Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Gene drive strategies of pest control in agricultural systems: challenges and opportunities

17836
M. Legros, J. M. Marshall, S. Macfadyen, K. R. Hayes, A. Sheppard and L. G. Barrett,  Evolutionary Applications,  2021-07-26 14:04:32.
Abstract Recent advances in gene editing technologies have opened new avenues for genetic pest control strategies, in particular around the use of gene drives to suppress or modify pest populations. Significant uncertainty, however, surrounds the applicability of these strategies to novel target species, their efficacy in natural populations, and their eventual safety and acceptability as control methods. In this article we identify issues associated with the potential use of gene drives in agricultural systems, to control pests and diseases that impose a significant cost to agriculture around the world. We first review the need for innovative approaches, and provide an overview of the most relevant biological and ecological traits of agricultural pests that could impact the outcome of gene drive approaches. We then describe the specific challenges associated with using gene drives in agricultural systems, as well as the opportunities that these environments may offer, focusing in particular on the advantages of high-threshold gene drives. Overall we aim to provide a comprehensive view of the potential opportunities and the remaining uncertainties around the use of gene drives in agricultural systems.

Resistance to a CRISPR-based gene drive at an evolutionarily conserved site is revealed by mimicking genotype fixation

17940
S. Fuchs, W. Garrood, A. Beber, A. Hammond, R. Galizi, M. Gribble, G. Morselli, T.-Y. Hui, K. Willis, N. Kranjc, A. Burt, T. Nolan and A. Crisanti,  bioRxiv,  2021-07-26 13:48:52.
CRISPR-based homing gene drives can be designed to disrupt essential genes whilst biasing their own inheritance, leading to suppression of mosquito populations in the laboratory. This class of gene drives relies on CRISPR-Cas9 cleavage of a target sequence and copying (‘homing’) therein of the gene drive element from the homologous chromosome. However, target site mutations that are resistant to cleavage yet maintain the function of the essential gene are expected to be strongly selected for. Targeting functionally constrained regions where mutations are not easily tolerated should lower the probability of resistance. Evolutionary conservation at the sequence level is often a reliable indicator of functional constraint, though the actual level of underlying constraint between one conserved sequence and another can vary widely. Here we generated a novel gene drive in the malaria vector Anopheles gambiae , targeting an ultra-conserved target site in a haplosufficient essential gene (AGAP029113) required during mosquito development, which fulfils many of the criteria for the target of a population suppression gene drive. We then designed a selection regime to experimentally assess the likelihood of generation and subsequent selection of gene drive resistant mutations at its target site. We simulated, in a caged population, a scenario where the gene drive was approaching fixation, where selection for resistance is expected to be strongest. Continuous sampling of the target locus revealed that a single, restorative, in-frame nucleotide substitution was selected. Our findings show that ultra-conservation alone need not be predictive of a site that is refractory to target site resistance. Our strategy to evaluate resistance in vivo could help to validate candidate gene drive targets for their resilience to resistance and help to improve predictions of the invasion dynamics of gene drives in field populations. <h4>Author summary</h4> Gene drives have the potential to be applied as novel control strategy of disease-transmitting mosquitoes, by spreading genetic traits that suppress or modify the target population. Many gene drive elements work by recognising and cutting a specific target sequence in the mosquito genome and copying themselves into that target sequence allowing the gene drive to increase in frequency in the population. Like other mosquito control interventions, efficacy will greatly depend on minimising the development of resistance to the gene drive mechanism - most likely via a change in the target sequence that prevents further cutting. One strategy to reduce resistance is to target sequences that are highly conserved, which implies that changes cannot easily be tolerated. We developed a strategy that simulates high selection pressure, under which resistance is most likely to emerge, and therefore provides a stringent test of its propensity to arise. Unlike previous results with another gene drive, we recovered a resistant allele within a few generations of gene drive exposure and at high frequency. Our results show that conserved sequences can vary hugely in ability to tolerate mutations and highlights the need to functionally validate future candidate gene drive target sites for their robustness to resistance.

