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.
An introgressed gene causes meiotic drive in Neurospora sitophila
15125J. Svedberg, A. A. Vogan, N. A. Rhoades, D. Sarmarajeewa, D. J. Jacobson, M. Lascoux, T. M. Hammond and H. Johannesson, bioRxiv, 2020.01.29.923946. 2020-01-30 15:58:21.
In this study, we identify the gene responsible for spore killing in Sk-1 by generating both long and short-read genomic data and by using these data to perform a genome wide association test. By phylogenetic analysis, we demonstrate that the gene is likely to have been introgressed from the closely related species N. hispaniola, and we identify three subclades of N. sitophila, one where Sk-1 is fixed, another where Sk-1 is absent, and a third where both killer and sensitive strain are found. We show that spore killing can be suppressed through an RNA interference based genome defense pathway known as meiotic silencing by unpaired DNA.
First Field Release of a Genetically Engineered, Self-Limiting Agricultural Pest Insect: Evaluating Its Potential for Future Crop Protection
7251A. M. Shelton, S. J. Long, A. S. Walker, M. Bolton, H. L. Collins, L. Revuelta, L. M. Johnson and N. I. Morrison, Frontiers in Bioengineering and Biotechnology, 7:1-15. 2020-01-29 16:10:21.
Alternative, biologically-based approaches for pest management are sorely needed and one approach is to use genetically engineered insects. Herein we describe a series of integrated field, laboratory and modeling studies with the diamondback moth, Plutella xylostella, a serious global pest of crucifers. A “self-limiting” strain of Plutella xylostella (OX4319L), genetically engineered to allow the production of male-only cohorts of moths for field releases, was developed as a novel approach to protect crucifer crops. Wild-type females that mate with these self-limiting males will not produce viable female progeny. Our previous greenhouse studies demonstrated that releases of OX4319L males lead to suppression of the target pest population and dilution of insecticide-resistance genes. We report results of the first open-field release of a non-irradiated, genetically engineered self-limiting strain of an agricultural pest insect. In a series of mark-release-recapture field studies with co-releases of adult OX4319L males and wild-type counterparts, the dispersal, persistence and field survival of each strain were measured in a 2.83 ha cabbage field. In most cases, no differences were detected in these parameters. Overall, 97.8% of the wild-type males and 95.4% of the OX4319L males recaptured dispersed <35 m from the release point. The predicted persistence did not differ between strains regardless of release rate. With 95% confidence, 75% of OX4319L males released at a rate of 1,500 could be expected to live between 3.5 and 5.4 days and 95% of these males could be expected to be detected within 25.8–34.9 m from the release point. Moth strain had no effect on field survival but release rate did. Collectively, these results suggest similar field behavior of OX4319L males compared to its wild-type counterpart. Laboratory studies revealed no differences in mating competitiveness or intrinsic growth rates between the strains and small differences in longevity. Using results from these studies, mathematical models were developed that indicate release of OX4319L males should offer efficacious pest management of P. xylostella. Further field studies are recommended to demonstrate the potential for this self-limiting P. xylostella to provide pest suppression and resistance management benefits, as was previously demonstrated in greenhouse studies.
Autosomal suppression and fitness costs of an old driving X chromosome in Drosophila testacea
7363G. Keais, S. Lu and S. Perlman, Journal of Evolutionary Biology, 2020-01-28 21:58:18.
Driving X chromosomes (XDs) are meiotic drivers that bias their own transmission through males by killing Y-bearing gametes. These chromosomes can in theory spread rapidly in populations and cause extinction, but many are found as balanced polymorphisms or as ?cryptic? XDs shut down by drive suppressors. The relative likelihood of these outcomes, as well as the evolutionary pathways through which they come about, are not well-understood. An XD was recently discovered in the mycophagous fly, Drosophila testacea, presenting the opportunity to compare this XD with the well-studied XD of its sister species, Drosophila neotestacea. Comparing features of independently evolved XDs in young sister species is a promising avenue towards understanding how XDs and their counteracting forces change over time. In contrast to the XD of D. neotestacea, we find that the XD of D. testacea is old, with its origin predating the radiation of three species: D. testacea, D. neotestacea, and their shared sister species, Drosophila orientacea. Motivated by the suggestion that older XDs should be more deleterious to carriers, we assessed the effect of the XD on both male and female fertility. Unlike what is known from D. neotestacea, we found a strong fitness cost in females homozygous for the XD in D. testacea: a large proportion of homozygous females failed to produce offspring after being housed with males for several days. Our male fertility experiments show that while XD male fertility is lower under sperm depleting conditions, XD males have comparable fertility to males carrying a standard X chromosome under a free mating regime, which may better approximate conditions in wild populations of D. testacea. Lastly, we demonstrate the presence of autosomal suppression of X chromosome drive. Our results provide support for a model of XD evolution where the dynamics of young XDs are governed by fitness consequences in males, whereas in older XD systems, both suppression and fitness consequences in females likely supersede male fitness costs.
Public Opinion Towards Gene Drive as a Pest Control Approach for Biodiversity Conservation and the Association of Underlying Worldviews
7348E. A. MacDonald, J. Balanovic, E. D. Edwards, W. Abrahamse, B. Frame, A. Greenaway, R. Kannemeyer, N. Kirk, F. Medvecky, T. L. Milfont, J. C. Russell and D. M. Tompkins, Environmental Communication-a Journal of Nature and Culture, 15:1-16. 2020-01-27 21:27:11.
Synthetic gene drive approaches are nascent technologies with potential applicability for pest control for conservation purposes. Responsible science mandates that society be engaged in a dialogue over new technology, particularly where there exist global ramifications as with gene drive. We hypothesize that public attitudes towards gene drive are not formed on scientific knowledge or demographics alone, but are heavily influenced by underlying worldviews, which encapsulate a broad and interactive system of attitudes, beliefs, and values. To test this, we conducted a national survey in New Zealand (n = 8199) and found that respondents clustered into four distinct segments with underlying worldviews, better able to explain attitudes toward gene drive than either the participants' scientific knowledge or other explanatory factors such demographics, political ideology or religiosity. We found that the use of gene drive for biodiversity conservation currently has moderate (32%) levels of support in New Zealand but that varied substantially across the four segments. Should gene drive become a technically viable approach for pest control, understanding the worldviews that shape public decision-making can guide a more empathetic engagement process and empower society to participate in informed decision-making about if and how gene drive should be used for conservation purposes.
Regulation of GM Organisms for Invasive Species Control
6701H. J. Mitchell and D. Bartsch, Frontiers in Bioengineering and Biotechnology, 7:1-11. 2020-01-21 18:17:37.
Invasive species can cause significant harm to the environment, agriculture, and human health, but there are often very limited tools available to control their populations. Gene drives (GD) have been proposed as a new tool which could be used to control or eliminate such species. Here, GD describes a variety of molecular biology applications which all enable the introduction of genetic elements at a higher than expected frequency. These elements can change the genotypes in target populations rapidly with consequences either for (intrinsic) fitness or host-parasite interaction, or both. Beneficial applications are foreseen for human and animal health, agriculture, or nature conservation. This rapidly developing technology is likely to have major impacts in the fight against various diseases, pests, and invasive species. The majority of GD applications involve genetic engineering and novel traits. Therefore, applicants and GMO regulators need to interact to achieve the benefits in innovation while cautiously avoiding unacceptable risks. The release into the environment may include transboundary movement and replacement of target populations, with potential impact on human/animal health and the environment. This article summarizes knowledge-based discussions to identify information gaps and analyzes scenarios for responsible introduction of GD organisms into the environment. It aims to connect the latest scientific developments with regulatory approaches and decision-making.
A transcomplementing gene drive provides a flexible platform for laboratory investigation and potential field deployment
6668V. López Del Amo, A. L. Bishop, H. M. Sánchez C, J. B. Bennett, X. Feng, J. M. Marshall, E. Bier and V. M. Gantz, Nature Communications, 11:352. 2020-01-17 18:00:23.
