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.
The sterile insect technique is protected from evolution of mate discrimination
21768J. J. Bull and R. Gomulkiewicz, PeerJ, 10:e13301. 2022-04-18 07:53:47.
Background The sterile insect technique (SIT) has been used to suppress and even extinguish pest insect populations. The method involves releasing artificially reared insects (usually males) that, when mating with wild individuals, sterilize the broods. If administered on a large enough scale, the sterility can collapse the population. Precedents from other forms of population suppression, especially chemicals, raise the possibility of resistance evolving against the SIT. Here, we consider resistance in the form of evolution of female discrimination to avoid mating with sterile males. Is resistance evolution expected? Methods We offer mathematical models to consider the dynamics of this process. Most of our models assume a constant-release protocol, in which the same density of males is released every generation, regardless of wild male density. A few models instead assume proportional release, in which sterile releases are adjusted to be a constant proportion of wild males. Results We generally find that the evolution of female discrimination, although favored by selection, will often be too slow to halt population collapse when a constant-release implementation of the SIT is applied appropriately and continually. The accelerating efficacy of sterile males in dominating matings as the population collapses works equally against discriminating females as against non-discriminating females, and rare genes for discrimination are too slow to ascend to prevent the loss of females that discriminate. Even when migration from source populations sustains the treated population, continued application of the SIT can prevent evolution of discrimination. However, periodic premature cessation of the SIT does allow discrimination to evolve. Likewise, use of a ‘proportional-release’ protocol is also prone to escape from extinction if discriminating genotypes exist in the population, even if those genotypes are initially rare. Overall, the SIT is robust against the evolution of mate discrimination provided care is taken to avoid some basic pitfalls. The models here provide insight for designing programs to avoid those pitfalls.
Propagation of seminal toxins through binary expression gene drives could suppress populations
21691J. Hurtado, S. Revale and L. M. Matzkin, Scientific Reports, 12:6332. 2022-04-15 08:22:57.
Gene drives can be highly effective in controlling a target population by disrupting a female fertility gene. To spread across a population, these drives require that disrupted alleles be largely recessive so as not to impose too high of a fitness penalty. We argue that this restriction may be relaxed by using a double gene drive design to spread a split binary expression system. One drive carries a dominant lethal/toxic effector alone and the other a transactivator factor, without which the effector will not act. Only after the drives reach sufficiently high frequencies would individuals have the chance to inherit both system components and the effector be expressed. We explore through mathematical modeling the potential of this design to spread dominant lethal/toxic alleles and suppress populations. We show that this system could be implemented to spread engineered seminal proteins designed to kill females, making it highly effective against polyandrous populations.
Mendelian nightmares: the germline-restricted chromosome of songbirds
21724P. Borodin, A. Chen, W. Forstmeier, S. Fouché, L. Malinovskaya, Y. Pei, R. Reifová, F. J. Ruiz-Ruano, S. A. Schlebusch, M. Sotelo-Muñoz, A. Torgasheva, N. Vontzou and A. Suh, Chromosome Res, 2022-04-13 09:33:56.
Germline-restricted chromosomes (GRCs) are accessory chromosomes that occur only in germ cells. They are eliminated from somatic cells through programmed DNA elimination during embryo development. GRCs have been observed in several unrelated animal taxa and show peculiar modes of non-Mendelian inheritance and within-individual elimination. Recent cytogenetic and phylogenomic evidence suggests that a GRC is present across the species-rich songbirds, but absent in non-passerine birds, implying that over half of all 10,500 bird species have extensive germline/soma genome differences. Here, we review recent insights gained from genomic, transcriptomic, and cytogenetic approaches with regard to the genetic content, phylogenetic distribution, and inheritance of the songbird GRC. While many questions remain unsolved in terms of GRC inheritance, elimination, and function, we discuss plausible scenarios and future directions for understanding this widespread form of programmed DNA elimination.
Meiotic drive in chronic lymphocytic leukemia compared with other malignant blood disorders
22219V. Jonsson, H. Awan, N. D. Jones, T. B. Johannesen, K. Thogersen, B. A. Steig, G. Andorsdottir and G. E. Tjonnfjord, Scientific Reports, 12:6138. 2022-04-12 15:37:58.
The heredity of the malignant blood disorders, leukemias, lymphomas and myeloma, has so far been largely unknown. The present study comprises genealogical investigations of one hundred and twelve Scandinavian families with unrelated parents and two or more cases of malignant blood disease. For comparison, one large family with related family members and three hundred and forty-one cases of malignant blood disease from the Faroese population was included. The inheritance is non-Mendelian, a combination of genomic parental imprinting and feto-maternal microchimerism. There is significantly more segregation in maternal than in paternal lines, predominance of mother-daughter combinations in maternal lines, and father-son combinations in paternal lines. Chronic lymphocytic leukemia is the most frequent diagnosis in the family material, and chronic lymphocytic leukemia has a transgenerational segregation that is unique in that inheritance of susceptibility to chronic lymphocytic leukemia is predominant in males of paternal lines. Male offspring with chronic lymphocytic leukemia in paternal lines have a birth-order effect, which is manifest by the fact that there are significantly more male patients late in the sibling line. In addition, there is contravariation in chronic lymphocytic leukemia, i.e. lower occurrence than expected in relation to other diagnoses, interpreted in such a way that chronic lymphocytic leukemia remains isolated in the pedigree in relation to other diagnoses of malignant blood disease. Another non-Mendelian function appears in the form of anticipation, i.e. increased intensity of malignancy down through the generations and a lower age at onset of disease than otherwise seen in cases from the Cancer Registers, in acute lymphoblastic leukemia, for example. It is discussed that this non-Mendelian segregation seems to spread the susceptibility genes depending on the gender of the parents and not equally to all children in the sibling line, with some remaining unaffected by susceptibility i.e. "healthy and unaffected", due to a birth order effect. In addition, anticipation is regarded as a non-Mendelian mechanism that can amplify, <
The non-Mendelian behavior of plant B chromosomes
21722J. Chen, J. A. Birchler and A. Houben, Chromosome Res, 2022-04-12 09:30:19.
B chromosomes, also known as supernumerary chromosomes, are dispensable elements in the genome of many plants, animals, and fungi. Many B chromosomes have evolved one or more drive mechanisms to transmit themselves at a higher frequency than predicted by Mendelian genetics, and these mechanisms counteract the tendency of non-essential genetic elements to be lost over time. The frequency of Bs in a population results from a balance between their effect on host fitness and their transmission rate. Here, we will summarize the findings of the drive process of plant B chromosomes, focusing on maize and rye.
A homing suppression gene drive with multiplexed gRNAs maintains high drive conversion efficiency and avoids functional resistance alleles
22572E. Yang, M. Metzloff, A. M. Langmuller, X. J. Xu, A. G. Clark, P. W. Messer and J. Champer, G3-Genes Genomes Genetics, 13. 2022-04-08 09:02:04.
Gene drives are engineered alleles that can bias inheritance in their favor, allowing them to spread throughout a population. They could potentially be used to modify or suppress pest populations, such as mosquitoes that spread diseases. CRISPR/Cas9 homing drives, which copy themselves by homology-directed repair in drive/wild-type heterozygotes, are a powerful form of gene drive, but they are vulnerable to resistance alleles that preserve the function of their target gene. Such resistance alleles can prevent successful population suppression. Here, we constructed a homing suppression drive in Drosophila melanogaster that utilized multiplexed gRNAs to inhibit the formation of functional resistance alleles in its female fertility target gene. The selected gRNA target sites were close together, preventing reduction in drive conversion efficiency. The construct reached a moderate equilibrium frequency in cage populations without apparent formation of resistance alleles. However, a moderate fitness cost prevented elimination of the cage population, showing the importance of using highly efficient drives in a suppression strategy, even if resistance can be addressed. Nevertheless, our results experimentally demonstrate the viability of the multiplexed gRNAs strategy in homing suppression gene drives.
Cas9-mediated maternal-effect and derived resistance alleles in a gene-drive strain of the African malaria vector mosquito, Anopheles gambiae
21663R. Carballar-Lejarazú, T. Tushar, T. B. Pham and A. A. James, Genetics, 2022-04-07 15:16:08.
