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.
Effects of a blood-free mosquito diet on fitness and gonotrophic cycle parameters of laboratory reared Anopheles gambiae sensu stricto
30929Mosi, F.A., Rutha, I., Velez, R. et al., Parasites and Vectors, 17. 2024-07-24 15:43:32.
The current rise of new innovative tools for mosquito control, such as the release of transgenic mosquitoes carrying a dominant lethal gene and Wolbachia-based strategies, necessitates a massive production of mosquitoes in the insectary. However, currently laboratory rearing depends on vertebrate blood for egg production and maintenance. This practice raises ethical concerns, incurs logistical and cost limitations, and entails potential risk associated with pathogen transmission and blood storage. Consequently, an artificial blood-free diet emerges as a desirable alternative to address these challenges. This study aims to evaluate the effects of a previously formulated artificial blood-free diet (herein referred to as BLOODless) on Anopheles gambiae (An. gambiae s.s.; IFAKARA) gonotrophic parameters and fitness compared with bovine blood. The study was a laboratory-based comparative evaluation of the fitness, fecundity and fertility of An. gambiae s.s. (IFAKARA) reared on BLOODless versus vertebrate blood from founder generation (F0) to eighth generation (F8). A total of 1000 female mosquitoes were randomly selected from F0, of which 500 mosquitoes were fed with bovine blood (control group) and the other 500 mosquitoes were fed with BLOODless diet (experimental group). The feeding success, number of eggs per female, hatching rate and pupation rate were examined post-feeding. Longevity and wing length were determined as fitness parameters for adult male and female mosquitoes for both populations. While blood-fed and BLOODless-fed mosquitoes showed similar feeding success, 92.3% [95% confidence interval (CI) 89.7–94.9] versus 93.6% (95% CI 90.6–96.6), respectively, significant differences emerged in their reproductive parameters. The mean number of eggs laid per female was significantly higher for blood-fed mosquitoes (P < 0.001) whereas BLOODless-fed mosquitoes had significantly lower hatching rates [odds ratio (OR) 0.17, 95% CI 0.14–0.22, P < 0.001]. Wing length and longevity were similar between both groups. This study demonstrates the potential of the BLOODless diet as a viable and ethical alternative to vertebrate blood feeding for rearing An. gambiae s.s. This breakthrough paves the way for more efficient and ethical studies aimed at combating malaria and other mosquito-borne diseases.
Culex-Transmitted Diseases: Mechanisms, Impact, and Future Control Strategies using Wolbachia
31030Madhav, M.; Blasdell, K.R.; Trewin, B.; Paradkar, P.N.; López-Denman, A.J., Viruses, 16:1134. 2024-07-15 11:40:32.
Mosquitoes of the Culex genus are responsible for a large burden of zoonotic virus transmission globally. Collectively, they play a significant role in the transmission of medically significant diseases such as Japanese encephalitis virus and West Nile virus. Climate change, global trade, habitat transformation and increased urbanisation are leading to the establishment of Culex mosquitoes in new geographical regions. These novel mosquito incursions are intensifying concerns about the emergence of Culex-transmitted diseases and outbreaks in previously unaffected areas. New mosquito control methods are currently being developed and deployed globally. Understanding the complex interaction between pathogens and mosquitoes is essential for developing new control strategies for Culex species mosquitoes. This article reviews the role of Culex mosquitos as vectors of zoonotic disease, discussing the transmission of viruses across different species, and the potential use of Wolbachia technologies to control disease spread. By leveraging the insights gained from recent successful field trials of Wolbachia against Aedes-borne diseases, we comprehensively discuss the feasibility of using this technique to control Culex mosquitoes and the potential for the development of next generational Wolbachia-based control methods.
Assessing CRISPR/Cas9 potential in SDG3 attainment: malaria elimination—regulatory and community engagement landscape
30888Snuzik, A., Malaria Journal, 23. 2024-07-07 21:42:05.