CRISPR-based gene drives can spread through wild populations by biasing their own transmission above the 50% value predicted by Mendelian inheritance. These technologies offer population-engineering solutions for combating vector-borne diseases, managing crop pests, and supporting ecosystem conservation efforts. Current technologies raise safety concerns for unintended gene propagation. Herein, we address such concerns by splitting the drive components, Cas9 and gRNAs, into separate alleles to form a trans-complementing split–gene-drive (tGD) and demonstrate its ability to promote super-Mendelian inheritance of the separate transgenes. This dual-component configuration allows for combinatorial transgene optimization and increases safety by restricting escape concerns to experimentation windows. We employ the tGD and a small–molecule-controlled version to investigate the biology of component inheritance and resistant allele formation, and to study the effects of maternal inheritance and impaired homology on efficiency. Lastly, mathematical modeling of tGD spread within populations reveals potential advantages for improving current gene-drive technologies for field population modification.
Broad dengue neutralization in mosquitoes expressing an engineered antibody
6706A. Buchman, S. Gamez, M. Li, I. Antoshechkin, H.-H. Li, H.-W. Wang, C.-H. Chen, M. J. Klein, J.-B. Duchemin, J. E. Crowe, Jr., P. N. Paradkar and O. S. Akbari, PLOS Pathogens, 16:e1008103. 2020-01-16 18:18:14.
Author summary With limited success of traditional vector control methods to curb dengue infections and more than half of the world’s population still at risk, there is a need for novel strategies to reduce its impact on public health. Recent advances in genetic technologies has allowed for precise modifications of mosquito genome to make them resistant to infections, thus breaking the transmission cycle. Here we generated engineered Ae. aegypti mosquitoes efficiently expressing a DENV-targeting single-chain variable fragment (scFv) derived from a previously characterized broadly neutralizing human antibody, which blocked infection and transmission in these mosquitoes. To our knowledge, this is the first example of an engineered transgene capable of rendering Ae. aegypti mosquitoes 100% refractory to all four serotypes of DENV. The engineered mosquitoes, in future, could easily be paired with a gene drive, capable of spreading the transgene throughout wild disease-transmitting mosquito populations and preventing further DENV transmission. Since a number of diverse and well-characterized antibodies exist against other arboviruses (eg chikungunya and Zika, this work also provides a proof-of-concept principle for developing similar genetic strategies for reducing the impact of these arboviruses.
Development of a confinable gene drive system in the human disease vector Aedes aegypti
6697M. Li, T. Yang, N. P. Kandul, M. Bui, S. Gamez, R. Raban, J. Bennett, H. M. Sánchez C, G. C. Lanzaro, H. Schmidt, Y. Lee, J. M. Marshall and O. S. Akbari, eLife, 9:e51701. 2020-01-16 18:07:34.
Aedes aegypti is the principal mosquito vector for many arboviruses that increasingly infect millions of people every year. With an escalating burden of infections and the relative failure of traditional control methods, the development of innovative control measures has become of paramount importance. The use of gene drives has sparked significant enthusiasm for genetic control of mosquitoes; however, no such system has been developed in Ae. aegypti. To fill this void, here we develop several CRISPR-based split gene drives for use in this vector. With cleavage rates up to 100% and transmission rates as high as 94%, mathematical models predict that these systems could spread anti-pathogen effector genes into wild populations in a safe, confinable and reversible manner appropriate for field trials and effective for controlling disease. These findings could expedite the development of effector-linked gene drives that could safely control wild populations of Ae. aegypti to combat local pathogen transmission.
The potential cost-effectiveness of controlling dengue in Indonesia using wMel Wolbachia released at scale: a modelling study
14326O. J. Brady, D. D. Kharisma, N. N. Wilastonegoro, K. M. Reilly, E. Hendricx, L. S. Bastos, L. Yakob and D. S. Shepard, medRxiv, 2020.01.11.20017186. 2020-01-16 17:55:32.
Wolbachia releases in high density urban areas is expected to be highly cost-effective and could potentially be the first cost saving intervention for dengue. Sites with strong public health infrastructure, fiscal capacity, and community support should be prioritized.
Optimal control and analysis of a modified trojan Y-Chromosome strategy
11491M. A. Beauregard, R. D. Parshad, S. Boon, H. Conaway, T. Griffin and J. J. Lyu, Ecological Modelling, 416. 2020-01-15 20:19:52.
The Trojan Y Chromosome (TYC) strategy is a promising eradication method that attempts to manipulate the female to male ratio to promote the reduction of the population of an invasive species. The manipulation stems from an introduction of sex-reversed males, called supermales, into an ecosystem. The offspring of the supermales is guaranteed to be male. Mathematical models have shown that the population can be driven to extinction with a continuous supply of supermales. In this paper, a new model of the TYC strategy is introduced and analyzed that includes two important modeling characteristics, that are neglected in all previous models. First, the new model includes intraspecies competition for mates. Second, a strong Allee effect is included. Several conclusions about the strategy via optimal control are established. These results have large scale implications for the biological control of invasive species.
Antiviral effectors and gene drive strategies for mosquito population suppression or replacement to mitigate arbovirus transmission by Aedes aegypti
6634A. E. Williams, A. W. E. Franz, W. R. Reid and K. E. Olson, Insects, 11:1-18. 2020-01-12 20:05:33.
The mosquito vector Aedes aegypti transmits arthropod-borne viruses (arboviruses) of medical importance, including Zika, dengue, and yellow fever viruses. Controlling mosquito populations remains the method of choice to prevent disease transmission. Novel mosquito control strategies based on genetically manipulating mosquitoes are being developed as additional tools to combat arbovirus transmission. Genetic control of mosquitoes includes two basic strategies: population suppression and population replacement. The former aims to eliminate mosquito populations while the latter aims to replace wild populations with engineered, pathogen-resistant mosquitoes. In this review, we outline suppression strategies being applied in the field, as well as current antiviral effector genes that have been characterized and expressed in transgenic Ae. aegypti for population replacement. We discuss cutting-edge gene drive technologies that can be used to enhance the inheritance of effector genes, while highlighting the challenges and opportunities associated with gene drives. Finally, we present currently available models that can estimate mosquito release numbers and time to transgene fixation for several gene drive systems. Based on the recent advances in genetic engineering, we anticipate that antiviral transgenic Ae. aegypti exhibiting gene drive will soon emerge; however, close monitoring in simulated field conditions will be required to demonstrate the efficacy and utility of such transgenic mosquitoes.
Metaphor, Trust and Support for Non-native Species Control
13833P. A. Kohl, S. J. Collins and M. Eichholz, Environmental Communication, 14:672-685. 2020-01-07 15:29:47.
This experimental study used a representative sample of U.S. residents (N = 1,042) to test whether the use of the term "invasive" increases support for non-native species control efforts. The term invasive had a small influence on support for two out of three non-native species control methods. We also found stronger support for control methods using gene editing technologies than control methods using poison.
Wolbachia transinfections in Culex quinquefasciatus generate cytoplasmic incompatibility
6224T. H. Ant, C. Herd, F. Louis, A. B. Failloux and S. P. Sinkins, Insect Molecular Biology, 29:1-8. 2020-01-06 21:43:12.