CRISPR/Cas9 technologies are important tools for the development of gene-drive systems to modify mosquito vector populations to control the transmission of pathogens that cause diseases such as malaria. However, one of the challenges for current Cas9-based drive systems is their ability to produce drive-resistant alleles resulting from insertions and deletions (indels) caused principally by nonhomologous end-joining following chromosome cleavage. Rapid increases in the frequency of such alleles may impair gene-drive dynamics. We explored the generation of indels in the germline and somatic cells in female gene-drive lineages using a series of selective crosses between a gene-drive line, AgNosCd-1, and wild-type mosquitoes. We find that potential drive-resistant mutant alleles are generated largely during embryonic development, most likely caused by deposition of the Cas9 endonuclease and guide RNAs in oocytes and resulting embryos by homozygous and hemizygous gene-drive mothers.
A multi-disciplinary approach for a building common understanding of genetic engineering for malaria control in Burkina Faso
21637L. Pare Toe, N. Barry, A. D. Ky, S. Kekele, W. I. Meda, K. Bayala, et al., Humanities and Social Sciences Communications, 9. 2022-04-05 08:18:54.
Genetic engineering is a complex topic, even for scientists working in other areas, and even more so for those who lack a formal scientific training. To help gene specialists and affected communities talk with one another, international guidance documents have been published that promote dialogue and exchanges. The current paper explores collaboration among scientists of different disciplines as well as between scientists, the local communities, mediated by theatre actors to develop a conversation about Target Malaria’s work on genetic technologies to modify mosquitoes for malaria elimination in Burkina Faso. It focuses on the co-construction of meaning of key scientific concepts with a view to fostering productive collaboration between scientists and the local community. The community provided feedback on what was shared with them regarding the science being developed in the lab and in the field, which in turn informed aspects of the research itself, and the nature of the collaboration between the scientists and the local community.
Governing Gene Drive Technologies: A Qualitative Interview Study
23410N. de Graeff, K. R. Jongsma, J. E. Lunshof and A. L. Bredenoord, AJOB Empirical Bioethics, 13:107-124. 2022-04-04 12:10:12.
Gene drive technologies (GDTs) bias the inheritance of a genetic element within a population of non-human organisms, promoting its progressive spread across this population. If successful, GDTs may be used to counter intractable problems such as vector-borne diseases. A key issue in the debate on GDTs relates to what governance is appropriate for these technologies. While governance mechanisms for GDTs are to a significant extent proposed and shaped by professional experts, the perspectives of these experts have not been explored in depth.Methods A total of 33 GDT experts from different professional disciplines were interviewed to identify, better understand, and juxtapose their perspectives on GDT governance. The pseudonymized transcripts were analyzed thematically.Results Three main themes were identified: (1) engagement of communities, stakeholders, and publics; (2) power dynamics, and (3) decision-making. There was broad consensus amongst respondents that it is important to engage communities, stakeholders, and publics. Nonetheless, respondents had diverging views on the reasons for doing so and the timing and design of engagement. Respondents also outlined complexities and challenges related to engagement. Moreover, they brought up the power dynamics that are present in GDT research. Respondents stressed the importance of preventing the recurrence of historical injustices and reflected on dilemmas regarding whether and to what extent (foreign) researchers can legitimately make demands regarding local governance. Finally, respondents had diverging views on whether decisions about GDTs should be made in the same way as decisions about other environmental interventions, and on the decision-making model that should be used to decide about GDT deployment.Conclusions The insights obtained in this interview study give rise to recommendations for the design and evaluation of GDT governance. Moreover, these insights point to unresolved normative questions that need to be addressed to move from general commitments to concrete obligations.
Expanding the flexibility of genome editing approaches for population control of the malaria mosquito
22226N. Kranjc, Imperial College London-PhD, 2022-04-01 15:50:55.
Discovery and adaptation of CRISPR-Cas systems for genome editing have allowed us to gain an efficient and yet simple tool for genetic manipulation in various fields of molecular biology and biotechnology. One of the most promising applications is the use of CRISPR-Cas9 endonuclease for gene drive systems as a population control strategy for various insect pests of medical and agricultural importance. Use of CRISPR-Cas9 endonuclease in gene drive applications has shown great promise in the laboratory, particularly for the control of Anopheles gambiae, the major vector of malaria. However, the performance of such gene drives can be limited by the range of available target sequences and by a propensity of existing endonuclease formulations to generate resistant mutations that hinder the gene drive’s efficiency. To expand the flexibility of gene drive systems, computational analysis was performed to identify additional Cas9 orthologs and their specificities that could usefully augment the targeting range of endonuclease-based gene drives. Two alternative variants of CRISPR-Cas endonucleases found in the bacterial species Lactobacillus rhamnosus and Bacteroides fragilis were assessed for their potential to expand the targeting space in the genome Anopheles gambiae. In addition, a computational tool was developed that evaluates neighbouring sequences to the target site to measure both its likely functional constraint and its likely propensity for DNA repair that could generate in-frame alleles. Using this approach we were able to generate a prioritized list of Anopheles gambiae target sites for gene drive applications that are less likely to be compromised by resistant alleles.
Toward a CRISPR-Cas9-Based Gene Drive in the Diamondback Moth Plutella xylostella
24426X. Xu, T. Harvey-Samuel, H. A. Siddiqui, J. X. D. Ang, M. E. Anderson, C. M. Reitmayer, E. Lovett, P. T. Leftwich, M. You and L. Alphey, The CRISPR Journal, 5:224-236. 2022-04-01 10:25:39.
Promising to provide powerful genetic control tools, gene drives have been constructed in multiple dipteran insects, yeast, and mice for the purposes of population elimination or modification. However, it remains unclear whether these techniques can be applied to lepidopterans. Here, we used endogenous regulatory elements to drive Cas9 and single guide RNA (sgRNA) expression in the diamondback moth (DBM), Plutella xylostella, and test the first split gene drive system in a lepidopteran. The DBM is an economically important global agriculture pest of cruciferous crops and has developed severe resistance to various insecticides, making it a prime candidate for such novel control strategy development. A very high level of somatic editing was observed in Cas9/sgRNA transheterozygotes, although no significant homing was revealed in the subsequent generation. Although heritable Cas9-medated germline cleavage as well as maternal and paternal Cas9 deposition were observed, rates were far lower than for somatic cleavage events, indicating robust somatic but limited germline activity of Cas9/sgRNA under the control of selected regulatory elements. Our results provide valuable experience, paving the way for future construction of gene drives or other Cas9-based genetic control strategies in DBM and other lepidopterans.
Overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors
21579N. A. Ratcliffe, J. P. Furtado Pacheco, P. Dyson, H. C. Castro, M. S. Gonzalez, P. Azambuja and C. B. Mello, Parasites and Vectors, 15:112. 2022-03-31 12:47:27.
This article presents an overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors. It first briefly summarises some of the disease-causing pathogens vectored by insects and emphasises the need for innovative control methods to counter the threat of resistance by both the vector insect to pesticides and the pathogens to therapeutic drugs. Subsequently, the state of art of paratransgenesis is described, which is a particularly ingenious method currently under development in many important vector insects that could provide an additional powerful tool for use in integrated pest control programmes. The requirements and recent advances of the paratransgenesis technique are detailed and an overview is given of the microorganisms selected for genetic modification, the effector molecules to be expressed and the environmental spread of the transgenic bacteria into wild insect populations. The results of experimental models of paratransgenesis developed with triatomines, mosquitoes, sandflies and tsetse flies are analysed. Finally, the regulatory and safety rules to be satisfied for the successful environmental release of the genetically engineered organisms produced in paratransgenesis are considered.
Comparison of Ground Release and Drone-Mediated Aerial Release of Aedes aegypti Sterile Males in Southern Mexico: Efficacy and Challenges
21574C. F. Marina, P. Liedo, J. G. Bond, A. R. Osorio, J. Valle, R. Angulo-Kladt, Y. Gómez-Simuta, I. Fernández-Salas, A. Dor and T. Williams, Insects, 13. 2022-03-31 12:43:15.
