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.
Gene Editing and Genetic Control of Hemipteran Pests: Progress, Challenges and Perspectives
22757I. D. Pacheco, L. L. Walling and P. W. Atkinson, Frontiers in Bioengineering and Biotechnology, 10. 2022-06-07 08:02:11.
The origin of the order Hemiptera can be traced to the late Permian Period more than 230 MYA, well before the origin of flowering plants 100 MY later in during the Cretaceous period. Hemipteran species consume their liquid diets using a sucking proboscis; for phytophagous hemipterans their mouthparts (stylets) are elegant structures that enable voracious feeding from plant xylem or phloem. This adaptation has resulted in some hemipteran species becoming globally significant pests of agriculture resulting in significant annual crop losses. Due to the reliance on chemical insecticides for the control of insect pests in agricultural settings, many hemipteran pests have evolved resistance to insecticides resulting in an urgent need to develop new, species-specific and environmentally friendly methods of pest control. The rapid advances in CRISPR/Cas9 technologies in model insects such as Drosophila melanogaster, Tribolium castaneum, Bombyx mori, and Aedes aegypti has spurred a new round of innovative genetic control strategies in the Diptera and Lepidoptera and an increased interest in assessing genetic control technologies for the Hemiptera. Genetic control approaches in the Hemiptera have, to date, been largely overlooked due to the problems of introducing genetic material into the germline of these insects. The high frequency of CRISPR-mediated mutagenesis in model insect species suggest that, if the delivery problem for Hemiptera could be solved, then gene editing in the Hemiptera might be quickly achieved. Significant advances in CRISPR/Cas9 editing have been realized in nine species of Hemiptera over the past 4 years. Here we review progress in the Hemiptera and discuss the challenges and opportunities for extending contemporary genetic control strategies into species in this agriculturally important insect orderr.
Beware the Unknown: Views on Genetic Technology in Conservation
H. G. W. Dixson, J. Balanovic, F. Medvecky, E. D. Edwards and E. A. MacDonald, Narrative Inquiry in Bioethics, 12. 2022-06-06 08:59:56.Artificial Gene Drive (GD) may offer a number of transformative impacts on society. Despite potential usage in the area of conservation, GD remains largely unfamiliar to the public and little is known about their views. In our study, participants from New Zealand were placed in groups based upon one of four worldviews. They had a brief free word association session before considering a concise, technical definition of GD and were asked to discuss their views. Overall, discussions made use of narrative devices that expressed caution and concern around large-scale technological intervention with the natural world. However, specific worldviews presented unique themes. While fears of human overstep causing uncontrollable feedback across wild species and environments were universally present, this differed according to the group's worldview. We conclude that conversations on such technologies, especially those relating to gene modification, provide insight into deep-rooted social, cultural and even metaphysical concerns that transcend the technology's stated purpose.
Establishment of Wolbachia infection in Aedes aegypti from Pakistan via embryonic microinjection and semi-field evaluation of general fitness of resultant mosquito population
22856M. S. Sarwar, N. Jahan, A. Ali, H. K. Yousaf and I. Munzoor, Parasites and Vectors, 15:191. 2022-06-06 08:36:19.
BACKGROUND: Dengue is a mosquito-borne viral disease that is mainly spread by Aedes aegypti. It is prevalent on five continents, predominantly in tropical and sub-tropical zones across the world. Wolbachia bacteria have been extensively used in vector control strategies worldwide. The focus of the current study was to obtain a natural population of Ae. aegypti harbouring Wolbachia and to determine the impact of this bacteria on the new host in a semi-field environment. METHODS: Wolbachia-infected Aedes albopictus was collected from the city of Lahore, Punjab, Pakistan, and Wolbachia were successfully introduced into laboratory-reared Ae. aegypti via embryonic microinjection. The stable vertical transmission of wAlbB in the host population was observed for eight generations, and the impact of Wolbachia on the general fitness of the host was evaluated in semi-field conditions. RESULTS: In the laboratory and semi-field experiments, wAlbB Wolbachia presented a strong cytoplasmic incompatibility (CI) effect, evidenced as zero egg hatching, in crosses between Wolbachia-infected males and wild (uninfected) females of Ae. aegypti. Wolbachia infection had no noticeable impact on the general fitness (P > 0.05), fecundity, body size (females and males) and mating competitiveness of the new host, Ae. aegypti. However, there was a significant decrease in female fertility (egg hatch) (P < 0.001). In addition, under starvation conditions, there was a remarkable decrease (P < 0.0001) in the life span of Wolbachia-infected females compared to uninfected females (4 vs. > 5 days, respectively). CONCLUSIONS: Wolbachia strain wAlbB has a great potential to control the dengue vector in Ae. aegypti populations by producing 100% CI with a limited burden on its host in natural field conditions. This strain can be used as a biological tool against vector-borne diseases.
Non-Mendelian segregation and transmission drive of B chromosomes
22725J. P. M. Camacho, Chromosome Research, 2022-06-03 07:58:27.
Selfish genetic elements (SGE) get a transmission advantage (drive) thanks to their non-Mendelian inheritance. Here I identify eight steps during the reproductive cycle that can be subverted by SGEs to thrive in natural populations. Even though only three steps occur during meiosis, most cases of segregation distortion are considered “meiotic drive sensu lato.” As this is a source of unnecessary contradictions, I suggest always using the term “transmission ratio distortion” (TRD). Chromosomal SGEs (e.g., B chromosomes) exhibit almost all types of TRD. In plants, the best-studied type of TRD for B chromosomes occurs post-meiotically during male gametophyte maturation. However, in animals, the two main types are pre-meiotic and meiotic TRDs, in all cases associated with gonotaxis (i.e., a preference of B chromosomes for germ cells). Frequently, TRD drivers in genic SGEs (e.g., t-alleles and segregation distorters in Drosophila) are paralogous copies of genes from the standard genome, whereas their targets can be other genes or satellite DNA (satDNA). As B chromosomes are often rich in satDNA and contain paralogous copies of A chromosome genes, perhaps their drive mechanisms are similar to those of genic SGEs. So far, the only association between a B chromosome gene and TRD is the gene haplodizer in Nasonia vitripennis. The discovery of B-genes controlling B-drive in other species does not appear to be far off, but experimental crosses will be needed to simultaneously test the TRD of a given B chromosome and the expression of its genes.
The maize abnormal chromosome 10 meiotic drive haplotype: a review
22690R. K. Dawe, Chromosome Research, 2022-06-02 14:35:18.
The maize abnormal chromosome 10 (Ab10) haplotype encodes a meiotic drive system that converts heterochromatic knobs into centromere-like bodies that are preferentially segregated through female meiosis. Ab10 was first described in the 1940s and has been intensively studied. Here I provide a comprehensive review of the literature, starting from the discovery of knobs and Ab10, preceding through the classic literature, and finishing with molecular structure and mechanisms. The defining features of the Ab10 haplotype are its two specialized kinesins, Kinesin driver and TR-1 kinesin, that activate neocentromeres at knobs containing different classes of the tandem repeat. In most Ab10 haplotypes, the two kinesin/knob systems cooperate to promote maximum meiotic drive. However, recent interpretations suggest that each kinesin/knob system can function as an independent meiotic driver and that in some cases they compete with each other. Ab10 is present at low frequencies throughout the genus Zea and has significantly expanded genome size by promoting the formation of knobs throughout the genome.
Testing non-autonomous antimalarial gene drive effectors using self-eliminating drivers in the African mosquito vector Anopheles gambiae
22689D. A. Ellis, G. Avraam, A. Hoermann, C. A. S. Wyer, Y. X. Ong, G. K. Christophides and N. Windbichler, PLOS Genetics, 18:e1010244. 2022-06-02 14:26:57.
Author summary Gene drive is a method that allows the genetic modification of entire populations of harmful organisms. Their application to tackle invasive species, agricultural pests or insect disease vectors has been suggested. For example, they could reduce the capacity of malaria mosquitoes to transmit this deadly disease to humans by producing effector molecules inhibiting the development of the Plasmodium parasite in the mosquito vector. We describe a strategy to modularize and test multiple transgenes destined for release, and to introduce only the minimal set of modifications needed into a mosquito population. We show how some elements, once no longer needed, can be made to self-eliminate from populations and we also study how several independent gene drive traits, located in different parts of the genome, can interact and propagate at the level of mosquito cage populations.
