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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Aerial release of Aedes aegypti male mosquitoes using an unmanned aerial vehicle: a novel control strategy

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Valdez-Delgado KM, Ríos-Delgado JC, Nettel-Cruz JA, Angulo-Kladt R, Villarreal-Treviño C.,  Salud Pública de México,  65. 2023-12-12 14:17:22.
Objective. To development of a methodology for the chilling, handling, transport, and release of male Aedes aegypti mosquitoes, reared in insectary conditions to release in the field with unmanned vehicles to compete sexually with wild males in the field. Materials and methods. A population of Ae. aegypti from different areas in Tapachula, Chiapas, was used. Laboratory tests were conducted: Effect of temperature and cooling time on the knockdown, recovery of males, and copulatory success. Results. The chilling temperature of 3 ± 1ºC for 30 min, was used as a knockdown temperature before handling, packing, transportation, and aerial release. The males subjected to the entire process, including the semi-field aerial release test, showed normal sexual behavior activity, obtaining 100% of females inseminated. Conclusion. These results present the feasibility of applying a new control methodology using unmanned aerial vehicle (UAV) as support for the sterile insect release technique (SIT), use of Wolbachia or both, in male Ae. aegypti, for the design of strategies to control their populations.

The Sterile Insect Technique can efficiently reduce the reproduction of the spotted wing drosophila (Drosophila suzukii) in strawberry

28688
B. Gard, A. Panel, A. Labbetoul, N. Bosshard, A. Xuereb, B. Cariou, A. Debelle, C. Oliva, S. Fellous,  bioRxiv,  2023-12-11 13:19:11.
The spotted wing drosophila (SWD) Drosophila suzukii (Diptera: Drosophilidae) is a highly problematic pest in soft fruit crops. Since its introduction in Europe in 2008, no satisfying nor environment-friendly control method has emerged against this species. The sterile insect technique (SIT) has proven efficient at controlling numerous fruit fly species. In recent years, key elements of SIT against D. suzukii have become available, leading to the publication of encouraging results. However, field- and field-like experiments are notoriously under the influence of various, often unidentified factors granting the need for replicated studies. In this experiment, we assayed the efficacy of a high-performance strain at reducing the reproduction of D. suzukii in complex, yet replicated and controlled conditions. Two ratios of sterile to fertile insects (5:1 and 1:1) using bisexual releases were compared to a control treatment with fertile, wild flies only. The presence of sterile individuals at a 5:1 ratio significantly reduced fly reproduction, measured after 5 days, by an approximate threefold factor. However, the proportion of infested fruits in the treated plots remained unaffected. The number of available berries in the cage appeared as an unexpected determinant of fly infestation, suggesting undocumented density-dependent processes. The success of this assay opens the door to larger scales experiments, over several generations, and, in the near future, the field-evaluation of the efficacy of the SIT to control D. suzukii.

Population suppression with dominant female-lethal alleles is boosted by homing gene drive

28685
Jinyu Zhu, Jingheng Chen, Yiran Liu, Xuejiao Xu, Jackson Champer,  bioRxiv,  2023-12-07 10:24:25.
Methods to suppress pest insect populations using genetic constructs and repeated releases of male homozygotes have recently been shown to be an attractive alternative to older sterile insect technique based on radiation. Female-specific lethal alleles have substantially increased power, but still require large, sustained transgenic insect releases. Gene drive alleles bias their own inheritance to spread throughout populations, potentially allowing population suppression with a single, small-size release. However, suppression drives often suffer from efficiency issues, and the most well-studied type, homing drives, tend to spread without limit. In this study, we show that coupling female-specific lethal alleles with homing gene drive allowed substantial improvement in efficiency while still retaining the self-limiting nature (and thus confinement) of a lethal allele strategy. Using a mosquito model, we show the required releases sizes for population elimination in a variety of scenarios, including different density growth curves, with comparisons to other systems. Resistance alleles reduced the power of this method, but these could be overcome by targeting an essential gene with the drive while also providing rescue. A proof-of-principle demonstration of this system in Drosophila melanogaster was effective in both basing its inheritance and achieving high lethality among females that inherit the construct in the absence of antibiotic. Overall, our study shows that substantial improvements can be achieved in female-specific lethal systems for population suppression by combining them with a gene drive.