Culex quinquefasciatus is an important mosquito vector of a number of viral and protozoan pathogens of humans and animals, and naturally carries the endosymbiont Wolbachia pipientis, strain wPip. Wolbachia are used in two distinct vector control strategies: firstly, population suppression caused by mating incompatibilities between mass-released transinfected males and wild females; and secondly, the spread of pathogen transmission-blocking strains through populations. Using embryonic microinjection, two novel Wolbachia transinfections were generated in C. quinquefasciatus using strains native to the mosquito Aedes albopictus: a wAlbB single infection, and a wPip plus wAlbA superinfection. The wAlbB infection showed full bidirectional cytoplasmic incompatibility (CI) with wild-type C. quinquefasciatus in reciprocal crosses. The wPipwAlbA superinfection showed complete unidirectional CI, and therefore population invasion potential. Whereas the wAlbB strain showed comparatively low overall densities, similar to the native wPip, the wPipwAlbA superinfection reached over 400-fold higher densities in the salivary glands compared to the native wPip, suggesting it may be a candidate for pathogen transmission blocking.
Scenario analysis on the use of rodenticides and sex-biasing gene drives for the removal of invasive house mice on islands
6221M. E. Serr, R. X. Valdez, K. S. Barnhill-Dilling, J. Godwin, T. Kuiken and M. Booker, Biological Invasions, 2020-01-06 21:34:59.
Since the 1960s conservation efforts have focused on recovering island biodiversity by eradicating invasive rodents. These eradication campaigns have led to considerable conservation gains, particularly for nesting seabirds. However, eradications are complex and lengthy endeavors and are even more challenging when humans are co-inhabitants of the targeted island. Furthermore, the method of eradication matters and recent proposals to consider genetic technologies for rodent eradication require specific scrutiny. One such technology is the potential use of a gene drive for biasing offspring sex ratios in invasive house mice, Mus musculus, that would spread and prevent the production of one sex, allowing die-off from lack of reproduction and natural attrition. Practitioners can gain insight into the potential for adoption of this technology from examining stakeholder engagement. This paper uses scenario analysis to address the eradication of rodents on inhabited and uninhabited islands, by specifically comparing the traditional approach of using rodenticides with sex-biasing gene drives. Concurrently the International Union for Conservation of Nature is assessing the risks and value of gene drives in general for conservation. Hence, we make the case that the ethical challenges with the use of gene drive sex-biasing techniques and the effectiveness of this tool will rely as much on its public acceptance and its democratic use as the actual science used to construct the technology.
Beyond Mendelian genetics: Anticipatory biomedical ethics and policy implications for the use of CRISPR together with gene drive in humans.
6227M. W. Nestor and R. L. Wilson, Journal of Bioethical Inquiry, 2020:1-12. 2020-01-03 21:43:18.
Clustered regularly interspaced short palindromic repeats (CRISPR) genome editing has already reinvented the direction of genetic and stem cell research. For more complex diseases it allows scientists to simultaneously create multiple genetic changes to a single cell. Technologies for correcting multiple mutations in an in vivo system are already in development. On the surface, the advent and use of gene editing technologies is a powerful tool to reduce human suffering by eradicating complex disease that has a genetic etiology. Gene drives are CRISPR mediated alterations to genes that allow them to be passed on to subsequent populations at rates that approach one hundred per cent transmission. Therefore, from an anticipatory biomedical ethics perspective, it is possible to conceive gene drive being used with CRISPR to permanently ameliorate aberrant genes from wild-type populations containing mutations. However, there are also a number of possible side effects that could develop as the result of combining gene editing and gene drive technologies in an effort to eradicate complex diseases. In this paper, we critically analyse the hypothesis that the combination of CRISPR and gene drive will have a deleterious effect on human populations from an ethical perspective by developing an anticipatory ethical analysis of the implications for the use of CRISPR together with gene drive in humans.
Gene drives : equity demands civility
6184N. Kofler, Nature, 565:25. 2020-01-03 19:10:06.
At the 14th Conference of the Parties of the United Nations Convention on Biological Diversity late last year, I witnessed the rapid deterioration of a crucial discussion. It was on the potential of synthetic biology in environmental conservation. What started as heckling turned into a yelling match of misinformation. Such disruptive behaviour robbed the global community of a rare opportunity to debate gene drives in a meaningful way. Sidelined young scientists, country delegates and others watched in disbelief.
Technology Factsheet: Gene Drives
7265J. Lunshof, C. Shachar, R. Edison, A. Jayanti, Belfer Center for Science and International Affairs, 2020-01-01 17:03:29.
Gene drives can be defined as genetic elements that pass from parents to unusually high numbers of their offspring due to biased inheritance (sometimes referred to as the possession of “selfish” genetic elements).1,2 There are different ways of achieving this biased inheritance needed for a drive, but the shared outcome is one where the offspring of a parent carrying a certain genetic variant has over a 50% likelihood of inheriting it. With regular inheritance, in the absence of a gene drive, each of the two alleles carried by a parent are equally likely to be inherited by offspring. By implementing modern gene editing technology, such as CRISPR, gene drives can be manufactured by humans to intentionally suppress a target population or spread a trait through a population. For example, gene drives could be used to target weeds, spreading a trait that would reverse their evolved resistance to non-toxic herbicides. Gene drives could also be used for human health purposes, in particular for the control of vector-borne diseases, such as malaria through populations of mosquitos. There are many outstanding governance questions with regards to the specific research, development, testing, and deployment of gene drives—including who should be taking ownership of drafting regulations and policy. At this stage, few countries currently have regulations that are defined specifically for gene drive, and in most countries the closest relevant regulations are those written for a broader swath of gene editing technologies. As there becomes more momentum around the potentially unique opportunities of gene drives though, it is important for U.S. legislators and policymakers to remain engaged in the technology’s technical, ethical, and practical progress and consider technology-specific governance.
A comparison of the Trojan Y Chromosome strategy to harvesting models for eradication of nonnative species
J. J. Lyu, P. J. Schofield, K. M. Reaver, M. Beauregard and R. D. Parshad, Natural Resource Modeling, 2019-12-31 20:21:43.The Trojan Y Chromosome strategy (TYC) is a promising eradication method for biological control of nonnative species. The strategy works by manipulating the sex ratio of a population through the introduction of supermales that guarantee male offspring. In the current study, we compare the TYC method with a pure harvesting strategy. We also analyze a hybrid harvesting model that mirrors the TYC strategy. The dynamic analysis leads to results on stability of solutions and bifurcations of the model. Several conclusions about the different strategies are established via optimal control methods. In particular, the results affirm that either a pure harvesting or hybrid strategy may work better than the TYC method at controlling a nonnative species population. Recommendations for resource managers Where harvesting is feasible, it is as effective if not more effective than the classical TYC method. Therein managers may attempt harvesting female fish while stocking males or harvesting both male and female fishes. Managers may attempt linear harvesting, saturating density-dependent harvesting, and unbounded density-dependent harvesting. Linear harvesting is seen to be the most effective. We caution against the outright use of harvesting due to various density-dependent effects that may arise. To this end hybrid models that involve a combination of harvesting and TYC-type methods might be a better strategy. One may also use harvesting as a tool in mesocosm settings to predict the efficacy of the TYC strategy in the wild.
A typology of community and stakeholder engagement based on documented examples in the field of novel vector control
6032C. E. Schairer, R. Taitingfong, O. S. Akbari and C. S. Bloss, PLoS Neglected Tropical Diseases, 13:e0007863. 2019-12-30 20:46:44.
Background Despite broad consensus on the importance of community and stakeholder engagement (CSE) for guiding the development, regulation, field testing, and deployment of emerging vector control technologies (such as genetically engineered insects), the types of activities pursued have varied widely, as have the outcomes. We looked to previous CSE efforts for clarity about appropriate methods and goals. Our analysis yielded a typology of CSE, and related vocabulary, that describes distinctions that funders, organizers, and scholars should make when proposing or evaluating CSE. Methods We compiled available formal documentation of CSE projects, starting with projects mentioned in interviews with 17 key informants. Major features of these examples, including the initiators, target groups, timing, goals, and methods were identified using qualitative coding. Based on these examples, subcategories were developed for a subset of features and applied to the identified cases of CSE in the documents. Co-occurrence of subcategorized features was examined for patterns. Results We identified 14 documented examples CSE projects, which were comprised of 28 distinct CSE activities. We found no clear patterns with respect to timing. However, we found that grouping examples according to whether initiators or targets could enact the immediate desired outcome could help to clarify relationships between goals, methods, and targets.