Elimination of malaria has become a United Nations member states target: Target 3.3 of the sustainable development goal no. 3 (SDG3). Despite the measures taken, the attainment of this goal is jeopardized by an alarming trend of increasing malaria case incidence. Globally, there were an estimated 241 million malaria cases in 2020 in 85 malaria-endemic countries, increasing from 227 million in 2019. Malaria case incidence was 59, which means effectively no changes in the numbers occurred, compared with the baseline 2015. Jennifer Doudna—co-inventor of CRISPR/Cas9 technology—claims that CRISPR holds the potential to lessen or even eradicate problems lying in the centre of SDGs. On the same note, CRISPR/Cas9-mediated mosquito-targeting gene drives (MGD) are perceived as a potential means to turn this trend back and put momentum into the malaria elimination effort. This paper assessed two of the critical elements of the World Health Organization Genetically modified mosquitoes (WHO GMM) Critical Pathway framework: the community and stakeholders’ engagement (inability to employ widely used frameworks, segmentation of the public, ‘bystander’ status, and guidelines operationalization) and the regulatory landscape (lex generali, ‘goldilocks dilemma’, and mode of regulation) concerning mosquito-oriented gene drives (MGD) advances. Based on the assessment findings, the author believes that CRISPR/Cas-9-mediated MGD will not contribute to the attainment of SDG3 (Target 3.3), despite the undisputable technology’s potential. This research pertains to the state of knowledge, legal frameworks, and legislature, as of November 2022.
Programming tumor evolution with selection gene drives to proactively combat drug resistance
30886Leighow, S.M., Reynolds, J.A., Sokirniy, I. et al., Nature Biotechnology, 2024-07-07 21:29:46.
Most targeted anticancer therapies fail due to drug resistance evolution. Here we show that tumor evolution can be reproducibly redirected to engineer therapeutic opportunity, regardless of the exact ensemble of pre-existing genetic heterogeneity. We develop a selection gene drive system that is stably introduced into cancer cells and is composed of two genes, or switches, that couple an inducible fitness advantage with a shared fitness cost. Using stochastic models of evolutionary dynamics, we identify the design criteria for selection gene drives. We then build prototypes that harness the selective pressure of multiple approved tyrosine kinase inhibitors and employ therapeutic mechanisms as diverse as prodrug catalysis and immune activity induction. We show that selection gene drives can eradicate diverse forms of genetic resistance in vitro. Finally, we demonstrate that model-informed switch engagement effectively targets pre-existing resistance in mouse models of solid tumors. These results establish selection gene drives as a powerful framework for evolution-guided anticancer therapy.
Revisiting Wolbachia detections: Old and new issues in Aedes aegypti mosquitoes and other insects
30882Perran A. Ross, Ary A. Hoffmann, Ecology and Evolution, 14. 2024-07-07 21:12:05.
Wolbachia continue to be reported in species previously thought to lack them, particularly Aedes aegypti mosquitoes. The presence of Wolbachia in this arbovirus vector is considered important because releases of mosquitoes with transinfected Wolbachia are being used around the world to suppress pathogen transmission and these efforts depend on a lack of Wolbachia in natural populations of this species. We previously assessed papers reporting Wolbachia in natural populations of Ae. aegypti and found little evidence that seemed convincing. However, since our review, more and more papers are emerging on Wolbachia detections in this species. Our purpose here is to evaluate these papers within the context of criteria we previously established but also new criteria that include the absence of releases of transinfections within the local areas being sampled which has contaminated natural populations in at least one case where novel detections have been reported. We also address the broader issue of Wolbachia detection in other insects where similar issues may arise which can affect overall estimates of this endosymbiont more generally. We note continuing shortcomings in papers purporting to find natural Wolbachia in Ae. aegypti which are applicable to other insects as well.
Mark–Release–Recapture (MRR) of Sterile Male Aedes albopictus (Skuse) in Sri Lanka: Field Performance of Sterile Males and Estimation of the Wild Mosquito Population Density
30876Hapugoda, Menaka, Nilmini Silva Gunawardena, Tharaka Ranathunge, Jeremy Bouyer, Hamidou Maiga, Kankanige Karunathilake, Gayan Parakrama Withanage, Indika Weerasinghe, Bazoumana B. D. Sow, and Jeevanie Harishchandra, Insects, 15:466. 2024-07-02 13:27:59.