Risk management recommendations for environmental releases of gene drive modified insects

17829
Y. Devos, J. D. Mumford, M. B. Bonsall, D. C. M. Glandorf and H. D. Quemada,  Biotechnology Advances,  2021-07-25 13:02:06.
The ability to engineer gene drives (genetic elements that bias their own inheritance) has sparked enthusiasm and concerns. Engineered gene drives could potentially be used to address long-standing challenges in the control of insect disease vectors, agricultural pests and invasive species, or help to rescue endangered species. However, risk concerns and uncertainty associated with potential environmental release of gene drive modified insects (GDMIs) have led some stakeholders to call for a global moratorium on such releases or the application of other strict precautionary measures to mitigate perceived risk assessment and risk management challenges. Instead, we provide recommendations that may help to improve the relevance of risk assessment and risk management frameworks for environmental releases of GDMIs. These recommendations include: (1) developing additional and more practical risk assessment guidance to ensure appropriate levels of safety; (2) making policy goals and regulatory decision-making criteria operational for use in risk assessment so that what constitutes harm is clearly defined; (3) ensuring a more dynamic interplay between risk assessment and risk management to manage uncertainty through closely interlinked pre-release modelling and post-release monitoring; (4) considering potential risks against potential benefits, and comparing them with those of alternative actions to account for a wider (management) context; and (5) implementing a modular, phased approach to authorisations for incremental acceptance and management of risks and uncertainty. Along with providing stakeholder engagement opportunities in the risk analysis process, the recommendations proposed may enable risk managers to make choices that are more proportionate and adaptive to potential risks, uncertainty and benefits of GDMI applications, and socially robust.

The Aedes aegypti (Diptera: Culicidae) hsp83 Gene Promoter Drives Strong Ubiquitous DsRed and ZsGreen Marker Expression in Transgenic Mosquitoes

18145
S. H. Webster and M. J. Scott,  Journal of Medical Entomology,  2021-07-24 17:29:43.
Transgenic strains of the mosquito disease vector Aedes aegypti (L.) are being developed for population suppression or modification. Transgenic mosquitoes are identified using fluorescent protein genes. Here we describe DsRed and ZsGreen marker genes driven by the constitutive Ae. aegypti heat shock protein 83 (hsp83) promoter in transgenic mosquitoes. Transgenic larvae and pupae show strong full body expression of the red and green fluorescent proteins. This greatly assists in screening for transgenic individuals while making new or maintaining already established lines. Transient marker gene expression after embryo microinjection was readily visible in developing larvae allowing the separation of individuals that are more likely to produce transgenic offspring. The strongly expressed marker genes developed in this study should facilitate the detection of transgenic Ae. aegypti larvae or pupae in the field.

Sex separation of Aedes spp. mosquitoes for sterile insect technique application: a review

17905
B. M. Moran-Aceves, C. F. Marina, A. Dor, P. Liedo and J. Toledo,  Entomologia Experimentalis Et Applicata,  10. 2021-07-24 15:04:30.
Separation of the sexes is necessary for the application of the sterile insect technique (SIT) in mosquitoes due to the hematophagous habits and disease vector activity of the females. In this review we analyze the history, current status, and future perspectives for the development of genetic sexing strains (GSS) of Aedes mosquitoes (Diptera: Culicidae). Various genetic control methods for mosquitoes are reviewed, as are their need for sex-separation methods. We focus on areas of opportunity where GSS developed with classical genetic methods can be used. Regulatory restrictions and social acceptance of various control methods are analyzed. We conclude that the development of GSS by classical methods represents the most viable option for separation of the sexes and the application of large-scale SIT programs within an area-wide integrated vector management (AW-IVM) approach.