Sterile males of Aedes aegypti were released once a week for 8 weeks to evaluate the dispersal efficiency of ground and aerial drone release methods in a rural village of 26 Ha in southern Mexico. Indoor and outdoor BG-Sentinel traps were placed in 13–16 houses distributed throughout the village. The BG traps were activated 48 h after the release of the sterile males and functioned for a 24 h period following each release. Over the 8-week period of simultaneous ground and aerial releases, an average of 85,117 ± 6457 sterile males/week were released at ground level and 86,724 ± 6474 sterile males/week were released using an aerial drone. The ground release method resulted in higher numbers of captured males (mean = 5.1 ± 1.4, range 1.1–15.7 sterile males/trap) compared with the aerial release method (mean = 2.6 ± 0.8, range 0.5–7.3 sterile males/trap) (p < 0.05). Similarly, the prevalence of traps that captured at least one sterile male was significantly higher for ground release compared to the aerial release method (p < 0.01). The lower numbers of sterile males captured in the aerial release method could be due to mortality or physical injury caused by the chilling process for immobilization, or the compaction of these insects during transport and release. However, aerial releases by a two-person team distributed insects over the entire village in just 20 min, compared to ~90 min of work for a five-person team during the ground release method. Ground release also resulted in higher aggregations of males and some villagers reported feeling discomfort from the presence of large numbers of mosquitoes in and around their houses. We conclude that modifications to the handling and transport of sterile males and the design of containers used to store males are required to avoid injury and to improve the efficiency of aerial releases for area-wide SIT-based population suppression programs targeted at mosquito vectors of human disease.
Genetic Stability and Fitness of Aedes aegypti Red-Eye Genetic Sexing Strains With Pakistani Genomic Background for Sterile Insect Technique Applications
22452M. Misbah-ul-Haq, D. O. Carvalho, L. D. de la Fuente, A. A. Augustinos and K. Bourtzis, Frontiers in Bioengineering and Biotechnology, 10. 2022-03-31 09:37:56.
The mosquito species Aedes aegypti is the primary transmitter of viruses that cause endemic diseases like dengue in Pakistan. It is also a cause of other vector-borne diseases like yellow fever, Zika fever, and chikungunya, which significantly impact human health worldwide. In the absence of efficient vaccines (except for yellow fever) or drugs, vector control methods, such as the sterile insect technique (SIT), have been proposed as additional tools for the management of these diseases. Mosquito SIT programs are based on the release of sterile males and it is important female releases to be ideally zero or to be kept at a minimum, since females are the ones that bite, blood-feed and transmit pathogens. Recently, an Ae. aegypti genetic sexing strain (GSS), with and without a recombination-suppressing inversion (Inv35), was developed using the eye color as a selectable marker, with males having black eyes and females red eyes. In the present study, we introgressed the sexing features and the Inv35 of the Ae. aegypti red-eye GSS into the Pakistani genomic background aiming to their future use for SIT applications in the country. Both introgressed strains, the Red-eye GSS-PAK and the Red-eye GSS/Inv35-PAK, were evaluated in respect to their genetic stability and biological quality by assessing parameters like recombination rate, fecundity, fertility, pupal and adult recovery, time of development, pupal weight, survival, and flight ability in comparison with a wild Pakistani population (PAK). The results suggest that the sexing features and the recombination suppression properties of Inv35 were not affected after their introgression into the local genomic background; however, some biological traits of the two newly constructed strains were affected, positively or negatively, suggesting that a thorough quality control analysis should be performed after the introgression of a GSS into a new genomic background prior to its use in SIT field trials or applications. The importance of using GSS with local genomic background for SIT applications against Aedes aegypti is also discussed.
Prescribing engagement in environmental risk assessment for gene drive technology
21689S. Hartley, A. Kokotovich and C. McCalman, Regulation and Governance, 2022-03-29 08:17:38.
Abstract Gene drive technology is a nascent biotechnology with the potential to purposefully alter or eliminate a species. There have been broad calls for engagement to inform gene drive governance. Over the past seven years, the gene drive community has been developing risk assessment guidelines to determine what form future gene drive risk assessments take, including whether and how they involve engagement. To explore who is developing these guidelines and how engagement in risk assessment is being prescribed, we conduct a document analysis of gene drive risk assessment guideline documents from 2014 to 2020. We found that a narrow set of organizations have developed 10 key guideline documents and that with only one exception the documents prescribe a narrow, vague, or completely absent role for engagement in gene drive risk assessment. Without substantively prescribed engagement in guidelines, the relevance, rigor, and trustworthiness of gene drive risk assessment and governance will suffer.
Mathematical modelling to assess the feasibility of Wolbachia in malaria vector biocontrol
22650S. Andreychuk and L. Yakob, Journal of Theoretical Biology, 542. 2022-03-29 06:30:06.
Releasing mosquitoes transinfected with the endosymbiotic bacterium Wolbachia is a novel strategy for interrupting vector-borne pathogen transmission. Following its success in controlling arboviruses spread by Aedes aegypti, this technology is being adapted for anopheline malaria vectors. However, antagonistic interactions between Wolbachia and naturally resident Asaia bacteria in malaria vectors have been demonstrated experimentally, potentially jeopardising Wolbachia biocontrol. We developed the first mathematical model accounting for interspecific competition between endosymbionts to assess the feasibility of this novel strategy for controlling malaria. First, Asaia prevalences among natural mosquito populations were compared with simulations parametrized with rates of Asaia transmission reported from laboratory studies. Discrepancies between projections and natural Asaia prevalences indicated potential overestimation of Asaia transmissibility in artificial laboratory settings. With parametrization that matches natural Asaia prevalence, simulations identified redundancies in Asaia's many infection routes (vertical, sexual and environmental). This resilience was only overcome when Wolbachia conferred very high resistance to environmental infection with Asaia, resulting in Wolbachia fixation and Asaia exclusion. Wolbachia's simulated spread was prevented when its maternal transmission was impeded in coinfected mosquitoes and the pre-control Asaia prevalence was beyond a threshold of 60-75%. This theoretical assessment highlights critical next steps in laboratory experiments to inform this strategy's feasibility. (c) 2022 The Author(s). Published by Elsevier Ltd.
Finding the strongest gene drive: Simulations reveal unexpected performance differences between Anopheles homing suppression drive candidates
21566S. E. Champer, I. K. Kim, A. G. Clark, P. W. Messer and J. Champer, bioRxiv, 2022.03.28.486009. 2022-03-28 12:29:28.
Recent experiments have produced several Anopheles gambiae homing gene drives that disrupt female fertility genes, thereby eventually inducing population collapse. Such drives may be highly effective tools to combat malaria. One such homing drive, based on the zpg promoter driving CRISPR/Cas9, was able to eliminate a cage population of mosquitoes. A second version, purportedly improved upon the first by incorporating an X-shredder element (which biases inheritance towards male offspring), was similarly successful. Here, we re-analyze the data of each of these gene drives and suggest an alternative interpretation of their performance. We assess each suppression drive within an individual-based simulation framework that models mosquito population dynamics in continuous space. We find that the combined homing/X-shredder drive is actually less effective at population suppression within the context of our mosquito population model. In particular, the combined drive often fails to completely suppress the population, instead resulting in an unstable equilibrium between drive and wild-type alleles. By contrast, otherwise similar drives based on the nos promoter may prove to be more promising candidates for future development due to potentially superior performance.Competing Interest StatementThe authors have declared no competing interest.
Cytoplasmic incompatibility: A Wolbachia toxin–antidote mechanism comes into view
21546M. Hochstrasser, Current Biology, 32:R287-R289. 2022-03-28 11:56:01.
The Wolbachia cidA and cidB genes promote bacterial endosymbiont inheritance through the host female germline. CidB is now shown to load into maturing sperm nuclei. Following fertilization, it disrupts paternal chromosome condensation, triggering embryonic arrest if not countered by CidA in Wolbachia-infected eggs.
B-A Chromosome Translocations Possessing an A Centromere Partly Overcome the Root-Restricted Process of Chromosome Elimination in Aegilops speltoides
21726D. Li, A. Ruban, J. Fuchs, H. Kang and A. Houben, Frontiers in Cell and Developmental Biology, 10. 2022-03-28 09:37:44.