Dengue is an important mosquito-borne disease in Sri Lanka. The Sterile Insect Technique (SIT) is an environment-friendly and novel method that can suppress dengue vector mosquitoes in Sri Lanka. This study aimed to evaluate the field performance of sterile males and the density of wild male Aedes albopictus (Skuse) using a Mark–Release–Recapture (MRR) assay. Laboratory-colonized male pupae were exposed to 50 Gy gamma using a Co60 source. Sterile males (approx. 10,000) marked with fluorescent dust were released weekly for 4 consecutive weeks (January–February 2021) in a geographically isolated 30 ha site in Gampaha. Results show sterile males could disperse up to 543.8 m with a mean distance of 255.1 ± 44.6 m and survive up to 6 days with a mean life expectancy of 3.55 ± 2.32 days. A high field mating competitiveness of sterile males based on a Fried value of 0.47 ± 0.007 and significant induced sterility in the wild eggs in the second generation were found. The mean wild male mosquito population density was 163 males/ha. The data generated will be useful for designing future trials in Sri Lanka and other countries with similar situations.
No Such Thing as Containment? Gene Drives for Conservation and the (Im)possibility of an Island
30864Boersma, K., Bovenkerk, B. and Ludwig, D., Philosophy and Technology, 37:75. 2024-07-02 12:23:47.
This article explores the use of islands as tools of geographical and intellectual containment - or what we call “islanding” - in the scientific and policy literature about gene drive technologies in conservation. In the first part of the article, we explore the narrative of contained gene drive use on islands and discuss how it juggles notions of localness and localization of gene drives and their (test) releases. We question the possibility and narrative of containing the spread of gene drives technologically or geographically, and argue that the gene drives for conservation literature strategically combines contradictory and reductive understandings of islands and containment. The second part of the article is devoted to reflection on nonlocal concerns about gene drives and the possibility of local gene drive decisions. We argue that attempts to legitimize local gene drives through local decision-making evade normative concerns about their nonlocalizability and risk instrumentalizing local communities for nonlocal agendas. Our overarching conceptual aim is therefore to open up a domain of thinking around the possibility of demarcation in our world – of our political, normative decisions, and of our reality – and to argue for the vital importance of reflection on this possibility in technological decision-making.
Escalation of genome defense capacity enables control of an expanding meiotic driver
30862Peiwei Chen, Katherine C. Pan, Eunice H. Park, Yicheng Luo, Yuh Chwen G. Lee, Alexei A. Aravin, bioRxiv, 2024-07-02 12:14:34.
From RNA interference to chromatin silencing, diverse genome defense pathways silence selfish genetic elements to safeguard genome integrity1,2. Despite their diversity, different defense pathways share a modular organization, where numerous specificity factors identify diverse targets and common effectors silence them. In the PIWI-interacting RNA (piRNA) pathway, which controls selfish elements in the metazoan germline, diverse target RNAs are first identified by complementary base pairing with piRNAs and then silenced by PIWI-clade nucleases via enzymatic cleavage1,3. Such a binary architecture allows the defense systems to be readily adaptable, where new targets can be captured via the innovation of new specificity factors4,5. Thus, our current understanding of genome defense against lineage-specific selfish genes has been largely limited to the evolution of specificity factors, while it remains poorly understood whether other types of innovations are required. Here, we describe a new type of innovation, which escalates the defense capacity of the piRNA pathway to control a recently expanded selfish gene in Drosophila melanogaster. Through an in vivo RNAi screen for repressors of Stellate—a recently evolved and expanded selfish meiotic driver6–8—we discovered a novel defense factor, Trailblazer. Trailblazer is a transcription factor that promotes the expression of two PIWI-clade nucleases, Aub and AGO3, to match Stellate in abundance. Recent innovation in the DNA-binding domain of Trailblazer enabled it to drastically elevate Aub and AGO3 expression in the D. melanogaster lineage, thereby escalating the silencing capacity of the piRNA pathway to control expanded Stellate and safeguard fertility. As copy-number expansion is a recurrent feature of diverse selfish genes across the tree of life9–12, we envision that augmenting the defense capacity to quantitatively match selfish genes is likely a repeatedly employed defense strategy in evolution.
