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.
Meiotic Cas9 expression mediates gene conversion in the male and female mouse germline
19726A. J. Weitzel, H. A. Grunwald, C. Weber, R. Levina, V. M. Gantz, S. M. Hedrick, E. Bier and K. L. Cooper, PLOS Biology, 19:e3001478. 2021-12-23 12:46:23.
Highly efficient gene conversion systems have the potential to facilitate the study of complex genetic traits using laboratory mice and, if implemented as a “gene drive,” to limit loss of biodiversity and disease transmission caused by wild rodent populations. We previously showed that such a system of gene conversion from heterozygous to homozygous after a sequence targeted CRISPR/Cas9 double-strand DNA break (DSB) is feasible in the female mouse germline. In the male germline, however, all DSBs were instead repaired by end joining (EJ) mechanisms to form an “insertion/deletion” (indel) mutation. These observations suggested that timing Cas9 expression to coincide with meiosis I is critical to favor conditions when homologous chromosomes are aligned and interchromosomal homologydirected repair (HDR) mechanisms predominate. Here, using a Cas9 knock-in allele at the Spo11 locus, we show that meiotic expression of Cas9 does indeed mediate gene conversion in the male as well as in the female germline. However, the low frequency of both HDR and indel mutation in both male and female germlines suggests that Cas9 may be expressed from the Spo11 locus at levels too low for efficient DSB formation. We suggest that more robust Cas9 expression initiated during early meiosis I may improve the efficiency of gene conversion and further increase the rate of “super-mendelian” inheritance from both male and female mice.
Weakly deleterious natural genetic variation amplifies probability of resistance in multiplexed gene drive systems
19904B. S. Khatri and A. Burt, bioRxiv, 2021.12.23.473701. 2021-12-23 08:31:18.
Evolution of resistance is a major barrier to successful deployment of gene drive systems to suppress natural populations. Multiplexed guide RNAs that require resistance mutations in all target cut sites is a promising strategy to overcome resistance. Using novel stochastic simulations that accurately model evolution at very large population sizes, we explore the probability of resistance due to three important mechanisms: 1) non-homologous end-joining mutations, 2) single nucleotide mutants arising de novo or, 3) single nucleotide polymorphisms pre-existing as standing variation. If the fraction of functional end-joining mutants is rare, we show that standing variation dominates, via a qualitatively new phenomenon where weakly deleterious variants significantly amplify the probability of multi-site resistance. This means resistance can be probable even with many target sites in not very large populations. This result has broad application to resistance arising in multi-site evolutionary scenarios including the evolution of vaccine escape mutations in large populations.Competing Interest StatementThe authors have declared no competing interest.
Interaction Between Entomology and Gene Technology: Bt-transgenic and Gene Drives for Pests Control .
20105J. C. Ndayıragıje, T. Özek, H. Çevik and İ. Karaca, Türk Bilim ve Mühendislik Dergisi, 3:108-115. 2021-12-22 17:00:56.
Pest control is the major agricultural activity for increasing crop productivity thus insuring food security. Recent pest management programs are depending too much on chemical pesticides, which are a threat to our health and environment. One of the greatest entomological achievements for the benefits of plant protection is the use of Bacillus thuringiensis to produce transgenic plants resisting pests. However, such organisms comprise inconveniences against human health and biodiversity in terms of genetic pollution. In many countries, the use of Genetically Modified Organisms is prohibited. This study review on integration of growing gene technology with actual scientific achievements can help to determine a sustainable solution to the pest’s problem. In this way, many literatures were referred on to comparatively criticize the effectiveness, safety and sustainability of gene drive over Bt transgenic based on scientific soundness. Gene drive technology is a new technic consisting of gene engineering and on-field monitoring of its transgenes. The case in point is the inappropriateness of Bt-transgenes. Practically, gene drive can be an alternative to Bacillus thuringiensis in pest control for increased safety and environmental protection.
chinmo-mutant spermatogonial stem cells cause mitotic drive by evicting non-mutant neighbors from the niche
19728C. Y. Tseng, M. Burel, M. Cammer, S. Harsh, M. S. Flaherty, S. Baumgartner and E. A. Bach, Developmental Cell, 2021-12-22 12:51:45.
Niches maintain a finite pool of stem cells via restricted space and short-range signals. Stem cells compete for limited niche resources, but the mechanisms regulating competition are poorly understood. Using the Drosophila testis model, we show that germline stem cells (GSCs) lacking the transcription factor Chinmo gain a competitive advantage for niche access. Surprisingly, chinmo(-/-) GSCs rely on a new mechanism of competition in which they secrete the extracellular matrix protein Perlecan to selectively evict non-mutant GSCs and then upregulate Perlecan-binding proteins to remain in the altered niche. Over time, the GSC pool can be entirely replaced with chinmo(-/-) cells. As a consequence, the mutant chinmo allele acts as a gene drive element; the majority of offspring inherit the allele despite the heterozygous genotype of the parent. Our results suggest that the influence of GSC competition may extend beyond individual stem cell niche dynamics to population-level allelic drift and evolution.
Temporal Viability of Aedes aegypti and Aedes albopictus Eggs Using Two Hygroscopic Substances as Preservatives under a Sterile Insect Technique (SIT) Program in Southern Mexico
19721E. N. Martínez-García, E. E. Díaz-González, C. F. Marina, J. G. Bond, J. J. Rodríguez-Rojas, G. Ponce-García, R. M. Sánchez-Casas and I. Fernández-Salas, Insects, 13. 2021-12-21 12:31:48.
Dengue and other Aedes-borne diseases have dramatically increased over the last decades. The Sterile Insect Technique (SIT) has been successfully used as part of integrated pest strategies to control populations of insect-plant and livestock pests and is currently being tested as a potential method to reduce mosquito populations in an environmentally friendly approach. However, during the mass rearing steps needed to produce millions of mosquitoes, egg storage and preservation are essential for a certain amount of time. Eggs of Aedes aegypti have a chorionic pad that functions as a sticky substance to glue them onto the inner walls of larval breeding sites. The chorionic pad is chemically made of hyaluronic acid, a hygroscopic compound, responsible to protect them from desiccation over time. Two commercial products with hygroscopic properties, hydrolyzed collagen, and Hyalurosmooth®, both were tested to assess their ability to prolong egg life storage for A. aegypti and A. albopictus. Results showed that 85–95% of Ae. aegypti eggs were able to hatch up to week 8 after being treated with both hydrophilic compounds, compared with the control 66.3%. These two substances showed promising effects for keeping Ae. aegypti eggs viable during prolonged storage in mass rearing insect production focused on vector control SIT programs.
Three Decades of Malaria Vector Control in Sudan: The Plausible Role of Sterile Insect Technique (SIT)
19977A. Elaagip and A. Adedapo, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:51:34.
In Northern State, Sudan, a feasibility study for sterile insect technique (SIT) in an area-wide integrated pest management was established for the first time in an African country. The aim of the study was to see whether it is feasible, from a technical, an economical and a biological perspective, to use sterile male mosquitoes to control mosquito populations in designated areas in the African context. The project was focussed on Anopheles arabiensis, one of the major malaria vectors. Meteorological data, larval surveillance and population genetic studies were carried out on the disease vectors. The first phase of the study focussed on the development of an efficient sex-separation system, development of dose-sterility curves for the pupal and adult stages and testing of a range of doses in competition experiments to determine effective sterility dose. This stage was followed by a semi-field phase that monitored their swarming and mating behaviours, effectiveness of irradiated males in competitive experiments with wild males and insemination rates. Information regarding irradiation and transportation of irradiated males were also obtained during the study. Unfortunately, the SIT study was terminated in 2017 before starting field release of irradiated males. In spite of the challenges, such investment need not be totally abandoned as valuable experience has been gained and capacity built, which are of high value to malaria control program in Sudan.
Perspectives into Genetic Manipulations for Control of Dengue Vector (Aedes aegypti Linnaeus, 1762) with Reference to Progress in Indian Experiments
19975R. Chatterjee, S. Bhattacharya and B. K. Tyagi, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:46:45.
Vector-borne diseases like malaria, dengue, chikungunya, Japanese encephalitis, Zika and others claim millions of lives across the globe annually, and as such their control has become an ardent necessity. Past attempts over the decades have introduced vector control through chemical, biological and environmental means. However, these measures, already in place, failed to completely bring down the mortality rates from vector-borne diseases, most of which lack a vaccine to prevent epidemics or even a specific antidote to treat patients. The modern development of technologies such as the release of insects carrying a dominant lethal (RIDL) gene system, an example of transgenesis; the Wolbachia-based cytoplasmic incompatibility inducing infertility in female insects, an example of paratransgenesis; and the revolutionary gene drive (CRISPR/Cas9) technology, has their roots in the sterile insect technology (SIT), which worked by creating sterilized males through irradiation to compete with their wild counterparts and subsequently mate with females in nature to produce infertile eggs; a technology meant to gradually and finally exterminate the vector population in nature. These technologies have shown great promise, albeit many imperfections, particularly regarding acceptance by the concerned societies. As far as vector control is concerned, we have attempted to simplify their definitions for the common man so that the intricate scientific jargon about these technologies do not instill any fear or doubts to the end users.
