pose a significant burden to global health. Current control strategies with insecticides are only moderately effective. Scalable solutions are needed to reduce the transmission risk of these diseases. Symbionts and genome engineering–based mosquito control strategies have been proposed to address these problems. Bacterial, fungal, and viral symbionts affect mosquito reproduction, reduce mosquito lifespan, and block pathogen transmission. Field tests of endosymbiont Wolbachia-based methods have yielded promising results, but there are hurdles to overcome due to the large-scale rearing and accurate sex sorting required for Wolbachia-based suppression approaches and the ecological impediments to Wolbachia invasion in replacement approaches. Genome engineering–based methods, in which mosquitoes are genetically altered for the modification or suppression of wild populations, offer an additional approach for control of mosquito-borne diseases. In particular, the use of gene drive alleles that bias inheritance in their favor is a potentially powerful approach. Several drives are frequency dependent, potentially giving them broadly similar population dynamics to Wolbachia. However, public acceptance and the behavior of released drives in natural mosquito populations remain challenges. We summarize the latest developments and discuss the knowledge gaps in both symbiont- and gene drive–based methods.
Assessment of drive efficiency and resistance allele formation of a homing gene drive in the mosquito Aedes aegypti
32128Xiaozhen Yang, Xuejiao Xu, et al., bioRxiv, 2024-10-03 09:34:32.
Aedes aegypti, known for transmitting viruses such as dengue, zika, and yellow fever, poses a significant public health threat. Conventional insecticides give rise to a range of issues, including ecological contamination and insect resistance. Hence, there is a pressing demand for environmentally friendly, safer, and more efficacious strategies for mosquito control. With the rapid advancement of the CRISPR/Cas9 system in gene function exploration and pest population control, substantial progress has been achieved in utilizing CRISPR/Cas9-based gene drive systems across various mosquito species. Only a few studies on gene drive technology have been conducted in A. aegypti. In this study, we constructed two complete drives for A. aegypti with different Cas9 promoters, each targeting kmo. Our drive based on Pub-Cas9 had limited activity, but one with exu-Cas9 exhibited super-Mendelian inheritance rates of approximately 60%. We observed low but detectable somatic activity of the drive and no evidence of maternally deposited Cas9. Germline resistance allele formation rates were similar to drive conversion rates, but most wild-type alleles in the germline remained uncut. Injections into the exu-Cas9 drive line had 100% knockout efficiency among surviving offspring at three separate target genes. These results support the development and application of novel genetic pest control technologies aimed at combating A. aegypti.
Wolbachia infection in Aedes aegypti does not affect its vectorial capacity for Dirofilaria immitis
32124Shirozu, T., Regilme, M.A.F., Ote, M. et al., Scientific Reports, 14. 2024-10-03 09:25:30.
Mosquito-borne diseases such as dengue and filariasis are a growing public health concern in endemic countries. Biological approaches, such as the trans-infection of Wolbachia pipientis in mosquitoes, are an alternative vector control strategy, especially for arthropod-borne viruses such as dengue. In the present study, the effect of Wolbachia (wMel strain) on the vectorial capacity of Aedes aegypti for Dirofilaria immitis was studied. Our results showed that Wolbachia does not affect the phenotype of mosquito survival or the prevalence, number, and molting rate of third-stage larvae in both susceptible and resistant strains of Ae. aegypti. RNA-seq analysis of Malpighian tubules at 2 days post-infection with D. immitis showed the differentially expressed genes (DEGs) with and without wMel infection. No characteristic immune-related gene expression patterns were observed among the DEGs. No significant change in the amount of Wolbachia was observed in the Ae. aegypti after D. immitis infection. Our results suggest that infection of D. immitis in Ae. aegypti populations will not interfere with Wolbachia-based vector control strategies in dengue-endemic areas where cases of D. immitis are present. This study demonstrated the veterinary medical validity of a dengue control program using Wolbachia.
Stable introduction of Wolbachia wPip into invasive Anopheles stephensi for potential malaria control
32022Yongkang Liang, Julian Liu, et al., PLoS Neglected Tropical Diseases, 2024-10-01 16:23:02.
Recent efforts have successfully utilized the endosymbiotic bacterium Wolbachia to control mosquito-transmitted viral diseases like dengue in multiple countries. However, similar initiatives have been limited in combating malaria, the most devastating and deadly mosquito-borne disease, which claims over half a million lives each year. This is primarily due to the difficulty in establishing a stable, maternally inheritable Wolbachia infection in Anopheles, the mosquito vector responsible for malaria transmission. A significant concern in malaria control is the invasion of the urban malaria vector Anopheles stephensi into Africa, where malaria burden is highest, and over 40% of the population resides in urban areas. Building on the previous breakthrough of establishing Wolbachia strain wAlbB in An. stephensi, the author has now achieved a second stable infection by transferring the wPip strain from Culex pipiens into this mosquito species using embryonic microinjection. The resultant transinfected HP1 line induces nearly complete cytoplasmic incompatibility when crossed with wild mosquitoes, displays robust fitness and male mating competitiveness, and exhibits strong resilience against heat stress. These advantageous traits position the HP1 line as a promising candidate for further development in malaria control.
Current status of the sterile insect technique for the suppression of mosquito populations on a global scale
32019Bouyer, J., Infectious Diseases of Poverty, 13. 2024-10-01 16:03:32.