Modeling the Evolution of S. pombe Populations with Multiple Killer Meiotic Drivers
30860José Fabricio López Hernández, Boris Y Rubinstein, Robert L Unckless, Sarah E Zanders, G3 Genes|Genomes|Genetics, 2024-07-02 12:10:39.
Meiotic drivers are selfish genetic loci that can be transmitted to more than half of the viable gametes produced by a heterozygote. This biased transmission gives meiotic drivers an evolutionary advantage that can allow them to spread over generations until all members of a population carry the driver. This evolutionary power can also be exploited to modify natural populations using synthetic drivers known as ‘gene drives.’ Recently, it has become clear that natural drivers can spread within genomes to birth multicopy gene families. To understand intragenomic spread of drivers, we model the evolution of two or more distinct meiotic drivers in a population. We employ the wtf killer meiotic drivers from Schizosaccharomyces pombe, which are multicopy in all sequenced isolates, as models. We find that a duplicate wtf driver identical to the parent gene can spread in a population unless, or until, the original driver is fixed. When the duplicate driver diverges to be distinct from the parent gene, we find that both drivers spread to fixation under most conditions, but both drivers can be lost under some conditions. Finally, we show that stronger drivers make weaker drivers go extinct in most, but not all, polymorphic populations with absolutely linked drivers. These results reveal the strong potential for natural meiotic drive loci to duplicate and diverge within genomes. Our findings also highlight duplication potential as a factor to consider in the design of synthetic gene drives.
Exploration of the potential of a boosted sterile insect technique to control fruit flies in mango orchards
30856Esther Gnilane Diouf, Thierry Brévault, Saliou Ndiaye, Cyril Piou, Pest Management Science, 2024-06-28 15:39:38.
An innovative version of the sterile insect technique (SIT) for pest control, called boosted SIT, relies on the use of sterile males coated with a biocide to control a target wild pest population of the same species. The objective of the present study was to assess the relevance of such technology to control the fruit fly Bactrocera dorsalis and fruit losses in mango orchards using. An agent-based simulation model named BOOSTIT was used to explore the reduction of fruit losses thank to sterile male fruit flies control and economic benefits according to different strategies of sterile male release. The simulation considered a landscape of 30.25 ha made up of four mango orchards. The SIT and the boosted SIT reduced fruit losses when releases were made before the mango fruiting period. According to model simulations, releases should be performed at least seven times at 2-week intervals and with a sterile/wild male ratio of at least 10:1. Considering the benefit/cost ratio (BCR), few releases should be done with a late start date. The BCR showed economic gains from the two control methods, the number of saved fruits and BCR being higher for SIT. Our simulations showed that SIT would have better results than the boosted SIT to contribute to an effective control of Bactrocera dorsalis at the scale of a small landscape. We highlight the need for laboratory studies of other types of pathogen to find a suitable one with higher incubation time and lower cost. © 2024 Society of Chemical Industry.
Eliminating malaria vectors with precision-guided sterile males
30852Reema A. Apte, Andrea L. Smidler, James J. Pai, et al, Applied Biological Sciences, 121. 2024-06-28 12:20:46.