Aedes Control Using Sterile Insect Technique (SIT) in Malaysia
19973W. A. Nazni, G.-N. Teoh, S. I. Shaikh Norman Hakimi, M. A. Muhammad Arif, M. Tanusshni, M. A. Nuradila, A. Nurfarahin Hanini, I. A. Shazia, A.-M. Tan, H. Rabizah, M. D. Ahmad Zainuri, A. Hasnor Hadi, Y.-L. Cheong, A. Norazah, H. Maiga, R. S. Lees and L. H, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:41:43.
The continued occurrence of massive outbreaks of Aedes-borne viral diseases of dengue, chikungunya, Zika and yellow fever, in spite of intensive and extensive application of conventional control measures, necessitates application of new tools, such as sterile insect technique (SIT), to stem the tide. Sterile insect technique is a form of biological control method, whereby sterile male insects are released in overwhelming numbers in the wild. These sterile males compete with the wild males to mate with the wild females. The females mated with sterile males will produce sterile eggs that will not hatch. Sustained release of sterile males over a period of time will lead to suppression or elimination of the natural population. Sterility is induced by gamma ray from the radioisotope of cobalt-60 and cesium-137 or X-ray. SIT is safe, cost-effective and environmentally non-polluting, and insects are unable to develop resistance to this method. SIT has a strong track record of success in elimination of agricultural pests, and this led to increased interest in using SIT against mosquitoes of public health importance. Studies and trials against Aedes were conducted in the 1960s and, more recently, against Ae. albopictus with promising results. Attempts were also made to apply SIT for the control of Aedes in several countries. Malaysia’s first experience with SIT was in the 1990s, when the Malaysian Nuclear Agency teamed with the MARDI and local universities to sterilise an agricultural pest, the diamondback moth. To prepare for the possible threat of introducing the Old World screw worm (Chrysomya bezziana) into Australia from neighbouring countries, from 1995 to 2000, Australia and Malaysia undertook a collaborative myiasis control research project located at the Institut Haiwan, Kluang, Malaysia. The project assisted in suppression trials of the screw worm in Malaysia and supported research that developed and evaluated improved Old World screw worm suppression and eradication techniques. In 2014, in collaboration with the Malaysian Nuclear Agency, the IMR conducted preliminary studies to determine the optimum sterilising dose of gamma irradiation against Ae. aegypti. In addition, the impact of sterilisation on the biological parameters of Ae. aegypti was also determined. The most effective sterilising dose that did not adversely affect the male was determined to be 55 Gy. Subsequently, a new initiative of field release of sterile Aedes aegypti males for the control of dengue was initiated in 2019. This 2-year programme will aim to release gamma ray-sterilised Ae. aegypti males in three trial sites to reduce the natural mosquito population to a level below the threshold required for dengue transmission. To ensure public acceptance, public engagement, a prerequisite for a successful release programme, will be conducted intensively prior to the release.
Integrated Management of Malaria Vectors in Africa
19971R. Mbabazi, K. Maredia, B. B. El-Sayed, A. K. Babumba, M. Savadogo and O. Akinbo, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:36:56.
Malaria disease is a major public health burden in Africa. The control of malaria vectors is a critical component for prevention, management, and eradication of malaria disease. This chapter presents information on the current status of malaria vector control in Africa with emphasis on integrated vector management (IVM) programs. The chapter highlights innovative and emerging technologies such as sterile insect technique, gene drive, Wolbachia-based biological control, and other technologies for malaria vector control in Africa which can be integrated into IVM programs. The chapter also provides global resources on malaria vector management programs.
Engineering RNA Interference-Based Dengue Virus Resistance in the Mosquito Vector Aedes aegypti: The Current Status and Future Directions
19969S. D. Denipitiyage, Y. I. N. S. Gunawardene, Z. Federico and R. S. Dassanayake, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:32:49.
Dengue is an acute, febrile disease caused by the dengue viruses (DENV) comprising four serotypes and transmitted by the mosquito vector Ae. aegypti. DENV are single-stranded, positive-sense RNA viruses of the family Flaviviridae. Dengue is declared as a current significant challenge in the Southeast Asia, imposing growing burden on infected populations. To date, dengue control has mostly relied on vector control strategies which have largely become ineffective. There is, therefore, an urgent need for novel vector control strategies. Development of genetically modified mosquito vectors to manipulate disease-vectoring populations has gathered increased interest in recent time. RNAi-mediated viral resistance contributes to the suppression of viruses, including DENV in the mosquito vector Ae. aegypti. With recent advances in the field of molecular biology, we and other scientists are continuing to engineer genes that confer virus resistance to reduce transmission rates of DENV and introducing these genes into the mosquito genome. Even though scientists successfully generated mosquito refractory to DENV2–4, no mosquito refractory to all four serotypes has been developed to date. This limitation can be overcome by systematic analysis of the molecular mechanisms of RNAi in the mosquito vector Ae. aegypti. An enhanced understanding of RNAi function in the mosquito vector Ae. aegypti will facilitate the application of RNAi to control the transmission of the dengue disease in the future. Here, based on current understanding of the RNAi, we discuss the mechanisms of RNAi in the mosquito vector Ae. aegypti. We also provide guidelines for optimal design of RNAi experiments in Ae. aegypti with the possible risks associated with them along with proposed solutions.
Wolbachia: Biological Control Strategy Against Arboviral Diseases
19967I. Mohanty, A. Rath and R. K. Hazra, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:27:44.
Arboviral diseases like dengue, chikungunya, and Zika are among the major causes of mortality and morbidity in human population. The limited control methods together with lack of antiviral therapies and effective vaccines have paved way for new approaches. One such approach to reduce the ever alarming conflagration of vector-borne diseases is based on biological strategy that reduces or blocks pathogen transmission in the vector. In this context, Wolbachia, an endosymbiont in mosquitoes, is explored as a novel and ecofriendly control strategy. Wolbachia seems to confer resistance to diverse RNA viruses protecting lives from virus-induced mortality. This review envisages the deployment of Wolbachia technology in controlling several arboviral diseases.
Wolbachia Endosymbiont and Mosquito Vectors, with Emphasis on Lymphatic Filariasis Elimination
19965I. P. Sunish, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:24:11.
Wolbachia are maternally inherited intracellular bacteria, known to alter early development and mitotic processes in their hosts. They are frequently observed as a reproductive parasite, capable of inducing feminization, parthenogenesis, male killing, or cytoplasmic incompatibility. A total of 18 clades of Wolbachia have been reported, almost exclusively in arthropods. Wolbachia-based strategies have been proposed for the control of disease vectors. Wolbachia-based population suppression and transmission blocking can work in species not commonly infected with Wolbachia in the wild. However, efficient maintenance and spread of Wolbachia infection into field populations is crucial to the success of this strategy. Property of cytoplasmic incompatibility (CI) can be used to reduce the density of mosquito field populations through inundative releases of incompatible males in order to sterilize females. In semi-field condition at La Reunion, the LR[wPip(Is)] males of Culex quinquefasciatus successfully competed with field males in mating with field females. Depletion of Wolbachia endobacteria by antibiotic therapy prevents larval moulting and kills adult filarial worms. This strategy could act as an adjunct to vector control and is being exploited for the elimination of lymphatic filariasis.
Laboratory Biosafety in Handling Genetically Modified Mosquitoes
19963J. Charles, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:19:52.
One of the novel approaches in controlling vector-borne diseases is to release genetically modified mosquitoes in nature. Trial studies are done in different phases by the researches, both in the laboratory and in the fields. Before a GM mosquito is validated to be ready for field release, the same has to rigorously go through several phase studies, and Phase I being the laboratory is the most significant to set the future of the GM mosquito for future investigations. Though the risk of handling GM mosquitoes in laboratory is low, nevertheless there is a prescribed list of DOs and DON’Ts, and the laboratory workers are needed to strictly follow the SOPs or basic principles of biosafety like handling administrative controls, using biosafety equipment, wearing personal protective equipment, etc. The laboratory also should have a proper design as per the risk assessment. Accordingly, the biosafety laboratories (BSL) are classified into four types: type 1, 2, 3 and 4. The risks are assessed as per the factors in the host, vector and donor sequences and the environmental factors and their activities in such environments. As GMMs are of low risk, BSL 1 and 2 are enough for their manipulation, but occasionally BSL 3 may be needed. There may be chances of spillage on the working surfaces during manipulation of the genes which can be remedied by the spill management protocols. Biological wastes may be generated in all areas of manipulation. These can be properly treated by either chemical disinfection or autoclaving and disposed of by incineration. These wastes should be segregated in colour-coded bags before disposal. There may be some risks while transporting GMMs to distant places. They should be packed securely in triple-layer pack and sent for disposal following IATA and other road rules. For each process of the manipulation of gene, a separate standard operating procedure (SOP) should be maintained which has to be updated whenever any change in the procedure is made.