Modifying mosquitoes to suppress disease transmission: Is the long wait over?
22854J. R. Powell, Genetics, 2022-06-02 08:31:17.
For more than 50 years it has been a dream of medical entomologists and public health workers to control diseases like malaria and dengue fever by modifying, through genetics and other methods, the arthropods that transmit them to humans. A brief synopsis of the history of these efforts as applied to mosquitoes is presented; none proved to be effective in reducing disease prevalence. Only in the last few years have novel approaches been developed or proposed that indicate the long wait may be over. Three recent developments are particularly promising: CRISPR-Cas9 driven genetic modification, shifting naturally occurring allele frequencies, and microbe-based modifications. The last is the furthest along in implementation. Dengue fever incidence has been reduced between 40% and 96% in 4 different regions of the world where Wolbachia-infected Aedes aegypti have been established in the field. It is not yet clear how sustainable such control programs will prove to be, but there is good reason for optimism. In light of this, the time is ripe for reinvigorated research on vectors, especially genetics. Vector-borne diseases primarily affect under-developed countries and thus have not received the attention they deserve from wealthier countries with well-developed and funded biomedical research establishments.
A meiotic driver alters sperm form and function in house mice: a possible example of spite
22697L. Winkler and A. K. Lindholm, Chromosome Research, 2022-06-01 14:48:38.
The ability to subvert independent assortment of chromosomes is found in many meiotic drivers, such as the t haplotype in house mice Mus musculus, in which the t-bearing chromosomal homolog is preferentially transmitted to offspring. This is explained by a poison-antidote system, in which developing + and t sperm in testes of + /t males are exposed to 'poison' coded by t loci, from which t sperm are protected, allowing t sperm an overwhelming fertilisation advantage in monogamous matings. This system is thought to result in poorly and normally motile sperm subpopulations within + /t sperm, leaving t sperm unharmed. Conversely, we found that the fastest quartile of sperm from + /t males swam more slowly, both forwards and along their travel path, and had reduced straightness and linearity, compared to the fastest quartile of + / + sperm. Moreover, sperm from + /t males had shorter tails and narrower heads than + / + sperm, and these morphological differences covaried with motility differences. Finally, + /t traits did not show evidence of bimodal distributions. We conclude that the t haplotype drive results in lasting damage to the motility of both + and t developing sperm, although previous studies indicate that + must be more harmed than t sperm. This damage to all sperm may explain the low success of + /t males in sperm competition with + / + males, seen in earlier studies. We propose that the harm the t causes to itself could be termed 'spiteful', which may also be common to other gamete-harming meiotic drive systems.
Wolbachia interacts with the microbiome to shape fitness-associated traits during seasonal adaptation in Drosophila melanogaster
22693L. P. Henry, M. Fernandez, S. Wolf and J. Ayroles, bioRxiv, 2022.05.31.494239. 2022-06-01 14:39:02.
The microbiome contributes to many different host traits, but its role in host adaptation remains enigmatic. The fitness benefits of the microbiome often depend on ecological conditions, but fluctuations in both the microbiome and environment modulate these fitness benefits. Moreover, vertically transmitted bacteria might constrain the ability of both the microbiome and host to respond to changing environments. Drosophila melanogaster provides an excellent system to investigate the evolutionary effects of interactions between the microbiome and the environment. To address this question, we created field mesocosms of D. melanogaster undergoing seasonal adaptation with and without the vertically transmitted bacteria, Wolbachia pipientis. Sampling temporal patterns in the microbiome revealed that Wolbachia constrained microbial diversity. Furthermore, interactions between Wolbachia and the microbiome contributed to fitness-associated traits. Wolbachia often exerted negative fitness effects on hosts, and the microbiome modulated these effects. Our work supports recent theoretical advances suggesting that hosts in temporally fluctuating environments benefit from flexible microbial associations with low transmission fidelity--specifically when changes in the microbiome can better enable host phenotypes to match environment change. We conclude by exploring the consequences of complex interactions between Wolbachia and the microbiome for our understanding of eco-evolutionary processes and the utility of Wolbachia in combating vector-borne disease.Competing Interest StatementThe authors have declared no competing interest.
Exploring value change
25095T. E. de Wildt and V. J. Schweizer, Prometheus, 38. 2022-06-01 10:02:19.
This article aims to explore the use of cross-impact balances (CIB) to identify scenarios of value change. The possibility of value change has received little attention in the literature on value-sensitive design (VSD). Examples of value change include the emergence of new values and changes in the relative importance of values. Value change could lead to a mismatch between values embedded in technology and the way they are currently considered in society. Such a mismatch could result in a lack of acceptability of technologies, increasing social tensions and injustices. However, methods to study value change in the VSD literature are rare. CIB is a scenario tool that can study systems characterized by feedback loops that are hard to describe mathematically. This is often the case when aiming to define values and their relationships. We demonstrate the use of CIB to identify scenarios of value change using two cases: digital voice assistants and gene drive organisms. Our findings show that CIB is helpful in building scenarios of value change, even in instances where the operationalization of values is complex. CIB also helps us to understand the mechanisms of value change and evaluate when such mechanisms occur. Finally, we find that CIB is particularly useful for social learning and explanatory modelling. CIB can therefore contribute to the design of value-sensitive technologies.
Modeling the impact of genetically modified male mosquitoes in the spatial population dynamics of Aedes aegypti
23212M. R. da Silva, P. H. G. Lugão, F. Prezoto and G. Chapiro, Scientific Reports, 12:9112. 2022-06-01 06:29:36.
The mosquito Aedes aegypti is the primary vector of diseases such as dengue, Zika, chikungunya, and yellow fever. Improving control techniques requires a better understanding of the mosquito’s life cycle, including spatial population dynamics in endemic regions. One of the most promising techniques consists of introducing genetically modified male mosquitoes. Several models proposed to describe this technique present mathematical issues or rely on numerous parameters, making their application challenging to real-world situations. We propose a model describing the spatial population dynamics of the Aedes aegypti in the presence of genetically modified males. This model presents some mathematical improvements compared to the literature allowing deeper mathematical analysis. Moreover, this model relies on few parameters, which we show how to obtain or estimate from the literature. Through numerical simulations, we investigate the impacts of environmental heterogeneity, the periodicity of genetically modified male releases, and released genetically modified males quantity on the population dynamics of Aedes aegypti. The main results point to that the successful application of this vector control technique relies on releasing more than a critical amount of modified males with a frequency exceeding a specific critical value.
Combined Trojan Y Chromosome Strategy and Sterile Insect Technique to Eliminate Mosquitoes: Modelling and Analysis
23051J. Lyu, M. Gu, S. Wang and K. Cheng, Mathematical Problems in Engineering, 2022:2373350. 2022-05-27 15:09:13.
Sterile insect technique has been successfully applied in the control of agricultural pests; however, it has a limited ability to control mosquitoes. A promising alternative approach is the Trojan Y Chromosome strategy, which works by manipulating the sex ratio of a population through the introduction of YY supermales that guarantee male offspring. To take the advantages of both approaches, a combined Trojan Y chromosome strategy and sterile insect technique (TYC-SIT) strategy considering intraspecies competition is modeled. The pure TYC method is compared with the pure SIT method by cancelling one-state variable. The dynamical analysis leads to results on both local and global stabilities of this combined TYC-SIT model. Optimal control analysis is also implemented to investigate the optimal mechanisms for extinction of mosquitoes. In particular, the numerical results affirm that the combined TYC-SIT enables near elimination of mosquitoes and works better than the pure TYC or pure SIT method. These conclusions have great significance for species controls with an XX-XY sex determinism system or ZZ-ZW system.
Optimization of Aedes albopictus (Diptera: Culicidae) Mass Rearing through Cost-Effective Larval Feeding
22626M. Kavran, A. Puggioli, S. Šiljegović, D. Čanadžić, N. Laćarac, M. Rakita, A. Ignjatović Ćupina, F. Balestrino, D. Petrić and R. Bellini, Insects, 13. 2022-05-26 07:11:26.