The World Health Organization (WHO) has emphasized the urgent need for alternative strategies to chemical insecticides for controlling mosquito populations, particularly the invasive Aedes species, which are known vectors of arboviruses. Among these alternative approaches, the sterile insect technique (SIT) is experiencing rapid development, with numerous pilot trials being conducted worldwide. This review aims to elucidate the principles of SIT and highlight the significant recent advancements that have facilitated its scalability. I also employ a phased conditional approach to categorize the progression of 39 projects, drawing on peer reviewed studies, press releases and direct communication with project managers. This review indicates that a substantial number of projects illustrate the efficacy of SIT in suppressing Aedes populations, with one project even demonstrating a reduction in dengue incidence. I offer several recommendations to mitigate potential failures and address the challenges of compensation and overcompensation when implementing SIT field trials. Furthermore, I examine the potential implications of male mating harassment on the effectiveness of SIT in reducing disease transmission. This comprehensive assessment underscores the promise of SIT as a viable strategy for mosquito control. The insights gained from these trials not only contribute to the understanding of SIT’s effectiveness but also highlight the importance of careful project management and ecological considerations in the pursuit of public health objectives.
Communicating the uncertainties associated with genetic biocontrol approaches: insights from communicators, science journalists and scientists in Africa
32538Tonui, W. K., Ogoyi, D., Thuo, C., Tareh, C., et al., Journal of Science Communication, 23. 2024-09-25 12:13:55.
Genetic biocontrol approaches, such as gene drive technology is rapidly gaining interest from scientists and public health professionals due to their potential to overcome many challenges of current malaria control tools and strategies. This is particularly the case in Africa where the burden of malaria is most significant. Uncertainty exists about whether these approaches will work, how effective they might be, who is controlling them, and potential unintended consequences for human health and the environment. Therefore, efforts to enhance the understanding of genetic engineering and biotechnology are needed, to ensure that accurate information about this technology is disseminated in the media by science communicators including the journalists and scientists. In this practice insight, we review the outcomes from workshops and courses hosted by the African Genetic Biocontrol Consortium aimed at equipping communicators and journalists with skilful techniques to proficiently articulate the uncertainties associated with genetic biocontrol interventions to the African public. we discuss the gaps and provide insight on how communicators can address some of the basic challenges of developing effective communication and decision-making for genetic biocontrol approaches in Africa.
To CRISPR or Not to CRISPR? Ethical Considerations in Gene-Editing Insects
31614Brendan Parent, Meghan Barrett, American Entomologist, 70:54-57. 2024-09-18 21:33:47.
Genetically modified corn has helped feed the world (Hernandes-Lopes et al. 2023). Genetically modified mosquitoes could help eliminate devastating diseases like malaria (Hammond and Galizi 2017). Plainly, gene editing can serve some important human interests. Still, many people object to it. While some concerns have little scientific validity, there are valid ethical concerns that should be addressed. A concern many people share is the potential impact of genetically edited insects on the environment. Gene drives are “selfish” genetic elements that are transmitted to progeny at unusually high rates and thus spread rapidly through populations. As a result, they are capable of modifying an entire population or species. The most widely discussed use of gene drives is in the prevention of malaria, the leading cause of human illness and death in many parts of the world (CDC 2021), where gene drives could be used to control mosquito populations. At present, however, there are no sure-fire strategies to “recall” a gene drive once it has been released (Hammond and Galizi 2017). Given the many unintended environmental impacts of other technological advancements and our uncertainties about the impacts of using gene drives (Ahmad et al. 2022), it makes sense to have similar concerns about this form of gene editing. Granted, it is possible that the extraordinary benefits to human life of such a gene drive, if successful, outweigh the risks of any unintended environmental consequences. This is particularly likely to be true if convincing measures like “terminator genes” can be employed to control genetically edited insect populations in the wild (Hammond et al. 2021). Given the serious promise and ethical concerns of this technology, the National Academy of Sciences has published guidelines for responsible research that include self-governance and government regulation, evaluating gene drives on a case-by-case basis (NASEM 2016). So, while risks of environmental harm are important, we can now see how they might not be decisive: first, the corresponding benefits might be very weighty; second, the risks might be mitigable.
B chromosome and its non-Mendelian inheritance in Atractylodes lancea
Hara K, Kikuchi S, Inoue M, Tsusaka T, Sakurai M, Tanabe H, et al., PLoS One, 2024-09-18 21:06:03.Supernumerary B chromosomes contribute to intraspecific karyotypic variation. B chromosomes have been detected in more than 2000 organisms; they possess unique and diverse features, including non-Mendelian inheritance. Here, we report one or more B chromosomes in the gynodioecious plant Atractylodes lancea. Among 54 A. lancea lines, 0–2 B chromosomes were detected in both hermaphroditic and female plants, with the B chromosomes appearing as DAPI-bright regions within the nuclei. Genomic in situ hybridization revealed that the B chromosomes had no conserved A chromosome DNA sequences, confirmed by fluorescence in situ hybridization probed with independently dissected B chromosomes. In male meiosis, the B chromosome did not pair with an A chromosome and was therefore eliminated; accordingly, only 20.1% and 18.6% of these univalent B chromosomes remained at the end of meiosis for the 1B lines of KY17-148 and KY17-118, respectively. However, we also found that B chromosomes were transmitted from male parents in 40.8%–44.2% and 47.2% of the next generation; although these transmission rates from male parents were not essentially different from Mendelian inheritance (0.5), the transmission of gametes carrying B chromosomes increased through fertilization or seed development. B chromosomes were transmitted from three of four 1B female parents to 64.3%–92.6% of the next generation, suggesting B chromosome accumulation. We propose that the B chromosome of A. lancea has a specific sequence and persists via non-Mendelian inheritance from female parents. Overall, A. lancea, with its unique characteristics, is a promising model for understanding the structure, evolution, and mechanism of non-Mendelian inheritance of B chromosomes.
Viral gene drive spread during herpes simplex virus 1 infection in mice
31625Walter, M., Haick, A.K., Riley, R. et al., Nature Communications, 15. 2024-09-17 21:18:39.