Safety Assessment of Novel Genetic Technologies for Vector Control: National and International Perspectives
19961V. Ahuja, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:15:26.
Novel genetic technologies provide an alternative approach for control of vectors particularly those carrying deadly pathogens. Genetic control technologies aim to either suppress target populations or modify the vector by introducing a heritable factor that reduces or blocks their ability to transmit the diseases. These technologies are thus referred to as population suppression or population modification approaches. Both these approaches offer significant advantages for vector control; however, there are associated biosafety concerns related to possible ecosystem interactions. Therefore, extensive testing on a case-by-case basis is required before these can be used as a public health intervention. This paper provides details of the international initiatives towards development of guidelines and status of regulations in India.
Measuring Public Attitudes to Releases of Transgenic Mosquitoes for Disease Control, with Special Reference to Dengue and Malaria
19958L. A. De Las Llagas and M. S. T. Gunigundo, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:10:05.
Since the advent of DDT in public health and agriculture, science leaped forward with revolutionary technology such as gene drive or editing, thus making it possible to develop alternative approaches to address vector-borne diseases. However, their utilization and sustenance in public life are dependent on public attitude, i.e., societal awareness and social acceptance. In the face of strong skepticism against genetically modified organisms in both developed and developing countries, public acceptance is therefore a requirement (Boete and Beisel 2013, and Bohannon 2002, as cited in De Souza et al. Understanding the requirements and factors necessary for the acceptance of genetically modified mosquitoes as a potential malaria control tool in Ghana: a questionnaire survey, AsPac J Biol Biotechnol 21(3):76–88, 2013).
Experiences and Outcomes from a Worldwide Training Programme on Genetically Modified Vectors (GMVs) Related Biosafety for Human Health and the Environment
19956B. K. Tyagi, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 11:04:33.
Partial to virtual lack of any impact on control of vectors of human diseases, especially mosquitoes, warranted urgent search for new alternate technologies which will be safe, economical and environment-friendly, on one hand, and integrate with other tools and methodologies of the integrated vector management (IVM), on the other. Past few decades have witnessed surge of many effective and sustainable genetically and biotechnologically developed de novo technologies which tend to control mosquito vectors by working either to suppress (transgenesis) or replace (paratransgenesis), besides an array of other physiological interventions, on the vector populations. Several technologies such as, for example, Release of insect carrying Dominant Lethal (RIDL) gene system, Wolbachia (an endocellular symbiotic bacterium naturally present in many arthropods) induced cytoplasmic incompatibility (CI) resulting in unviable egg production and transforming dengue vectors (Aedes spp.) and malaria vectors (e.g., Anopheles stephensi) into resistant to respective pathogens, i.e., viruses and Plasmodium, have offered promise in controlling vector-borne diseases. Notwithstanding unchallengeable significance, these technologies have also raised many questions from both societies and governments of many countries. To alleviate their scepticism and other queries, many international organizations conducted meetings to generate consensus for guidelines, but even this helped marginally to pacify global interrogations. It was, therefore, considered opportune by the Tropical Disease Research (TDR)/WHO to set up a series of multi-regional training workshops in Africa (Bamako, Mali), Asia (Madurai, India) and Latin America (Medellin, Colombia) between 2008 and 2011 (WHO 2015). About 150 trainees were drawn from as diverse disciplines/walks of life as science, health departments, academics, social, legal, non-governmental organization. The outcome, inculcated from the experiences expressed by the trainees themselves post-workshops, has been very encouraging as they all found the training courses highly beneficial to comprehend genetically modified vectors/mosquitoes (GMV/GMM) related biosafety to the human and the environment and thus become a potential ambassador in their areas or countries to strongly communicate and advocate about the lasting benefits of the various genetically evolved technologies in the control of mosquitoes responsible for transmission of dengue and malaria, in particular.
Advances in Aedes Mosquito Vector Control Strategies Using CRISPR/Cas9
19929P. D. S. U. Wickramasinghe, G. N. Silva, Y. I. N. Silva Gunawardene and R. S. Dassanayake, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 09:39:52.
Advancements in genetic engineering have resulted in the development of mosquitoes with impaired vector competence, thereby limiting acquisition and transmission of pathogens. The main dengue (DENV) vector, Aedes aegypti, is an invasive species that have spread unwittingly across the world as a result of human trade and travel. The Ae. aegypti mosquito species has spread across tropical and subtropical regions, with higher presence in urban regions where rapid breeding patterns have shown in artificial containers. Identification of and treating an adequate number of mosquito breeding sites as a control measure have been done for the past couple of years, and yet improvement is far from the expectations, even with well-funded and well-organized initiatives. In order to stop the pathogen transmission, genetically modified mosquitoes (GMM) needs to be created and released. Despite many Aedes-related achievements, GMM creation has been challenging. The spread of particular genetic elements that impair vector competence, trigger deleterious recessive mutations, or skew a population's sex ratio can be used to prevent the spread of vector disease, or eradicate invasive organisms in a species-specific and eco-friendly manner. In recent years, genome editing strategies have evolved to make use of a variety of nucleases, ranging from sequence-specific zinc finger nucleases to modular TALENs (transcription activator-like effector nucleases) and most recently, RNA-guided nucleases adapted from bacterial adaptive immune systems, dubbed CRISPR/Cas (clustered regularly interspaced palindromic repeats/CRISPR associated systems). By combining these methods, a new era in gene editing had emerged. Generally, both of these gene editing technologies utilize sequence-specific nucleases to generate double-stranded DNA breaks (or nicks) in the target sequence, resulting in desired DNA modifications using endogenous DNA repair mechanisms. Since cells with DNA lesions are unable to divide further, the nuclease-generated strand breaks must be rapidly repaired by the cell to maintain the viability. CRISPR/Cas has been widely accepted for use in a variety of organisms, including insect species, with only minor optimization steps needed thus far. CRISPR/Cas9 technology transformed the process of engineering nucleases capable of cleaving complex genomic sequences. A complementary guide RNA (gRNA) directs the Cas9 endonuclease's operation to the specific DNA target site, enabling the editing of virtually any DNA sequence without complex protein engineering and selection procedures. Apart from genome editing, the specificity and flexibility of the CRISPR/Cas9 method enables unprecedented rapid development of genetically modified organisms with mutation systems for disease vector insect control. The stability and expression of the gene construct generated by CRISPR/Cas9 or any other method must be addressed before GMM are released, in order to make sure that pathogen transmission and formulation are interrupted robustly and completely. Spreading foreign antipathogen genes through gene drive strategies among wild mosquito populations strengthens the case for a more streamlined approach. Major fields that must be adequately assessed include risk evaluation and management, conducting studies to ensure human and environmental protection, developing effective control strategies built on comprehensive gene-driving systems, and adequately addressing the ethical, legal, and social consequences of GMM release. Although GMM is theoretically feasible as a disease control method, field releases should be made only when strong scientific evidence of human and environmental protection and effectiveness are presented, and public acceptance is addressed appropriately. This chapter discusses the diverse technological advances in generating Ae. aegypti mosquitoes which are resistant to dengue virus (DENV) and other diseases, as well as the biosafety and risk assessment of these procedures. Additionally, the chapter outlines a convincing path forward for developing successful genetic-based DENV control strategies based on CRISPR/Cas9, which could be expanded to control other arboviruses while maintaining biosafety.
Genetic Improvements to the Sterile Insect Technique (SIT) for the Control of Mosquito Population
19927P. V. D. Dilani, Y. I. N. S. Gunawardene and R. S. Dassanayake, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 09:33:58.