Aedes (Stegomyia) albopictus (Skuse, 1895) is an invasive important medical and veterinary pest species. The sterile insect technique (SIT) involves the mass rearing of males, and their sterilization and release into the habitat to compete with wild males. Our research objective was to compare the effectiveness of three larval diet recipes (IAEA-BY, BCWPRL, and MIX-14) in the laboratory rearing of Ae. albopictus males to evaluate the available economical feeding alternatives. The separation of sexes was done in the pupal stage by sieving. Reared males were tested for flight capacity and longevity. The application of the BCWPRL diet resulted in a higher portion of sieved male pupae than females, but the development of males was the slowest, and the number of obtained males (pupae and adults) was lower compared to the other two diets. The adult mean survival time was the highest in males fed with MIX-14 and the lowest in males fed with IAEA-BY. Males fed by IAEA-BY also demonstrated higher initial mortality in the adult stage. The diets BCWPRL and MIX-14 are economically more convenient than IAEA-BY (2.28 and 5.30 times cheaper, respectively). The cheapest diet, MIX-14, might represent a candidate for replacing the effective but still expensive IAEA-BY larval diet, providing lower costs of sterile male production.
Reply to: Assessing the efficiency of Verily’s automated process for production and release of male Wolbachia-infected mosquitoes
22643J. E. Crawford, K. C. Hopkins, A. Buchman, T. Zha, P. Howell, E. Kakani, J. R. Ohm, N. Snoad, L. Upson, J. Holeman, P. Massaro, S. L. Dobson, F. S. Mulligan and B. J. White, Nature Biotechnology, 2022-05-26 06:34:15.
We appreciate the comments from Bouyer et al. under their mandate as a United Nations agency program (‘to promote the safe and appropriate use of nuclear techniques and related technologies in food and agriculture’) on our paper1 . The centuries-old fight against mosquito-borne disease has entered a new phase that is both exciting and fast-moving. Many promising technologies and techniques have been developed in the past 2 decades, including mosquito colonies stably infected with Wolbachia2 mosquitoes3,4, a CRISPR–Cas9-based gene drive5 nations of these techniques with older approaches (that is, irradiated Wolbachia releases6,7 , genetically modified sterile and even combi). In a world where more than half of all humans are at risk of contracting mosquito-borne diseases across a range of economic and geographic landscapes, we think that an array of tools will be needed to turn the tide against the massive public health burden of these diseases.
Assessing the efficiency of Verily’s automated process for production and release of male Wolbachia-infected mosquitoes
22641J. Bouyer, H. Maiga and M. J. B. Vreysen, Nature Biotechnology, 2022-05-26 06:27:58.
A paper by Crawford et al.1 titled ‘Efficient production of male Wolbachia-infected Aedes aegypti mosquitoes enables large-scale suppression of wild populations’ reports a mosquito control suppression trial carried out from2017 to 2018 in Fresco Country, California, USA1 . Between 7.5 million and 14.4 million Wolbachia-infected male mosquitoes were released during the study, which achieved suppression rates of 69% and 95%, respectively. Although the work provided important insights for future Aedes genetic control programs—particularly the information on the immigration of fertile females into release areas—the paper contains several omissions and errors. Below, we discuss how these relate to three main areas: regulatory oversight, entomological efficiency and, finally, cost efficiency.
Recommendations for environmental risk assessment of gene drive applications for malaria vector control
22586J. B. Connolly, J. D. Mumford, D. C. M. Glandorf, S. Hartley, O. T. Lewis, S. W. Evans, G. Turner, C. Beech, N. Sykes, M. B. Coulibaly, J. Romeis, J. L. Teem, W. Tonui, B. Lovett, A. Mankad, A. Mnzava, S. Fuchs, T. D. Hackett, W. G. Landis, J. M. Marshall, Malar J, 21:152. 2022-05-25 09:36:02.
Building on an exercise that identified potential harms from simulated investigational releases of a population suppression gene drive for malaria vector control, a series of online workshops identified nine recommendations to advance future environmental risk assessment of gene drive applications.
Perplexing dynamics of Wolbachia proteins for cytoplasmic incompatibility
22582T. Harumoto and T. Fukatsu, PLOS Biology, 20:e3001644. 2022-05-25 09:23:59.
The mechanism of symbiont-induced cytoplasmic incompatibility has been a long-lasting mystery. This Primer explores a new study on Wolbachia’s Cif proteins in PLOS Biology that provides supportive evidence for the “Host-Modification Model,” although the alternative “Toxin-Antidote Model” is still in the running.
A nickase Cas9 gene-drive system promotes super-Mendelian inheritance in Drosophila
22584V. L. Del Amo, S. S. Juste and V. M. Gantz, Cell Rep, 39:110843. 2022-05-24 09:32:51.
CRISPR-based gene-drives have been proposed for managing insect populations, including disease-transmitting mosquitoes, due to their ability to bias their inheritance toward super-Mendelian rates (>50%). Current technologies use a Cas9 that introduces DNA double-strand breaks into the opposing wild-type allele to replace it with a copy of the gene-drive allele via DNA homology-directed repair. However, the use of different Cas9 versions is unexplored, and alternative approaches could increase the available toolkit for gene-drive designs. Here, we report a gene-drive that relies on Cas9 nickases that generate staggered paired nicks in DNA to propagate the engineered gene-drive cassette. We show that generating 5' overhangs in the system yields efficient allelic conversion. The nickase gene-drive arrangement produces large, stereotyped deletions that are advantageous to eliminate viable animals carrying small mutations when targeting essential genes. Our nickase approach should expand the repertoire for gene-drive arrangements aimed at applications in mosquitoes and beyond.
The Cif proteins from Wolbachia prophage WO modify sperm genome integrity to establish cytoplasmic incompatibility
22570R. Kaur, B. A. Leigh, I. T. Ritchie and S. R. Bordenstein, PLOS Biology, 20:e3001584. 2022-05-24 08:55:13.
In Drosophila melanogaster, germline expression of the Wolbachia proteins CifA and CifB causes cytoplasmic incompatibility, but how this impairs male reproduction remains unclear. This study shows how Cif proteins encoded by the endosymbiont prophage invade the fly’s gametic nuclei and modify the histone-protamine transition of spermatogenesis.
Wolbachia 16S rRNA haplotypes detected in wild Anopheles stephensi in eastern Ethiopia
22568E. Waymire, S. Duddu, S. Yared, D. Getachew, D. Dengela, S. R. Bordenstein, M. Balkew, S. Zohdy, S. R. Irish and T. E. Carter, Parasites and Vectors, 15:178. 2022-05-24 08:50:15.
About two out of three Ethiopians are at risk of malaria, a disease caused by the parasites Plasmodium falciparum and Plasmodium vivax. Anopheles stephensi, an invasive vector typically found in South Asia and the Middle East, was recently found to be distributed across eastern and central Ethiopia and is capable of transmitting both P. falciparum and P. vivax. The detection of this vector in the Horn of Africa (HOA) coupled with widespread insecticide resistance requires that new methods of vector control be investigated in order to control the spread of malaria. Wolbachia, a naturally occurring endosymbiotic bacterium of mosquitoes, has been identified as a potential vector control tool that can be explored for the control of malaria transmission. Wolbachia could be used to control the mosquito population through suppression or potentially decrease malaria transmission through population replacement. However, the presence of Wolbachia in wild An. stephensi in eastern Ethiopia is unknown. This study aimed to identify the presence and diversity of Wolbachia in An. stephensi across eastern Ethiopia.
Strategies to Mitigate Establishment under the Wolbachia Incompatible Insect Technique
23104S. Soh, S. H. Ho, J. Ong, A. Seah, B. S. Dickens, K. W. Tan, J. R. Koo, A. R. Cook, S. Sim, C. H. Tan, L. C. Ng and J. T. Lim, Viruses, 14. 2022-05-24 08:10:53.
The Incompatible Insect Technique (IIT) strategy involves the release of male mosquitoes infected with the bacterium Wolbachia. Regular releases of male Wolbachia-infected mosquitoes can lead to the suppression of mosquito populations, thereby reducing the risk of transmission of vector-borne diseases such as dengue. However, due to imperfect sex-sorting under IIT, fertile Wolbachia-infected female mosquitoes may potentially be unintentionally released into the environment, which may result in replacement and failure to suppress the mosquito populations. As such, mitigating Wolbachia establishment requires a combination of IIT with other strategies. We introduced a simple compartmental model to simulate ex-ante mosquito population dynamics subjected to a Wolbachia-IIT programme. In silico, we explored the risk of replacement, and strategies that could mitigate the establishment of the released Wolbachia strain in the mosquito population. Our results suggest that mitigation may be achieved through the application of a sterile insect technique. Our simulations indicate that these interventions do not override the intended wild type suppression of the IIT approach. These findings will inform policy makers of possible ways to mitigate the potential establishment of Wolbachia using the IIT population control strategy.