Gene drives are genetic modifications designed to propagate efficiently through a population. Most applications rely on homologous recombination during sexual reproduction in diploid organisms such as insects, but we recently developed a gene drive in herpesviruses that relies on co-infection of cells by wild-type and engineered viruses. Here, we report on a viral gene drive against human herpes simplex virus 1 (HSV-1) and show that it propagates efficiently in cell culture and during HSV-1 infection in mice. We describe high levels of co-infection and gene drive-mediated recombination in neuronal tissues during herpes encephalitis as the infection progresses from the site of inoculation to the peripheral and central nervous systems. In addition, we show evidence that a superinfecting gene drive virus could recombine with wild-type viruses during latent infection. These findings indicate that HSV-1 achieves high rates of co-infection and recombination during viral infection, a phenomenon that is currently underappreciated. Overall, this study shows that a viral gene drive could spread in vivo during HSV-1 infection, paving the way toward therapeutic applications.
Overcoming drug-resistant tumors with selection gene drives
31594Hui Wang, Mingqi Xie, Cell Genomics, 4. 2024-09-17 12:48:55.
Drug resistance is a major hurdle prohibiting effective treatment of many diseases, including cancer. Using model-guided designs, Leighow et al.1 engineered a dual-switch selection gene drive system custom designed to combat drug-resistant tumors. By demonstrating remarkable killing efficacies in preclinical models using human non-small lung cancer cells in vitro and in mice, this work describes an attractive mindset to develop next-generation anticancer therapies.
Applications of Mathematical Programming to Genetic Biocontrol
31592Váleri N. Vásquez, John M. Marshall, SIAM Journal on Applied Mathematics, 84. 2024-09-17 12:36:59.
We review existing approaches to optimizing the deployment of genetic biocontrol technologies—tools used to prevent vector-borne diseases such as malaria and dengue—and formulate a mathematical program that enables the incorporation of crucial ecological and logistical details. The model is comprised of equality constraints grounded in discretized dynamic population equations, inequality constraints representative of operational limitations including resource restrictions, and an objective function that jointly minimizes the count of competent mosquito vectors and the number of transgenic organisms released to mitigate them over a specified time period. We explore how nonlinear programming (NLP) and mixed integer nonlinear programming (MINLP) can advance the state of the art in designing the operational implementation of three distinct transgenic public health interventions, two of which are presently in active use around the world.
Mark–Release–Recapture Trial with Aedes albopictus (Diptera, Culicidae) Irradiated Males: Population Parameters and Climatic Factors
31590Amaro FIF, Soares P, Velo E, et al, Insects, 15. 2024-09-17 12:23:28.
Aedes albopictus mosquitoes spread arboviruses like dengue, Zika, or chikungunya. The Sterile Insect Technique (SIT) can be used as a prevention and control tool against Ae. albopictus populations. Mark–release–recapture (MRR) trials are fundamental to estimate the size of the wild population in target areas and to determine the dispersal capacity and survival of sterile males in open field conditions. Environmental conditions can affect the MRR trial’s results; thus, the influence of climatic factors on the first MRR trial with Ae. albopictus marked sterile males conducted in Portugal was analyzed. In October 2022, for three consecutive weeks at two different release points, 84,000 sterile males were released over 50 ha of the study area, in the municipality of Faro, Southern Portugal, and mosquitoes were recaptured by human landing collection (HLC) one, two, four, and six days after release. Distance travelled, daily survival, and life expectancy in the field were estimated for the released sterile males and the influence of climatic factors was analyzed. Despite no statistically significant association being found with humidity, temperature, and precipitation, it is crucial to plan MRRs, considering weather conditions for a more efficient application of the SIT in an integrated vector management program.
Effectiveness of Wolbachia-mediated sterility coupled with sterile insect technique to suppress adult Aedes aegypti populations in Singapore: a synthetic control study
31580Bansal, Somya, et al., The Lancet Planetary Health, 8:617-628. 2024-09-17 10:04:54.
In this synthetic control study, we conducted a large-scale, field trial of IIT-SIT targeting Aedes aegypti among high-rise public housing estates in Singapore, an equatorial city state. Routinely collected data from a large, nationwide surveillance system of 57 990 unique mosquito traps, combined with a high-dimensional set of anthropogenic and environmental confounders were collected to ascertain mosquito abundance and its key drivers. Four townships were selected as the intervention groups (approximate population size of 607 872 residents as of 2022), wherein interventions that combined ITT with SIT over the course of the study period were conducted. Townships were subject to releases of wAlbB-SG male A aegypti mosquitoes twice a week. Data were assessed over the course of epidemiological weeks (EWs), which provide the finest temporal resolution of recorded Wolbachia release schedule and mosquito abundance data. A novel synthetic control framework was then developed to account for the non-randomised and staggered adoption setting of the intervention across trial sectors to identify the direct suppressive effectiveness of IIT-SIT on female A aegypti populations, the spillover effects in non-release areas, and the effect of the intervention on other mosquito populations such as Aedes albopictus. Furthermore, we recalculated effectiveness in terms of calendar time, time since intervention, and over multiple sites to examine heterogeneities in IIT-SIT effectiveness. Between EW27 2018 and EW26 2022, Wolbachia releases were conducted across 117 sectors, of which 97 had sufficient trap data, which were collected between EW8 2019 and EW26 2022. We found that Wolbachia-based IIT-SIT reduced wild-type female A aegypti populations by a mean of 62·01% (95% CI 60·68 to 63·26) by 3 months, 78·40% (77·56 to 79·18) by 6 months, and 91·32% (90·95 to 91·66) by at least 18 months of releases. We also found a smaller but non-negligible spillover suppression effect that gradually increased over time (mean spillover intervention effectiveness 61·02% [95% CI 57·89 to 63·72] in adjacent, non-intervention sectors). Although no consistent change in A albopictus populations was seen across the four intervention townships after Wolbachia releases, the average intervention effectiveness on the A albopictus population across all release sectors was –25·80% (95% CI –30·93 to –21·05), which was driven by increases in two towns.