Mosquito-borne diseases are becoming a major health problem worldwide. At present, the principal method of controlling these diseases entirely depends on the mosquito vector control strategies. However, traditional control methods which are focussed on reducing mosquito populations through environmental management and the application of insecticides are largely ineffective. Hence, various control methods, including the release of sterile insect technique (SIT), have been proposed for the reduction of the mosquito population. As a species-specific control strategy, SIT offers considerable environmental benefits and a chemical-free option for insect control. However, the application of the SIT to mosquito control consistently suffered from lack of efficient sexing system, high fitness cost and operational difficulty in ionizing radiation, density-dependent nature of the target mosquito population and various other technical issues. The intervention of genetic engineering has led to several improvements in the operation or security of SIT programmes. The advent of mosquito transgenesis has paved the way for novel approaches in mosquito control. One possibility is a release of insects carrying dominant lethal (RIDL) strategy by engineering self-limiting gene, which offers solutions for many drawbacks of traditional SIT by providing genetic sterilization, genetic sexing, genetic containment and provision of genetic markers while maintaining its environmentally benign and species-specific utility. The success of this strategy often depends on how genetic modification affects the fitness of the mosquitoes. With several improvements and modifications allowing minimum fitness load, RIDL is now available for a wide range of mosquitoes such as Aedes aegypti, Aedes albopictus and Anopheles stephensi with field-testing possibilities. However, with solid epidemiological evidence and community support, widespread implementation of these strategies might reverse the current alarming global mosquito vector-borne diseases.
Field Trials of Gene Drive Mosquitoes: Lessons from Releases of Genetically Sterile Males and Wolbachia-infected Mosquitoes
19925J. M. Marshall and V. N. Vásquez, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 09:27:08.
The discovery of CRISPR-based gene editing and its application to homing-based gene drive has been greeted with excitement, for its potential to control mosquito-borne diseases on a wide scale, and concern, for the invasiveness and potential irreversibility of a release. At the same time, CRISPR-based gene editing has enabled a range of self-limiting gene drive systems to be engineered with much greater ease, including (1) threshold-dependent systems, which tend to spread only when introduced above a certain threshold population frequency, and (2) temporally self-limiting systems, which display transient drive activity before being eliminated by virtue of a fitness cost. As these CRISPR-based gene drive systems are yet to be field-tested, plenty of open questions remain to be addressed, and insights can be gained from precedents set by field trials of other novel genetics-based and biological control systems, such as trials of Wolbachia-transfected mosquitoes, intended for either population replacement or suppression, and trials of genetically sterile male mosquitoes, either using the RIDL system (release of insects carrying a dominant lethal gene) or irradiation. We discuss lessons learned from these field trials and implications for a phased exploration of gene drive technology, including homing-based gene drive, chromosomal translocations, and split gene drive as a system potentially suitable for an intermediate release.
Arthropods of Medical Importance: Need for Genetic and Other Innovative Vector Control Technologies, with Emphasis on Eco-biosocial and Environmental Considerations.
19923B. K. Tyagi, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 09:22:08.
Among the world’s known vector groups, viz. arthropods, snails and rodents, the most important vectors originate from arthropods, the jointed legs. Arthropods are doubtlessly regarded as the most dominant creatures on the Earth due largely to their remarkable structural and behavioural diversity, besides humongous species preponderance. Of course, some of these arthropods are serious pests and/or vectors of human and animal diseases—deadly, debilitating and economy destructing. According to an estimate, arthropod species make approximately 80% of the global biological diversity. Born some 350–400 million years ago, they have of course achieved, to the utter envy of all other animal forms, a formidable genetic diversity and robustness so much so that they have virtually captivated pivotal human attention for centuries. They serve as a spectacular model of bioprospecting or laboratory experiments mostly because they are found in abundance, breed prodigiously and are exceptionally easier to culture or cultivate. For the aforesaid reasons, arthropods are also the easy target for genetic manipulations such as the transgenesis (using the release of insect carrying dominant lethal (RIDL) gene system or gene drive-based genome editing, e.g. CRISPR/Cas9, to suppress or replace the vector population) or paratransgenesis (e.g. deploying endosymbiont Wolbachia-induced cytoplasmic incompatibility for replacing natural vector population). In particular, the advent of CRISPR technology has excited the potential to engineer new game-changing technologies and innovative systems that can be used to control wild populations of mosquitoes. Two developments of particular interest are a self-limiting system termed precision-guided sterile insect technique (pgSIT) and a homing-based gene drive (HGD). The unique features of these systems can make them valuable tools to control vector mosquitoes in the future. All these biotechnological advancements in vector control are designed to fit well in the multi-methodical integrated vector management (IVM) strategy.
The Effects of Boric Acid Sugar Bait on Wolbachia Trans-Infected Male Aedes albopictus (ZAP Males®) in Laboratory Conditions
19917V. S. Aryaprema, W. A. Qualls, K. L. Dobson, S. L. Dobson and R.-D. Xue, Insects, 13. 2021-12-21 09:06:57.
The field release of Wolbachia trans-infected male mosquitoes, as well as the use of toxic sugar baits, is a novel and promising candidate technique for integrated mosquito management programs. However, the methods of action of the two techniques may not be complementary, because the Wolbachia method releases mosquitoes into the environment expecting a wild population reduction in subsequent generations while the toxic baits are intended to reduce the wild population by killing mosquitoes. This laboratory study was conducted to evaluate the effectiveness of boric acid toxic sugar baits on Wolbachia trans-infected male Aedes albopictus, relative to wild-type Ae. albopictus males. Wolbachia trans-infected (ZAP male®) and the wild-type Ae. albopictus males were exposed separately to 1% boric acid in a 10% sucrose solution in BugDorms. In the control test, the two groups were exposed to 10% sucrose solution without boric acid. Percent mortalities were counted for 24 h, 48 h and 72 h post exposure periods. The results show that 1% boric acid toxic sugar bait can effectively kill ZAP males under laboratory conditions, and the effectiveness was significantly higher after 24 h and 48 h, compared to wild-type male Ae. albopictus. This finding will help in planning and coordinating integrated mosquito management programs, including both Wolbachia trans-infected mosquito releases and the use of toxic sugar baits against Ae. albopictus.
Genetically Modified and other Innovative Vector Control Technologies
19912B. K. Tyagi, SpringerLink, 2021-12-21 08:48:19.
This book comprehensively covers the latest development in developing and deploying the genetically modified vectors, particularly Anopheles and Aedes mosquitoes responsible for transmitting malaria parasites and dengue viruses, the most deadly and/or debilitating among all the vector-borne diseases. It is considered timely and commensurate to bring about a book dealing with the various ecological, biological and social as well as regulatory aspects for the deployment of genetically modified vectors in special context with the biosafety of humans, his associates, and the environment. Written by an array of specialists and experts in various subjects of genetically modified organisms, this book centrally addresses the (i) basic principles of the genetic manipulation of vectors and they are potential impact on human and the environment, (ii) ecological, biological, ethical, legal and social implications of the use of genetically modified vectors, (iii) identification of potential hazards; assessment and management of risks for human and environment; risk/benefit analysis, (iv) principles and practices for the assessment and management of biosecurity and biosafety in laboratories (and in the field), (v) guiding principles for creation and management of institutional or national biosafety review boards and ethics review committees, and (vi) development and application of a biosafety regulatory framework and its related legal principles at national levels for securing the development and use of vector control methods based on genetic modification strategies.
Safe Application of Genetically Modified Mosquito (GMM) to Combat Dengue and Chikungunya Depends on Socioeconomic Status and Social Acceptance in the Developing Countries: A Comprehensive Analysis
19898M. N. Islam, Genetically Modified and other Innovative Vector Control Technologies, 2021-12-21 08:16:32.
The emerging and re-emerging vector-borne diseases are a serious public health problem throughout the world. It has been observed that more than 100 countries and approximately half of the world’s population are at risk on vector-borne diseases (VBDs). The global burden of the vector-borne diseases is unacceptably high. It alludes toward their functional inappropriateness, untimeliness, and irrelevance in controlling vectors and vector-borne diseases. Modern technologies, coupled with other appropriate ones within the precincts of integrated vector management (IVM), can tide over this situation posed by conventional, mostly insecticide-based, methodologies. A lot of challenges, obstacles, and interruptive factors have warranted urgent deployment of new approaches for the control of VBDs keeping in mind the inbuilt ethical, social, and regulatory issues. Genetically modified mosquito (GMM) technology is a complex and highly sophisticated biotechnological intervention for suppression of vector populations. Wolbachia-associated sterile insect technique (SIT) has been proved highly significant and effective for replacement of mosquito populations. Adopting a highly sophisticated GMM technology to suppress or replace the mosquito populations’ density is a big question in developing countries because their priority is directed to foremost fulfill the basic human rights to sustain. Yet, notwithstanding foreseeable bottlenecks, of paramount importance is the need to deploy GMM technology with due consideration to socioeconomic factors and availability of advanced biotechnological facilities during the application of GMM in the developing countries.