Some eukaryotes exhibit dramatic genome size differences between cells of different organs, resulting from the programmed elimination of chromosomes. Aegilops speltoides is an annual diploid species from the Poaceae family, with a maximum number of eight B chromosomes (Bs) in addition to its inherent seven pairs of standard A chromosomes (As). The Bs of this species undergo precise elimination in roots early in embryo development. In areal parts of the plant, the number of Bs is stable. To affect the root restricted process of B chromosome elimination, we employed X-ray mutagenesis, and different types of restructured Bs were identified. Standard Bs were observed in all analyzed shoots of mutagenized plants, while B-A translocations were only observed in 35.7% of F1 plants. In total 40 different B variants inconsistently escaped the elimination process in roots. As a result, mosaicism of B chromosome variants was found in roots. Only a small B chromosome fragment fused to an A chromosome was stably maintained in roots and shoots across F1 to F3 generations. The absence of B-A translocation chromosomes possessing a derived B centromere in root cells implies that the centromere of the B is a key component of the chromosome elimination process.
Field Suppression of Spotted Wing Drosophila (SWD) (Drosophila suzukii Matsumura) Using the Sterile Insect Technique (SIT)
21241R. A. Homem, Z. Mateos-Fierro, R. Jones, D. Gilbert, A. R. McKemey, G. Slade and M. T. Fountain, Insects, 13. 2022-03-26 06:14:15.
Drosophila suzukii (spotted wing drosophila—SWD) is an economically important pest of soft and stone fruit worldwide. Control relies on broad-spectrum insecticides, which are neither fully effective nor environmentally sustainable. The sterile insect technique (SIT) is a proven, effective and environmentally friendly pest-management tool. Here, we investigated, for the first time, the potential of using SIT to control D. suzukii in field conditions without physical barriers that limit insect invasion. A proprietary method of rearing and irradiation with X-rays was used to obtain males that were 99% sterile. Sterile males were released twice per week from April to October 2021 on a site in Kent, UK, where everbearing strawberries were grown in open polytunnels. The infestation of wild female D. suzukii was monitored weekly using red sticky traps with dry lure at the treated site and at two similar control sites that did not receive sterile male releases. Releases of sterile males suppressed the wild female D. suzukii population by up to 91% in comparison with the control sites. We thus demonstrated the feasibility of SIT to achieve season-long control of D. suzukii using early, sustained and dynamically targeted releases of sterile males. This provides a promising environmentally friendly method to control this important pest.
Evolution of eukaryotic centromeres by drive and suppression of selfish genetic elements
21559T. Kumon and M. A. Lampson, Seminars in Cell and Developmental Biology, 2022-03-25 12:12:40.
Despite the universal requirement for faithful chromosome segregation, eukaryotic centromeres are rapidly evolving. It is hypothesized that rapid centromere evolution represents an evolutionary arms race between selfish genetic elements that drive, or propagate at the expense of organismal fitness, and mechanisms that suppress fitness costs. Selfish centromere DNA achieves preferential inheritance in female meiosis by recruiting more effector proteins that alter spindle microtubule interaction dynamics. Parallel pathways for effector recruitment are adaptively evolved to suppress functional differences between centromeres. Opportunities to drive are not limited to female meiosis, and selfish transposons, plasmids and B chromosomes also benefit by maximizing their inheritance. Rapid evolution of selfish genetic elements can diversify suppressor mechanisms in different species that may cause hybrid incompatibility.
Opening up, closing down, or leaving ajar? How applications are used in engaging with publics about gene drive
21287A. W. Russell, A. Stelmach, S. Hartley, L. Carter and S. Raman, Journal of Responsible Innovation, 2022-03-22 12:32:50.
Public engagement and responsible innovation are strongly emphasised in gene drive research, together with the goal of addressing societal challenges, notably, malaria and environmental conservation. We aim to explore whether public engagement is used to ‘open up' or ‘close down' opportunities to shape gene drive research. Drawing on interviews with gene drive developers and stakeholders, we investigate how the public communication of gene drive is conceived. We find that traditional closing-down tendencies remain, but that there are new and encouraging opening-up approaches. Consistent with responsible innovation thinking, these frame gene drive as multifaceted, context-dependent and requiring deeper deliberation. We also identify a third ‘leaving ajar’ approach that seeks to engage with and respond to local communities and modify technological applications to be more acceptable. Innovation system constraints may well temper current aspirations to open up; framing public conversations around understandings of public good could offer a way forward.
CRISPR-mediated knockout of cardinal and cinnabar eye pigmentation genes in the western tarnished plant bug
21243C. C. Heu, R. J. Gross, K. P. Le, D. M. LeRoy, B. Fan, J. J. Hull, C. S. Brent and J. A. Fabrick, Scientific Reports, 12. 2022-03-22 06:19:14.
The western tarnished plant bug, Lygus hesperus, is a key hemipteran pest of numerous agricultural, horticultural, and industrial crops in the western United States and Mexico. A lack of genetic tools in L. hesperus hinders progress in functional genomics and in developing innovative pest control methods such as gene drive. Here, using RNA interference (RNAi) against cardinal (LhCd), cinnabar (LhCn), and white (LhW), we showed that knockdown of LhW was lethal to developing embryos, while knockdown of LhCd or LhCn produced bright red eye phenotypes, in contrast to wild-type brown eyes. We further used CRISPR/Cas9 (clustered regularly interspaced palindromic repeats/CRISPR-associated) genome editing to generate germline knockouts of both LhCd (Card) and LhCn (Cinn), producing separate strains of L. hesperus characterized by mutant eye phenotypes. Although the cardinal knockout strain Card exhibited a gradual darkening of the eyes to brown typical of the wild-type line later in nymphal development, we observed bright red eyes throughout all life stages in the cinnabar knockout strain Cinn, making it a viable marker for tracking gene editing in L. hesperus. These results provide evidence that CRISPR/Cas9 gene editing functions in L. hesperus and that eye pigmentation genes are useful for tracking the successful genetic manipulation of this insect.
An agent-based model to simulate the boosted Sterile Insect Technique for fruit fly management
22556E. G. Diouf, T. Brévault, S. Ndiaye, E. Faye, A. Chailleux, P. Diatta and C. Piou, Ecological Modelling, 468:109951. 2022-03-18 14:58:33.
The sterile insect technique (SIT) is a method of biological control of pests and disease vector insects. It includes mass-rearing and release of sterile males of the target species so that wild females mated with sterile males would not produce offspring. An innovative version of this technique, called boosted SIT, relies on the use of sterile males as vectors of biocides to trigger an epizootic in the wild fruit fly population. We built an agent-based model to assess the feasibility of this technique and main modalities of field implementation for the control of the Oriental fruit fly, Bactrocera dorsalis, using the entomopathogenic fungi, Metarizhium anisopliae, as a biocide. The model, called BOOSTIT (BactrOcera dOrsaliS boosTed sIT), simulates the spatio-temporal population dynamics of fruit flies in three different realistic landscape contexts. The releases of infected and uninfected sterile males were simulated and allowed the transmission of the pathogen within the wild fly population as a result of interactions between individuals. A main output was the measurement of losses in mango production. Validation of the model was done by comparing the simulated population dynamics with data from field monitoring (pheromone traps) in three landscapes of the Niayes area in Senegal. The population dynamics of wild flies were then simulated in an intensive cropping and mono-mango cultivar landscape under three scenarios: (1) without the release of sterile males, (2) with the release of non-contaminated sterile males (SIT) and (3) with the release of sterile contaminated males (boosted SIT). The results showed that SIT and boosted SIT strongly reduced the density of wild flies and the amount of infested fruits. Although parameters of the pathogen transfer between individuals need to be studied more deeply, results encourage the implementation of field trials to validate the efficacy of boosted SIT to control fruit flies.
Symbionts and gene drive: two strategies to combat vector-borne disease
21029G.-H. Wang, J. Du, C. Y. Chu, M. Madhav, G. L. Hughes and J. Champer, Trends in Genetics, 2022-03-18 07:56:11.
Mosquitoes bring global health problems by transmitting parasites and viruses such as malaria and dengue. Unfortunately, current insecticide-based control strategies are only moderately effective because of high cost and resistance. Thus, scalable, sustainable, and cost-effective strategies are needed for mosquito-borne disease control. Symbiont-based and genome engineering-based approaches provide new tools that show promise for meeting these criteria, enabling modification or suppression approaches. Symbiotic bacteria like Wolbachia are maternally inherited and manipulate mosquito host reproduction to enhance their vertical transmission. Genome engineering-based gene drive methods, in which mosquitoes are genetically altered to spread drive alleles throughout wild populations, are also proving to be a potentially powerful approach in the laboratory. Here, we review the latest developments in both symbionts and gene drive-based methods. We describe some notable similarities, as well as distinctions and obstacles, relating to these promising technologies.