Novel molecular approaches to combat vectors and vector-borne viruses: Special focus on RNA interference (RNAi) mechanisms
22657A. Agarwal, D. K. Sarma, D. Chaurasia and H. S. Maan, Acta Tropica, 2022-05-24 06:45:12.
Vector-borne diseases, such as dengue, chikungunya, zika, yellow fever etc pose significant burden among the infectious diseases globally, especially in tropical and sub-tropical regions. Globalization, deforestation, urbanization, climate change, uncontrolled population growth, inadequate waste management and poor vector-management infrastructure have all contributed to the expansion of vector habitats and subsequent increase in vector-borne diseases throughout the world. Conventional vector control methods, such as use of insecticides, have significant negative environmental repercussions in addition to developing resistance in vectors. Till date, a very few vaccines or antiviral therapies have been approved for the treatment of vector borne diseases. In this review, we have discussed emerging molecular approaches like CRISPR (clustered regularly interspaced short palindromic repeats)/Cas-9, sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), Wolbachia (virus transmission blocking) and RNA interference (RNAi) to combat vector and vector-borne viruses. Due to the extensive advancements in RNAi research, a special focus has been given on its types, biogenesis, mechanism of action, delivery and experimental studies evaluating their application as anti-mosquito and anti-viral agent. These technologies appear to be highly promising in terms of contributing to vector control and antiviral drug development, and hence can be used to reduce global vector and vector-borne disease burden.
Quality Control and Mating Performance of Irradiated Glossina palpalis gambiensis Males
22546K. Ilboudo, K. Camara, E. W. Salou and G. Gimonnea, Insects, 13. 2022-05-19 08:04:34.
The biological quality of sterile male insects produced in a mass-rearing facility is a prerequisite for the success of the SIT, which is a component of area-wide integrated pest management (AW-IPM). Indeed, sterile male insects released in the field must have a good mating performance in order to compete with wild males, but they must also present the required level of sterility. In the present study, the biological quality of sterile male Glossina palpalis gambiensis produced in a mass-rearing insectary was assessed through quality control testing. The mating performance of irradiated males was assessed in walk-in field cages. Irradiation had no effect on adult emergence but significantly reduced the percentage of operational flies (from 89.58% to 79.87%) and male survival (from 5 to 4 days, on average). However, irradiation did not impact the sterile male insemination potential, with all females inseminated and more than 80% of the spermathecae completely filled. The rate of induced sterility in females was 89.67% due to a dose rate decrease of the radiation source. Moreover, sterile males were able to compete successfully with untreated fertile males for untreated females in walk-in field cages. This study confirmed that the flies were still competitive and stressed the importance of regularly checking the radiation source parameters.
Elimination of a closed population of the yellow fever mosquito, Aedes aegypti, through releases of self-limiting male mosquitoes
22519P. B. Patil, S. K. Dasgupta, K. Gorman, A. Pickl-Herk, M. Puinean, A. McKemey, B. Char, U. B. Zehr and S. R. Barwale, PLOS Neglected Tropical Diseases, 16:e0010315. 2022-05-16 09:19:04.
Author summary Aedes aegypti L. species is the primary vector responsible for transmission of the dengue virus worldwide including chikungunya, yellow fever and Zika virus. The experiment presented in the manuscript represents a study undertaken to demonstrate suppression of the wild type Ae. aegypti population in large outdoor field cages with natural exposure to the environment (physically-contained field cage facility) by sustained releases of male adults of OX513A Ae. aegypti strain. This investigation is a phase-2 contained study as per the World Health Organization guidelines for evaluation of genetically modified organisms and was recommended by the Indian regulatory board. This experiment demonstrates suppression of wild type Ae. aegypti population by sustained releases of OX513A male adults in a contained facility. The prospect of the project is to demonstrate and implement the technology for controlling/suppression of the Ae. aegypti vector in the open field environment.
Bayesian network-based risk assessment of synthetic biology: Simulating CRISPR-Cas9 gene drive dynamics in invasive rodent management
22516E. A. Brown, S. R. Eikenbary and W. G. Landis, Risk Analysis, 2022-05-14 07:22:34.
Gene drive technology has been proposed to control invasive rodent populations as an alternative to rodenticides. However, this approach has not undergone risk assessment that meets criteria established by Gene Drives on the Horizon, a 2016 report by the National Academies of Sciences, Engineering, and Medicine. To conduct a risk assessment of gene drives, we employed the Bayesian network-relative risk model to calculate the risk of mouse eradication on Southeast Farallon Island using a CRISPR-Cas9 homing gene drive construct. We modified and implemented the R-based model "MGDrivE" to simulate and compare 60 management strategies for gene drive rodent management. These scenarios spanned four gene drive mouse release schemes, three gene drive homing rates, three levels of supplemental rodenticide dose, and two timings of rodenticide application relative to gene drive release. Simulation results showed that applying a supplemental rodenticide simultaneously with gene drive mouse deployment resulted in faster eradication of the island mouse population. Gene drive homing rate had the highest influence on the overall probability of successful eradication, as increased gene drive accuracy reduces the likelihood of mice developing resistance to the CRISPR-Cas9 homing mechanism.
Aquatic invasive species specialists’ perceptions on the importance of genetic tools and concepts to inform management
22482T. A. Bernos, K. M. Jeffries and N. E. Mandrak, Biological Invasions, 24:1863-1879. 2022-05-14 07:09:36.
Perceptions related to the importance of genetic research influence the mobilization of genetic tools and concepts to inform conservation actions. Research characteristics, stakeholders’ perspectives, knowledge, and social linkages with geneticists influence the outcome of genetic information for management practices. We surveyed a broad range of aquatic invasive species (AIS) specialists whose opinions, perspectives, and decisions influence AIS decision-making. We assessed perceptions related to the importance of genetic tools and concepts, as well as the appropriateness of genetic biocontrol, and tested whether their expertise, background, and experience influenced perceptions in a predictable way. While perceptions towards genetic tools and concepts were generally heterogeneous, there was a high consensus (84%) related to the importance of eDNA. Most predictors were weakly correlated with importance ratings. Specialists’ genetic knowledge was the strongest predictor of higher importance ratings: the odds of AIS specialists giving higher ratings increased by up to 1.5-fold with increasing genetic knowledge. When evaluating the appropriateness of genetic biocontrol, level of support was lower for approaches based on gene editing (58%) than those relying on traditional hatchery techniques (70%). Support for gene editing varied by geographic location and with specialists’ knowledge of genetics and AIS management. These findings suggest that perceptions towards genetic research vary between genetic tools and concepts and are shaped by the interplay of individual’s values, expertise, experience, and background. To collaborate more effectively, genetic scientists must understand the extent of genetic knowledge of their AIS management partners and recognize that their conceptions of the conservation genetics research-practice space may vary.
Simple, sensitive, and cost-effective detection of wAlbB Wolbachia in Aedes mosquitoes, using loop mediated isothermal amplification combined with the electrochemical biosensing method
22480P. Thayanukul, B. Lertanantawong, W. Sirawaraporn, S. Charasmongkolcharoen, T. Chaibun, R. Jittungdee and P. Kittayapong, PLOS Neglected Tropical Diseases, 16:e0009600. 2022-05-13 07:05:35.
Author summary Mosquito-borne diseases such as dengue, chikungunya, zika, and yellow fever are transmitted to humans mainly by the bites of Aedes aegypti mosquitoes. Controlling the vectors of these diseases relies mostly on the use of insecticides. However, the efficiency has been reduced through the development of insecticide resistance in mosquitoes. Wolbachia is an endosymbiotic bacterium that is naturally found in 40% of insects, including mosquitoes. The bacterium can protect its insect hosts from viral infections and can also cause sterility in insect host populations, therefore, providing an opportunity to use it for human disease control. Application of a Wolbachia trans-infected mosquitoes needs simple, rapid and sensitive methods for detecting the bacteria in released mosquitoes. In this paper, we develop the methods of LAMP and BIOSENSORS for detecting wAlbB Wolbachia in mosquitoes. Our positive LAMP reaction can be visualized by color change from violet to blue at a sensitivity of ≥ 10 pg of genomic DNA. When used in combination with the BIOSENSOR method, the sensitivity increases a millionfold without losing specificity. Our study suggests that both developed methods, either used in combination or stand-alone, are efficient and cost-effective, hence, they could be applied for routine surveys of Wolbachia in mosquito control programs that use Wolbachia-based approaches.