Malaria vector control tools in emergency settings: What do experts think? Results from a DELPHI survey
19785C. Boete, S. Burza, E. Lasry, S. Moriana and W. Robertson, Conflict and Health, 15:11. 2021-12-20 14:16:22.
Background The use and implementation of novel tools for malaria control such as long lasting impregnated bednets (LLINs) and Indoor Residual Spraying (IRS) over the last decade has contributed to a substantial reduction in malaria burden globally. However numerous challenges exist particularly in relation to vector control in emergency settings. This study seeks to explore expert opinion on the utility of existing tools within the emergency context setting and to better understand the attitude towards emerging and innovative tools (including Genetically Modified Mosquitoes) to augment current approaches. Methods 80 experts in the field of malaria and vector control were invited to participate in a two-round Delphi survey. They were selected through a combination of literature (academic and policy publications) review and snowball sampling reflecting a range of relevant backgrounds including vector control experts, malaria programme managers and emergency response specialists. The survey was conducted online through a questionnaire including the possibility for free text entry, and concentrated on the following topics: Utility and sustainability of current vector control tools, both in and outside emergency settings Feasibility, utility and challenges of emerging vector control tools, both in and outside emergency settings Current and unmet research priorities in malaria vector control and in malaria control in general. Results 37 experts completed the first round and 31 completed the second round of the survey. There was a stronger consensus about the increased utility of LLIN compared to IRS in all settings, while insecticide-treated covers and blankets ranked very high only in emergency settings. When considering the combination of tools, the ones deemed most interesting always involved LLINs and IRS regardless of the setting, and the acceptability and the efficacy at reducing transmission are essential characteristics. Regarding perceptions of tools currently under development, consensus was towards improvement of existing tools rather than investing in novel approaches and the majority of respondents expressed distrust for genetic approaches. Conclusion Malaria vector control experts expressed more confidence for tools whose efficacy is backed up by epidemiological evidence, hence a preference for the improvement rather than the combination of existing tools. Moreover, while several novel tools are under development, the majority of innovative approaches did not receive support, particularly in emergency settings. Stakeholders involved in the development of novel tools should involve earlier and raise awareness of the potential effectiveness amongst a wider range of experts within the malaria community to increase acceptability and improve early adoption once the evidence base is established.
Gene Editing in the Wild: Shaping Decisions through Broad Public Deliberation
19701M. K. Gusmano, G. E. Kaebnick, K. J. Maschke, C. P. Neuhaus and B. C. Wills, The Hastings Center Report, 51. 2021-12-14 19:46:28.
The essays in this special report grew out of a project funded by the National Science Foundation (with NSF award number 1827935). Gregory E. Kaebnick and Michael K. Gusmano were co-principal investigators on the project, and Karen J. Maschke and Carolyn P. Neuhaus were coinvestigators. Ben Curran Wills was project manager and research assistant. Genetic editing technologies have long been used to modify domesticated nonhuman animals and plants. Recently, attention and funding have also been directed toward projects for modifying nonhuman organisms in the shared environment—that is, in the “wild.” Interest in gene editing nonhuman organisms for wild release is motivated by a variety of goals, and such releases hold the possibility of significant, potentially transformative benefit. The technologies also pose risks and are often surrounded by a high uncertainty. Given the stakes, scientists and advisory bodies have called for public engagement in the science, ethics, and governance of gene editing research in nonhuman organisms. Most calls for public engagement lack details about how to design a broad public deliberation, including questions about participation, how to structure the conversations, how to report on the content, and how to link the deliberations to policy. We summarize the key design elements that can improve broad public deliberations about gene editing in the wild.
Genetic Control in Historical Perspective: The Legacy of India’s Genetic Control of Mosquitoes Unit
19652R. Wilbanks, Hastings Center Report, 51:S11-S18. 2021-12-14 18:54:15.
Abstract In the early 1970s, a World Health Organization-initiated and United States-funded project released lab-reared mosquitoes outside New Delhi in the first large-scale field trials of the genetic control of mosquitoes. Despite partnering with the Indian Council of Medical Research and investing significantly in outreach to local communities at the release sites, the project was embroiled in controversy and became an object of vehement debate within the Indian parliament and diplomatic contretemps between the United States and India. This early episode of genetic control research demonstrates how a scientific collaboration was entangled in geopolitics and shaped by the legacy of colonialism. This historical case study has implications for public deliberation in the present, pointing to the challenges of shared decision-making in the context of structural inequality, the way that a backdrop of military interest in a technology can impede trust, and the long-term consequences of projects that foster mistrust.
Deficits of Public Deliberation in U.S. Oversight for Gene Edited Organisms
19650J. Kuzma, Hastings Center Report, 51 Suppl 2:S25-s33. 2021-12-14 18:49:23.
Environmental releases of gene edited (GEdOs) and gene drive organisms (GDOs) will likely occur under conditions of high uncertainty and in complex socioecological systems. Therefore, public deliberation is especially important to account for diverse interpretations of safety, risks, and benefits; to draw on experiential and public wisdom in areas of proposed release; to ameliorate dangers of technological optimism; and to increase the public legitimacy of decisions. Yet there is a "democratic deficit" in the United States' oversight system for GEdOs and GDOs, as unconflicted experts, publics, and skeptical stakeholders are most often excluded from decision-making and unavailable to critically examine potential risks and benefits or raise broader concerns about socioeconomic or cultural impacts. This article argues for the need to open up decision-making for GEdOs and GDOs, discusses the challenges for doing so within the current oversight framework, and finally, proposes institutional, policy, and attitudinal changes that are likely important for overcoming barriers to public deliberation.
Public Deliberation about Gene Editing in the Wild
19648M. K. Gusmano, G. E. Kaebnick, K. J. Maschke, C. P. Neuhaus and B. C. Wills, Hastings Center Report, 51 Suppl 2:S2-s10. 2021-12-14 18:42:52.
Genetic editing technologies have long been used to modify domesticated nonhuman animals and plants. Recently, attention and funding have also been directed toward projects for modifying nonhuman organisms in the shared environment-that is, in the "wild." Interest in gene editing nonhuman organisms for wild release is motivated by a variety of goals, and such releases hold the possibility of significant, potentially transformative benefit. The technologies also pose risks and are often surrounded by a high uncertainty. Given the stakes, scientists and advisory bodies have called for public engagement in the science, ethics, and governance of gene editing research in nonhuman organisms. Most calls for public engagement lack details about how to design a broad public deliberation, including questions about participation, how to structure the conversations, how to report on the content, and how to link the deliberations to policy. We summarize the key design elements that can improve broad public deliberations about gene editing in the wild.
Empowering Indigenous Knowledge in Deliberations on Gene Editing in the Wild
19646R. Taitingfong and A. Ullah, Hastings Center Report, 51 Suppl 2:S74-s84. 2021-12-14 18:38:07.
Proposals to release genetically engineered organisms in the wild raise complex ethical issues related to their safe and equitable implementation. While there is broad agreement that community and public engagement is vital to decision-making in this context, more discussion is needed about who should be engaged in such activities and in what ways. This article identifies Indigenous peoples as key stakeholders in decisions about gene-editing in the wild and argues that engagement activities need not only include Indigenous peoples but also be designed, conducted, and analyzed in ways that confront longstanding power imbalances that dismiss Indigenous expertise. We offer specific recommendations to guide deliberative activities to not only be inclusive of Indigenous peoples but also to empower their diverse, situated knowledges. We call on those committed to the inclusive design of broad public deliberation to pursue strategies that shift dominant power dynamics to include Indigenous communities in more meaningful ways.
The Decision Phases Framework for Public Engagement: Engaging Stakeholders about Gene Editing in the Wild
19643S. K. Barnhill-Dilling, A. Kokotovich and J. A. Delborne, Hastings Center Report, 51 Suppl 2:S48-s61. 2021-12-14 18:30:37.
Some experts and advocates propose environmental biotechnologies such as genetic engineering, gene drive systems, and synthetic biology as potential solutions to accelerating rates of species loss. While these tools may offer hope for a seemingly intractable problem, they also present potential governance challenges for which innovative decision-making systems are required. Two of the perennial governance challenges include, when are broader stakeholder groups involved in these decisions and who exactly should be involved? We propose the decision phases framework-which includes research and development, regulatory review, and deployment, management, and monitoring-as a framework for identifying which stakeholders might be best suited for different phases throughout the innovation and deployment of emerging environmental biotechnologies for species protection.
Diverse mating phenotypes impact the spread of wtf meiotic drivers in Schizosaccharomyces pombe
20396J. F. L. Hernandez, R. M. Helston, J. J. Lange, R. B. Billmyre, S. H. Schaffner, M. T. Eickbush, S. McCroskey and S. E. Zanders, Elife, 10:30. 2021-12-13 09:37:02.