Wolbachia as translational science: controlling mosquito-borne pathogens

17799
E. P. Caragata, H. L. C. Dutra, P. H. F. Sucupira, A. G. A. Ferreira and L. A. Moreira,  Trends in Parasitology,  2021-07-22 20:54:55.
In this review we examine how exploiting the Wolbachia?mosquito relationship has become an increasingly popular strategy for controlling arbovirus transmission. Field deployments of Wolbachia-infected mosquitoes have led to significant decreases in dengue virus incidence via high levels of mosquito population suppression and replacement, emphasizing the success of Wolbachia approaches. Here, we examine how improved knowledge of Wolbachia?host interactions has provided key insight into the mechanisms of the essential phenotypes of pathogen blocking and cytoplasmic incompatibility. And we discuss recent studies demonstrating that extrinsic factors, such as ambient temperature, can modulate Wolbachia density and maternal transmission. Finally, we assess the prospects of using Wolbachia to control other vectors and agricultural pest species.

CRISPR/Cas-9 mediated knock-in by homology dependent repair in the West Nile Virus vector Culex quinquefasciatus Say

17811
D.-K. Purusothaman, L. Shackleford, M. A. E. Anderson, T. Harvey-Samuel and L. Alphey,  Scientific Reports,  11:14964. 2021-07-22 14:14:08.
Culex quinquefasciatus Say is a mosquito distributed in both tropical and subtropical regions of the world. It is a night-active, opportunistic blood-feeder and vectors many animal and human diseases, including West Nile Virus and avian malaria. Current vector control methods (e.g. physical/chemical) are increasingly ineffective; use of insecticides also imposes hazards to both human and ecosystem health. Advances in genome editing have allowed the development of genetic insect control methods, which are species-specific and, theoretically, highly effective. CRISPR/Cas9 is a bacteria-derived programmable gene editing tool that is functional in a range of species. We describe the first successful germline gene knock-in by homology dependent repair in C. quinquefasciatus. Using CRISPR/Cas9, we integrated an sgRNA expression cassette and marker gene encoding a fluorescent protein fluorophore (Hr5/IE1-DsRed, Cq7SK-sgRNA) into the kynurenine 3-monooxygenase (kmo) gene. We achieved a minimum transformation rate of 2.8%, similar to rates in other mosquito species. Precise knock-in at the intended locus was confirmed. Insertion homozygotes displayed a white eye phenotype in early-mid larvae and a recessive lethal phenotype by pupation. This work provides an efficient method for engineering C. quinquefasciatus, providing a new tool for developing genetic control tools for this vector.

Using Moderate Transgene Expression to Improve the Genetic Sexing System of the Australian Sheep Blow Fly Lucilia cuprina

17753
Y. Yan, M. E. Williamson and M. J. Scott,  Insects,  11. 2021-07-19 14:36:16.
The sterile insect technique (SIT) is a promising strategy to control the Australian sheep blow fly Lucilia cuprina, a major pest of sheep. We have previously developed a transgenic embryonic sexing system (TESS) for this pest to facilitate the potential SIT application. TESS carry two transgenes, a tetracycline transactivator (tTA) driver and a tTA-activated pro-apoptotic effector. TESS females die at the embryonic stage unless tetracycline is supplied in the diet. However, undesired female sterility was observed in some TESS strains without tetracycline due to expression of tTA in ovaries. Here we investigate if TESS that combine transgenes with relatively low/moderate expression/activity improves the fertility of TESS females. tTA driver lines were evaluated for tTA expression by quantitative real time PCR and/or by crossing with a tTA-activated RFPex effector line. Fertility and lethality tests showed that a TESS strain containing a driver line with moderate tTA expression and an effector line showing moderate pro-apoptotic activity could recover the fertility of parental females and eliminated all female offspring at the embryonic stage. Consequently, such a strain could be further evaluated for an SIT program for L. cuprina, and such a “moderate strategy” could be considered for the TESS development in other pest species.