Intronic gRNAs for the Construction of Minimal Gene Drive Systems
22478A. Nash, P. Capriotti, A. Hoermann, P. A. Papathanos and N. Windbichler, Frontiers in Bioengineering and Biotechnology, 10. 2022-05-12 07:00:08.
Gene drives are promising tools for the genetic control of insect vector or pest populations. CRISPR-based gene drives are generally highly complex synthetic constructs consisting of multiple transgenes and their respective regulatory elements. This complicates the generation of new gene drives and the testing of the behavior of their constituent functional modules. Here, we explored the minimal genetic components needed to constitute autonomous gene drives in Drosophila melanogaster. We first designed intronic gRNAs that can be located directly within coding transgene sequences and tested their functions in cell lines. We then integrated a Cas9 open reading frame hosting such an intronic gRNA within the Drosophila rcd-1r locus that drives the expression in the male and female germlines. We showed that upon removal of the fluorescent transformation marker, the rcd-1rd allele supports efficient gene drive. We assessed the propensity of this driver, designed to be neutral with regards to fitness and host gene function, to propagate in caged fly populations. Because of their simplicity, such integral gene drives could enable the modularization of drive and effector functions. We also discussed the possible biosafety implications of minimal and possibly recoded gene drives.
Lessons learned from the introduction of genetically engineered crops: relevance to gene drive deployment in Africa
22491H. Quemada, Transgenic Res, 2022-05-11 07:27:12.
The application of gene drives to achieve public health goals, such as the suppression of Anopheles gambiae populations, or altering their ability to sustain Plasmodium spp. infections, has received much attention from researchers. If successful, this genetic tool can contribute greatly to the wellbeing of people in regions severely affected by malaria. However, engineered gene drives are a product of genetic engineering, and the experience to date, gained through the deployment of genetically engineered (GE) crops, is that GE technology has had difficulty receiving public acceptance in Africa, a key region for the deployment of gene drives. The history of GE crop deployment in this region provides good lessons for the deployment of gene drives as well
Double-tap gene drive uses iterative genome targeting to help overcome resistance alleles
22286A. L. Bishop, V. López Del Amo, E. M. Okamoto, Z. Bodai, A. C. Komor and V. M. Gantz, Nat Commun, 13:2595. 2022-05-09 08:10:07.
Homing CRISPR gene drives could aid in curbing the spread of vector-borne diseases and controlling crop pest and invasive species populations due to an inheritance rate that surpasses Mendelian laws. However, this technology suffers from resistance alleles formed when the drive-induced DNA break is repaired by error-prone pathways, which creates mutations that disrupt the gRNA recognition sequence and prevent further gene-drive propagation. Here, we attempt to counteract this by encoding additional gRNAs that target the most commonly generated resistance alleles into the gene drive, allowing a second opportunity at gene-drive conversion. Our presented "double-tap" strategy improved drive efficiency by recycling resistance alleles. The double-tap drive also efficiently spreads in caged populations, outperforming the control drive. Overall, this double-tap strategy can be readily implemented in any CRISPR-based gene drive to improve performance, and similar approaches could benefit other systems suffering from low HDR frequencies, such as mammalian cells or mouse germline transformations.
Adversarial interspecies relationships facilitate population suppression by gene drive in spatially explicit models
22288Y. Liu, W. Teo, H. Yang and J. Champer, bioRxiv, 2022.05.08.491087. 2022-05-08 08:15:29.
Suppression gene drives are designed to bias their inheritance and increase in frequency in a population, disrupting an essential gene in the process. When the frequency is high enough, the population will be unable to reproduce above the replacement level and could be eliminated. CRISPR suppression drives based on the homing mechanism have already seen success in the laboratory, particularly in malaria mosquitoes. However, several models predict that the use of these drives in realistic populations with spatial structure may not achieve complete success. This is due to the ability of wild-type individuals to escape the drive and reach empty areas with reduced competition, allowing them to achieve high reproductive success and leading to extinction-recolonization cycles across the landscape. Here, we extend our continuous space gene drive framework to include two competing species or predator-prey species pairs. We find in both discrete-generation and mosquito-specific models that the presence of a competing species or predator can greatly facilitate drive-based suppression, even for drives with modest efficiency. However, the presence of a competing species also substantially increases the frequency of outcomes in which the drive is lost before suppression is achieved. These results are robust in models with seasonal population fluctuations. We also found that suppression can be somewhat more difficult if targeting a predator with strong predator-prey interactions. Our results illustrate the difficulty of predicting outcomes of interventions that could substantially affect the populations of interacting species in complex ecosystems. However, our results are also potentially promising for the prospects of less powerful gene drives in achieving successful elimination of target pest populations.Competing Interest StatementThe authors have declared no competing interest.
Local adaptation of Aedes aegypti mosquitoes to Wolbachia-induced fitness costs
22208P. A. Ross and A. A. Hoffmann, bioRxiv, 2022.05.06.490959. 2022-05-06 15:19:41.
Aedes aegypti mosquito eggs can remain quiescent for many months before hatching, allowing populations to persist through unfavorable conditions. Aedes aegypti infected with the Wolbachia strain wMel have been released in tropical and subtropical regions for dengue control. wMel reduces the viability of quiescent eggs, but this physiological cost might be expected to evolve in natural mosquito populations that frequently experience stressful conditions. We therefore compared the costs of wMel infection for quiescent egg viability in field-derived and laboratory populations. Quiescent egg viability was highly variable in wMel-infected populations, with greater costs of wMel in field-derived populations. In contrast, there was little variation between matched field-derived and long-term laboratory populations lacking wMel, suggesting that laboratory adaptation does not influence this trait and that differences are due to wMel infection. Comparisons of populations collected a year apart show a decline in costs under laboratory rearing conditions involving a rapid turnover of mosquito generations; this pattern was consistent across populations despite their origin, suggesting adaptation of mosquitoes to the wMel infection under laboratory conditions. Reciprocal crossing experiments confirm that differences in quiescent egg viability were mainly due to the genetic background and not Wolbachia alone. wMel-infected mosquitoes hatching from long-term quiescent eggs showed partial loss of cytoplasmic incompatibility and female infertility, highlighting additional costs of long-term quiescence. Our study provides the first evidence for a shift in Wolbachia phenotypic effects following deliberate field release and establishment and it highlights interactions between Wolbachia infections and local adaptation. The unexpected changes in fitness costs observed here suggest potential tradeoffs with undescribed fitness benefits of the wMel infection.Competing Interest StatementThe authors have declared no competing interest.
The principles driving gene drives for conservation
22295S. Hartley, R. Taitingfong and P. Fidelman, Environmental Science and Policy, 135:36-45. 2022-05-04 08:30:40.
Gene drive technology is an emerging biotechnology with the potential to address some of the most intractable global biodiversity conservation issues. Scientists are exploring potential gene drive applications for managing invasive species and building resilience in keystone species threatened by climate change. The possibility to use gene drive for these conservation purposes has triggered significant interest in how to govern its development and eventual applications. This includes a plethora of documents prescribing governance principles, which can be a sensible response to the governance gap created by emerging technologies and help shore up legitimacy. We conducted qualitative documentary analysis to examine the range and substance of principles emerging in the governance of conservation gene drive. Such analysis aimed to better understand the aspirations guiding these applications and how scientists and other experts imagine their responsibility in this field. We found a collection of recommendations and prescriptions that could be organised into a set of seven emerging principles intended to shape the governance of gene drive in conservation: broad and empowered engagement; public acceptance; decision-making informed by broad ranging considerations, state and international collaboration; ethical frameworks; diverse expertise; and responsible self-regulation by developers. We lay bare these emergent principles, analyzing the way in which they are valued, prioritized, and their strengths and weaknesses. By identifying these prescriptive principles, stakeholders can further interrogate their merits and shortcomings and identify more concrete ways that governance frameworks might embody them.