Differential viral RNA methylation contributes to pathogen blocking in Wolbachia-colonized arthropods
20977T. Bhattacharya, L. Yan, J. M. Crawford, H. Zaher, I. L. G. Newton and R. W. Hardy, PLoS Pathogens, 18:e1010393. 2022-03-16 07:40:04.
Arthropod endosymbiont Wolbachia pipientis is part of a global biocontrol strategy to reduce the replication of mosquito-borne RNA viruses such as alphaviruses. We previously demonstrated the importance of a host cytosine methyltransferase, DNMT2, in Drosophila and viral RNA as a cellular target during pathogen-blocking. Here we report a role for DNMT2 in Wolbachia-induced alphavirus inhibition in Aedes species. Expression of DNMT2 in mosquito tissues, including the salivary glands, is elevated upon virus infection. Notably, this is suppressed in Wolbachia-colonized animals, coincident with reduced virus replication and decreased infectivity of progeny virus. Ectopic expression of DNMT2 in cultured Aedes cells is proviral, increasing progeny virus infectivity, and this effect of DNMT2 on virus replication and infectivity is dependent on its methyltransferase activity. Finally, examining the effects of Wolbachia on modifications of viral RNA by LC-MS show a decrease in the amount of 5-methylcytosine modification consistent with the down-regulation of DNMT2 in Wolbachia colonized mosquito cells and animals. Collectively, our findings support the conclusion that disruption of 5-methylcytosine modification of viral RNA is a vital mechanism operative in pathogen blocking. These data also emphasize the essential role of epitranscriptomic modifications in regulating fundamental alphavirus replication and transmission processes.
Could species-focused suppression of Aedes aegypti, the yellow fever mosquito, and Aedes albopictus, the tiger mosquito, affect interacting predators? An evidence synthesis from the literature
20971J. A. S. Bonds, C. M. Collins and L.-C. Gouagna, Pest Management Science, 2022-03-16 07:20:33.
The risks of Aedes aegypti and Aedes albopictus nuisance and vector-borne diseases are rising and the adverse effects of broad-spectrum insecticide application has promoted species-specific techniques, such as sterile insect technique (SIT) and other genetic strategies, as contenders in their control operations. When specific vector suppression is proposed, potential effects on predators and wider ecosystem are some of the first stakeholder questions. These are not the only Aedes vectors of human diseases, but are those for which SIT and genetic strategies are of most interest. They vary ecologically and in habitat origin, but both have behaviourally human-adapted forms with expanding ranges. The aquatic life stages are where predation is strongest due to greater resource predictability and limited escape opportunity. These vectors' anthropic forms usually use ephemeral water bodies and man-made containers as larval habitats; predators that occur in these are mobile, opportunistic and generalist. No literature indicates that any predator depends on larvae of either species. As adults, foraging theory predicts these mosquitoes are of low profitability to predators. Energy expended hunting and consuming will mostly outweigh their energetic benefit. Moreover, as adult biomass is mobile and largely disaggregated, any predator is likely to be a generalist and opportunist. This work, which summarises much of the literature currently available on the predators of Ae. aegypti and Ae. albopictus, indicates it is highly unlikely that any predator species depends on them. Species-specific vector control to reduce nuisance and disease is thus likely to be of negligible or limited impact on non-target predators
Evaluation of Additional Drosophila suzukii Male-Only Strains Generated Through Remobilization of an FL19 Transgene
25425A. Yamamoto, A. K. Yadav and M. J. Scott, Frontiers in Bioengineering and Biotechnology, 10. 2022-03-15 08:27:00.
Drosophila suzukii (D. suzukii) (Matsumura, 1931; Diptera: Drosophilidae), also known as spotted wing Drosophila, is a worldwide pest of fruits with soft skins such as blueberries and cherries. Originally from Asia, D. suzukii is now present in the Americas and Europe and has become a significant economic pest. Growers largely rely on insecticides for the control of D. suzukii. Genetic strategies offer a species-specific environmentally friendly way for suppression of D. suzukii populations. We previously developed a transgenic strain of D. suzukii that produced only males on a diet that did not contain tetracycline. The strain carried a single copy of the FL19 construct on chromosome 3. Repeated releases of an excess of FL19 males led to suppression of D. suzukii populations in laboratory cage trials. Females died as a consequence of overexpression of the tetracycline transactivator (tTA) and tTA-activated expression of the head involution defective proapoptotic gene. The aim of this study was to generate additional male-only strains that carried two copies of the FL19 transgene through crossing the original line with a piggyBac jumpstarter strain. Males that carried either two chromosome 3 or a singleX-linked transgene were identified through stronger expression of the red fluorescent protein marker gene. The brighter fluorescence of the X-linked lines was likely due to dosage compensation of the red fluorescent protein gene. In total, four X-linked lines and eleven lines with two copies on chromosome 3 were obtained, of which five were further examined. All but one of the strains produced only males on a diet without tetracycline. When crossed with wild type virgin females, all of the five two copy autosomal strains examined produced only males. However, the single copy X-linked lines did not show dominant female lethality. Five of the autosomal lines were further evaluated for productivity (egg to adult) and male competition. Based on these results, the most promising lines have been selected for future population suppression experiments with strains from different geographical locations.
Modelling homing suppression gene drive in haplodiploid organisms
21016Y. Liu and J. Champer, bioRxiv, 2021.10.12.464047. 2022-03-15 06:38:01.
Gene drives have shown great promise for suppression of pest populations. These engineered alleles can function by a variety of mechanisms, but the most common is the CRISPR homing drive, which converts wild-type alleles to drive alleles in the germline of heterozygotes. Some potential target species are haplodiploid, in which males develop from unfertilized eggs and thus have only one copy of each chromosome. This prevents drive conversion, a substantial disadvantage compared to diploids where drive conversion can take place in both sexes. Here, we study homing suppression gene drives in haplodiploids and find that a drive targeting a female fertility gene could still be successful. However, such drives are less powerful than in diploids and suffer more from functional resistance alleles. They are substantially more vulnerable to high resistance allele formation in the embryo due to maternally deposited Cas9 and gRNA and also to somatic cleavage activity. Examining spatial models where organisms move over a continuous landscape, we find that haplodiploid suppression drives surprisingly perform nearly as well as in diploids, possibly due to their ability to spread further before inducing strong suppression. Together, these results indicate that gene drive can potentially be used to effectively suppress haplodiploid populations.Competing Interest StatementThe authors have declared no competing interest.
Combining two Genetic Sexing Strains allows sorting of non-transgenic males for Aedes genetic control
20642C. Lutrat, M. Burckbuchler, R. P. Olmo, R. Beugnon, A. Fontaine, T. Baldet, J. Bouyer and E. Marois, bioRxiv, 2022.03.11.483912. 2022-03-12 08:15:59.
Chemical control of the mosquito vectors Aedes albopictus and Aedes aegypti is costly, unsustainable, and increasingly ineffective due to the spread of insecticide resistance. The Sterile Insect Technique is an autocidal control tactic that represents a valuable alternative but is limited by the slow, error-prone, and wasteful sex-separation stage. Here, we present four genetic sexing strains (two for each Aedes species) based on fluorescence markers linked to the m and M sex loci, allowing the isolation of transgenic males. Furthermore, we show how combining these sexing strains allows the production of non-transgenic males. Scaling-up would allow the sorting of 100,000 neonate male larvae in under 1.5 hour with 0.01-0.1% female contamination. The resulting males present similar survival and flight ability to laboratory-reared wild-type males. By facilitating the sorting of transgenic or non-transgenic males, these Genetic Sexing Strains should enable a major upscaling in control programmes against these major vectors.Competing Interest StatementThe authors have declared no competing interest.
California Residents’ Perceptions of Gene Drive Systems to Control Mosquito-Borne Disease
20593C. E. Schairer, C. Triplett, O. S. Akbari and C. S. Bloss, Frontiers in Bioengineering and Biotechnology, 10. 2022-03-10 11:37:23.