Combating mosquito-borne diseases using genetic control technologies

17735
G.-H. Wang, S. Gamez, R. R. Raban, J. M. Marshall, L. Alphey, M. Li, J. L. Rasgon and O. S. Akbari,  Nature Communications,  12:4388. 2021-07-19 13:06:45.
Mosquito-borne diseases, such as dengue and malaria, pose significant global health burdens. Unfortunately, current control methods based on insecticides and environmental maintenance have fallen short of eliminating the disease burden. Scalable, deployable, genetic-based solutions are sought to reduce the transmission risk of these diseases. Pathogen-blocking Wolbachia bacteria, or genome engineering-based mosquito control strategies including gene drives have been developed to address these problems, both requiring the release of modified mosquitoes into the environment. Here, we review the latest developments, notable similarities, and critical distinctions between these promising technologies and discuss their future applications for mosquito-borne disease control.

The Possible Role of Microorganisms in Mosquito Mass Rearing

17741
L. Chersoni, A. Checcucci, M. Malfacini, A. Puggioli, F. Balestrino, M. Carrieri, I. Piunti, M. L. Dindo, P. Mattarelli and R. Bellini,  Insects,  12. 2021-07-15 13:10:37.
In Europe, one of the most significant mosquitoes of public health importance is Aedes albopictus (Skuse), an allochthonous species of Asian origin. One of the most promising control methods against Aedes albopictus is the sterile insect technique (SIT), which consists of mass rearing the target species, separation of males from females, and male exposure to sterilizing ionizing radiation. Once released in the environment, the sterile males are expected to search for wild females to mate with. If mating occurs, no offspring is produced. The quality of sterile males is a crucial aspect in SIT programs in order to optimize effectiveness and limit production costs. The integration of probiotic microorganisms in larval and adult mosquito diets could enhance the quality parameters of the released sterile males. In this review, we attempt to give the most representative picture of the present knowledge on the relationships between gut microbiota of mosquitoes and the natural or artificial larval diet. Furthermore, the possible use of probiotic microorganisms for mosquito larvae rearing is explored. Based on the limited amount of data found in the literature, we hypothesize that a better understanding of the interaction between mosquitoes and their microbiota may bring significant improvements in mosquito mass rearing for SIT purposes.

Sterile Insect Technique (SIT) and Its Applications

17733
K. Bourtzis and M. J. B. Vreysen,  Insects,  12. 2021-07-13 15:57:10.
Although most insect species have a beneficial role in the ecosystems, some of them represent major plant pests and disease vectors for livestock and humans. During the last six–seven decades, the sterile insect technique (SIT) has been used as part of area-wide integrated pest management strategies to suppress, contain, locally eradicate or prevent the (re)invasion of insect pest populations and disease vectors worldwide. This Special Issue on “Sterile insect technique (SIT) and its applications”, which consists of 27 manuscripts (7 reviews and 20 original research articles), provides an update on the research and development efforts in this area. The manuscripts report on all the different components of the SIT package including mass-rearing, development of genetic sexing strains, irradiation, quality control as well as field trials.

Autocatalytic-protection for an unknown locus CRISPR-Cas countermeasure for undesired mutagenic chain reactions

17969
E. Schonfeld, E. Schonfeld and D. Schonfeld,  Journal of Theoretical Biology,  528:110831. 2021-07-11 13:41:33.
The mutagenic chain reaction (MCR) is a genetic tool to use a CRISPR–Cas construct to introduce a homing endonuclease, allowing gene drive to influence whole populations in a minimal number of generations (Esvelt et al., 2014, Gantz and Bier, 2015, Gantz and Bier, 2016). The question arises: if an active genetic terror event is released into a population, could we prevent the total spread of the undesired allele (Gantz, et al., 2015, Webber et al., 2015)? Thus far, effective protection methods require knowledge of the terror locus (Grunwald et al., 2019). Here we introduce a novel approach, an autocatalytic-Protection for an Unknown Locus (a-PUL), whose aim is to spread through a population and arrest and decrease an active terror event’s spread without any prior knowledge of the terror-modified locus, thus allowing later natural selection and ERACR drives to restore the normal locus (Hammond et al., 2017). a-PUL, using a mutagenic chain reaction, includes (i) a segment encoding a non-Cas9 endonuclease capable of homology-directed repair suggested as Type II endonuclease Cpf1 (Cas12a), (ii) a ubiquitously-expressed gene encoding a gRNA (gRNA1) with a U4AU4 3′-overhang specific to Cpf1 and with crRNA specific to some desired genomic sequence of non-coding DNA, (iii) a ubiquitously-expressed gene encoding two gRNAs (gRNA2/gRNA3) both with tracrRNA specific to Cas9 and crRNA specific to two distinct sites of the Cas9 locus, and (iv) homology arms flanking the Cpf1/gRNA1/gRNA2/gRNA3 cassette that are identical to the region surrounding the target cut directed by gRNA1 (Khan, 2016, Zetsche et al., 2015). We demonstrate the proof-of-concept and efficacy of our protection construct through a Graphical Markov model and computer simulation.