Transient Introgression of Wolbachia into Aedes aegypti Populations Does Not Elicit an Antibody Response to Wolbachia Surface Protein in Community Members
22655E. Lee, T. Hien Nguyen, T. Yen Nguyen, S. Nam Vu, N. Duong Tran, L. Trung Nghia, Q. Mai Vien, T. Dong Nguyen, R. Kriiger Loterio, I. Iturbe-Ormaetxe, H. A. Flores, S. L. O'Neill, D. Anh Dang, C. P. Simmons and J. E. Fraser, Pathogens, 11. 2022-05-03 06:41:58.
Wolbachia is an endosymbiotic bacterium that can restrict the transmission of human pathogenic viruses by Aedes aegypti mosquitoes. Recent field trials have shown that dengue incidence is significantly reduced when Wolbachia is introgressed into the local Ae. aegypti population. Female Ae. aegypti are anautogenous and feed on human blood to produce viable eggs. Herein, we tested whether people who reside on Tri Nguyen Island (TNI), Vietnam developed antibodies to Wolbachia Surface Protein (WSP) following release of Wolbachia-infected Ae. aegypti, as a measure of exposure to Wolbachia. Paired blood samples were collected from 105 participants before and after mosquito releases and anti-WSP titres were measured by ELISA. We determined no change in anti-WSP titres after ~30 weeks of high levels of Wolbachia-Ae. aegypti on TNI. These data suggest that humans are not exposed to the major Wolbachia surface antigen, WSP, following introgression of Wolbachia-infected Ae. aegypti mosquitoes.
New weapons to fight malaria transmission: A historical view
22487W. Huang, S.-J. Cha and M. Jacobs-Lorena, Entomological Research, 2022-05-02 07:19:32.
The stagnation of our fight against malaria in recent years, mainly due to the development of mosquito insecticide resistance, argues for the urgent development of new weapons. The dramatic evolution of molecular tools in the last few decades led to a better understanding of parasite?mosquito interactions and coalesced in the development of novel tools namely, mosquito transgenesis and paratransgenesis. Here we provide a historical view of the development of these new tools and point to some remaining challenges for their implementation in the field.
International shipments of Wolbachia-infected mosquito eggs: towards the scaling-up of World Mosquito Program operations
23390J. A. Denton, D. A. Joubert, A. A. Goundar and J. R. L. Gilles, Scientific and Technical Review, 41:91-99. 2022-05-01 08:01:14.
The Wolbachia insect control method, employed by the World Mosquito Program (WMP), relies on introgressing Wolbachia through target Aedes aegypti populations to reduce the incidence of dengue. Since 2010, the WMP has been producing Wolbachia-infected mosquitoes at numerous sites across the globe for release in 11 countries. As the technology has matured, greater focus has been placed on mosquito production at larger central facilities for transport to remote release sites, both domestically and internationally. Of particular note is the production of Wolbachia-infected mosquitoes at the WMP's Australian production facility for successful international deployments in Fiji, Vanuatu, Kiribati and Sri Lanka. This requires careful management of both production and supply-chain processes to ensure that the quality of the mosquito eggs, specifically the hatch rate and Wolbachia infection rate, is maintained. To ensure the cost-effectiveness and scalability of the Wolbachia method, these processes will be further refined to facilitate deployment from large centralised production facilities.
The fate of a suppressed X-linked meiotic driver: experimental evolution in Drosophila simulans
22676H. Bastide, D. Ogereau, C. Montchamp-Moreau and P. R. Gérard, Chromosome Research, 2022-04-30 07:53:46.
Sex-ratio (SR) meiotic drivers are X-linked selfish genetic elements that promote their own transmission by preventing the production of Y-bearing sperm, which usually lowers male fertility. The spread of SR drivers in populations is expected to trigger the evolution of unlinked drive suppressors, a theoretically predicted co-evolution that has been observed in nature. Once completely suppressed, the drivers are expected either to decline if they still affect the fitness of their carriers, or to evolve randomly and possibly get fixed if the suppressors eliminate their deleterious effects. To explore this issue, we used the Paris sex-ratio system of Drosophila simulans in which drive results from the joint effect of two elements on the X chromosome: a segmental duplication and a deficient allele of the HP1D2 gene. We set up six experimental populations starting with 2/3 of X chromosomes carrying both elements (X(SR)) in a fully suppressing background. We let them evolve independently during almost a hundred generations under strong sexual competition, a condition known to cause the rapid disappearance of unsuppressed Paris X(SR) in previous experimental populations. In our study, the fate of X(SR) chromosomes varied among populations, from extinction to their maintenance at a frequency close to the starting one. While the reasons for these variable outcomes are still to be explored, our results show that complete suppression can prevent the demise of an otherwise deleterious X(SR) chromosome, turning a genetic conflict into cooperation between unlinked loci. Observations in natural populations suggest a contrasting fate of the two elements: disappearance of the duplication and maintenance of deficient HP1D2 alleles.
Epistatic selection on a selfish Segregation Distorter supergene: drive, recombination, and genetic load
22103B. Navarro-Dominguez, C.-H. Chang, C. L. Brand, C. A. Muirhead, D. C. Presgraves and A. M. Larracuente, eLife, 11:e78981. 2022-04-29 09:52:33.
In this work, we investigate the evolution and genomic consequences of an autosomal, multilocus, male meiotic drive system, Segregation Distorter (SD) in the fruit fly, Drosophila melanogaster. In African populations, the predominant SD chromosome variant, SD-Mal, is characterized by two overlapping, paracentric inversions on chromosome arm 2R and nearly perfect (~100%) transmission. We study the SD-Mal system in detail, exploring its components, chromosomal structure, and evolutionary history. Our findings reveal a recent chromosome-scale selective sweep mediated by strong epistatic selection for haplotypes carrying Sd, the main driving allele, and one or more factors within the double inversion. While most SD-Mal chromosomes are homozygous lethal, SD-Mal haplotypes can recombine with other, complementing haplotypes via crossing over, and with wildtype chromosomes via gene conversion. SD-Mal chromosomes have nevertheless accumulated lethal mutations, excess non-synonymous mutations, and excess transposable element insertions. Therefore, SD-Mal haplotypes evolve as a small, semi-isolated subpopulation with a history of strong selection. These results may explain the evolutionary turnover of SD haplotypes in different populations around the world, and have implications for supergene evolution broadly.
CRISPR/Cas9 mediates efficient site-specific mutagenesis of the odorant receptor co-receptor (Orco) in the malaria vector Anopheles sinensis
22554Y. Wang, X. F. He, L. Qiao, Z. R. Yu, B. Chen and Z. B. He, Pest Management Science, 11. 2022-04-28 14:52:27.
BACKGROUND Anopheles sinensis is the most widely distributed mosquito species and is the main transmitter of Plasmodium vivax malaria in China. Most previous research has focused on the mechanistic understanding of biological processes in An. sinensis and novel ways of interrupting malaria transmission. However, the development of functional genomics and genetics-based vector control strategies against An. sinensis remain limited because of insufficient site-specific genome editing tools. RESULTS We report the first successful application of the CRISPR/Cas9 mediated knock-in for highly efficient, site-specific mutagenesis in An. sinensis. The EGFP marker gene driven by the 3 x P3 promoter was precisely integrated into the odorant receptor co-receptor (Orco) by direct injections of Cas9 protein, double-stranded DNA donor, and Orco-gRNA. We achieved a mutation rate of 3.77%, similar to rates in other mosquito species. Precise knock-in at the intended locus was confirmed by polymerase chain reaction (PCR) amplification and sequencing. The Orco mutation severely impaired mosquito sensitivity to some odors and their ability to locate and discriminate a human host. CONCLUSION Orco was confirmed as a key mediator of multiple olfactory-driven behaviors in the An. sinensis life cycle, highlighting the importance of Orco as a key molecular target for malaria control. The results also demonstrated that CRISPR/Cas9 was a simple and highly efficient genome editing technique for An. sinensis and could be used to develop genetic control tools for this vector. (c) 2022 Society of Chemical Industry.
Engineering a self-eliminating transgene in the yellow fever mosquito, Aedes aegypti
21920K. Chae, C. Dawson, C. Valentin, B. Contreras, J. Zapletal, K. M. Myles and Z. N. Adelman, PNAS Nexus, 2022-04-28 08:54:37.