Biomphalaria glabrata Granulin Increases Resistance to Schistosoma mansoni Infection in Several Biomphalaria Species and Induces the Production of Reactive Oxygen Species by Haemocytes
13835J. R. Hambrook, A. A. Gharamah, E. A. Pila, S. Hussein and P. C. Hanington, Genes, 11:12. 2019-12-28 15:36:48.
In this study, we demonstrate that in vivo addition of Biomphalaria glabrata pro-granulin (BgGRN) can reduce Schistosoma mansoni infection success in numerous Biomphalaria sp. when challenged with different S. mansoni strains. We also demonstrate that cleavage of BgGRN into individual granulin subunits by elastase results in the stimulation of haemocytes to produce reactive oxygen species.
Mathematical modeling of self-contained CRISPR gene drive reversal systems
6023M. G. Heffel and G. C. Finnigan, Scientific Reports, 9:20050. 2019-12-27 20:31:43.
There is a critical need for further research into methods to control biological populations. Numerous challenges to agriculture, ecological systems, and human health could be mitigated by the targeted reduction and management of key species (e.g. pests, parasites, and vectors for pathogens). The discovery and adaptation of the CRISPR/Cas editing platform co-opted from bacteria has provided a mechanism for a means to alter an entire population. A CRISPR-based gene drive system can allow for the forced propagation of a genetic element that bypasses Mendelian inheritance which can be used to bias sex determination, install exogenous information, or remove endogenous DNA within an entire species. Laboratory studies have demonstrated the potency by which gene drives can operate within insects and other organisms. However, continued research and eventual application face serious opposition regarding issues of policy, biosafety, effectiveness, and reversal. Previous mathematical work has suggested the use of modified gene drive designs that are limited in spread such as daisy chain or underdominance drives. However, no system has yet been proposed that allows for an inducible reversal mechanism without requiring the introduction of additional individuals. Here, we study gene drive effectiveness, fitness, and inducible drive systems that could respond to external stimuli expanding from a previous frequency-based population model. We find that programmed modification during gene drive propagation could serve as a potent safeguard to either slow or completely reverse drive systems and allow for a return to the original wild-type population.
Experimental population modification of the malaria vector mosquito, Anopheles stephensi
6182T. B. Pham, C. H. Phong, J. B. Bennett, K. Hwang, N. Jasinskiene, K. Parker, D. Stillinger, J. M. Marshall, R. Carballar-Lejarazú and A. A. James, PLOS Genetics, 15:e1008440. 2019-12-19 19:05:32.
The experimental introduction of manipulated genes into insect species has a long history in basic genetics. Recent advances in genome editing technologies have spurred considerable effort to exploit these methodologies to provide genetic solutions to some of the worst medical and agricultural problems caused by insects. Insect population suppression and population modification approaches have been proposed to control transmission of vector-borne diseases, including malaria. We used small cage trials to explore the efficacy of non-drive and gene-drive releases to deliver anti-malarial effector genes to a vector mosquito, Anopheles stephensi. We show that both approaches can work to introduce genes to high percentages, but as expected, the gene-drive approaches were more efficient in that they needed only a single release with a much lower number of released insects. The gene-drive females in our studies exhibited a significant load that resulted in some cage populations going to extinction. Furthermore, the accumulation of drive-resistant target genes prevented full introduction of the transgenes in those cages that did not go extinct. While none of the strains evaluated here are proposed for open release, these laboratory cage trials reveal features that can be used to improve next-generation gene-drive strains for population modification.
Gene drives for schistosomiasis transmission control
6341T. Maier, N. J. Wheeler, E. K. O. Namigai, J. Tycko, R. E. Grewelle, Y. Woldeamanuel, K. Klohe, J. Perez-Saez, S. H. Sokolow, G. A. De Leo, T. P. Yoshino, M. Zamanian and J. Reinhard-Rupp, PLoS Neglected Tropical Diseases, 13:e0007833. 2019-12-19 18:18:55.
Schistosomiasis is one of the most important and widespread neglected tropical diseases (NTD), with over 200 million people infected in more than 70 countries; the disease has nearly 800 million people at risk in endemic areas. Although mass drug administration is a cost-effective approach to reduce occurrence, extent, and severity of the disease, it does not provide protection to subsequent reinfection. Interventions that target the parasites' intermediate snail hosts are a crucial part of the integrated strategy required to move toward disease elimination. The recent revolution in gene drive technology naturally leads to questions about whether gene drives could be used to efficiently spread schistosome resistance traits in a population of snails and whether gene drives have the potential to contribute to reduced disease transmission in the long run. Responsible implementation of gene drives will require solutions to complex challenges spanning multiple disciplines, from biology to policy. This Review Article presents collected perspectives from practitioners of global health, genome engineering, epidemiology, and snail/schistosome biology and outlines strategies for responsible gene drive technology development, impact measurements of gene drives for schistosomiasis control, and gene drive governance. Success in this arena is a function of many factors, including gene-editing specificity and efficiency, the level of resistance conferred by the gene drive, how fast gene drives may spread in a metapopulation over a complex landscape, ecological sustainability, social equity, and, ultimately, the reduction of infection prevalence in humans. With combined efforts from across the broad global health community, gene drives for schistosomiasis control could fortify our defenses against this devastating disease in the future.
Articulating ‘free, prior and informed consent’ (FPIC) for engineered gene drives
5800George, D. R., T. Kuiken and J. A. Delborne, Proceedings of the Royal Society B: Biological Sciences, 286:20191484.. 2019-12-19 14:30:32.
Recent statements by United Nations bodies point to free, prior and informed consent (FPIC) as a potential requirement in the development of engineered gene drive applications. As a concept developed in the context of protecting Indigenous rights to self-determination in land development scenarios, FPIC would need to be extended to apply to the context of ecological editing. Without an explicit framework of application, FPIC could be interpreted as a narrowly framed process of community consultation focused on the social implications of technology, and award little formal or advisory power in decision-making to Indigenous peoples and local communities. In this paper, we argue for an articulation of FPIC that attends to issues of transparency, iterative community-scale consent, and shared power through co-development among Indigenous peoples, local communities, researchers and technology developers. In realizing a comprehensive FPIC process, researchers and developers have an opportunity to incorporate enhanced participation and social guidance mechanisms into the design, development and implementation of engineered gene drive applications.
Fitness consequences of a non-recombining sex-ratio drive chromosome can explain its prevalence in the wild
5797Dyer, K. A. and D. W. Hall, Proceedings of the Royal Society B: Biological Sciences, 286:20192529. 2019-12-19 14:27:34.
Understanding the pleiotropic consequences of gene drive systems on host fitness is essential to predict their spread through a host population. Here, we study sex-ratio (SR) X-chromosome drive in the fly Drosophila recens, where SR causes the death of Y-bearing sperm in male carriers. SR males only sire daughters, which all carry SR, thus giving the chromosome a transmission advantage. The prevalence of the SR chromosome appears stable, suggesting pleiotropic costs. It was previously shown that females homozygous for SR are sterile, and here, we test for additional fitness costs of SR. We found that females heterozygous for SR have reduced fecundity and that male SR carriers have reduced fertility in conditions of sperm competition. We then use our fitness estimates to parametrize theoretical models of SR drive and show that the decrease in fecundity and sperm competition performance can account for the observed prevalence of SR in natural populations. In addition, we found that the expected equilibrium frequency of the SR chromosome is particularly sensitive to the degree of multiple mating and performance in sperm competition. Together, our data suggest that the mating system of the organism should be carefully considered during the development of gene drive systems.