Deployment of tethered gene drive for confined suppression in continuous space requires avoiding drive wave interference
31622Ruobing Feng, Jackson Champer, Molecular Ecology, 33. 2024-09-16 21:13:35.
Gene drives have great potential for suppression of pest populations and removal of exotic invasive species. CRISPR homing suppression drive is a powerful but unconfined drive, posing risks of uncontrolled spread. Thus, developing methods for confining a gene drive is of great significance. Tethered drive combines a confined system such as Toxin-Antidote Recessive Embryo drive with a strong drive such as a homing suppression drive. It can prevent the homing drive from spreading beyond the confined drive and can be constructed readily, giving it good prospects for future development. However, we have found that care must be taken when deploying tethered drive systems in some scenarios. Simulations of tethered drive in a panmictic population model reveal that successful deployment requires a proper release ratio between the two components, tailored to prevent the suppression drive from eliminating the confined system before it has the chance to spread. Spatial models where the population moves over a one-dimensional landscape display a more serious phenomenon of drive wave interference between the two tethered drive components. If the faster suppression drive wave catches up to the confined drive wave, success is still possible, but it is dependent on drive performance and ecological parameters. Two-dimensional simulations further restrict the parameter range for drive success. Thus, careful consideration must be given to drive performance and ecological conditions, as well as specific release proposals for potential application of tethered drive systems.
Population suppression by release of insects carrying a dominant sterile homing gene drive targeting doublesex in Drosophila
34760Chen, W., Guo, J., Liu, Y. et al., Nature Communications, 15. 2024-09-14 09:17:45.
CRISPR homing gene drives can suppress pest populations by targeting female fertility genes, converting wild-type alleles into drive alleles in the germline of drive heterozygotes. fsRIDL (female-specific Release of Insects carrying a Dominant Lethal) is a self-limiting population suppression strategy involving continual release of transgenic males carrying female lethal alleles. Here, we propose an improved pest suppression system called “Release of Insects carrying a Dominant-sterile Drive” (RIDD), combining performance characteristics of homing drive and fsRIDL. We construct a split RIDD system in Drosophila melanogaster by creating a 3-gRNA drive disrupting the doublesex female exon. Drive alleles bias their inheritance in males, while drive alleles and resistance alleles formed by end-joining cause dominant female sterility. Weekly releases of RIDD males progressively suppressed and eventually eliminated cage populations. Modeling shows that RIDD is substantially stronger than SIT and fsRIDL. RIDD is also self-limiting, potentially allowing targeted population suppression.
A model-informed target product profile for population modification gene drives for malaria control
31339Agastya Mondal, Héctor M. Sánchez C., John M. Marshall, medRxiv, 2024-09-03 18:44:21.
As reductions in malaria transmission in sub-Saharan Africa stagnate, gene drive-modified mosquitoes represent one of the most promising novel tools for continued disease control. In order to advance from the laboratory to the field, gene drives will be assessed against target product profiles, planning tools that list minimum criteria products should satisfy as they progress through the development pipeline. Here, we use an eco-epidemiological model to investigate parameter values for population modification gene drives that satisfy two previously-discussed target outcomes: a 50% reduction in clinical malaria incidence for a duration (window-of-protection) of at least three years, and a time-to-impact of less than one year. We consider two African settings, Burkina Faso and Kenya, where gene drive mosquitoes are currently being researched, and consider three transmission intensities at each. For the gene drive product, we explore rates of homing and resistance allele generation, fitness costs associated with gene drive and non-functional resistance alleles, and the efficacy of the effector gene(s) at reducing mosquito-to-human transmission. We find that when the window-of-protection criterion is satisfied, the time-to-impact criterion also is. Target outcomes are most influenced by the fitness cost associated with the gene drive allele and effector gene efficacy. Resistance allele parameters are also highly influential on target outcomes, and determine how long the gene drive allele persists in the population after most available wild-type alleles have been cleaved. Low rates of functional resistance allele generation are preferred, while costly non-functional resistance alleles will allow the drive allele to outcompete them. Homing rates already achieved for Anopheles gene drives do not need to be improved upon. A conundrum exists whereby the most important product parameters for predicting field efficacy are those that can only be reliably measured in the field, which presents a challenge for assessment of product readiness.
Autosomal suppression of sex-ratio meiotic drive influences the dynamics of X and Y chromosome coevolution
31322Anjali Gupta, Robert L Unckless, Journal of Heredity, 2024-09-03 15:54:00.
Sex-ratio meiotic drivers are selfish genes or gene complexes that bias the transmission of sex chromosomes resulting in skewed sex ratios. Existing theoretical models have suggested the maintenance of a four-chromosome equilibrium (with driving and standard X and suppressing and susceptible Y) in a cyclic dynamic, studies of natural populations have failed to capture this pattern. Although there are several plausible explanations for this lack of cycling, interference from autosomal suppressors has not been studied using a theoretical population genetic framework even though autosomal suppressors and Y-linked suppressors coexist in natural populations of some species. In this study, we use a simulation-based approach to investigate the influence of autosomal suppressors on the cycling of sex chromosomes. Our findings demonstrate that the presence of an autosomal suppressor can hinder the invasion of a Y-linked suppressor under some parameter space, thereby impeding the cyclic dynamics, or even the invasion of Y-linked suppression. Even when a Y-linked suppressor invades, the presence of an autosomal suppressor can prevent cycling. Our study demonstrates the potential role of autosomal suppressors in preventing sex chromosome cycling and provides insights into the conditions and consequences of maintaining both Y-linked and autosomal suppressors.
Bunyamwera Virus Infection of Wolbachia-Carrying Aedes aegypti Mosquitoes Reduces Wolbachia Density
31318Lefteri, D.A.; Rainey, S.M.; Murdochy, S.M.; Sinkins, S.P., Viruses, 16. 2024-09-03 15:42:46.