Earth system interventions as technologies of the Anthropocene

17730
J. L. Reynolds,  Environmental Innovation and Societal Transitions,  40:132-146. 2021-07-10 15:16:46.
Earth system interventions (ESIs)—intentional large-scale interventions in Earth systems—are not entirely new. However, in response to threats to sustainability, particularly from climate change and biodiversity loss, some scientists and others are researching, developing, and using new, largely technological ESIs. These include carbon dioxide removal, solar geoengineering, in situ genetically modified organisms, gene drive organisms, de-extinction, and high-tech ecosystem restoration. Some emerging ESIs appear to be effective and feasible, both technically and economically, and may be necessary to achieve important sustainability and human welfare objectives. They also pose serious environmental risks. This paper identifies more than a dozen social, political, and ethical challenges that are common across many of the emerging technological ESIs. Governance could mitigate and manage these issues, and it would be made more effective and robust by understanding and treating new ESIs as such and as a potentially transformative set of innovations in human-Earth system relations.

Improvement of the Mass-Rearing Protocols for the South American Fruit Fly for Application of the Sterile Insect Technique

17764
T. Mastrangelo, A. Kovaleski, B. Maset, M. D. Costa, C. Barros, L. A. Lopes and C. Caceres,  Insects,  12. 2021-07-09 14:59:26.
The existing rearing protocols for Anastrepha fraterculus must be reviewed to make economically viable the production of sterile flies for their area-wide application. Additionally, evidence of sexual incompatibility between a long-term mass-reared Brazilian strain and wild populations has been found. To address these issues, this study aimed to refine rearing protocols and to assess the suitability of an A. fraterculus strain for the mass production of sterile flies. A series of bioassays were carried out to evaluate incubation times for eggs in a bubbling bath and to assess the temporal variation of egg production from ovipositing cages at different adult densities. A novel larval diet containing carrageenan was also evaluated. Egg incubation times higher than 48 h in water at 25 °C showed reduced larval and pupal yields. Based on egg production and hatchability, the density of 0.3 flies/cm2 can be recommended for adult cages. The diet with carrageenan was suitable for mass production at egg-seeding densities between 1.0 and 1.5 mL of eggs/kg of diet, providing higher insect yields than a corn-based diet from Embrapa. Even after two years of being reared under the new rearing protocols, no sexual isolation was found between the bisexual strain and wild flies.

Comparative response to post-production process of two Anastrepha ludens strains: Application in the sterile insect technique