Controlling the principal African malaria vector, the mosquito Anopheles gambiae, is considered essential to curtail malaria transmission. However, existing vector control technologies rely on insecticides, which are becoming increasingly ineffective. Sterile insect technique (SIT) is a powerful suppression approach that has successfully eradicated a number of insect pests, yet the A. gambiae toolkit lacks the requisite technologies for its implementation. SIT relies on iterative mass releases of nonbiting, nondriving, sterile males which seek out and mate with monandrous wild females. Once mated, females are permanently sterilized due to mating-induced refractoriness, which results in population suppression of the subsequent generation. However, sterilization by traditional methods renders males unfit, making the creation of precise genetic sterilization methods imperative. Here, we introduce a vector control technology termed precision-guided sterile insect technique (pgSIT), in A. gambiae for inducible, programmed male sterilization and female elimination for wide-scale use in SIT campaigns. Using a binary CRISPR strategy, we cross separate engineered Cas9 and gRNA strains to disrupt male-fertility and female-essential genes, yielding >99.5% male sterility and >99.9% female lethality in hybrid progeny. We demonstrate that these genetically sterilized males have good longevity, are able to induce sustained population suppression in cage trials, and are predicted to eliminate wild A. gambiae populations using mathematical models, making them ideal candidates for release. This work provides a valuable addition to the malaria genetic biocontrol toolkit, enabling scalable SIT-like confinable, species-specific, and safe suppression in the species.
Germline Cas9 promoters with improved performance for homing gene drive
30488Du, J., Chen, W., Jia, X. et al., Nature Communications, 15:4560. 2024-06-04 16:50:42.
Gene drive systems could be a viable strategy to prevent pathogen transmission or suppress vector populations by propagating drive alleles with super-Mendelian inheritance. CRISPR-based homing gene drives convert wild type alleles into drive alleles in heterozygotes with Cas9 and gRNA. It is thus desirable to identify Cas9 promoters that yield high drive conversion rates, minimize the formation rate of resistance alleles in both the germline and the early embryo, and limit somatic Cas9 expression. In Drosophila, the nanos promoter avoids leaky somatic expression, but at the cost of high embryo resistance from maternally deposited Cas9. To improve drive efficiency, we test eleven Drosophila melanogaster germline promoters. Some achieve higher drive conversion efficiency with minimal embryo resistance, but none completely avoid somatic expression. However, such somatic expression often does not carry detectable fitness costs for a rescue homing drive targeting a haplolethal gene, suggesting somatic drive conversion. Supporting a 4-gRNA suppression drive, one promoter leads to a low drive equilibrium frequency due to fitness costs from somatic expression, but the other outperforms nanos, resulting in successful suppression of the cage population. Overall, these Cas9 promoters hold advantages for homing drives in Drosophila species and may possess valuable homologs in other organisms.
Upscaling irradiation protocols of Aedes albopictus pupae within an SIT program in Reunion Island
30485Marquereau, L., Yamada, H., Damiens, D. et al., Scientific Reports, 14. 2024-06-04 16:44:56.
The implementation of the sterile insect technique against Aedes albopictus relies on many parameters, in particular on the success of the sterilization of males to be released into the target area in overflooding numbers to mate with wild females. Achieving consistent sterility levels requires efficient and standardized irradiation protocols. Here, we assessed the effects of exposure environment, density of pupae, irradiation dose, quantity of water and location in the canister on the induced sterility of male pupae. We found that the irradiation of 2000 pupae in 130 ml of water and with a dose of 40 Gy was the best combination of factors to reliably sterilize male pupae with the specific irradiator used in our control program, allowing the sterilization of 14000 pupae per exposure cycle. The location in the canister had no effect on induced sterility. The results reported here allowed the standardization and optimization of irradiation protocols for a Sterile Insect Technique program to control Ae. albopictus on Reunion Island, which required the production of more than 300,000 sterile males per week.
Simulation-based economic evaluation of the Wolbachia method in Brazil: a cost-effective strategy for dengue control
30927Ivan Ricardo Zimmermann, Ricardo Ribeiro Alves Fernandes, Márcia Gisele Santos da Costa, et al, The Lancet Regional Health - Americas, 35. 2024-06-03 15:30:09.