The effect of migration on transmission of Wolbachia in Nilaparvata lugens

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Zhigang Liu, Tiejun Zhou,  Mathematical Biosciences and Engineering,  20. 2023-12-06 13:40:37.
Brown planthopper Nilaparvata lugens, which can transmit rice ragged stunt virus, is a serious and damaging pest to rice plants. Rice plants can protect themselves from the associated diseases of N.lugens by either suppressing or replacing N.lugens by releasing N.lugens infected by a special strain of Wolbachia wStri. The long-distance migration habit of N.lugens is one of the important precursors leading up to the large-scale occurrence of N.lugens. To study the effect of migration on the transmission of Wolbachia in N.lugens, a Wolbachia spreading dynamics model with migration of N.lugens between two patches is put forward. The existence and local stability conditions of equilibrium points of the system and its subsystems are obtained. Moreover, the effects of migration on the dynamic properties and the control of N.lugens are analyzed; the results show that the system can exhibit a bistable phenomenon, and the migration can change the stability of equilibrium infected with wStri from stable to unstable. The quantitative control methods for the migration of the insect N.lugens are proposed, which provide a theoretical guidance for future field experiments. Lastly, we use the Markov chain Monte Carlo (MCMC) method to estimate the parameters of the wild N.lugens migration model based on limited observational data; the numerical simulation results show that migration can increase the quantity of N.lugens, which is consistent with the relevant experimental results.

Transformative Approaches for Sustainable Weed Management: The Power of Gene Drive and CRISPR-Cas9

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Kumam, Y.; Trick, H.N.; Vara Prasad, P.V.; Jugulam, M.,  Genes,  14. 2023-12-06 13:31:23.
Weeds can negatively impact crop yields and the ecosystem’s health. While many weed management strategies have been developed and deployed, there is a greater need for the development of sustainable methods for employing integrated weed management. Gene drive systems can be used as one of the approaches to suppress the aggressive growth and reproductive behavior of weeds, although their efficacy is yet to be tested. Their popularity in insect pest management has increased, however, with the advent of CRISPR-Cas9 technology, which provides specificity and precision in editing the target gene. This review focuses on the different types of gene drive systems, including the use of CRISPR-Cas9-based systems and their success stories in pest management, while also exploring their possible applications in weed species. Factors that govern the success of a gene drive system in weeds, including the mode of reproduction, the availability of weed genome databases, and well-established transformation protocols are also discussed. Importantly, the risks associated with the release of weed populations with gene drive-bearing alleles into wild populations are also examined, along with the importance of addressing ecological consequences and ethical concerns.

Viruses that ‘infect’ viruses: Cas12f1 and Cas9 gene drive in HSV1

28673
Hongsheng Dai, Qiaorui Yao, Zhuangjie Lin, Keyuan Lai, Xianyin Zeng, Guangxiong Lei, Tongwen Zhang,  bioRxiv,  2023-12-06 12:08:32.
Cas9-based synthetic gene drives constitute some minimal elements capable of editing DNA with sequence specificity. However, they face high resistance rate and mitigation strategies developed so far are difficult to implement. Here, we engineered herpes simplex virus type 1 (HSV1) as a vector for gene drive, generated viruses carrying either Cas9 or Cas12f1 gene drives, and compared their performance in spreading the gene drive and causing resistance. Based on phenotypical staining and NGS sequencing, we showed that HSV1 supported fast and effective transmission of gene drive, and Cas12f1 gene drive yielded higher conversion and lower resistance than Cas9 gene drive. Cas12f1 gene drive is a promising alternative to Cas9 gene drive, and HSV1 is a reliable and fast platform to evaluate gene drive. Gene drive viruses worked like pathogens that specifically infect viruses and could potentially be used to attenuate viral infection.