Gene drive: progress and prospects
5795Wedell, N., T. A. R. Price and A. K. Lindholm, Proceedings of the Royal Society B: Biological Sciences, 286:20192709. 2019-12-19 14:25:02.
Gene drive is a naturally occurring phenomenon in which selfish genetic elements manipulate gametogenesis and reproduction to increase their own transmission to the next generation. Currently, there is great excitement about the potential of harnessing such systems to control major pest and vector populations. If synthetic gene drive systems can be constructed and applied to key species, they may be able to rapidly spread either modifying or eliminating the targeted populations. This approach has been lauded as a revolutionary and efficient mechanism to control insect-borne diseases and crop pests. Driving endosymbionts have already been deployed to combat the transmission of dengue and Zika virus in mosquitoes. However, there are a variety of barriers to successfully implementing gene drive techniques in wild populations. There is a risk that targeted organisms will rapidly evolve an ability to suppress the synthetic drive system, rendering it ineffective. There are also potential risks of synthetic gene drivers invading nontarget species or populations. This Special Feature covers the current state of affairs regarding both natural and synthetic gene drive systems with the aim to identify knowledge gaps. By understanding how natural drive systems spread through populations, we may be able to better predict the outcomes of synthetic drive release.
Ancient gene drives: an evolutionary paradox
5792Price, T. A. R., R. Verspoor and N. Wedell, Proceedings of the Royal Society B: Biological Sciences, 286:20192267. 2019-12-19 14:21:02.
Selfish genetic elements such as selfish chromosomes increase their transmission rate relative to the rest of the genome and can generate substantial cost to the organisms that carry them. Such segregation distorters are predicted to either reach fixation (potentially causing population extinction) or, more commonly, promote the evolution of genetic suppression to restore transmission to equality. Many populations show rapid spread of segregation distorters, followed by the rapid evolution of suppression. However, not all drivers display such flux, some instead persisting at stable frequencies in natural populations for decades, perhaps hundreds of thousands of years, with no sign of suppression evolving or the driver spreading to fixation. This represents a major evolutionary paradox. How can drivers be maintained in the long term at stable frequencies? And why has suppression not evolved as in many other gene drive systems? Here, we explore potential factors that may explain the persistence of drive systems, focusing on the ancient sex-ratio driver in the fly Drosophila pseudoobscura. We discuss potential solutions to the evolutionary mystery of why suppression does not appear to have evolved in this system, and address how long-term stable frequencies of gene drive can be maintained. Finally, we speculate whether ancient drivers may be functionally and evolutionarily distinct to young drive systems.
Transcontinental dispersal of Anopheles gambiae occurred from West African origin via serial founder events
14311H. Schmidt, Y. Lee, T. C. Collier, M. J. Hanemaaijer, O. D. Kirstein, A. Ouledi, M. Muleba, D. E. Norris, M. Slatkin, A. J. Cornel and G. C. Lanzaro, Communications Biology, 2. 2019-12-19 12:47:18.
Here we present population genomic analyses of 111 specimens sampled from west to east Africa, including the first whole genome sequences from oceanic islands, the Comoros.
Exterminator genes: The right to say no to ethics dumping
5654Bassey-Orovwuje, M., J. Thomas and T. Wakeford, Development, 62:121-127. 2019-12-17 18:09:38.
The scientific-industrial complex is promoting a new wave of genetically modified organisms, in particular gene drive organisms, using the same hype with which they tried to persuade society that GMOs would be a magic bullet to solve world hunger. The Gates Foundation claims that GDOs could help wipe out diseases such as malaria. Powerful conservation lobby groups claim GDOs will protect engendered species. Not only are the benefits from GDOs based, like their predecessors, on flawed ecological thinking, but they are backed by the same agri-business interests that have devastated agroecological farming systems. The rights of communities to say ‘no’ to new genetic technologies is being eroded, despite United Nations agreements, such as the Convention on Biological Diversity, which call for the free, prior and informed consent of affected communities to be respected. By exporting their field trials to countries with weak regulatory regimes and lowering of the standards of consent the Gates Foundation’s Target Malaria project has already been guilty of ethics dumping. These developments demonstrate the urgent need to democratize the development of new technologies.
A selfish genetic element linked to increased lifespan impacts metabolism in female house mice
5652Lopes, P. C. and A. K. Lindholm, The Journal of Experimental Biology, 2019:212704. 2019-12-17 18:01:15.
Gene drive systems can lead to the evolution of traits that further enhance the transmission of the driving element. In gene drive, one allele is transmitted to offspring at a higher frequency than the homologous allele. This has a range of consequences, which generally include a reduction in fitness of the carrier of the driving allele, making such systems “selfish”. The t haplotype is one such driver, found in house mice. It is linked to a reduction in litter size in matings among heterozygous animals, but also to increased lifespan in wild females that carry it. Here, we tested whether carrying the t haplotype was associated with altered resting metabolic rate (RMR). We show that females carrying the t haplotype decrease RMR as they increase in size, compared to wildtype females or males of either genotype. Our study elucidates a plausible mechanism by which a selfish genetic element increases lifespan.
A cross-sectional survey of biosafety professionals regarding genetically modified insects
5650O’Brochta, D. A., W. K. Tonui, B. Dass and S. James, Applied Biosafety, 2019:1-9. 2019-12-17 17:57:33.
Background:Genetic technologies such as gene editing and gene drive create challenges for existing frameworks used to assess risk and make regulatory determinations by governments and institutions. Insect genetic technologies including transgenics, gene editing, and gene drive may be particularly challenging because of the large and increasing number of insect species being genetically modified and the degree of familiarity with these organisms and technologies by biosafety officials charged with making containment decisions.Methods:An anonymous online survey of biosafety professionals was distributed to the membership of ABSA International, a global society of biosafety professionals, to investigate their perspectives on their preparedness to meet these new challenges.Results:Existing guidance used to make containment decisions for nongenetically modified insects was widely seen as adequate, and most respondents thought the available guidance for making containment decisions for genetically modified insects with and without gene drives was inadequate. Most respondents reported having less confidence in their decisions concerning containment of genetically modified insects compared to decisions involving genetically modified microbes, (noninsect) animals, and plants.Conclusions:These results reveal a need for additional support for biosafety professionals to improve the quality of and confidence in containment decisions regarding genetically modified insects with and without gene drive. These needs might be addressed by increasing training, updating existing guidance, creating new guidance, and creating a third-party accreditation entity to support institutions. Sixty percent of the respondents said they either would or might use a voluntary third-party accreditation service to support insect containment decisions.
The potential for a released autosomal X-shredder becoming a driving-Y chromosome and invasively suppressing wild populations of malaria mosquitoes
5648Alcalay, Y., S. Fuchs, R. Galizi, F. Bernardini, R. E. Haghighat-Khah, D. B. Rusch, J. R. Adrion, M. W. Hahn, P. Tortosa and P. A. Papathanos, bioRxiv, 2019:860551. 2019-12-17 17:51:02.
Synthetic sex-ratio distorters based on X-chromosome shredding are predicted to be more efficient than sterile males for population suppression of malaria mosquitoes using genetic control. X chromosome shredding operates through the targeted elimination of X-chromosome-bearing gametes during male spermatogenesis, resulting in males that have a high fraction of male offspring. Strains harboring autosomal constructs containing a modified endonuclease I-PpoI have now been developed in the malaria mosquito Anopheles gambiae, resulting in strong sex-ratio distortion towards males. Data are being gathered for these strains for submission of regulatory dossiers for contained use and subsequent field release in West Africa. Since autosomal X shredders are transmitted in a Mendelian fashion and can be selected against their frequency in the population is expected to decline once releases are halted. However, any unintended transfer of the X-shredder to the Y-chromosome could theoretically change these dynamics: This could lead to 100% transmission of the newly Y-linked X-shredder to the predominant male-biased offspring and its insulation from negative selection in females, resulting in its potential spread in the population and ultimately to suppression. Here, we analyze plausible mechanisms whereby an autosomal X-shredder could become linked to the Y-chromosome after release and provide data regarding its potential for activity should it become linked to the Y-chromosome. Our results strongly suggest that Y-chromosome linkage through remobilization of the transposon used for the initial genetic transformation is unlikely, and that, in the unexpected event that the X-shredder becomes linked to the Y-chromosome, expression and activity of the X-shredder would likely be inhibited by meiotic sex chromosome inactivation. We conclude that a functioning X-shredding based Y-drive resulting from a naturally induced transposition or translocation of the transgene onto the Y-chromosome is unlikely.