Meiotic drivers are genetic elements that break Mendel's law of segregation to be transmitted into more than half of the offspring produced by a heterozygote. The success of a driver relies on outcrossing (mating between individuals from distinct lineages) because drivers gain their advantage in heterozygotes. It is, therefore, curious that Schizosaccharomyces pombe, a species reported to rarely outcross, harbors many meiotic drivers. To address this paradox, we measured mating phenotypes in S. pombe natural isolates. We found that the propensity for cells from distinct clonal lineages to mate varies between natural isolates and can be affected both by cell density and by the available sexual partners. Additionally, we found that the observed levels of preferential mating between cells from the same clonal lineage can slow, but not prevent, the spread of a wtf meiotic driver in the absence of additional fitness costs linked to the driver. These analyses reveal parameters critical to understanding the evolution of S. pombe and help explain the success of meiotic drivers in this species. eLife digest The fission yeast, Schizosaccharomyces pombe, is a haploid organism, meaning it has a single copy of each of its genes. S. pombe cells generally carry one copy of each chromosome and can reproduce clonally by duplicating these chromosomes and then dividing into two cells. However, when the yeast are starving, they can reproduce sexually. This involves two cells mating by fusing together to create a 'diploid zygote', which contains two copies of each gene. The zygote then undergoes 'meiosis', a special type of cell division in which the zygote first duplicates its genome and then divides twice. This results in four haploid spores which are analogous to sperm and eggs in humans that each contain one copy of the genome. The spores will grow and divide normally when conditions improve. The genes carried by each of the haploid spores depend on the cells that formed the zygote. If the two 'parent' yeast had the same version or 'allele' of a gene, all four spores will have it in their genome. However, if the two parents have different alleles, only 50% of the offspring will carry each version. Although this is usually the case, there are certain alleles, called meiotic drivers, that are transmitted to all offspring even in situations where it is only carried by one parent. Meiotic drivers can be found in many organisms, including mammals, but their behavior is easiest to study in yeast. Meiotic drivers known as killers achieve this by disposing of any 'sister' spores that do not inherit the same allele of this gene. This 'killing' can only happen when only one of the 'parents' carries the driver. This scenario is thought to rarely occur in species that inbreed, as inbreeding leads to both gene copies being the same. However, this does not appear to be the case for S. pombe, which contain a whole family of killer meiotic drivers, the wtf genes, despite also being reported to mainly inbreed. To investigate this contradiction, Lopez Hernandez et al. isolated several genetically distinct populations of S.pombe. These isolates were grown together to determine how often the each one would outcross (mate with an individual from a different population) or inbreed. The results found that levels of inbreeding varied between isolates. Next, Lopez Hernandez et al. used mathematical modelling and experimental evolution analyses to study how wtf drivers spread amongst these populations. This revealed that wtf genes spread faster in populations with more outcrossing. In some instances, the wtf driver was linked to a gene that could harm the population. In these cases, Lopez Hernandez et al. found than inbreeding could purge these drivers and stop them from spreading the dangerous alleles through the population. Lopez Hernandez et al. establish a simple experimental system to model driver evolution and experimentally demonstrate how key parameters, such as outcrossing rates, affect the spread of these genes. Understanding how meiotic drivers spread is important, as these systems could potentially be used to modify populations important to humans, such as crops or disease vectors.
Exploiting a Y chromosome-linked Cas9 for sex selection and gene drive
19623S. Gamez, D. Chaverra-Rodriguez, A. Buchman, N. P. Kandul, S. C. Mendez-Sanchez, J. B. Bennett, C. H. Sánchez, T. Yang, I. Antoshechkin, J. E. Duque, P. A. Papathanos, J. M. Marshall and O. S. Akbari, Nature Communications, 7202. 2021-12-10 21:34:38.
CRISPR-based genetic engineering tools aimed to bias sex ratios, or drive effector genes into animal populations, often integrate the transgenes into autosomal chromosomes. However, in species with heterogametic sex chromsomes (e.g. XY, ZW), sex linkage of endonucleases could be beneficial to drive the expression in a sex-specific manner to produce genetic sexing systems, sex ratio distorters, or even sex-specific gene drives, for example. To explore this possibility, here we develop a transgenic line of Drosophila melanogaster expressing Cas9 from the Y chromosome. We functionally characterize the utility of this strain for both sex selection and gene drive finding it to be quite effective. To explore its utility for population control, we built mathematical models illustrating its dynamics as compared to other state-of-the-art systems designed for both population modification and suppression. Taken together, our results contribute to the development of current CRISPR genetic control tools and demonstrate the utility of using sex-linked Cas9 strains for genetic control of animals.
Evolution of B Chromosomes: From Dispensable Parasitic Chromosomes to Essential Genomic Players
19731M. Johnson Pokorná and R. Reifová, Frontiers in Genetics, 12:727570. 2021-12-09 12:58:40.
B chromosomes represent additional chromosomes found in many eukaryotic organisms. Their origin is not completely understood but recent genomic studies suggest that they mostly arise through rearrangements and duplications from standard chromosomes. They can occur in single or multiple copies in a cell and are usually present only in a subset of individuals in the population. Because B chromosomes frequently show unstable inheritance, their maintenance in a population is often associated with meiotic drive or other mechanisms that increase the probability of their transmission to the next generation. For all these reasons, B chromosomes have been commonly considered to be nonessential, selfish, parasitic elements. Although it was originally believed that B chromosomes had little or no effect on an organism's biology and fitness, a growing number of studies have shown that B chromosomes can play a significant role in processes such as sex determination, pathogenicity and resistance to pathogens. In some cases, B chromosomes became an essential part of the genome, turning into new sex chromosomes or germline-restricted chromosomes with important roles in the organism's fertility. Here, we review such cases of "cellular domestication" of B chromosomes and show that B chromosomes can be important genomic players with significant evolutionary impact.
Genomic insertion locus and Cas9 expression in the germline affect CRISPR/Cas9-based gene drive performance in the yellow fever mosquito Aedes aegypti
19603W. R. Reid, J. Lin, A. E. Williams, R. Juncu, K. E. Olson and A. W. E. Franz, bioRxiv, 2021.12.08.471839. 2021-12-08 18:56:04.
The yellow fever mosquito Aedes aegypti is a major vector of arthropod-borne viruses, including dengue, chikungunya, and Zika. A novel approach to mitigate arboviral infections is to generate mosquitoes refractory to infection by overexpressing antiviral effector molecules. Such an approach requires a mechanism to spread these antiviral effectors through a population, for example, by using CRISPR/Cas9-based gene drive systems. Here we report an autonomous single-component gene drive system in Ae. aegypti that is designed for persistent population replacement. Critical to the design of a single-locus autonomous gene drive is that the selected genomic locus be amenable to both gene drive and the appropriate expression of the antiviral effector. In our study, we took a reverse engineering approach to target two genomic loci ideal for the expression of antiviral effectors and further investigated the use of three promoters for Cas9 expression (nanos, β2-tubulin, or zpg) for the gene drive. We found that both promoter selection and genomic target site strongly influenced the efficiency of the drive, resulting in 100% inheritance in some crosses. We also observed the formation of inheritable gene drive blocking indels (GDBI) in the genomic locus with the highest levels of gene drive. Overall, our drive system forms a platform for the further testing of driving antipathogen effector genes through Ae. aegypti populations.Competing Interest StatementThe authors have declared no competing interest.
Modeling impact and cost-effectiveness of driving-Y gene drives for malaria elimination in the Democratic Republic of the Congo
19594N. Metchanun, C. Borgemeister, G. Amzati, J. von Braun, M. Nikolov, P. Selvaraj and J. Gerardin, Evolutionary Applications, 2021-12-07 17:59:09.
Malaria elimination will be challenging in countries that currently continue to bear high malaria burden. Sex-ratio distorting gene drives, such as driving-Y, could play a role in an integrated elimination strategy if they can effectively suppress vector populations. Using a spatially explicit, agent-based model of malaria transmission in eight provinces spanning the range of transmission intensities across the Democratic Republic of the Congo, we predict the impact and cost-effectiveness of integrating driving-Y gene drive mosquitoes in malaria elimination strategies that include existing interventions such as insecticide-treated nets and case management of symptomatic malaria. Gene drive mosquitoes could eliminate malaria and were the most cost-effective intervention overall if the drive component was highly effective with at least 95% X-shredder efficiency at relatively low fertility cost, and associated cost of deployment below 7.17 $int per person per year. Suppression gene drive could be a cost-effective supplemental intervention for malaria elimination, but tight constraints on drive effectiveness and cost ceilings may limit its feasibility.