Scientists developing gene drive mosquitoes for vector control must understand how residents of affected areas regard both the problem of mosquito-borne disease and the potential solutions offered by gene drive. This study represents an experiment in public engagement at an early stage of technology development, intended to inform lab scientists about public attitudes toward their research and inspire consideration and conversation about the social ramifications of creating mosquitoes with gene drive. Online focus groups with California residents explored views on mosquito-borne disease risk, current mosquito control methods, and the proposed development and use of different classes of gene drives to control Ae. aegypti. Rather than a dogmatic rejection of genetic engineering or gene drive, many participants expressed pragmatic concerns with cost, control, the ability to narrowly target specific species, and the challenges of mistrust and institutional cooperation. Work like this can inform the alignment of community priorities and the professional priorities of scientists and vector control specialists.
Wolbachia wAlbB inhibits bluetongue and epizootic hemorrhagic fever viruses in Culicoides midge cells
20630M. L. Matthews, H. O. Covey, B. S. Drolet and C. L. Brelsfoard, Medical and Veterinary Entomology, 2022-03-10 07:56:14.
Abstract Culicoides midges are hematophagous insects that transmit arboviruses of veterinary importance. These viruses include bluetongue virus (BTV) and epizootic hemorrhagic fever virus (EHDV). The endosymbiont Wolbachia pipientis Hertig spreads rapidly through insect host populations and has been demonstrated to inhibit viral pathogen transmission in multiple mosquito vectors. Here, we have demonstrated a replication inhibitory effect on BTV and EHDV in a Wolbachia (wAlbB strain)-infected Culicoides sonorensis Wirth and Jones W8 cell line. Viral replication was significantly reduced by day 5 for BTV and by day 2 for EHDV as detected by real-time polymerase chain reaction (RT-qPCR) of the non-structural NS3 gene of both viruses. Evaluation of innate cellular immune responses as a cause of the inhibitory effect showed responses associated with BTV but not with EHDV infection. Wolbachia density also did not play a role in the observed pathogen inhibitory effects, and an alternative hypothesis is suggested. Applications of Wolbachia-mediated pathogen interference to impact disease transmission by Culicoides midges are discussed.
No Sting in the Tail for Sterile Bisex Queensland Fruit Fly (Bactrocera tryoni Froggatt) Release Programs
20589O. L. Reynolds, D. Collins, B. C. Dominiak and T. Osborne, Insects, 2022-03-09 11:29:49.
Global markets do not tolerate the presence of fruit fly (Tephritidae) in horticultural produce. A key method of control for tephritidae pests, is the sterile insect technique (SIT). Several countries release a bisex strain, i.e., males and females, however the sterile male is the only sex which contributes to wild population declines when released en masse. In commercial orchards, there are concerns that sterile females released as part of bisex strains, may oviposit, i.e., ‘sting’ and cause damage to fruit, rendering it unmarketable. Australia has released a bisex strain of sterile Queensland fruit fly, Bactrocera tryoni Froggatt, for several decades to suppress wild pest populations, particularly in peri-urban and urban environments. Here, we assessed fruit damage in two commercially grown stone fruit orchards where bisex sterile B. tryoni were released, and in an orchard that did not receive sterile flies. The number of detected stings were higher in only one SIT release orchard, compared with the control; however, there was no difference between SIT and control orchards in the number of larvae detected. We showed that there is no evidence that sterile female B. tryoni released in large numbers caused stings, or damage that led to downgraded or unsaleable fruit. The bisex strain of sterile B. tryoni is recommended for use in commercial stone-fruit orchards, under the conditions in which this trial was conducted.
Rescue by gene swamping as a gene drive deployment strategy
20587K. D. Harris and G. Greenbaum, bioRxiv, 2022.03.08.483503. 2022-03-08 11:25:49.
Gene drives are genetic constructs that can spread deleterious alleles with potential application to population suppression of harmful species. Given that a gene drive can potentially spill over to other populations or even other species, control measures and fail-safes strategies must be considered. Gene drives are designed to generate a rapid demographic decline, while at the same time generating a dynamic change in the population’s genetics. Since these evolutionary and demographic processes are linked and are expected to occur at a similar time-scale during gene drive spread, feedback between these processes may significantly affect the outcome of deployment. To study this feedback and to understand how it affects gene drive spillovers, we developed a gene drive model that combines evolutionary and demographic dynamics in a two-population setting. The model demonstrates how feedback between evolutionary and demographic dynamics can generate additional outcomes to those generated by the evolutionary dynamics alone. We identify an outcome of particular interest, where the short-term suppression of the target population is followed by gene swamping and loss of the gene drive. This outcome could be useful for designing gene drive deployments that temporarily suppress the population, but ultimately do not remain in the population. Using our model, we demonstrate the robustness of this outcome to spillover and to the evolution of resistance, and suggest that it could be used as a fail-safe strategy for gene drive deployment.Competing Interest StatementThe authors have declared no competing interest.
Selfish migrants: How a meiotic driver is selected to increase dispersal
20575J. N. Runge, H. Kokko and A. K. Lindholm, J Evol Biol, 2022-03-07 10:54:44.
Meiotic drivers are selfish genetic elements that manipulate meiosis to increase their transmission to the next generation to the detriment of the rest of the genome. One example is the t haplotype in house mice, which is a naturally occurring meiotic driver with deleterious traits-poor fitness in polyandrous matings and homozygote inviability or infertility-that prevent its fixation. Recently, we discovered and validated a novel effect of t in a long-term field study on free-living wild house mice and with experiments: t-carriers are more likely to disperse. Here, we ask what known traits of the t haplotype can select for a difference in dispersal between t-carriers and wildtype mice. To that end, we built individual-based models with dispersal loci on the t and the homologous wildtype chromosomes. We also allow for density-dependent expression of these loci. The t haplotype consistently evolves to increase the dispersal propensity of its carriers, particularly at high densities. By examining variants of the model that modify different costs caused by t, we show that the increase in dispersal is driven by the deleterious traits of t, disadvantage in polyandrous matings and lethal homozygosity or male sterility. Finally, we show that an increase in driver-carrier dispersal can evolve across a range of values in driver strength and disadvantages.
Gene drives and population persistence vs elimination: The impact of spatial structure and inbreeding at low density
20529P. J. Beaghton and A. Burt, Theoretical Population Biology, 2022-03-03 08:28:52.
Synthetic gene drive constructs are being developed to control disease vectors, invasive species, and other pest species. In a well-mixed random mating population a sufficiently strong gene drive is expected to eliminate a target population, but it is not clear whether the same is true when spatial processes play a role. In species with an appropriate biology it is possible that drive-induced reductions in density might lead to increased inbreeding, reducing the efficacy of drive, eventually leading to suppression rather than elimination, regardless of how strong the drive is. To investigate this question we analyse a series of explicitly solvable stochastic models considering a range of scenarios for the relative timing of mating, reproduction, and dispersal and analyse the impact of two different types of gene drive, a Driving Y chromosome and a homing construct targeting an essential gene. We find in all cases a sufficiently strong Driving Y will go to fixation and the population will be eliminated, except in the one life history scenario (reproduction and mating in patches followed by dispersal) where low density leads to increased inbreeding, in which case the population persists indefinitely, tending to either a stable equilibrium or a limit cycle. These dynamics arise because Driving Y males have reduced mating success, particularly at low densities, due to having fewer sisters to mate with. Increased inbreeding at low densities can also prevent a homing construct from eliminating a population. For both types of drive, if there is strong inbreeding depression, then the population cannot be rescued by inbreeding and it is eliminated. These results highlight the potentially critical role that low-density-induced inbreeding and inbreeding depression (and, by extension, other sources of Allee effects) can have on the eventual impact of a gene drive on a target population.
EVITA Dengue: a cluster-randomized controlled trial to EValuate the efficacy of Wolbachia-InfecTed Aedes aegypti mosquitoes in reducing the incidence of Arboviral infection in Brazil
20526M. H. Collins, G. E. Potter, M. D. T. Hitchings, E. Butler, M. Wiles, J. K. Kennedy, S. B. Pinto, A. B. M. Teixeira, A. Casanovas-Massana, N. G. Rouphael, G. A. Deye, C. P. Simmons, L. A. Moreira, M. L. Nogueira, D. A. T. Cummings, A. I. Ko, M. M. Teixeir, Trials, 23:185. 2022-03-02 08:20:38.