Plasmodium falciparum (Haemosporodia: Plasmodiidae) and O’nyong-nyong virus development in a transgenic Anopheles gambiae (Diptera: Culicidae) strain
5634Mumford, J. D., C. A. Long, S. C. Weaver, K. Miura, E. Wang, R. Rotenberry, E. M. Dotson and M. Q. Benedict, " Journal of Medical Entomology, 56:936-941. 2019-12-17 16:55:10.
ransgenic Anopheles gambiae Giles (Diptera: Culicidae) mosquitoes have been developed that confer sexual sterility on males that carry a transgene encoding a protein which cuts ribosomal DNA. A relevant risk concern with transgenic mosquitoes is that their capacity to transmit known pathogens could be greater than the unmodified form. In this study, the ability to develop two human pathogens in these transgenic mosquitoes carrying a homing endonuclease which is expressed in the testes was compared with its nontransgenic siblings. Infections were performed with Plasmodium falciparum (Welch) and o’nyong-nyong virus (ONNV) and the results between the transgenic and nontransgenic sibling females were compared. There was no difference observed with ONNV isolate SG650 in intrathoracic infections or the 50% oral infectious dose measured at 14 d postinfection or in mean body titers. Some significant differences were observed for leg titers at the medium and highest doses for those individuals in which virus titer could be detected. No consistent difference was observed between the transgenic and nontransgenic comparator females in their ability to develop P. falciparum NF54 strain parasites. This particular transgene caused no significant effect in the ability of mosquitoes to become infected by these two pathogens in this genetic background. These results are discussed in the context of risk to human health if these transgenic individuals were present in the environment.
Genetically engineering wild mice to combat Lyme disease: An ecological perspective
5631Snow, A. A., BioScience, 69:746-756. 2019-12-17 16:51:55.
Genetic engineering of wild populations has been proposed for reducing human diseases by altering pathogens’ hosts. For example, CRISPR- based genome editing may be used to create white-footed mice (Peromyscus leucopus) that are resistant to the Lyme disease spirochete vectored by blacklegged ticks (Ixodes scapularis). Toward this goal, academic researchers are developing Lyme-resistant and tick-resistant white-footed mice, which are a primary pathogen reservoir for Lyme disease in the United States. If field trials on small, experimental islands are successful, the project would scale up to the larger islands of Nantucket and Martha’s Vineyard, Massachusetts, and possibly to the mainland, most likely with a local gene drive to speed the traits’ proliferation, pending approvals from relevant constituents. Despite considerable publicity, this project has yet to be evaluated by independent professional ecologists. In the present article, I discuss key ecological and evolutionary questions that should be considered before such genetically engineered mice are released into natural habitats
What risk assessments of genetically modified organisms can learn from institutional analyses of public health risks
5628Rajan, S. R. and D. K. Letourneau, Journal of Biomedicine and Biotechnology, 2012:8. 2019-12-17 16:46:43.
The risks of genetically modified organisms (GMOs) are evaluated traditionally by combining hazard identification and exposure estimates to provide decision support for regulatory agencies. We question the utility of the classical risk paradigm and discuss its evolution in GMO risk assessment. First, we consider the problem ofuncertainty, by comparing risk assessment for environmental toxins in the public health domain with genetically modified organisms in the environment; we use the specific comparison of an insecticide to a transgenic, insecticidal food crop. Next, we examine normal accident theory (NAT) as a heuristic to consider runaway effects ofGMOs, such as negative community level consequences of gene flow from transgenic, insecticidal crops. These examples illustrate how risk assessments are made more complex and contentious by both their inherent uncertainty and the inevitability of failure beyond expectation in complex systems. We emphasize the value of conducting decision-support research, embracing uncertainty, increasing transparency, and building interdisciplinary institutions that can address the complex interactions between ecosystems and society. In particular, we argue against black boxing risk analysis, and for a program to educate policy makers about uncertainty and complexity, so that eventually, decision making is not the burden that falls upon scientists but is assumed by the public at large
Design and analysis of CRISPR-based underdominance toxin-antidote gene drives
5626Champer, J., S. E. Champer, I. Kim, A. G. Clark and P. W. Messer, bioRxiv, 861435:861435. 2019-12-17 16:38:34.
CRISPR gene drive systems offer a mechanism for transmitting a desirable transgene throughout a population for purposes ranging from vector-borne disease control to invasive species suppression. In this simulation study, we model and assess the performance of several CRISPR-based underdominance gene drive constructs employing toxin-antidote principles. These drives disrupt the wild-type version of an essential gene using a CRISPR nuclease (the toxin) while simultaneously carrying a recoded version of the gene (the antidote). Drives of this nature allow for releases that could be potentially confined to a desired geographic location. This is because such drives have a nonzero invasion threshold frequency, referring to the critical frequency required for the drive to spread through the population. We model drives which target essential genes that are either haplosufficient or haplolethal, using nuclease promoters with expression restricted to the germline, promoters that additionally result in cleavage activity in the early embryo from maternal deposition, and promoters that have ubiquitous somatic expression. We also study several possible drive architectures, considering both “same-site” and “distant-site” systems, as well as several reciprocally targeting drives. Together, these drive variants provide a wide range of invasion threshold frequencies and options for both population modification and suppression. Our results suggest that CRISPR toxin-antidote underdominance drive systems could allow for the design of highly flexible and potentially confinable gene drive strategies.
Disrupting female flight in the vector Aedes aegypti
5624O'Leary, S. and Z. N. Adelman, bioRxiv, 862300:862300. 2019-12-17 16:35:43.
Aedes aegypti is a vector of dengue, chikungunya, and Zika viruses. Current vector control strategies such as community engagement, source reduction, and insecticides have not been sufficient to prevent viral outbreaks. Thus, interest in novel strategies involving genetic engineering is growing. Female mosquitoes rely on flight to mate with males and obtain a bloodmeal from a host. We hypothesized that knockout of genes specifically expressed in female mosquitoes associated with the indirect flight muscles would result in a flightless female mosquito. With the CRISPR-Cas9 system, we performed embryonic microinjections of Cas9 protein and guide RNAs specific to genes hypothesized to control flight in mosquitoes, and have obtained genetic knockouts in several genes specifically expressed in the flight-muscle, including those specific to female flight muscle. Analysis of the phenotype of these female-specific gene knockout mutants resulted in flightless females and flying males. While further assessment is required, this work lays the groundwork for a mechanism of population control that is female-specific for the Ae. aegypti vector.
Maintenance of fertility in the face of meiotic drive
5622Meade, L., S. Finnegan, R. Kad, K. Fowler and A. Pomiankowsk, The American Naturalist, 2019:2019. 2019-12-17 16:32:30.
Selfish genetic elements that gain a transmission advantage through the destruction of sperm have grave implications for drive male fertility. In the X-linked SR meiotic drive system of a stalk-eyed fly, we found that drive males have greatly enlarged testes and maintain high fertility despite the destruction of half their sperm, even when challenged with fertilizing large numbers of females. Conversely, we observed reduced allocation of resources to the accessory glands that probably explains the lower mating frequency of SR males. Body size and eyespan were also reduced, which are likely to impair viability and pre-copulatory success. We discuss the potential evolutionary causes of these differences between drive and standard males.