A population modification gene drive targeting both Saglin and Lipophorin impairs Plasmodium transmission in Anopheles mosquitoes

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Emily I Green, Etienne Jaouen, Dennis Klug, Roenick Proveti Olmo, Amandine Gautier, Stéphanie Blandin, Eric Marois,  eLife,  12. 2023-12-06 11:55:36.
Lipophorin is an essential, highly expressed lipid transport protein that is secreted and circulates in insect hemolymph. We hijacked the Anopheles coluzzii Lipophorin gene to make it co-express a single-chain version of antibody 2A10, which binds sporozoites of the malaria parasite Plasmodium falciparum. The resulting transgenic mosquitoes show a markedly decreased ability to transmit Plasmodium berghei expressing the P. falciparum circumsporozoite protein to mice. To force the spread of this anti-malarial transgene in a mosquito population, we designed and tested several CRISPR/Cas9-based gene drives. One of these is installed in, and disrupts, the pro-parasitic gene Saglin and also cleaves wild-type Lipophorin, causing the anti-malarial modified Lipophorin version to replace the wild type and hitch-hike together with the Saglin drive. Although generating drive-resistant alleles and showing instability in its gRNA-encoding multiplex array, the Saglin-based gene drive reached high levels in caged mosquito populations and efficiently promoted the simultaneous spread of the antimalarial Lipophorin::Sc2A10 allele. This combination is expected to decrease parasite transmission via two different mechanisms. This work contributes to the design of novel strategies to spread antimalarial transgenes in mosquitoes, and illustrates some expected and unexpected outcomes encountered when establishing a population modification gene drive.

Homing-based gene drives can introgress rapidly into local genetic backgrounds with minimal chromosomal conversion in Anopheles gambiae

28663
Tony Nolan, Poppy Pescod, Giulia Bevivino et al.,  Research Square,  2023-12-06 10:02:37.
CRISPR-Cas9 gene drive control strategies use a homing selfish genetic element which induces a double-stranded break at the target site and is copied into the opposing chromosome, breaking an essential gene and ensuring super-Mendelian inheritance. During the copying process SNPs could potentially be transferred from one chromosome to another, converting tracts of the target to match the recipient. This would reduce the ability of gene drives to escape their genetic background of origin, with potential impacts on carrier fitness and the success of the strategy. In this study we use Anopheles gambiae strains with variation around the target site to determine the extent of chromosomal conversion during gene drive activity and the mechanism of inheritance bias. We confirm a homing-based mechanism and show that two thirds of homing events are resolved within 50 bp, showing that gene drive introgression into a wild strain can occur within one generation.

Germline transformation of the West Nile Virus and avian malaria vector Culex quinquefasciatus Say using the piggyBac transposon system

28653
Katherine Nevard, Rajdeep Kaur, Tim Harvey-Samuel,  bioRxiv,  2023-12-05 11:04:04.
Culex quinquefasciatus Say is a mosquito which acts as a vector for numerous diseases including West Nile Virus, lymphatic filariasis and avian malaria, over a broad geographical range. As the effectiveness of insecticidal mosquito control methods declines, the need has grown to develop genetic control methods to curb the spread of disease. The piggyBac transposon system - the most widely used genetic transformation tool in insects, including mosquitoes - generates quasi-random insertions of donor DNA into the host genome. However, despite the broad reported species range of piggyBac, previous attempts to use this tool to transform Culex quinquefasciatus mosquitoes have failed. Here we report the first successful transformation of Culex quinquefasciatus with the piggyBac transposon system. Using commercially synthesised piggyBac mRNA as a transposase source, we were able to generate three independent insertions of a ZsGreen fluorescent marker gene, with transformation efficiencies of up to 5%. Through this work, we have expanded the genetic toolkit available for the genetic manipulation of Culex mosquitoes and thus removed a barrier to developing novel genetic control methods in this important disease vector.