Promising genetics-based approaches are being developed to reduce or prevent the transmission of mosquito-vectored diseases. Less clear is how such transgenes can be removed from the environment, a concern that is particularly relevant for highly invasive gene drive transgenes. Here, we lay the groundwork for a transgene removal system based on single-strand annealing (SSA), a eukaryotic DNA repair mechanism. An SSA-based rescuer strain (kmoRG) was engineered to have direct repeat sequences (DRs) in the Ae. aegypti kynurenine 3-monooxygenase (kmo) gene flanking the intervening transgenic cargo genes, DsRED and EGFP. Targeted induction of DNA double-strand breaks (DSBs) in the DsRED transgene successfully triggered complete elimination of the entire cargo from the kmoRG strain, restoring the wild-type kmo gene and thereby normal eye pigmentation. Our work establishes the framework for strategies to remove transgene sequences during the evaluation and testing of modified strains for genetics-based mosquito control.
A New Approach to Develop Resistant Cultivars Against the Plant Pathogens: CRISPR Drives
21915M. I. Tek and K. Budak, Frontiers in Plant Science, 13. 2022-04-27 08:43:50.
CRISPR drive is a recent and robust tool that allows durable genetic manipulation of the pest population like human disease vectors such as malaria vector mosquitos. In recent years, it has been suggested that CRISPR drives can also be used to control plant diseases, pests, and weeds. However, using a CRISPR drive in Arabidopsis for the first time in 2021 has been shown to use this technology in plant breeding to obtain homozygous parental lines. This perspective has proposed using CRISPR drive to develop pathogen-resistant cultivars by disrupting the susceptibility gene (S). In the breeding program, CRISPR is used to create S-gene mutations in two parental lines of hybrid cultivars. However, CRISPR must be reapplied or long-term backcrossed for the parental line to obtain homozygous S-mutant cultivars. When a parental line crosses with different parental lines to develop new hybrids, heterozygous S-mutations could not resist in hybrid against the pathogen. CRISPR drives are theoretically valid to develop homozygous S-mutant plants against pathogens by only routine pollination after CRISPR drive transformation to just one parental line. This way, breeders could use this parental line in different crossing combinations without reapplying the genome-editing technique or backcrossing. Moreover, CRISPR drive also could allow the development of marker-free resistant cultivars with modifications on the drive cassette.
Pilot trial using mass field-releases of sterile males produced with the incompatible and sterile insect techniques as part of integrated Aedes aegypti control in Mexico
22224A. Martín-Park, A. Che-Mendoza, Y. Contreras-Perera, S. Pérez-Carrillo, H. Puerta-Guardo, J. Villegas-Chim, G. Guillermo-May, A. Medina-Barreiro, H. Delfín-González, R. Méndez-Vales, S. Vázquez-Narvaez, J. Palacio-Vargas, F. Correa-Morales, G. Ayora-Tal, PLoS Negl Trop Dis, 16:e0010324. 2022-04-26 15:46:43.
We implemented a controlled before-and-after quasi-experimental study in two suburban localities of Yucatan (Mexico): San Pedro Chimay (SPC), which received IIT-SIT, and San Antonio Tahdzibichén used as control. Release of wAlbB Ae. aegypti males at SPC extended for 6 months (July-December 2019), covering the period of higher Ae. aegypti abundance. Entomological indicators included egg hatching rates and outdoor/indoor adult females collected at the release and control sites. Approximately 1,270,000 lab-produced wAlbB-infected Ae. aegypti males were released in the 50-ha treatment area (2,000 wAlbB Ae. aegypti males per hectare twice a week in two different release days, totaling 200,000 male mosquitoes per week). The efficacy of IIT-SIT in suppressing indoor female Ae. aegypti density (quantified from a generalized linear mixed model showing a statistically significant reduction in treatment versus control areas) was 90.9% a month after initiation of the suppression phase, 47.7% two months after (when number of released males was reduced in 50% to match local abundance), 61.4% four months after (when initial number of released males was re-established), 88.4% five months after and 89.4% at six months after the initiation of the suppression phase. A proportional, but lower, reduction in outdoor female Ae. aegypti was also quantified (range, 50.0-75.2% suppression). CONCLUSIONS/SIGNIFICANCE: Our study, the first open-field pilot implementation of Wolbachia IIT-SIT in Mexico and Latin-America, confirms that inundative male releases can significantly reduce natural populations of Ae. aegypti. More importantly, we present successful pilot results of the integration of Wolbachia IIT-SIT within a IVM plan implemented by Ministry of Health personnel.
Recent advancements in CRISPR/Cas technology for accelerated crop improvement
21827D. Das, D. L. Singha, R. R. Paswan, N. Chowdhury, M. Sharma, P. S. Reddy and C. Chikkaputtaiah, Planta, 255:109. 2022-04-25 09:34:49.
The likelihood of reduced agricultural production due to highly turbulent climatic conditions increases as the global population expands. The second paradigm of stress-resilient crops with enhanced tolerance and increased productivity against various stresses is paramount to support global production and consumption equilibrium. Although traditional breeding approaches have substantially increased crop production and yield, effective strategies are anticipated to restore crop productivity even further in meeting the world’s increasing food demands. CRISPR/Cas, which originated in prokaryotes, has surfaced as a coveted genome editing tool in recent decades, reshaping plant molecular biology in unprecedented ways and paving the way for engineering stress-tolerant crops. CRISPR/Cas is distinguished by its efficiency, high target specificity, and modularity, enables precise genetic modification of crop plants, allowing for the creation of allelic variations in the germplasm and the development of novel and more productive agricultural practices. Additionally, a slew of advanced biotechnologies premised on the CRISPR/Cas methodologies have augmented fundamental research and plant synthetic biology toolkits. Here, we describe gene editing tools, including CRISPR/Cas and its imitative tools, such as base and prime editing, multiplex genome editing, chromosome engineering followed by their implications in crop genetic improvement. Further, we comprehensively discuss the latest developments of CRISPR/Cas technology including CRISPR-mediated gene drive, tissue-specific genome editing, dCas9 mediated epigenetic modification and programmed self-elimination of transgenes in plants. Finally, we highlight the applicability and scope of advanced CRISPR-based techniques in crop genetic improvement.
Biotechnological Road Map for Innovative Weed Management
22450A. C. S. Wong, K. Massel, Y. Lam, J. Hintzsche and B. S. Chauhan, Frontiers in Plant Science, 13. 2022-04-25 09:27:40.
In most agriculture farmlands, weed management is predominantly reliant on integrated weed management (IWM) strategies, such as herbicide application. However, the overuse and misuse of herbicides, coupled with the lack of novel active ingredients, has resulted in the uptrend of herbicide-resistant weeds globally. Moreover, weedy traits that contribute to weed seed bank persistence further exacerbate the challenges in weed management. Despite ongoing efforts in identifying and improving current weed management processes, the pressing need for novel control techniques in agricultural weed management should not be overlooked. The advent of CRISPR/Cas9 gene-editing systems, coupled with the recent advances in “omics” and cheaper sequencing technologies, has brought into focus the potential of managing weeds in farmlands through direct genetic control approaches, but could be achieved stably or transiently. These approaches encompass a range of technologies that could potentially manipulate expression of key genes in weeds to reduce its fitness and competitiveness, or, by altering the crop to improve its competitiveness or herbicide tolerance. The push for reducing or circumventing the use of chemicals in farmlands has provided an added incentive to develop practical and feasible molecular approaches for weed management, although there are significant technical, practical, and regulatory challenges for utilizing these prospective molecular technologies in weed management.
The evolutionary significance of meiotic drive
21913J. B. Searle and F. P.-M. de Villena, Heredity, 2022-04-25 08:34:39.
In this essay, we will focus on‘true meiotic drive’ where the distorted transmission does arise within meiosis itself (Zanders and Unckless2019),specifically in females. Here, the non-transmission of one of the products of meiotic division is inherent in the gametogenic process—with the formation of a polar body as the functionless by-product of division, with the egg continuing on as the viable entity. The meiotic drive is therefore the biased segregation in favour of one type of allele such that it is most commonly retained in the egg at the cost of the other type of allele, which most commonly ends up in the polar body. The biased segregation can occur at either the first or second division ofmeiosis—both of which generate a functionless polar body, suchthat there is ultimately only one viable product of the two divisions—the final version of the egg, which then becomes a zygote on fertilisation.