Genetic conversion of a split-drive into a full-drive element
19540G. Terradas, J. B. Bennett, Z. Li, J. M. Marshall and E. Bier, bioRxiv, 2021.12.05.471291. 2021-12-06 20:21:27.
Gene-drive systems offer an important new avenue for spreading beneficial traits into wild populations. Their core components, Cas9 and guide RNA (gRNA), can either be linked within a single cassette (full gene drive, fGD) or provided in two separate elements (split gene drive, sGD) wherein the gRNA-bearing element drives in the presence of an independent static source of Cas9. We previously designed a system engineered to turn split into full gene drives. Here, we provide experimental proof-of-principle for such a convertible system inserted at the spo11 locus, which is recoded to restore gene function. In multigenerational cage studies, the reconstituted spo11 fGD cassette initially drives with slower kinetics than the unlinked sGD element (using the same Mendelian vasa-Cas9 source), but eventually reaches a similar level of final introgression. Different kinetic behaviors may result from transient fitness costs associated with individuals co-inheriting Cas9 and gRNA transgenes during the drive process.
Nuclear transport genes recurrently duplicate by means of RNA intermediates in Drosophila but not in other insects
19591A. Mirsalehi, D. N. Markova, M. Eslamieh and E. Betrán, BMC Genomics, 22:876. 2021-12-06 17:52:07.
We find that most of the nuclear transport duplications in Drosophila are of a few classes of nuclear transport genes, RNA mediated and fast evolving. We also retrieve many pseudogenes for the Ran gene. Some of the duplicates are relatively young and likely contributing to the turnover expected for genes under strong but changing selective pressures. These duplications are potentially revealing what features of nuclear transport are under selection. Unlike in flies, we find only a few duplications when we study the Drosophila duplicated nuclear transport genes in dipteran species outside of Drosophila, and none in other insects.
The economic value of genetically engineered mosquitoes as a Malaria control strategy depends on local transmission rates
19788K. Lacy, K. A. Schaefer, D. P. Scheitrum and E. Y. Klein, Biotechnology Journal, 10. 2021-12-06 14:26:13.
This paper assesses the economic value of genetically engineered (GE) Anopheles gambiae mosquitoes as a malaria control strategy. We use an epidemiological-economic model of malaria transmission to evaluate this technology for a range of village-level transmission settings. In each setting, we evaluate public health outcomes following introduction of GE mosquitoes relative to a "status quo" baseline scenario. We also assess results both in contrast to-and in combination with-a Mass Drug Administration (MDA) strategy. We find that-in low transmission settings-the present value (PV) public health benefits of GE mosquito release are substantial, both relative to status quo dynamics and MDA. In contrast, in high transmission settings, the release of GE mosquitoes may increase steady-state infection rates. Our results indicate that there are substantial policy complementarities when GE mosquito release is combined with local MDA-the combined control strategy can lead to local eradication.
Towards Integrated Management of Dengue in Mumbai
19735P. N. Paradkar, P. R. Sahasrabudhe, M. Ghag Sawant, S. Mukherjee and K. R. Blasdell, Viruses, 13. 2021-12-04 13:10:23.
With increasing urbanisation, the dengue disease burden is on the rise in India, especially in large cities such as Mumbai. Current dengue surveillance in Mumbai includes municipal corporation carrying out specific activities to reduce mosquito breeding sites and the use of insecticides to suppress the adult mosquito populations. Clinical cases remain either underreported or misreported due to the restriction to government clinics, missing the large private health care sector. There is a need for an integrated approach to manage dengue outbreaks in Mumbai. There are various novel strategies available for use that can be utilised to improve disease detection, mosquito surveillance, and control of mosquito-borne diseases. These novel technologies are discussed in this manuscript. Given the complex ecosystem of mosquito-borne diseases in Mumbai, integrating data obtained from these technologies would support the ongoing mosquito control measures in Mumbai.
A flurry of sex-ratio distorters
19527A. A. Vogan, Nature Ecology and Evolution, 2021-12-03 19:49:56.
Two analyses of long-read sequencing show that the Winters sex-ratio distorter of Drosophila has been a part of a recent gene family expansion, coupled to the appearance of suppressors, in a genomic arms race driven by satellite DNA.
Rapid evolutionary dynamics of an expanding family of meiotic drive factors and their hpRNA suppressors
19515J. Vedanayagam, C. J. Lin and E. C. Lai, Nature Ecology and Evolution, 2021-12-03 17:20:42.
Meiotic drivers are a class of selfish genetic elements whose existence is frequently hidden due to concomitant suppressor systems. Accordingly, we know little of their evolutionary breadth and molecular mechanisms. Here, we trace the evolution of the Dox meiotic drive system in Drosophila simulans, which affects male-female balance (sex ratio). Dox emerged via stepwise mobilization and acquisition of multiple D. melanogaster gene segments including from protamine, which mediates compaction of sperm chromatin. Moreover, we reveal novel Dox homologs and massive amplification of Dox superfamily genes on X chromosomes of its closest sisters D. mauritiana and D. sechellia. Emergence of Dox loci is tightly associated with 359-class satellite repeats that flank de novo genomic copies. In concert, we find coordinated diversification of autosomal hairpin RNA-class siRNA loci that target subsets of Dox superfamily genes. Overall, we reveal fierce genetic arms races between meiotic drive factors and siRNA suppressors associated with recent speciation.
CRISPR-Cas9 effectors facilitate generation of single-sex litters and sex-specific phenotypes
19469C. Douglas, V. Maciulyte, J. Zohren, D. M. Snell, S. K. Mahadevaiah, O. A. Ojarikre, P. J. I. Ellis and J. M. A. Turner, Nature Communications, 12:6926. 2021-12-03 15:06:30.
Animals are essential genetic tools in scientific research and global resources in agriculture. In both arenas, a single sex is often required in surplus. The ethical and financial burden of producing and culling animals of the undesired sex is considerable. Using the mouse as a model, we develop a synthetic lethal, bicomponent CRISPR-Cas9 strategy that produces male- or female-only litters with one hundred percent efficiency. Strikingly, we observe a degree of litter size compensation relative to control matings, indicating that our system has the potential to increase the yield of the desired sex in comparison to standard breeding designs. The bicomponent system can also be repurposed to generate postnatal sex-specific phenotypes. Our approach, harnessing the technological applications of CRISPR-Cas9, may be applicable to other vertebrate species, and provides strides towards ethical improvements for laboratory research and agriculture.
Public Perceptions Regarding Genomic Technologies Applied to Breeding Farm Animals: A Qualitative Study
19920F. Z. Naab, D. Coles, E. Goddard and L. J. Frewer, BioTech, 10. 2021-12-03 09:13:38.
The societal acceptability of different applications of genomic technologies to animal production systems will determine whether their innovation trajectories will reach the commercialisation stage. Importantly, technological implementation and commercialisation trajectories, regulation, and policy development need to take account of public priorities and attitudes. More effective co-production practices will ensure the application of genomic technologies to animals aligns with public priorities and are acceptable to society. Consumer rejection of, and limited demand for, animal products developed using novel genomic technologies will determine whether they are integration into the food system. However, little is known about whether genomic technologies that accelerate breeding but do not introduce cross-species genetic changes are more acceptable to consumers than those that do. Five focus groups, held in the north east of England, were used to explore the perceptions of, and attitudes towards, the use of genomic technologies in breeding farm animals for the human food supply chain. Overall, study participants were more positive towards genomic technologies applied to promote animal welfare (e.g., improved disease resistance), environmental sustainability, and human health. Animal “disenhancement” was viewed negatively and increased food production alone was not perceived as a potential benefit. In comparison to gene editing, research participants were most negative about genetic modification and the application of gene drives, independent of the benefits delivered.
CRISPR gene-drive systems based on Cas9 nickases promote super-Mendelian inheritance in Drosophila
19471V. Lopez del Amo, S. Sanz Juste and V. M. Gantz, bioRxiv, 2021.12.01.470847. 2021-12-02 15:07:14.
CRISPR-based gene drive systems can be used to modify entire wild populations due to their ability to bias their own inheritance towards super-Mendelian rates (>100%). Current gene drives contain a Cas9 and a gRNA gene inserted at the location targeted by the gRNA. These gene products are able to cut the opposing wildtype allele, and lead to its replacement with a copy of the gene drive through the homology-directed DNA repair pathway. When this allelic conversion occurs in the germline it leads to the preferential inheritance of the engineered allele; a property that has been proposed to disseminate engineered traits for managing disease-transmitting mosquito populations. Here, we report a novel gene-drive strategy relying on Cas9 nickases which operates by generating staggered paired-nicks in the DNA to promote propagation of the gene drive allele. We show that only when 5' overhangs are generated, the system efficiently leads to allelic conversion. Further, the nickase gene-drive arrangement produces large stereotyped deletions, providing potential advantages for targeting essential genes. Indeed, the nickase-gene-drive design should expand the options available for gene drive designs aimed at applications in mosquitoes and beyond.