Wolbachia symbionts introduced into Aedes mosquitoes provide a highly effective dengue virus transmission control strategy, increasingly utilised in many countries in an attempt to reduce disease burden. Whilst highly effective against dengue and other positive-sense RNA viruses, it remains unclear how effective Wolbachia is against negative-sense RNA viruses. Therefore, the effect of Wolbachia on Bunyamwera virus (BUNV) infection in Aedes aegypti was investigated using wMel and wAlbB, two strains currently used in Wolbachia releases for dengue control, as well as wAu, a strain that typically persists at a high density and is an extremely efficient blocker of positive-sense viruses. Wolbachia was found to reduce BUNV infection in vitro but not in vivo. Instead, BUNV caused significant impacts on density of all three Wolbachia strains following infection of Ae. aegypti mosquitoes. The ability of Wolbachia to successfully persist within the mosquito and block virus transmission is partially dependent on its intracellular density. However, reduction in Wolbachia density was not observed in offspring of infected mothers. This could be due in part to a lack of transovarial transmission of BUNV observed. The results highlight the importance of understanding the complex interactions between multiple arboviruses, mosquitoes and Wolbachia in natural environments, the impact this can have on maintaining protection against diseases, and the necessity for monitoring Wolbachia prevalence at release sites.
Functional and evolutionary constraints of wtf killer meiotic drivers
31213Ananya Nidamangala Srinivasa, Samuel Campbell, Shriram Venkatesan, Nicole L Nuckolls, Jeffrey J Lange, Randal Halfmann, Sarah E Zanders, bioRxiv, 2024-08-29 10:38:59.
Killer meiotic drivers are selfish DNA loci that sabotage the gametes that do not inherit them from a driver+/driver- heterozygote. These drivers often employ toxic proteins that target essential cellular functions to cause the destruction of driver- gametes. Identifying the mechanisms of drivers can expand our understanding of infertility and reveal novel insights about the cellular functions targeted by drivers. In this work, we explore the molecular mechanisms underlying the wtf family of killer meiotic drivers found in fission yeasts. Each wtf killer acts using a toxic Wtfpoison protein that can be neutralized by a corresponding Wtfantidote protein. The wtf genes are rapidly evolving and extremely diverse. Here we found that self-assembly of Wtfpoison proteins is broadly conserved and associated with toxicity across the gene family, despite minimal amino acid conservation. In addition, we found the toxicity of Wtfpoison assemblies can be modulated by protein tags designed to increase or decrease the extent of the Wtfpoison assembly, implicating assembly size in toxicity. We also identified a conserved, critical role for the specific co-assembly of the Wtfpoison and Wtfantidote proteins in promoting effective neutralization of Wtfpoison toxicity. Finally, we engineered wtf alleles that encode toxic Wtfpoison proteins that are not effectively neutralized by their corresponding Wtfantidote proteins. The possibility of such self-destructive alleles reveals functional constraints on wtf evolution and suggests similar alleles could be cryptic contributors to infertility in fission yeast populations. As rapidly evolving killer meiotic drivers are widespread in eukaryotes, analogous self-killing drive alleles could contribute to sporadic infertility in many lineages.
Optimizing and synchronizing Aedes aegypti colony for Sterile Insect Technique application: Egg hatching, larval development, and adult emergence rate
31193Jennifer Thieme Castellon, Solomon Kibret Birhanie, Ale Macias, Rubi Casas, Jacob Hans, Michelle Q. Brown, Acta Tropica, 259. 2024-08-27 08:24:10.
Mosquito Sterile Insect Technique (SIT) programs can be developed in smaller agencies through synchronization of the colony development to take advantage of the natural male early emergence. This paper examined key aspects of Ae. aegypti colony synchronization work, including egg hatching, larval development, and adult emergence to produce sufficient numbers of adult male mosquitoes within a specific timeframe for irradiation and release. Our data indicated that a relatively low percentage of males are required for colony propagation. Additional results highlighted that fresher Ae. aegypti eggs could yield as high as a 93 % hatching success than older eggs when placed under vacuum pressure in yeast infused water for 1.5 h. Eggs that were one-month old hatched (93 %) better than older eggs (0–32 %). A higher egg density in the hatching flask was correlated to a lower hatch rate, and higher larval density was related to unsynchronized pupae and delayed adult emergence. By keeping Ae. aegypti larvae at reasonable density, over 95 % of adults emerged on the first two days of emergence – indicating a high synchronicity. A standardized colony maintenance protocol therefore renders a synchronized larval development and adult male emergence which are critical in SIT programs.
Population dynamics in spatial suppression gene drive models and the effect of resistance, density dependence, and life history
31190Xinyue Zhang, Weitang Sun, Isabel K. Kim, Philipp W. Messer, Jackson Champer, bioRxiv, 2024-08-27 08:13:04.
Due to their super-Mendelian inheritance, gene drive systems have the potential to provide revolutionary solutions to critical public health and environmental problems. For suppression drives, however, spatial structure can cause “chasing” population dynamics that may postpone target population elimination or even cause the drive to fail. In chasing, wild-type individuals elude the drive and recolonize previously suppressed areas. The drive can re-enter these recolonized areas, but often is not able to catch up to wild-type and finally eliminate it. Previous methods for chasing detection are only suitable to limited parameter ranges. In this study with expanded parameter ranges, we found that the shift from chasing dynamics to static equilibrium outcomes is continuous as drive performance is reduced. To quantify this, we defined a Weighted Average Nearest Neighbor statistic to assess the clustering degree during chasing, while also characterizing chasing by the per-generation chance of population elimination and drive loss. To detect chasing dynamics in local areas and to detect the start of chasing, we implemented Density-Based Spatial Clustering of Applications with Noise. Using these techniques, we determined the effect of arena size, resistance allele formation rate in both the germline and in the early embryo from maternally deposited Cas9, life history and reproduction strategies, and density-dependent growth curve shape on chasing outcomes. We found that larger real-world areas will be much more vulnerable to chasing and that species with overlapping generations, fecundity-based density dependence, and concave density-dependent growth curves have smaller and more clustered local chasing with a greater chance of eventual population elimination. We also found that embryo resistance and germline resistance hinder drive performance in different ways. These considerations will be important for determining the necessary drive performance parameters needed for success in different species, and whether future drives could potentially be considered as release candidates.