A homing rescue gene drive with multiplexed gRNAs reaches high frequency in cage populations but generates functional resistance

28651
Jingheng Chen, Shibo Hou, Ruobing Feng, Xuejiao Xu, Nan Liang, Jackson Champer,  bioRxiv,  2023-12-05 10:59:48.
CRISPR homing gene drive is a potent technology with considerable potential for managing populations of medically and agriculturally significant insects. It induces a bias in the inheritance of the drive allele in progeny, rapidly spreading desired genes throughout the population. Homing drives operate by Cas9 cleavage followed by homology-directed repair, copying the drive allele to the wild-type chromosome. However, resistance alleles formed by end-joining repair pose a significant obstacle to the spread of the drive. To address this challenge, we created a homing drive targeting the essential but haplosufficient hairy gene. Our strategy involves spreading the drive construct through the homing process, eliminating nonfunctional resistance, which are recessive lethal, while rescuing drive-carrying individuals with a recoded version of hairy. This strategy eliminates resistance more slowly than a previous strategy targeting haplolethal genes, but it may be easier to construct in non-model organisms. Our drive inheritance rate was moderate, and multigenerational cage studies showed quick drive spread to 96-97% of the population. However, the drive failed to reach the whole population due to the formation of functional resistance alleles, despite use of four gRNAs, a strategy that previously was successful at preventing functional resistance. Sequencing showed that these alleles had a large deletion and must have utilized an alternate start codon. The resistance allele had a modest fitness advantage over the drive in a cage study, which could prevent long-term persistence of the drive, especially if cargo genes had an additional fitness cost. Thus, revised design strategies targeting more essential regions of a target gene may often be necessary to avoid such functional resistance, even when using multiplexed gRNAs.

Reduced dengue incidence following city-wide wMel Wolbachia mosquito releases throughout three Colombian cities: Interrupted time series analysis and a prospective case-control study

28647
Velez ID, Tanamas SK, Arbelaez MP, Kutcher SC, Duque SL, Uribe A, et al.,  PLoS Neglected Tropical Diseases,  2023-12-05 10:26:43.
The introduction of Wolbachia (wMel strain) into Aedes aegypti mosquitoes reduces their capacity to transmit dengue and other arboviruses. Randomised and non-randomised studies in multiple countries have shown significant reductions in dengue incidence following field releases of wMel-infected Ae. aegypti. Stable introduction of wMel into local Ae. aegypti populations was associated with a significant and sustained reduction in dengue incidence across three Colombian cities. These results from the largest contiguous Wolbachia releases to-date demonstrate the real-world effectiveness of the method across large urban populations and, alongside previously published results, support the reproducibility of this effectiveness across different ecological settings.

Large-scale releases and establishment of wMel Wolbachia in Aedes aegypti mosquitoes throughout the Cities of Bello, Medellín and Itagüí, Colombia

28645
Velez ID, Uribe A, Barajas J, Uribe S, Ángel S, Suaza-Vasco JD, et al.,  PLoS Neglected Tropical Diseases,  2023-12-05 10:11:27.
The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and has been shown to reduce the transmission of dengue and other Aedes-borne viruses. Here we report the entomological results from phased, large-scale releases of Wolbachia infected Ae. aegypti mosquitoes throughout three contiguous cities located in the Aburrá Valley, Colombia. These results, from the largest contiguous releases of wMel Wolbachia mosquitoes to date, highlight the operational feasibility of implementing the method in large urban settings. Based on results from previous studies, we expect that Wolbachia establishment will be sustained long term. Ongoing monitoring will confirm Wolbachia persistence in local mosquito populations and track its establishment in the remaining areas.

Modelling and analysis of periodic impulsive releases of the Nilaparvata lugens infected with wStri-Wolbachia

28638
Xiangjun Dai, Qi Quan and Jianjun Jiao,  Journal of Biological Dynamics,  17:1. 2023-12-04 12:23:12.
In this paper, we formulate a population suppression model and a population replacement model with periodic impulsive releases of Nilaparvata lugens infected with wStri. The conditions for the stability of wild-N.lugens -eradication periodic solution of two systems are obtained by applying the Floquet theorem and comparison theorem. And the sufficient conditions for the persistence in the mean of wild N.lugens are also given. In addition, the sufficient conditions for the extinction and persistence of the wild N.lugens in the subsystem without wLug are also obtained. Finally, we give numerical analysis which shows that increasing the release amount or decreasing the release period are beneficial for controlling the wild N.lugens, and the efficiency of population replacement strategy in controlling wild populations is higher than that of population suppression strategy under the same release conditions.