Role of CRISPR Technology in Gene Editing of Emerging and Re-emerging Vector Borne Disease
21811K. K. Mahto, P. Prasad, M. Kumar, H. Dubey and A. Ranjan, Recent Advances in Pathogen Interactions, Immunity, and Vector Control Strategies, 2022-04-23 05:49:18.
Vector borne diseases are rampant across the world. Due to spread and estab-lishment of vector species in different geographical areas, vector adaptation and resistance towards many insecticides the only option left is vector control for vari-ous vector borne diseases. Recent advancement in the field of genome editing have provided a variety of tools like, CRISPR, a novel genome editing techniques which can be applied for the control and prevention of many deadly diseases like dengue, chikungunya, filariasis, Japanese encephalitis and Zika. The present chapter is aimed to discuss the recent advancement in genome editing tools such as, their applica-tion, challenges, and limitations in vector control. Additionally, this chapter would potentially be advantageous to understand the hurdles, knowledge gaps in eliminating vector borne disease.
Wolbachia endosymbionts in two Anopheles species indicates independent acquisitions and lack of prophage elements
21788S. Quek, L. Cerdeira, C. L. Jeffries, S. Tomlinson, T. Walker, G. L. Hughes and E. Heinz, Microbial Genomics, 8. 2022-04-21 06:52:58.
Wolbachia is a genus of obligate bacterial endosymbionts that infect a diverse range of arthropod species as well as filarial nematodes, with its single described species, Wolbachia pipientis, divided into several ‘supergroups’ based on multilocus sequence typing. Wolbachia strains in mosquitoes have been shown to inhibit the transmission of human pathogens, including Plasmodium malaria parasites and arboviruses. Despite their large host range, Wolbachia strains within the major malaria vectors of the Anopheles gambiae and Anopheles funestus complexes appear at low density, established solely on PCR-based methods. Questions have been raised as to whether this represents a true endosymbiotic relationship. However, recent definitive evidence for two distinct, high-density strains of supergroup B Wolbachia within Anopheles demeilloni and Anopheles moucheti has opened exciting possibilities to explore naturally occurring Wolbachia endosymbionts in Anopheles for biocontrol strategies to block Plasmodium transmission. Here, we utilize genomic analyses to demonstrate that both Wolbachia strains have retained all key metabolic and transport pathways despite their smaller genome size, with this reduction potentially attributable to degenerated prophage regions. Even with this reduction, we confirmed the presence of cytoplasmic incompatibility (CI) factor genes within both strains, with wAnD maintaining intact copies of these genes while the cifB gene was interrupted in wAnM, so functional analysis is required to determine whether wAnM can induce CI. Additionally, phy logenetic analysis indicates that these Wolbachia strains may have been introduced into these two Anopheles species via horizontal transmission events, rather than by ancestral acquisition and subsequent loss events in the Anopheles gambiae species complex. These are the first Wolbachia genomes, to our knowledge, that enable us to study the relationship between natural strain Plasmodium malaria parasites and their anopheline hosts.
Aedes aegypti abundance and insecticide resistance profiles in the applying Wolbachia to eliminate dengue trial
21790W. Tantowijoyo, S. K. Tanamas, I. Nurhayati, S. Setyawan, N. Budiwati, I. Fitriana, I. Ernesia, D. S. Wardana, E. Supriyati, E. Arguni, Y. Meitika, E. Prabowo, B. Andari, B. R. Green, L. Hodgson, E. Rancès, P. A. Ryan, S. L. O'Neill, K. L. Anders, M. R. A, PLOS Neglected Tropical Diseases, 16:e0010284. 2022-04-20 07:01:27.
The Applying Wolbachia to Eliminate Dengue (AWED) trial was a parallel cluster randomised trial that demonstrated Wolbachia (wMel) introgression into Ae. aegypti populations reduced dengue incidence. In this predefined substudy, we compared between treatment arms, the relative abundance of Ae. aegypti and Ae. albopictus before, during and after wMel-introgression. Between March 2015 and March 2020, 60,084 BG trap collections yielded 478,254 Ae. aegypti and 17,623 Ae. albopictus. Between treatment arms there was no measurable difference in Ae. aegypti relative abundance before or after wMel-deployments, with a count ratio of 0.96 (95% CI 0.76, 1.21) and 1.00 (95% CI 0.85, 1.17) respectively. More Ae. aegypti were caught per trap per week in the wMel-intervention arm compared to the control arm during wMel deployments (count ratio 1.23 (95% CI 1.03, 1.46)). Between treatment arms there was no measurable difference in the Ae. albopictus population size before, during or after wMel-deployment (overall count ratio 1.10 (95% CI 0.89, 1.35)). We also compared insecticide resistance phenotypes of Ae. aegypti in the first and second years after wMel-deployments. Ae. aegypti field populations from wMel-treated and untreated arms were similarly resistant to malathion (0.8%), permethrin (1.25%) and cyfluthrin (0.15%) in year 1 and year 2 of the trial. In summary, we found no between-arm differences in the relative abundance of Ae. aegypti or Ae. albopictus prior to or after wMel introgression, and no between-arm difference in Ae. aegypti insecticide resistance phenotypes. These data suggest neither Aedes abundance, nor insecticide resistance, confounded the epidemiological outcomes of the AWED trial.
A metapopulation approach to identify targets for Wolbachia-based dengue control
22221A. Reyna-Lara, D. Soriano-Paños, J. H. Arias-Castro, H. J. Martínez and J. Gómez-Gardeñes, Chaos, 32:041105. 2022-04-18 15:42:29.
Over the last decade, the release of Wolbachia-infected Aedes aegypti into the natural habitat of this mosquito species has become the most sustainable and long-lasting technique to prevent and control vector-borne diseases, such as dengue, zika, or chikungunya. However, the limited resources to generate such mosquitoes and their effective distribution in large areas dominated by the Aedes aegypti vector represent a challenge for policymakers. Here, we introduce a mathematical framework for the spread of dengue in which competition between wild and Wolbachia-infected mosquitoes, the cross-contagion patterns between humans and vectors, the heterogeneous distribution of the human population in different areas, and the mobility flows between them are combined. Our framework allows us to identify the most effective areas for the release of Wolbachia-infected mosquitoes to achieve a large decrease in the global dengue prevalence.
Environmental factors influence the local establishment of Wolbachia in Aedes aegypti mosquitoes in two small communities in central Vietnam [version 2]
21728N. T. Hien, D. D. Anh, N. H. Le, N. T. Yen, T. V. Phong, V. S. Nam, T. N. Duong, N. B. Nguyen, D. T. T. Huong, L. Q. Hung, C. N. T. Trinh, N. V. Hoang, V. Q. Mai, L. T. Nghia, N. T. Dong, L. H. Tho, S. Kutcher, T. P. Hurst, J. L. Montgomery, M. Woolfit, E, Gates Open Research, 5:147. 2022-04-18 09:54:42.
Background: The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and subsequently shown to reduce transmission of dengue and other pathogens, under both laboratory and field conditions. Here we describe the entomological outcomes of wMel Wolbachia mosquito releases in two small communities in Nha Trang City in central Vietnam. Methods: The wMel strain of Wolbachia was backcrossed into local Aedes aegypti genotype and mosquito releases were undertaken by community members or by staff. Field monitoring was undertaken to track Wolbachia establishment in local Ae. aegypti mosquito populations. Ecological studies were undertaken to assess relationships between environmental factors and the spatial and temporal variability in Wolbachia infection prevalence in mosquitoes. Results: Releases of wMel Wolbachia Ae. aegypti mosquitoes in two small communities in Nha Trang City resulted in the initial establishment of Wolbachia in the local Ae. aegypti mosquitopopulations, followed by seasonal fluctuations in Wolbachia prevalence. There was significant small-scale spatial heterogeneity in Wolbachia infection prevalence in the Tri Nguyen Village site, resulting in the loss of wMel Wolbachia infection in mosquitoes in north and center areas, despite Wolbachia prevalence remaining high in mosquitoes in the south area. In the second site, Vinh Luong Ward, Wolbachia has persisted at a high level in mosquitoes throughout this site despite similar seasonal fluctuations in wMel Wolbachia prevalence. Conclusion: Seasonal variation in Wolbachia infection prevalence in mosquitoes was associated with elevated temperature conditions, and was possibly due to imperfect maternal transmission of Wolbachia. Heterogeneity in Wolbachia infection prevalence was found throughout one site, and indicates additional factors may influence Wolbachia establishment.