Generating and testing the efficacy of reagents for CRISPR/Cas9 homology directed repair-based manipulations in Tribolium
31183Hannah C Markley, Kennedy J Helms, Megan Maar, Gabriel E Zentner, Michael J Wade, Andrew C Zelhof, Journal of Insect Science, 24. 2024-08-25 20:44:44.
CRISPR/Cas9 manipulations are possible in many insects and ever expanding. Nonetheless, success in one species and techniques developed for it are not necessarily applicable to other species. As such, the development and expansion of CRISPR-based (clustered regularly interspaced short palindromic repeats) genome-editing tools and methodologies are dependent upon direct experimentation. One useful technique is Cas9-dependent homologous recombination, which is a critical tool for studying gene function but also for developing pest related applications like gene drive. Here, we report our attempts to induce Cas9 homology directed repair (HDR) and subsequent gene drive in Tribolium castaneum (Herbst; Insecta: Coleoptera: Tenebrionidae). Utilizing constructs containing 1 or 2 target gRNAs in combination with Cas9 under 2 different promoters and corresponding homology arms, we found a high incidence of CRISPR/Cas9 induced mutations but no evidence of homologous recombination. Even though the generated constructs provide new resources for CRISPR/Cas9 modification of the Tribolium genome, our results suggest that additional modifications and increased sample sizes will be necessary to increase the potential and detection for HDR of the Tribolium genome.
Non-Mendelian transmission of X chromosomes: mechanisms and impact on sex ratios and population dynamics in different breeding systems
31181Sally Adams; Andre Pires-daSilva, Biochemical Society Transactions, 2024-08-25 20:35:26.
The non-Mendelian transmission of sex chromosomes during gametogenesis carries significant implications, influencing sex ratios and shaping evolutionary dynamics. Here we focus on known mechanisms that drive non-Mendelian inheritance of X chromosomes during spermatogenesis and their impact on population dynamics in species with different breeding systems. In Drosophila and mice, X-linked drivers targeting Y-bearing sperm for elimination or limiting their fitness, tend to confer unfavourable effects, prompting the evolution of suppressors to mitigate their impact. This leads to a complex ongoing evolutionary arms race to maintain an equal balance of males and females. However, in certain insects and nematodes with XX/X0 sex determination, the preferential production of X-bearing sperm through atypical meiosis yields wild-type populations with highly skewed sex ratios, suggesting non-Mendelian transmission of the X may offer selective advantages in these species. Indeed, models suggest X-meiotic drivers could bolster population size and persistence under certain conditions, challenging the conventional view of their detrimental effects. Furthering our understanding of the diverse mechanisms and evolutionary consequences of non-Mendelian transmission of X chromosomes will provide insights into genetic inheritance, sex determination, and population dynamics, with implications for fundamental research and practical applications.
A comprehensive review of Wolbachia-mediated mechanisms to control dengue virus transmission in Aedes aegypti through innate immune pathways
31172Iqra Mushtaq, Muhammad Sajjad Sarwar, Iqra Munzoor, Viral Immunology, 15. 2024-08-25 20:04:21.
The Dengue virus (DENV), primarily spread by Aedes aegypti and also by Aedes albopictus in some regions, poses significant global health risks. Alternative techniques are urgently needed because the current control mechanisms are insufficient to reduce the transmission of DENV. Introducing Wolbachia pipientis into Ae. aegypti inhibits DENV transmission, however, the underlying mechanisms are still poorly understood. Innate immune effector upregulation, the regulation of autophagy, and intracellular competition between Wolbachia and DENV for lipids are among the theories for the mechanism of inhibition. Furthermore, mainly three immune pathways Toll, IMD, and JAK/STAT are involved in the host for the suppression of the virus. These pathways are activated by Wolbachia and DENV in the host and are responsible for the upregulation and downregulation of many genes in mosquitoes, which ultimately reduces the titer of the DENV in the host. The functioning of these immune pathways depends upon the Wolbachia, host, and virus interaction. Here, we summarize the current understanding of DENV recognition by the Ae. aegypti’s immune system, aiming to create a comprehensive picture of our knowledge. Additionally, we investigated how Wolbachia regulates the activation of multiple genes associated with immune priming for the reduction of DENV.
Teosinte Pollen Drive guides maize diversification and domestication by RNAi
34650Berube, B., Ernst, E., Cahn, J. et al., Nature, 633:380-388. 2024-08-07 06:59:44.
Selfish genetic elements contribute to hybrid incompatibility and bias or ‘drive’ their own transmission1,2. Chromosomal drive typically functions in asymmetric female meiosis, whereas gene drive is normally post-meiotic and typically found in males. Here, using single-molecule and single-pollen genome sequencing, we describe Teosinte Pollen Drive, an instance of gene drive in hybrids between maize (Zea mays ssp. mays) and teosinte mexicana (Z. mays ssp. mexicana) that depends on RNA interference (RNAi). 22-nucleotide small RNAs from a non-coding RNA hairpin in mexicana depend on Dicer-like 2 (Dcl2) and target Teosinte Drive Responder 1 (Tdr1), which encodes a lipase required for pollen viability. Dcl2, Tdr1 and the hairpin are in tight pseudolinkage on chromosome 5, but only when transmitted through the male. Introgression of mexicana into early cultivated maize is thought to have been critical to its geographical dispersal throughout the Americas3, and a tightly linked inversion in mexicana spans a major domestication sweep in modern maize4. A survey of maize traditional varieties and sympatric populations of teosinte mexicana reveals correlated patterns of admixture among unlinked genes required for RNAi on at least four chromosomes that are also subject to gene drive in pollen from synthetic hybrids. Teosinte Pollen Drive probably had a major role in maize domestication and diversification, and offers an explanation for the widespread abundance of ‘self’ small RNAs in the germ lines of plants and animals.