Food for thought: Assessing the consumer welfare impacts of deploying irreversible, landscape-scale biotechnologies

28628
Michael S. Jones, Zachary S. Brown,  Food Policy,  121. 2023-12-04 10:24:17.
Genetically engineered insects have gained attention as regionally deployed pest control technologies, with substantial applications in agriculture for combatting intractable crop pests and diseases. One potential tool is a ‘gene drive’, using CRISPR-based gene editing. In gene drive, preferentially inherited, engineered traits are spread throughout a geographic area to reduce pest populations or inhibit disease transmission, while also potentially reducing pesticide use and crop prices. But the self-perpetuating nature of gene drives presents a consequence, in that consumers could eventually be limited to only host crops grown in the presence of these genetically engineered insects. In this study, we analyze potential consumer welfare impacts of these technologies using discrete choice experiment data from a representative sample of U.S. adults, examining preferences regarding gene drive use to control spotted wing drosophila in blueberries and Asian citrus psyllid in orange juice (OJ) production. We find smaller average discounts for gene drives versus increased conventional pesticide use or genetically modified crops. Only 27% and 25% of blueberry and OJ consumers, respectively, are estimated to derive disutility from gene drives. However, gene drive disutility for these consumers is so large that elimination of non-drive options from their choice sets results in negative (blueberries) or neutral (OJ) effects to aggregate consumer welfare when weighed against gains to other consumers from reduced prices. Positive welfare effects are recovered by retaining availability of non-gene-drive products. We argue that this type of analysis will be increasingly important as landscape-level biotechnologies are deployed to address challenges to agricultural sustainability.

Manipulating the Destiny of Wild Populations Using CRISPR

28626
Raban R, Marshall JM, Hay BA, Akbari OS.,  Annual Reviews,  57:361-390. 2023-12-04 09:57:57.
Genetic biocontrol aims to suppress or modify populations of species to protect public health, agriculture, and biodiversity. Advancements in genome engineering technologies have fueled a surge in research in this field, with one gene editing technology, CRISPR, leading the charge. This review focuses on the current state of CRISPR technologies for genetic biocontrol of pests and highlights the progress and ongoing challenges of using these approaches.

Anopheles gambiae on remote islands in the Indian Ocean: origins and prospects for malaria elimination by genetic modification of extant populations

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Ditter, R.E., Campos, M., Crepeau, M.W. et al.,  Scientific Reports,  13. 2023-11-29 16:40:50.
The mosquito Anopheles gambiae s.s. is a primary malaria vector throughout sub-Saharan Africa including the islands of the Comoros archipelago (Anjouan, Grande Comore, Mayotte and Mohéli). These islands are located at the northern end of the Mozambique Channel in eastern Africa. Previous studies have shown a relatively high degree of genetic isolation between the Comoros islands and mainland populations of A. gambiae, but the origin of the island populations remains unclear. Here, we analyzed phylogenetic relationships among island and mainland populations using complete mitochondrial genome sequences of individual A. gambiae specimens. This work augments earlier studies based on analysis of the nuclear genome. We investigated the source population of A. gambiae for each island, estimated the number of introductions, when they occurred and explored evidence for contemporary gene flow between island and mainland populations. These studies are relevant to understanding historical patterns in the dispersal of this important malaria vector and provide information critical to assessing their potential for the exploration of genetic-based vector control methods to eliminate this disease. Phylogenetic analysis and haplotype networks were constructed from mitogenome sequences of 258 A. gambiae from the four islands. In addition, 112 individuals from seven countries across sub-Saharan Africa and Madagascar were included to identify potential source populations. Our results suggest that introduction events of A. gambiae into the Comoros archipelago were rare and recent events and support earlier claims that gene flow between the mainland and these islands is limited. This study is concordant with earlier work suggesting the suitability of these oceanic islands as appropriate sites for conducting field trial releases of genetically engineered mosquitoes (GEMs).