17725
J. Arredondo, J. F. Aguirre-Medina, J. S. Meza, J. Cancino and F. Diaz-Fleischer,  Journal of Applied Entomology,  11. 2021-07-07 14:54:23.
The new desiccation-resistant (DR) strain of Anastrepha ludens Loew differs in its life-history traits from the non-selected strain (NS). Given the innate resistance of DR flies to stressors, it is necessary to determine the packing and shipment conditions for their use in the sterile insect technique (SIT). First, we used pupae to evaluate the interaction of hypoxia period (12, 24 and 36 hr) and temperature (15.3 (+/- 0.9), 19.5 (+/- 1.0), 25.5 (+/- 0.6) and 30.1 (+/- 0.5) C-o). Second, adults were exposed to densities of 1.0, 1.3 and 1.5 flies/cm(2) and chilling periods of 0, 3 and 5 hr. We observed a negative relationship of emergence and flight ability with hypoxia period and temperature in both strains especially when flies were exposed to 36 hr of hypoxia and 30celcius. Interestingly, knock-down time decreased as male density increased, but when chilling time increased, recovery time also increased. Both chilling time and male density had negative effects on male weight. Chilling time reduced male survival when exposed to desiccation, while both chilling time and male density decreased male survival under starvation conditions. Negative effects on number of matings were observed only on the first day after chilling but not on the following days. We found that DR flies survive approximately twice as long as flies from the NS strain when exposed to starvation or desiccation stressors. We discuss our results on the basis of the potential use of DR flies in SIT programmes.

Distinct spermiogenic phenotypes underlie sperm elimination in the Segregation Distorter meiotic drive system

17832
M. Herbette, X. L. Wei, C. H. Chang, A. M. Larracuente, B. Loppin and R. Dubruille,  PLOS Genetics,  17:26. 2021-07-06 13:14:02.
Here we show that SD/SD+ males of different genotypes but with similarly strong degrees of distortion have distinct spermiogenic phenotypes. In some genotypes, SD+ spermatids fail to fully incorporate protamines after the removal of histones, and degenerate during the individualization stage of spermiogenesis. In contrast, in other SD/SD+ genotypes, protamine incorporation appears less disturbed, yet spermatid nuclei are abnormally compacted, and mature sperm nuclei are eventually released in the seminal vesicle. Our analyses of different SD+ chromosomes suggest that the severity of the spermiogenic defects associates with the copy number of the Rsp satellite. We propose that when Rsp copy number is very high (> 2000), spermatid nuclear compaction defects reach a threshold that triggers a checkpoint controlling sperm chromatin quality to eliminate abnormal spermatids during individualization. Author summary In diploid organisms, both alleles of the same gene have an equal chance to be transmitted to the progeny. However, in many species including mammals, insects and plants, selfish genetic elements perturb gametogenesis in a way that favors their own transmission to the detriment of the homologous chromosome that does not carry them. In Drosophila melanogaster, Segregation Distorter (Sd) is a well-characterized selfish locus that induces, by still-unclear mechanisms, the elimination of sperm cells which contain the homologous second chromosome when this carries a large heterochromatic block of repetitive DNA called Rsp. Here, we show that in Sd males, the replacement of histones by sperm specific protamine-like proteins is perturbed in the differentiating Rsp sperm cells, which are then eliminated before their release in the seminal vesicle. However, in some genetic backgrounds, many spermatids Rsp tend to escape this elimination and defective sperm nuclei are found in the seminal vesicle. We show that these phenotypes are partly linked to the number of repeats in the Rsp block and can be modulated by suppressors present in the genetic background. Our work thus helps to understand how selfish loci exploit gametogenesis to favor their own transmission and highlights the essential role of heterochromatin in spermiogenesis progression.

Effect of the timing of pupal irradiation on the quality and sterility of oriental fruit flies (Diptera: Tephritidae) for use in Sterile Insect Technique