BACKGROUND: Arboviruses transmitted by Aedes aegypti including dengue, Zika, and chikungunya are a major global health problem, with over 2.5 billion at risk for dengue alone. There are no licensed antivirals for these infections, and safe and effective vaccines are not yet widely available. Thus, prevention of arbovirus transmission by vector modification is a novel approach being pursued by multiple researchers. However, the field needs high-quality evidence derived from randomized, controlled trials upon which to base the implementation and maintenance of vector control programs. Here, we report the EVITA Dengue trial design (DMID 17-0111), which assesses the efficacy in decreasing arbovirus transmission of an innovative approach developed by the World Mosquito Program for vector modification of Aedes mosquitoes by Wolbachia pipientis. METHODS: DMID 17-0111 is a cluster-randomized trial in Belo Horizonte, Brazil, with clusters defined by primary school catchment areas. Clusters (n = 58) will be randomized 1:1 to intervention (release of Wolbachia-infected Aedes aegypti mosquitoes) vs. control (no release). Standard vector control activities (i.e., insecticides and education campaigns for reduction of mosquito breeding sites) will continue as per current practice in the municipality. Participants (n = 3480, 60 per cluster) are children aged 6-11 years enrolled in the cluster-defining school and living within the cluster boundaries who will undergo annual serologic surveillance for arboviral infection. The primary objective is to compare sero-incidence of arboviral infection between arms. DISCUSSION: DMID 17-0111 aims to determine the efficacy of Wolbachia-infected mosquito releases in reducing human infections by arboviruses transmitted by Aedes aegypti and will complement the mounting evidence for this method from large-scale field releases and ongoing trials. The trial also represents a critical step towards robustness and rigor for how vector control methods are assessed, including the simultaneous measurement and correlation of entomologic and epidemiologic outcomes. Data from this trial will inform further the development of novel vector control methods. TRIAL REGISTRATION: ClinicalTrials.gov NCT04514107 . Registered on 17 August 2020 Primary sponsor: National Institute of Health, National Institute of Allergy and Infectious Diseases.
Increased biting rate and decreased Wolbachia density in irradiated Aedes mosquitoes
20487R. Moretti, E. Lampazzi, C. Damiani, G. Fabbri, G. Lombardi, C. Pioli, A. Desiderio, A. Serrao and M. Calvitti, Parasites and Vectors, 15:67. 2022-02-24 08:48:28.
Releasing considerable numbers of radiation-sterilized males is a promising strategy to suppress mosquito vectors. However, releases may also include small percentages of biting females, which translate to non-negligible numbers when releases are large. Currently, the effects of irradiation on host-seeking and host-biting behaviors have not been exhaustively investigated. Information is also lacking regarding the effects of sterilizing treatment on the endosymbiotic bacterium Wolbachia, which is known to affect the vector competence of infected mosquitos.
Regulation of genetically engineered (GE) mosquitoes as a public health tool: a public health ethics analysis
20480Z. Meghani, Globalization and Health, 18:21. 2022-02-21 08:33:18.
In recent years, genetically engineered (GE) mosquitoes have been proposed as a public health measure against the high incidence of mosquito-borne diseases among the poor in regions of the global South. While uncertainties as well as risks for humans and ecosystems are entailed by the open-release of GE mosquitoes, a powerful global health governance non-state organization is funding the development of and advocating the use of those bio-technologies as public health tools.
Wolbachia in Aedes koreicus: Rare Detections and Possible Implications
20475C. Damiani, A. Cappelli, F. Comandatore, F. Montarsi, A. Serrao, A. Michelutti, M. Bertola, M. V. Mancini, I. Ricci, C. Bandi and G. Favia, Insects, 13. 2022-02-21 08:21:51.
The emerging distribution of new alien mosquito species was recently described in Europe. In addition to the invasion of Aedes albopictus, several studies have focused on monitoring and controlling other invasive Aedes species, as Aedes koreicus and Aedes japonicus. Considering the increasing development of insecticide resistance in Aedes mosquitoes, new control strategies, including the use of bacterial host symbionts, are proposed. However, little is known about the bacterial communities associated with these species, thus the identification of possible candidates for Symbiotic Control is currently limited. The characterization of the natural microbiota of field-collected Ae. koreicus mosquitoes from North-East Italy through PCR screening, identified native infections of Wolbachia in this species that is also largely colonized by Asaia bacteria. Since Asaia and Wolbachia are proposed as novel tools for Symbiotic Control, our study supports their use for innovative control strategies against new invasive species. Although the presence of Asaia was previously characterized in Ae. koreicus, our study characterized this Wolbachia strain, also inferring its phylogenetic position. The co-presence of Wolbachia and Asaia may provide additional information about microbial competition in mosquito, and to select suitable phenotypes for the suppression of pathogen transmission and for the manipulation of host reproduction in Ae. koreicus.
Evaluation of anti-malaria potency of wild and genetically modified Enterobacter cloacae expressing effector proteins in Anopheles stephensi
20485H. Dehghan, S. H. Mosa-Kazemi, B. Yakhchali, N. Maleki-Ravasan, H. Vatandoost and M. A. Oshaghi, Parasites and Vectors, 15:63. 2022-02-19 08:43:23.
Malaria is one of the most lethal infectious diseases in tropical and subtropical areas of the world. Paratransgenesis using symbiotic bacteria offers a sustainable and environmentally friendly strategy to combat this disease. In the study reported here, we evaluated the disruption of malaria transmission in the Anopheles stephensi-Plasmodium berghei assemblage using the wild-type (WT) and three modified strains of the insect gut bacterium, Enterobacter cloacae.
Considerations for homology-based DNA repair in mosquitoes: Impact of sequence heterology and donor template source
20478J. X. D. Ang, K. Nevard, R. Ireland, D.-K. Purusothaman, S. A. N. Verkuijl, L. Shackleford, E. Gonzalez, M. A. E. Anderson and L. Alphey, PLOS Genetics, 18:e1010060. 2022-02-18 08:29:29.
Author summary The field of genetic control of mosquito vectors has progressed rapidly in recent years, especially in Cas9-based control systems, due to its robustness to elicit a species-specific and dispersive control of mosquito population. To generate a Cas9-based integration, Cas9 and sgRNA are used to cleave a chromosomal locus while a plasmid DNA donor, containing a genetic cargo flanked by sequences homologous to the chromosomal locus, is supplied as a repair template. This results in the cargo being copied into the genome through HDR. This form of integration, however, is currently one of the major bottlenecks for researchers as it involves a laborious process of microinjecting mosquito embryos and has rather low integration rates. In this study, we assessed the effects of homologous sequence mismatches and various donor template forms (i.e. plasmid, ssDNA, biotinylated ds/ssDNA) on HDR. We found that sequence mismatches and non-plasmid donors reduced the efficiency and integrity of integration, respectively. By analysing the direction and length of homologous sequence that was copied into the genome concurrently with the cargo, we inferred the mechanism responsible for the integrations observed in our study. These findings will be useful to guide future construct designs for optimal HDR rates in mosquitoes.
Gene drive mosquitoes can aid malaria elimination by retarding Plasmodium sporogonic development
20447A. Hoermann, T. Habtewold, P. Selvaraj, G. Del Corsano, P. Capriotti, M. G. Inghilterra, K. M. Temesgen, G. K. Christophides and N. Windbichler, bioRxiv, 2022.02.15.480588. 2022-02-17 09:41:11.
Gene drives hold promise for the genetic control of malaria vectors. The development of vector population modification strategies hinges on the availability of effector mechanisms impeding parasite development in transgenic mosquitoes. We augmented a midgut gene of the malaria mosquito Anopheles gambiae to secrete two exogenous antimicrobial peptides, Magainin 2 and Melittin. This small genetic modification, capable of efficient non-autonomous gene drive, hampers oocyst development in both Plasmodium falciparum and Plasmodium berghei. It delays the release of infectious sporozoites while it simultaneously reduces the lifespan of homozygous female transgenic mosquitoes. Modeling the spread of this modification using a large-scale agent-based model of malaria epidemiology reveals that it can break the cycle of disease transmission across a range of endemic settings.Competing Interest StatementThe authors have declared no competing interest.
An Ethical Overview of the CRISPR-Based Elimination of Anopheles gambiae to Combat Malaria
20442I. J. Wise and P. Borry, Journal of Bioethical Inquiry, 2022-02-17 09:30:10.