Wolbachia Transinfection Via Embryonic Microinjection

28593
Zhang, M., Xi, Z.,  Methods in Molecular Biology,  2739. 2023-11-29 16:22:25.
The process of transferring Wolbachia from one species to another to establish a stable, maternally inherited infection in the target species is known as transinfection. The success of transinfection is primarily achieved through embryonic microinjection, which is the most direct and efficient means of delivering Wolbachia into the germline of the target species and establishing stable maternal transmission. For the fundamental studies, transinfection is often used to characterize Wolbachia-host interactions, including Wolbachia host range, the role of host or bacterial factors in symbiosis, and evolution of Wolbachia-host associations. For the applied studies, use of transinfection to generate a novel infection in the target species is the first step to build the weapon for both population replacement and population suppression for controlling insect pests or their transmitted diseases. For the primary dengue vector Aedes aegypti and Anopheles vectors of malaria, which either do not naturally carry Wolbachia or are infected with strains that lack necessary features for implementation, transinfection can be established by introducing a novel strain capable of inducing both cytoplasmic incompatibility (CI) and pathogen blocking. For A. albopictus and Culex mosquito species, which naturally harbor CI-inducing Wolbachia, transinfection can be achieved by either introducing a novel strain to generate superinfection or replacing the native infection with a different Wolbachia strain in a symbiont-free line, which is derived from antibiotic treatment of the wild type. Here, we use A. aegypti as an example to describe the Wolbachia transinfection method, which can be adapted to other insect species, such as planthoppers, according to their specific developmental requirements.

Measuring Host Fitness Effects and Transmission of Wolbachia Strains in Aedes aegypti Mosquitoes

28587
Ross, P.A.,  Methods in Molecular Biology,  2739. 2023-11-29 15:49:58.
Lines of Aedes aegypti mosquitoes infected with heritable Wolbachia bacteria are being developed and released for arbovirus control. Coordinated releases of lab-reared Wolbachia mosquitoes have reduced local disease incidence by spreading virus-blocking Wolbachia strains and by crashing mosquito populations through incompatible male releases. The phenotypic effects of Wolbachia are diverse and depend on both genetics and the environment. Accurate assessments of Wolbachia effects in mosquitoes are essential, as such effects can make the difference between success and failure of a Wolbachia release program. This chapter provides guidelines for testing key Wolbachia host effects and transmission in Aedes aegypti: the most important arbovirus vector and the most common target of Wolbachia release programs. The protocols should be useful for evaluating mosquito strains prior to field release.

Procedures for the Detection of Wolbachia-Conferred Antiviral Protection in Drosophila melanogaster

28581
Chrostek, E.,  Methods in Molecular Biology,  2739. 2023-11-29 15:34:15.
Spread of Wolbachia infections in host populations may be enhanced by Wolbachia-conferred protection from viral pathogens. Wolbachia-infected Drosophila melanogaster survive the pathogenic effects of positive-sense single-stranded RNA virus infections at a higher rate than the flies without Wolbachia. The protection can occur with or without detectable reduction in virus titer. For the comparisons to be meaningful, Wolbachia-harboring and Wolbachia-free insects need to be genetically matched, and original populations of gut microbiota need to be restored after the removal of Wolbachia using antibiotics. Here, I describe the procedures needed to detect Wolbachia-conferred antiviral protection against Drosophila C virus measured as the difference in survival and viral titer between flies with and without Wolbachia.

Use of Drosophila Transgenics to Identify Functions for Symbiont Effectors

28574
Cortez, C.T., Murphy, R.O., Owens, I.M., Beckmann, J.F.,  Methods in Molecular Biology,  2739. 2023-11-29 14:35:56.
Wolbachia, one of the most successful and studied insect symbionts, and Drosophila, one of the most understood model insects, can be exploited as complementary tools to unravel mechanisms of insect symbiosis. Although Wolbachia itself cannot be grown axenically as clonal isolates or genetically manipulated by standard methods, its reproductive phenotypes, including cytoplasmic incompatibility (CI), have been elucidated using well-developed molecular tools and precise transgenic manipulations available for Drosophila melanogaster. Current research only scratches the surface of how Drosophila can provide a tool for understanding Wolbachia’s evolutionary success and the molecular roles of its genetic elements. Here, we briefly outline basic methodologies inherent to transgenic Drosophila systems that have already contributed significant advances in understanding CI, but may be unfamiliar to those who lack experience in Drosophila genetics. In the future, these approaches will continue providing significant insights into Wolbachia that undoubtedly will be extended to other insect symbionts and their biological capabilities.

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