An egg-sabotaging mechanism drives non-Mendelian transmission in mice
31028Frances E. Clark, Naomi L. Greenberg, Duilio M.Z.A. Silva, et al, Current Biology, 2024-08-05 11:40:23.
Selfish genetic elements drive in meiosis to distort their transmission ratio and increase their representation in gametes, violating Mendel’s law of segregation. The two established paradigms for meiotic drive, gamete killing and biased segregation, are fundamentally different. In gamete killing, typically observed with male meiosis, selfish elements sabotage gametes that do not contain them. By contrast, killing is predetermined in female meiosis, and selfish elements bias their segregation to the single surviving gamete (i.e., the egg in animal meiosis). Here, we show that a selfish element on mouse chromosome 2, Responder to drive 2 (R2d2), drives using a hybrid mechanism in female meiosis, incorporating elements of both killing and biased segregation. We propose that if R2d2 is destined for the polar body, it manipulates segregation to sabotage the egg by causing aneuploidy, which is subsequently lethal in the embryo, ensuring that surviving progeny preferentially contain R2d2. In heterozygous females, R2d2 orients randomly on the metaphase spindle but lags during anaphase and preferentially remains in the egg, regardless of its initial orientation. Thus, the egg genotype is either euploid with R2d2 or aneuploid with both homologs of chromosome 2, with only the former generating viable embryos. Consistent with this model, R2d2 heterozygous females produce eggs with increased aneuploidy for chromosome 2, increased embryonic lethality, and increased transmission of R2d2. In contrast to typical gamete killing of sisters produced as daughter cells in a single meiosis, R2d2 prevents production of any viable gametes from meiotic divisions in which it should have been excluded from the egg.
Gene drives: an alternative approach to malaria control?
30958Naidoo, K., Oliver, S.V., Gene Therapy, 2024-07-25 20:08:16.
Genetic modification for the control of mosquitoes is frequently touted as a solution for a variety of vector-borne diseases. There has been some success using non-insecticidal methods like sterile or incompatible insect techniques to control arbovirus diseases. However, control by genetic modifications to reduce mosquito populations or create mosquitoes that are refractory to infection with pathogens are less developed. The advent of CRISPR-Cas9-mediated gene drives may advance this mechanism of control. In this review, use and progress of gene drives for vector control, particularly for malaria, is discussed. A brief history of population suppression and replacement gene drives in mosquitoes, rapid advancement of the field over the last decade and how genetic modification fits into the current scope of vector control are described. Mechanisms of alternative vector control by genetic modification to modulate mosquitoes’ immune responses and anti-parasite effector molecules as part of a combinational strategy to combat malaria are considered. Finally, the limitations and ethics of using gene drives for mosquito control are discussed.
Developing genetic tools to control the Oriental fruit fly: Potential approaches and target genes
Nouhoun Traoré, Roberto Galizi, Mahamadi Kientega, Hamidou Maïga, et al, Journal of Applied Entomology, 2024-07-25 19:19:55.The Oriental fruit fly, Bactrocera dorsalis, is a pest of significant economic interest that damages horticulture and causes major economic losses worldwide. The main control measures are based on insecticides, which are being increasingly restricted due to the development of genetic resistance. Therefore, there is a crucial need for a novel, sustainable, and environmentally safe means of controlling this pest. Advances in genome editing, aided by the discovery of CRISPR-Cas9 tools and the development of gene drive systems, offer new alternatives for combating insect pests and vectors. Genetic suppression tools targeting key parameters could become powerful assets within the AW-IPM programme for controlling B. dorsalis. This literature review provides an overview of currently characterized genes that could be targeted for genetic suppression of B. dorsalis.
Selfing Promotes Spread and Introgression of Segregation Distorters in Hermaphroditic Plants
30952Hongru Wang, Léo Planche, Vladimir Shchur, Rasmus Nielsen, Molecular Biology and Evolution, 41. 2024-07-25 19:02:11.
Segregation distorters (SDs) are genetic elements that distort the Mendelian segregation ratio to favor their own transmission and are able to spread even when they incur fitness costs on organisms carrying them. Depending on the biology of the host organisms and the genetic architecture of the SDs, the population dynamics of SDs can be highly variable. Inbreeding is considered an effective mechanism for inhibiting the spread of SDs in populations, and can evolve as a defense mechanism against SDs in some systems. However, we show that inbreeding in the form of selfing in fact promotes the spread of SDs acting as pollen killers in a toxin–antidote system in hermaphroditic plants by two mechanisms: (i) By reducing the effective recombination rate between killer and antidote loci in the two-locus system and (ii) by increasing the proportion of SD alleles in individual flowers, rather than in the general gene-pool. We also show that in rice (Oryza sativa L.), a typical hermaphroditic plant, all molecularly characterized SDs associated with pollen killing were involved in population hybridization and have introgressed across different species. Paradoxically, these loci, which are associated with hybrid incompatibility and can be thought of as Bateson–Dobzhansky–Muller incompatibility loci are expected to reduce gene-flow between species, in fact cross species boundaries more frequently than random loci, and may act as important drivers of introgression.
Incompatible insect technique: insights on potential outcomes of releasing contaminant females: a proof of concept under semi-field conditions
30947Giulia Lombardi, Elena Lampazzi, Maurizio Calvitti, Pest Management Science, 2024-07-25 18:45:37.