The analytical review on futuristic use of CRISPR-Cpf1 aided gene drive technology
5618Satyam, R., N. Singh and T. Bhardwaj, International Journal of Trend in Scientific Research and Development, 2:525-530. 2019-12-17 16:27:59.
Organisms edited by gene editing or traditional selective breeding are typically less able to survive and reproduce which effectively prevents those alterations from spreading in the wild populations. This paper focuses on how the CRISPR-Cpf1 system can be used to build a Gene Drive capable of spreading particular alterations in the wild population, and its potential applications. Named for the ability to "drive" themselves and nearby genes through populations of organisms over many generations. Normally, the sexually reproducing organism comprises of 50-50% genetic information from both parents. But with gene drive, you can have 100% chance of passing a particular gene. The discovery of new Gene Editing Technology, based on the bacterial immune system, allow us to edit genome at specific sites with more precision, accuracy and ease. CRISPR Gene Drives including the edited version of the targeted gene and additional sequences with the DNA cutting Cpf1 protein and Guide RNA gene. When an organism containing a Gene Drive, mates with the wild counterparts, the offspring inherit one altered and one original copy of the target gene. The Guide RNAs Cpf1 directs to cut the original copy which is repaired by copying the altered gene as template synthesizing Gene Drive sequence in its place. Because the organism now has two identical copies of the alteration and the Gene Drive one on each chromosome, all of the organism will inherit both components. The same process will be repeated in subsequent generation causing the altered gene and Gene Drive to spread into the entire wild population. The Gene Drive technology has the potential to save millions of lives and give us unprecedented control over the natural world. This technology can be used to eradicate insect-born diseases, empower sustainable agriculture and promote ecological conservation.
An assessment of the immune costs associated with meiotic drive elements in Drosophila
5614Lea, J. K. and R. L. Unckless, Proceedings of the Royal Society B: Biological Sciences, 286:20191534. 2019-12-17 16:21:00.
Most organisms are constantly adapting to pathogens and parasites that exploit their host for their own benefit. Less studied, but perhaps more ubiquitous, are intragenomic parasites or selfish genetic elements. These include transposable elements, selfish B chromosomes and meiotic drivers that promote their own replication without regard to fitness effects on hosts. Therefore, intragenomic parasites are also a constant evolutionary pressure on hosts. Gamete-killing meiotic drive elements are often associated with large chromosomal inversions that reduce recombination between the drive and wild-type chromosomes. This reduced recombination is thought to reduce the efficacy of selection on the drive chromosome and allow for the accumulation of deleterious mutations. We tested whether gamete-killing meiotic drive chromosomes were associated with reduced immune defence against two bacterial pathogens in three species of Drosophila. We found little evidence of reduced immune defence in lines with meiotic drive. One line carrying the Drosophila melanogaster autosomal Segregation Distorter did show reduced defence, but we were unable to attribute that reduced defence to either genotype or immune gene expression differences. Our results suggest that though gamete-killing meiotic drive chromosomes probably accumulate deleterious mutations, those mutations do not result in reduced capacity for immune defence.
Invasive insects: Management methods explored
5612McLaughlin, G. M. and P. K. Dearden, Journal of Insect Science, 19:1-9. 2019-12-17 16:18:09.
Invasive insect species can act as a plague across the globe, capable of vast expansion and rapid, proliferate reproduction. The spread of pathogens of serious diseases such as malaria and Zika virus and damages to agricultural crops number some of the afflictions invasive insects provide to humans alone. Additionally, an escape from predators can fail to keep invasive insects in check, providing potential threats such as extra resource competition to native species when insects invade. A variety of methods are employed to combat these invasive species, each with their own varying levels of success. Here, we explore the more traditional methods of invasive insect pest control, such as pesticides and biological control. In lieu of several unintended consequences resulting from such practices, we suggest some should be abandoned. We evaluate the potential of new techniques, in particular, those with a genetic component, regarding the costs, benefits and possible consequences of implementing them. And finally, we consider which techniques should be the focus of future research, if we truly wish to manage or even eradicate invasive insects in their introduced lands.
Winning the tug-of-war between effector gene design and pathogen evolution in vector population replacement strategies
5609Marshall, J. M., R. R. Raban, N. P. Kandul, J. R. Edula, T. M. León and O. S. Akbari, Frontiers in Genetics, 10:1072. 2019-12-17 16:13:33.
While efforts to control malaria with available tools have stagnated, and arbovirus outbreaks persist around the globe, the advent of clustered regularly interspaced short palindromic repeat (CRISPR)-based gene editing has provided exciting new opportunities for genetics-based strategies to control these diseases. In one such strategy, called “population replacement”, mosquitoes, and other disease vectors are engineered with effector genes that render them unable to transmit pathogens. These effector genes can be linked to “gene drive” systems that can bias inheritance in their favor, providing novel opportunities to replace disease-susceptible vector populations with disease-refractory ones over the course of several generations. While promising for the control of vector-borne diseases on a wide scale, this sets up an evolutionary tug-of-war between the introduced effector genes and the pathogen. Here, we review the disease-refractory genes designed to date to target Plasmodium falciparum malaria transmitted by Anopheles gambiae, and arboviruses transmitted by Aedes aegypti, including dengue serotypes 2 and 3, chikungunya, and Zika viruses. We discuss resistance concerns for these effector genes, and genetic approaches to prevent parasite and viral escape variants. One general approach is to increase the evolutionary hurdle required for the pathogen to evolve resistance by attacking it at multiple sites in its genome and/or multiple stages of development. Another is to reduce the size of the pathogen population by other means, such as with vector control and antimalarial drugs. We discuss lessons learned from the evolution of resistance to antimalarial and antiviral drugs and implications for the management of resistance after its emergence. Finally, we discuss the target product profile for population replacement strategies for vector-borne disease control. This differs between early phase field trials and wide-scale disease control. In the latter case, the demands on effector gene efficacy are great; however, with new possibilities ushered in by CRISPR-based gene editing, and when combined with surveillance, monitoring, and rapid management of pathogen resistance, the odds are increasingly favoring effector genes in the upcoming evolutionary tug-of-war.
Identification and characterisation of a Masculinizer homolog in the diamondback moth Plutella xylostella
5607Harvey-Samuel, T., V. C. Norman, R. Carter, E. Lovett and L. Alphey, Insect Molecular Biology, 2019:2019. 2019-12-17 16:09:12.
Recently, a novel sex-determination system was identified in the silkworm (Bombyx mori) in which a piRNA encoded on the female-specific W chromosome silences a Z-linked gene (Masculinizer) which would otherwise initiate male sex-determination and dosage compensation. Masculinizer provides various opportunities for developing improved genetic pest management tools. A pest lepidopteran in which a genetic pest management system has been developed, but which would benefit greatly from such improved designs, is the diamondback moth, Plutella xylostella. However, Masculinizer has not yet been identified in this species. Here, focusing on the previously described ?masculinizing? domain of B. mori Masculinizer, we identify P. xylostella Masculinizer (PxyMasc). We show that PxyMasc is Z-linked, regulates sex-specific alternative splicing of doublesex and is necessary for male survival. Similar results in B. mori suggest this survival effect is possibly through failure to initiate male dosage compensation. The highly conserved function and location of this gene between these two distantly related lepidopterans suggests a deep role for Masculinizer in the sex-determination systems of the Lepidoptera.
A novel drug-inducible sex separation technique for insects
5605Kandul, N. P., J. Liu, A. D. Hsu, B. A. Hay and O. S. Akbari, bioRxiv, 2019:2019.12.13.875716. 2019-12-17 16:05:02.