Approximately a quarter of a billion people around the world suffer from malaria each year. Most cases are located in sub-Saharan Africa where Anopheles gambiae mosquitoes are the principal vectors of this public health problem. With the use of CRISPR-based gene drives, the population of mosquitoes can be modified, eventually causing their extinction. First, we discuss the moral status of the organism and argue that using genetically modified mosquitoes to combat malaria should not be abandoned based on some moral value of A. gambiae. Secondly, we argue that environmental impact studies should be performed to obtain an accurate account of the possible effects of a potential eradication of the organism. However, the risks from the purposeful extinction of A. gambiae should not overtake the benefits of eradicating malaria and risk assessments should be used to determine acceptable risks. Thirdly, we argue that the eventual release of the genetically modified mosquitoes will depend on transparency, community involvement, and cooperation between different nations.
A-to-I mRNA editing controls spore death induced by a fungal meiotic drive gene in homologous and heterologous expression systems
20415J. M. Lohmar, N. A. Rhoades, T. N. Patel, R. H. Proctor, T. M. Hammond and D. W. Brown, Genetics, 2022-02-16 16:59:28.
Spore killers are meiotic drive elements that can block development of sexual spores in fungi. In the maize ear rot and mycotoxin-producing fungus Fusarium verticillioides, a spore killer called SkK has been mapped to a 102-kb interval of chromosome V. Here, we show that a gene within this interval, SKC1, is required for SkK-mediated spore killing and meiotic drive. We also demonstrate that SKC1 is associated with at least four transcripts, two sense (sense-SKC1a and sense-SKC1b) and two antisense (antisense-SKC1a and antisense-SKC1b). Both antisense SKC1 transcripts lack obvious protein-coding sequences and thus appear to be non-coding RNAs. In contrast, sense-SKC1a is a protein-coding transcript that undergoes A-to-I editing to sense-SKC1b in sexual tissue. Translation of sense-SKC1a produces a 70 amino acid protein (Skc1a), whereas translation of sense-SKC1b produces an 84 amino acid protein (Skc1b). Heterologous expression analysis of SKC1 transcripts shows that sense-SKC1a also undergoes A-to-I editing to sense-SKC1b during the Neurospora crassa sexual cycle. Site directed mutagenesis studies indicate that Skc1b is responsible for spore killing in F. verticillioides and that it induces most meiotic cells to die in N. crassa. Finally, we report that SKC1 homologs are present in over 20 Fusarium species. Overall, our results demonstrate that fungal meiotic drive elements like SKC1 can influence the outcome of meiosis by hijacking a cell's A-to-I editing machinery and that the involvement of A-to-I editing in a fungal meiotic drive system does not preclude its horizontal transfer to a distantly related species.
A preliminary framework for understanding the governance of novel environmental technologies: Ambiguity, indeterminateness and drift
20412F. Rabitz, M. Feist, M. Honegger, J. Horton, S. Jinnah and J. Reynolds, Earth System Governance, 12:100134. 2022-02-16 16:13:59.
We propose a conceptual framework to explain why some technologies are more difficult to govern than others in global environmental governance. We start from the observation that some technologies pose transboundary environmental risks, some provide capacities for managing such risks, and some do both. For “ambiguous” technologies, potential risks and risk management capacities are uncertain, unknown or even unknowable. Governance systems are indeterminate towards ambiguous technologies, as existing norms, rules, scripts and routines do not imply default solutions under institutional focal points. Indeterminateness can lead to institutional drift, with risks accordingly remaining unmitigated and risk management capacities remaining unexploited. We use the cases of solar geoengineering, gene drive systems and bioinformatics for illustrating this framework. As technological ambiguity may often be irresolvable, we conclude that it might force us to confront the limits to anticipatory global decision-making on matters of long-term environmental sustainability.
Hoisted with his own petard: how sex-ratio meiotic drive in Drosophila affnis creates resistance alleles that limit its spread
20440W.-J. Ma, K. B. Patch, E. M. Knoles, M. M. Shoaib and R. L. Unckless, bioRxiv, 2022.02.14.480432. 2022-02-16 09:24:56.
Meiotic drivers are selfish genetic elements that tinker with gameto-genesis to bias their own transmission into the next generation of off-spring. Such tinkering can have significant consequences on gameto-genesis and end up hampering the spread of the driver. In Drosophila affrnis, sex-ratio meiotic drive is caused by an X-linked complex that, when in males with a susceptible Y chromosome, results in broods that are more than 95% female. Interestingly, D. affrnis males lacking a Y chromosome (XO) are fertile and males with the meiotic drive X and no Y produce only sons - effectively reversing the sex-ratio effect. Here, we show that meiotic drive dramatically increases the rate of nondisjunction of the Y chromosome (at least 50X), meaning that the driver is creating resistant alleles through the process of driving. We then model how the O might influence the spread, dynamics and equilibrium of the sex-ratio X chromosome. We find that the O can prevent the spread or reduce the equilibrium frequency of the sex-ratio X chromosome and it can even lead to oscillations in frequency. Finally, with reasonable parameters, the O is unlikely to lead to the loss of the Y chromosome, but we discuss how it might lead to sex-chromosome turnover indirectly.Competing Interest StatementThe authors have declared no competing interest.
Wolbachia Impacts Anaplasma Infection in Ixodes scapularis Tick Cells
20436K. M. Skinner, J. Underwood, A. Ghosh, A. S. Oliva Chavez and C. L. Brelsfoard, International Journal of Environmental Research and Public Health, 19. 2022-02-16 08:58:32.
The specific interactions of members of tick bacterial microbiota and their effects on pathogen transmission remains relatively unexplored. Here, we introduced a novel Wolbachia infection type into Ixodes scapularis tick cells and examined the antipathogenic effects on the intracellular pathogen Anaplasma phagocytophilum. An increase in A. phagocytophilum replication was observed in Wolbachia-infected tick cells. However, Wolbachia infection densities decreased when cells were serially passaged and ultimately the infection was lost. Host-cell immune response was also examined as an additional factor that could have affected A. phagocytophilum replication in Wolbachia-infected cells. In early passages post-Wolbachia infection, a decreased immune response was observed, but in later passages of cells with low Wolbachia densities, there was no change in the immune response. The results are discussed in relation to the importance of studying the interactions of the tick microbiota, the host cell, and the pathogen and the development of novel tick and tick-borne disease-control approaches.
A Closing Window of Opportunity for Gene Drive Governance in the United States
20445K. L. Warmbrod, M. Montague and G. K. Gronvall, Health Security, 20:3-5. 2022-02-15 09:35:05.
The COVID-19 pandemic has brought forth a number of biotechnological advances to enhance the public's health: new diagnostic tests, mRNA vaccines, and new antiviral medications. Biotechnology is also being used to address global challenges like climate change, food insecurity, and building the bioeconomy, which directly or indirectly improve public health. Gene drives are one such biotechnology. They are genetically engineered systems that can alter the inheritance patterns in a host species, such as a mosquito, so that a greater percentage of its progeny inherit a specific desired trait. Research and investments in biotechnology have been used to reduce arthropod-borne infectious diseases, such as malaria and Zika, and to manage or eliminate invasive species.2 Funding thus far has been adequate. For example, Target Malaria, a global consortium of researchers developing a gene drive to decrease the burden of malaria, has an average of US$11.5 million per year in funding.3 Although no gene drive has been released into the environment yet, technologies with similar attributes have been released in field trials, notably by Oxitec in Florida
Uniqueness and stability of periodic solutions for an interactive wild and Wolbachia-infected male mosquito model
20438R. Yan and Q. Sun, Journal of Biological Dynamics, 2022-02-15 09:03:48.
We investigate a mosquito population suppression model, which includes the release of Wolbachia-infected males causing incomplete cytoplasmic incompatibility (CI). The model consists of two sub-equations by considering the density-dependent birth rate of wild mosquitoes. By assuming the release waiting period T is larger than the sexual lifespan T¯ of Wolbachia-infected males, we derive four thresholds: the CI intensity threshold sh∗, the release amount thresholds g∗ and c∗, and the waiting period threshold T∗. From a biological view, we assume sh > sh∗ throughout the paper. When g∗ < c < c∗, we prove the origin E0 is locally asymptotically stable iff T < T∗, and the model admits a unique T-periodic solution iff T ≥ T∗, which is globally asymptotically stable. When c ≥ c∗, we show the origin E0 is globally asymptotically stable iff T ≤ T∗, and the model has a unique T-periodic solution iff T > T∗, which is globally asymptotically stable. Our theoretical results are confirmed by numerical simulations.