Releasing large numbers of Aedes albopictus males, carrying the artificially introduced Wolbachia ‘wPip’ strain, results in a decrease in the reproductive capacity of wild females due to a phenomenon known as cytoplasmic incompatibility (CI). This vector control strategy is referred to as the incompatible insect technique (IIT). However, its widespread implementation faces various challenges, including the complexity of removing fertile females from the males intended for release. Here, we present the results of semi-field experiments comparing the impact of minimal female co-release on two IIT modes: unidirectional CI-based (UnCI IIT) and bidirectional CI-based (BiCI IIT), specifically targeting Ae. albopictus. The contamination of ‘wPip’ infected females (2%) during male releases significantly weakened the overall effectiveness of IIT, emphasizing the need for thorough sex separation. Specifically, with UnCI IIT, despite the low rate of co-released females, there was a gradual rise in ‘wPip’ infection frequency, resulting in more compatible mating and subsequently higher rates of egg hatching. Conversely, this pattern was effectively mitigated in BiCI IIT owing to the reciprocal sterility between the wild-type and the ‘wPip’ infected populations. Through an experimental approach, conducted in a semi-field setting, we have contributed to advancing scientific understanding regarding the potential outcomes of implementing the IIT strategy in the absence of a complete sexing system. The results suggest that safety measures for mitigating the potential impacts of co-released females can be tailored according to the specific type of IIT being utilized. © 2024 Society of Chemical Industry.
Wolbachia endosymbionts in Drosophila regulate the resistance to Zika virus infection in a sex dependent manner
30938Ghada Tafesh-Edwards, Margarita Kyza Karaviot, Klea Markollari, et al, Frontiers in Microbiology, 15. 2024-07-24 16:02:48.
Drosophila melanogaster has been used extensively for dissecting the genetic and functional bases of host innate antiviral immunity and virus-induced pathology. Previous studies have shown that the presence of Wolbachia endosymbionts in D. melanogaster confers resistance to infection by certain viral pathogens. Zika virus is an important vector-borne pathogen that has recently expanded its range due to the wide geographical distribution of the mosquito vector. Here, we describe the effect of Wolbachia on the immune response of D. melanogaster adult flies following Zika virus infection. First, we show that the presence of Wolbachia endosymbionts promotes the longevity of uninfected D. melanogaster wild type adults and increases the survival response of flies following Zika virus injection. We find that the latter effect is more pronounced in females rather than in males. Then, we show that the presence of Wolbachia regulates Zika virus replication during Zika virus infection of female flies. In addition, we demonstrate that the antimicrobial peptide-encoding gene Drosocin and the sole Jun N-terminal kinase-specific MAPK phosphatase Puckered are upregulated in female adult flies, whereas the immune and stress response gene TotM is upregulated in male individuals. Finally, we find that the activity of RNA interference and Toll signaling remain unaffected in Zika virus-infected female and male adults containing Wolbachia compared to flies lacking the endosymbionts. Our results reveal that Wolbachia endosymbionts in D. melanogaster affect innate immune signaling activity in a sex-specific manner, which in turn influences host resistance to Zika virus infection. This information contributes to a better understanding of the complex interrelationship between insects, their endosymbiotic bacteria, and viral infection. Interpreting these processes will help us design more effective approaches for controlling insect vectors of infectious disease.
Infectivity of Plasmodium parasites to Aedes aegypti and Anopheles stephensi mosquitoes maintained on blood-free meals of SkitoSnack
Gonzales-Wartz, K.K., Sá, J.M., Lee, K. et al., Parasites and Vectors, 17. 2024-07-24 15:49:10.Aedes and Anopheles mosquitoes are responsible for tremendous global health burdens from their transmission of pathogens causing malaria, lymphatic filariasis, dengue, and yellow fever. Innovative vector control strategies will help to reduce the prevalence of these diseases. Mass rearing of mosquitoes for research and support of these strategies presently depends on meals of vertebrate blood, which is subject to acquisition, handling, and storage issues. Various blood-free replacements have been formulated for these mosquitoes, but none of these replacements are in wide use, and little is known about their potential impact on competence of the mosquitoes for Plasmodium infection. Colonies of Aedes aegypti and Anopheles stephensi were continuously maintained on a blood-free replacement (SkitoSnack; SS) or bovine blood (BB) and monitored for engorgement and hatch rates. Infections of Ae. aegypti and An. stephensi were assessed with Plasmodium gallinaceum and P. falciparum, respectively. Replicate colonies of mosquitoes were maintained on BB or SS for 10 generations of Ae. aegypti and more than 63 generations of An. stephensi. The odds of engorgement by SS- relative to BB-maintained mosquitoes were higher for both Ae. aegypti (OR = 2.6, 95% CI 1.3–5.2) and An. stephensi (OR 2.7, 95% CI 1.4–5.5), while lower odds of hatching were found for eggs from the SS-maintained mosquitoes of both species (Ae. aegypti OR = 0.40, 95% CI 0.26–0.62; An. stephensi OR = 0.59, 95% CI 0.36–0.96). Oocyst counts were similar for P. gallinaceum infections of Ae. aegypti mosquitoes maintained on SS or BB (mean ratio = [mean on SS]/[mean on BB] = 1.11, 95% CI 0.85–1.49). Similar oocyst counts were also observed from the P. falciparum infections of SS- or BB-maintained An. stephensi (mean ratio = 0.76, 95% CI 0.44–1.37). The average counts of sporozoites/mosquito showed no evidence of reductions in the SS-maintained relative to BB-maintained mosquitoes of both species. Aedes aegypti and An. stephensi can be reliably maintained on SS over multiple generations and are as competent for Plasmodium infection as mosquitoes maintained on BB. Use of SS alleviates the need to acquire and preserve blood for mosquito husbandry and may support new initiatives in fundamental and applied research, including novel manipulations of midgut microbiota and factors important to the mosquito life cycle and pathogen susceptibility.