Large sterile male releases are the gold standard for most insect population control methods and thus precise sex sorting is essential to the success of these technologies. Sex sorting is especially important for mosquito control because female mosquitoes bite and transmit diseases. However, current methods for insect sex sorting have deficiencies as they are error prone, low throughput, expensive, reduce male fitness, or lack cross species adaptability. Here we describe a novel drug-inducible system for insect sex-separation that demonstrates proof-of-principle for positive sex selection in D. melanogaster. The system exploits the toxicity of commonly used broad-spectrum antibiotics geneticin and puromycin and rescues only one sex. Sex specific rescue is achieved by inserting the sex-specific introns, TraF and DsxM, into the coding sequence of antibiotic resistance genes, NeoR or PuroR. We engineer a dual sex-sorter gene cassette and demonstrate sex specific, constitutive expression of NeoR and PuroR proteins in females and males, respectively. When raised on geneticin supplements, this sex-sorter line established 100% positive selection for female progeny, while the food supplemented with puromycin generated 100% male progeny. This system is 100% efficient and operates at remarkably low fitness costs in D. melanogaster. Since the described system exploits a conserved sex-specific splicing mechanism and reagents, which are active in many insects, it has the potential to be adaptable to insect species of medical and agricultural importance.
Gene drive and resilience through renewal with next generation Cleave and Rescue selfish genetic elements
5602Oberhofer, G., T. Ivy and B. A. Hay, bioRxiv, 2019:2019.2012.2013.876169. 2019-12-17 16:01:29.
Gene drive-based strategies for modifying populations face the problem that genes encoding cargo and the drive mechanism are subject to separation, mutational inactivation, and loss of efficacy. Resilience, an ability to respond to these eventualities in ways that restore population modification with functional genes is needed for long-term success. Here we show that resilience can be achieved through cycles of population modification with Cleave and Rescue (ClvR) selfish genetic elements. ClvR comprises a DNA sequence-modifying enzyme such as Cas9/gRNAs that disrupts endogenous versions of an essential gene, and a recoded version of the essential gene resistant to cleavage. ClvR spreads by creating conditions in which those lacking ClvR die because they lack functional versions of the essential gene. Cycles of modification can in principal be carried out if two ClvR elements targeting different essential genes are located at the same genomic position, and one of them, ClvRn+1, carries a Rescue transgene from an earlier element, ClvRn. ClvRn+1 should spread within a population of ClvRn, while also bringing about a decrease in its frequency. To test this hypothesis we first show that multiple ClvRs, each targeting a different essential gene, function when located at a common chromosomal position in Drosophila. We then show that when several of these also carry the Rescue from a different ClvR, they spread to transgene fixation in populations fixed for the latter, and at its expense. Therefore, genetic modifications of populations can be overwritten with new content, providing an ongoing point of control.
A bacterial gene-drive system efficiently edits and inactivates a high copy number antibiotic resistance locus
5595Valderrama, J. A., S. S. Kulkarni, V. Nizet and E. Bier, Nature Communications, 10:5726. 2019-12-17 15:48:28.
Gene-drive systems in diploid organisms bias the inheritance of one allele over another. CRISPR-based gene-drive expresses a guide RNA (gRNA) into the genome at the site where the gRNA directs Cas9-mediated cleavage. In the presence of Cas9, the gRNA cassette and any linked cargo sequences are copied via homology-directed repair (HDR) onto the homologous chromosome. Here, we develop an analogous CRISPR-based gene-drive system for the bacterium Escherichia coli that efficiently copies a gRNA cassette and adjacent cargo flanked with sequences homologous to the targeted gRNA/Cas9 cleavage site. This “pro-active” genetic system (Pro-AG) functionally inactivates an antibiotic resistance marker on a high copy number plasmid with ~ 100-fold greater efficiency than control CRISPR-based methods, suggesting an amplifying positive feedback loop due to increasing gRNA dosage. Pro-AG can likewise effectively edit large plasmids or single-copy genomic targets or introduce functional genes, foreshadowing potential applications to biotechnology or biomedicine.
Development of genetic control strategies for insect pests using CRISPR/Cas9 Développement de méthodes de lutte génétique contre de l’insecte nuisible basé sur le system CRISPR/Cas9
18505E. Green, Université de Strasbourg, 2019-12-17 14:20:21.
nsect pest control remains an important economic, environmental, and public health challenge. CRISPR/Cas9 gene drive (GD) is a novel genetic control strategy. GDs are genetic systems that can rapidly invade a population. This manuscript presents my efforts to develop gene drives in two important pest species, Anopheles gambiae, a major vector of malaria, and Drosophila suzukii, a global crop pest. The goals of this project were to develop a suppression gene drive in D. suzukii, to reduce population size, and a modification drive in An. gambiae, to reduce malaria transmission. While I was unable to produce a functional gene drive in D. suzukii, the efforts and protocols presented here can serve as a baseline for future work in this economically important crop pest. In An. gambiae, I successfully characterized two transgenic lines, one of which significantly blocks malaria transmission to a rodent model. Finally, I present my efforts to engineer a new modification gene drive strategy, indirect gene drive.
Genetic Control of Mosquitoes
5588Alphey, L., Annual Review of Entomology, 59:205-224. 2019-12-16 19:01:55.
Genetics can potentially provide new, species-specific, environmentally friendly methods for mosquito control. Genetic control strategies aim either to suppress target populations or to introduce a harm-reducing novel trait. Different approaches differ considerably in their properties, especially between self-limiting strategies, where the modification has limited persistence, and self-sustaining strategies, which are intended to persist indefinitely in the target population and may invade other populations. Several methods with different molecular biology are under development and the first field trials have been completed successfully.
Community Engagement Prior to a Small-Scale Pilot of the Sterile Insect Technique in Kwazulu-Natal, South Africa 2018
25918P. N. Manana, J. Zikhali, D. Dlamini, S. Gumede, N. Mabaso, T. Mpungose and G. Munhenga, Journal of Public Health and Disease Prevention, 2. 2019-12-16 13:14:53.
Approximately 165 000 listeners were engaged during two 30 minute radio interviews at a local radio station. Two hundred and fifty farm workers, several outpatients from primary health care facilities and 1400 secondary school pupils were given education on malaria transmission and control strategies including SIT. Furthermore, two road shows; one in areas around Mamfene and a second at KwaPhuza market, were done. In total, 447 falciparum-specific rapid diagnostic tests were conducted with 20 people testing positive. These patients were immediately treated for malaria. Conclusions: The campaigns showed that the majority of community members are informed concerning malaria transmission and control. However, there is a lack of understanding regarding the SIT as a vector control option. A more extensive public awareness programme on SIT as a vector control strategy is recommended to prepare the community of Mamfene for future small field pilot sterile male mosquito releases.
Mass-Rearing of Drosophila suzukii for Sterile Insect Technique Application: Evaluation of Two Oviposition Systems
17766F. Sassù, K. Nikolouli, S. Caravantes, G. Taret, R. Pereira, M. J. B. Vreysen, C. Stauffer and C. Cáceres, Insects, 10. 2019-12-12 15:07:36.
Drosophila suzukii (Diptera: Drosophilidae) is an invasive pest of a wide range of commercial soft-skinned fruits. To date, most management tactics are based on spraying of conventional and/or organic insecticides, baited traps, and netting exclusion. Interest has been expressed in using the sterile insect technique (SIT) as part of area-wide integrated pest management (AW-IPM) programs to control D. suzukii infestations. Mass-rearing protocols are one of the prerequisites for successful implementation of the SIT. To establish mass-rearing methods for this species, two different egg-collection systems were developed and compared with respect to the number of eggs produced, egg viability, pupa and adult recovery, adult emergence rate, and flight ability. Female flies kept in cages equipped with a wax panel produced significantly more eggs with higher viability and adult emergence rate, as compared to the netted oviposition system. The wax panel system was also more practical and less laborious regarding the collection of eggs. Furthermore, the wax panel oviposition system can be adapted to any size or design of an adult cage. In conclusion, this system bears great promise as an effective system for the mass production of D. suzukii for SIT.