Gene drive that results in addiction to a temperature-sensitive version of an essential gene triggers population collapse in Drosophila
19441G. Oberhofer, T. Ivy and B. A. Hay, Proceedings of the National Academy of Sciences, 118:e2107413118. 2021-12-01 20:58:01.
One strategy for population suppression seeks to use gene drive to spread genes that confer conditional lethality or sterility, providing a way of combining population modification with suppression. Stimuli of potential interest could be introduced by humans, such as an otherwise benign virus or chemical, or occur naturally on a seasonal basis, such as a change in temperature. Cleave and Rescue (ClvR) selfish genetic elements use Cas9 and guide RNAs (gRNAs) to disrupt endogenous versions of an essential gene while also including a Rescue version of the essential gene resistant to disruption. ClvR spreads by creating loss-of-function alleles of the essential gene that select against those lacking it, resulting in populations in which the Rescue provides the only source of essential gene function. As a consequence, if function of the Rescue, a kind of Trojan horse now omnipresent in a population, is condition dependent, so too will be the survival of that population. To test this idea, we created a ClvR in Drosophila in which Rescue activity of an essential gene, dribble, requires splicing of a temperature-sensitive intein (TS-ClvRdbe). This element spreads to transgene fixation at 23 °C, but when populations now dependent on Ts-ClvRdbe are shifted to 29 °C, death and sterility result in a rapid population crash. These results show that conditional population elimination can be achieved. A similar logic, in which Rescue activity is conditional, could also be used in homing-based drive and to bring about suppression and/or killing of specific individuals in response to other stimuli.
Applying functional genomics to the study of lamprey development and sea lamprey population control
19946J. R. York, R. E. Thresher and D. W. McCauley, Journal of Great Lakes Research, 47:S639-S649. 2021-12-01 09:30:24.
Lampreys are one of the few survivors of an ancient lineage of jawless vertebrates and have become an important study organism in numerous disciplines in the biological sciences, including evolutionary biology, embryology, ecology, physiology and biomedicine. At the same time, however, lampreys have created economic and ecological problems due, primarily, to the invasion of parasitic sea lamprey (Petromyzon marinus) into the North American Great Lakes and consequent negative impacts on local fish populations. Barriers, trapping and lampricide treatments have reduced these impacts, but concern for habitat restoration, non-target effects and possible evolution of resistance to lampricides suggests the need to develop additional strategies that supplement current control measures. The advent of functional genomics, and in particular CRISPR/Cas9 genome editing, offers a molecular approach to this on-going problem. Here, we review the successful application of functional genetic, transcriptomic, and CRISPR/Cas9 genome editing technologies in lampreys to address basic research questions in the fields of evolutionary and developmental biology. We then describe how these tools may be repurposed for use by fishery and conservation biologists to approach the problem of invasive sea lamprey from a molecular-genetic perspective.
New Arthropod Containment Recommendations Provide Essential Guidance for Safety of Gene Drive Research
19467S. James and D. O’Brochta, The American Journal of Tropical Medicine and Hygiene, tpmd211148. 2021-11-30 14:49:53.
Gene drive technologies have not yet been field tested, however, there are no data on the possible environmental or health effects of releasing gene drive–modified organisms. For this reason, there have been widespread calls for additional guidance on risk assessment and management, and some have even proposed a moratorium on gene drive research until such guidance is in place. One immediate need has been for guidance on appropriate containment measures that researchers should follow when investigating gene drive–modified organisms, given that these are meant to spread their transgenes by inter breeding with compatible local species. For example, a 2020 survey of biosafety professionals revealed that the majority felt existing guidance was inadequate for making risk assessments and containment decisions regarding gene drive–modified arthropods. Lack of standard guidance can lead to uneven application of containment measures among institutions and decreased public confidence in the research. The American Committee of Medical Entomology (ACME)of the American Society of Tropical Medicine and Hygiene has responded to this need with the recent publication of an addendum to its widely influential Arthropod ContainmentGuidelines. The new addendum6provides specific recommendations on containment practices for arthropods modified with engineered transgenes capable of gene drive.
New molecular genetic techniques: regulatory and societal considerations
19403Nielsen, K. M., AREA-WIDE INTEGRATED PEST MANAGEMENT: Development and Field Application, 2021-11-29 18:07:46.
A rapidly expanding toolbox of techniques available for genome editing provides the basis for a new continuum in types of modifications that can be introduced into a genome and blur the bimodal GMO vs. non-GMO (genetically modified organism) divide. Site-directed nucleases (SDN) are now used to modify existing nucleotides within genomes instead of adding recombined DNA as transgenes. Moreover, new gene drive approaches are in development based on SDNs. A number of potential drive applications have been reported, but uncertainties in trait stability and limitations in knowledge of the affected system at various temporal and spatial levels slow down their current uses. Adoption of new genome targeted technology takes place in a social context. The context will vary between countries and cultures, expressed in values, ethics, politics and priorities - that are translated into different regulatory approaches. Some developed products using new genome editing techniques clearly fall under internationally negotiated regulations of GMOs. However, other product outcomes of editing techniques challenge our current understanding and definition of GMOs. There is an urgent need for further research, for building international consensus and harmonizing regulatory approaches to facilitate categorization, predictability, transparency, trust and trade.
Genome editing and its applications for insect pest control: Curse or blessing?
19401Hacker, I. , and Schetelig, M. F, AREA-WIDE INTEGRATED PEST MANAGEMENT: Development and Field Application, 2021-11-29 18:00:39.
Gene and genome editing are described as cutting-edge research tools with the potential to tackle urgent global challenges in the management of agricultural pests and human disease vectors such as mosquitoes. The field is defined by the chances and challenges to interlink the disciplines of insect genomics, molecular biology, and pest control together with the need for clear risk assessment, policy development and public approval of the application of such novel technologies. The goal is to generate innovative and sustainable pest control solutions applied in the best interest for the environment and human society. Here, starting from available genome editing technologies, the current strategies and applications for insect pest control are discussed, including approaches to overcome the evolution of resistance alleles and other potential pitfalls to be expected from selective pressures resulting from gene drive applications. They are supplemented by views on regulatory, policy and ethical considerations that in our opinion will be necessary to define how the different tools can be used in the future in a safe and responsible way.
Area-wide management of fruit flies in a tropical mango growing area integrating the sterile insect technique and biological control: From a research to an operational programme
19391Liedo, P., Montoya, P. , and Toledo, J., AREA-WIDE INTEGRATED PEST MANAGEMENT: Development and Field Application, 2021-11-29 17:29:33.
The Sterile Insect Technique (SIT) has been successfully used for the control of fruit flies in a number of places in the world. One requirement for its successful application is that wild populations should be at low densities to achieve effective sterile to wild fly overflooding ratios. This has been an important reason that has limited its integration in fruit fly management in tropical fruit growing areas, where climate conditions and the availability of hosts all year-round results in high population densities. Here we report the results of a project where SIT integration into fruit fly management was evaluated under the tropical conditions of the mango growing area in the Soconusco region of Chiapas, Mexico. The basis for the area-wide integrated pest management (AW-IPM) approach was the knowledge of the population dynamics of the pest fruit flies in the region and of the fruit phenology. The main commercial mango growing areas are in the lowlands, where fruit fly populations are very low outside of the mango production season. Population densities are higher in the midlands and highlands, where alternate hosts are common in backyards and as part of the natural vegetation. We call these refuge areas, and the AW-IPM approach aimed at establishing a biological barrier with releases of parasitoids and sterile male fruit flies to suppress the fruit fly populations and prevent or minimize the dispersal of wild flies from the refuge areas to the mango orchards. In 2014, after two years of releases, fruit fly population densities were suppressed more than 70% in the release area and 65% in the entire area, including the lowlands with the mango orchards. With the support of fruit growers, state and federal governments, this project was continued and established as an operational AW-IPM programme. In 2016, after 4 years of programme implementation, the detection of wild flies was significantly reduced, and the number of batches of fruit that were rejected at the packing houses due to the detection of infested fruits was the lowest in the past 12 years, since the recording of these data was initiated. These indicators declined even further in 2017. The results obtained demonstrate that AW-IPM integrating the SIT can be applied successfully against fruit flies under tropical conditions with naturally high pest densities, providing there is adequate knowledge on the population dynamics of the fruit fly species present in the region.