17781
T. J. Fezza, P. A. Follett and T. E. Shelly,  Applied Entomology and Zoology,  8. 2021-07-05 17:37:25.
The Sterile Insect Technique (SIT) is a target-specific, biologically based method used to control pestiferous tephritids entailing the release of mass-reared, sterilized males of the target species to achieve sterile male x wild female matings. As documented for several tephritid species, sterilizing irradiation may have adverse effects on various biological parameters, including life span, flight ability, and mating competitiveness. To minimize these impacts and ensure sterility, released flies must be irradiated at a precise dose at a specific and uniform age. The objective of the present study was to determine the impact of pupal age at the time of irradiation on flight ability, male survival, fertility, and mating competitiveness for the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) irradiated at 100 Gy. We concluded that flies irradiated as pupae 4 days before emergence were significantly compromised with respect to flight ability and male survival when compared to flies irradiated 1 or 2 days before emergence. Additionally, we determined that crosses between males irradiated 1 day before emergence with non-irradiated females yielded significantly more pupae than the same cross with males irradiated at 2, 3, and 4 days before emergence. Although rare, the occurrence of pupae and emerged adults suggested low levels of fertility for flies irradiated as pupae 1 day before emergence, but complete sterility at 2, 3, and 4 days before emergence. These findings suggest that SIT programs can potentially irradiate pupae at 2 or 3 days before emergence without compromising the quality of the released flies, which would permit the distribution of flies over greater distances.

Gene drive that results in addiction to a temperature sensitive version of an essential gene triggers population collapse in Drosophila

17609
G. Oberhofer, B. Hay and T. Ivy,  bioRxiv,  2021.07.03.451005. 2021-07-04 14:38:01.
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 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. In 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 HEG-based drive, and to bring about suppression and/or killing of specific individuals in response to other stimuli.Competing Interest StatementThe authors have filed patent applications on ClvR and related 336 technologies (U.S. Application No. 15/970,728 and No. 16/673,823 ; provisional patent No. 337 CIT-8511-P )

Remating in Ceratitis capitata sterile males: Implications in sterile insect technique programmes

17827
M. Catala-Oltra, E. Llacer, O. Dembilio, I. Pla, A. Urbaneja and M. Perez-Hedo,  Journal of Applied Entomology,  8. 2021-07-02 14:57:45.
Sterile insect technique (SIT) is used, among other biological control tools, as a sustainable measure for the management of Ceratitis capitata Wiedemann (Diptera: Tephritidae) in many agricultural regions where this pest can trigger severe economic impacts. The tendency of wild females to remate multiple times has been deeply studied; it has been a common point of controversy when evaluating SIT programmes. Nevertheless, the remating potential of the released sterile males remains unknown. Here, under laboratory conditions, the remating capability of mass-reared sterile males was determined. Wild-type virgin females were offered to sterile males (Vienna-8 strain), which had the opportunity to mate up to four consecutive times. The remating assays were carried out at 24 hr, 48 hr, 4 days and 7 days after the first mating. At the end of each tested time period, males were divided according to their mating response, mated or unmated, and subsequently reused for the next round of mating assays. The frequency of successful remating in each tested time period was obtained. Insemination was confirmed by determining the sperm transfer in mated female spermathecae by quantitative real-time PCR. Our results demonstrate that 73% of the mass-reared sterile males were able to remate 24 hr after the first mating, 55% of which remated again the day after. Close to 25% of the V8 sterile males tended to copulate in all of the four mating opportunities. The qPCR analysis of the spermathecae contents verified an effective transfer of V8 sperm to wild females with every mating; 99% of copulations resulted in sperm transfer. These findings shed light on the remating potential of V8 sterile males, an aspect until now underestimated in many SIT programmes.

Preventing COVID-59

17604
Y. Erlich and D. Douek,  github,  2021-06-30 14:30:52.
SARS-CoV-2 is the third betacoronavirus to enter the human population in the past 20 years, revealing a concerning pattern. Clearly, preventing a future pandemic from such viruses is a critical priority. Previous studies have shown that shRNAs can be powerful suppressors of RNA viruses in transgenic animals and substantially reduce transmission. Thus, we propose the introduction of anti-betacoronavirus shRNAs using CRISPR/CAS9 gene drive into the horseshoe bat population, the natural reservoir of those viruses, to combat this pandemic threat at its source. Importantly, our approach is not expected to create any harm to bats and can benefit other animals in the ecosystem that contract betacoronaviruses from bats. We map the ethical and the technical aspects and suggest guidelines for moving forward with this proposal.

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