Dengue virus (DENV) is an arbovirus transmitted by Aedes aegypti mosquitoes, which can cause severe conditions such as hemorrhagic fever and dengue shock syndrome. These conditions are associated with adverse social, clinical, and economic consequences in Brazil. Herein, the Wolbachia mosquito replacement method is a promising dengue control strategy. We estimated the economic impact of implementing the Wolbachia mosquito replacement method in seven Brazilian cities. A mathematical microsimulation model tracked nearly 23 million inhabitants over a 20-year period, considering the transitions between five different health states (susceptible, inapparent, outpatient, hospitalised and death). Direct costs included local dengue control programs, Wolbachia implementation and dengue care. Indirect costs related to death and productivity loss, as well as disability-adjusted life-years (DALY) averted were also considered. Without Wolbachia, the model projected 1,762,688 reported dengue cases over 20 years. Implementing the Wolbachia method would avert at least 1,295,566 dengue cases, resulting in lower costs and greater effectiveness in all simulated cities. On average, for every 1000 inhabitants followed for 20 years, the Wolbachia method yielded a cost difference of USD 538,233.68 (BRL 2,691,168.40) and averted 5.56 DALYs. Net monetary benefits (NMB) were positive in all seven cities, ranging from USD 110.72 (BRL 553.59) to USD 1399.19 (BRL 6995.95) per inhabitant. Alternative scenarios have also shown a favourable return on investment with a positive benefit-cost ratio (BCR).
Curing mosquitoes with genetic approaches for malaria control
30356Mary Kefi, Victor Cardoso-Jaime, Sally A. Saab, George Dimopoulos, Trends in Parasitology, 2024-05-21 19:48:52.
Malaria remains a persistent global public health challenge because of the limitations of current prevention tools. The use of transgenic mosquitoes incapable of transmitting malaria, in conjunction with existing methods, holds promise for achieving elimination of malaria and preventing its reintroduction. In this context, population modification involves the spread of engineered genetic elements through mosquito populations that render them incapable of malaria transmission. Significant progress has been made in this field over the past decade in revealing promising targets, optimizing genetic tools, and facilitating the transition from the laboratory to successful field deployments, which are subject to regulatory scrutiny. This review summarizes recent advances and ongoing challenges in ‘curing’ Anopheles vectors of the malaria parasite.
Transformation of meiotic drive into hybrid sterility in Drosophila
30352Jackson Bladen, Hyuck-Jin Nam, Nitin Phadnis, bioRxiv, 2024-05-21 19:05:25.
Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. Here, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies.
A Y chromosome-linked genome editor for efficient population suppression in the malaria vector Anopheles gambiae
30350Ignacio Tolosana, Katie Willis, Austin Burt, Matthew Gribble, Tony Nolan, Andrea Crisanti, Federica Bernardini, bioRxiv, 2024-05-21 18:59:24.
Genetic control – the deliberate introduction of genetic traits to control a pest or vector population – offers a powerful tool to augment conventional mosquito control tools that have been successful in reducing malaria burden but that are compromised by a range of operational challenges. Self-sustaining genetic control strategies have shown great potential in laboratory settings but hesitancy due to their invasive and persistent nature may delay their implementation. Here instead we describe a self-limiting strategy, designed to have geographically and/or temporally restricted effect, based on a Y chromosome-linked genome editor (YLE). The YLE comprises a CRISPR-Cas9 construct that is always inherited by males yet generates an autosomal dominant mutation that is transmitted to over 90% of the offspring and results in female-specific sterility. Males are unaffected. To our knowledge, our system represents the first engineering of the Y chromosome to generate a genetic control strain for mosquitoes. Mathematical modelling shows that this YLE technology is up to 8 times more efficient for population suppression than optimal versions of other self-limiting strategies.
A small-molecule approach to restore female sterility phenotype targeted by a homing suppression gene drive in the fruit pest Drosophila suzukii
29887Ma S, Ni X, Chen S, Qiao X, Xu X, Chen W, et al., PLoS Genetics, 2024-05-07 16:10:19.
CRISPR-based gene drives offer promising prospects for controlling disease-transmitting vectors and agricultural pests. A significant challenge for successful suppression-type drive is the rapid evolution of resistance alleles. One approach to mitigate the development of resistance involves targeting functionally constrained regions using multiple gRNAs. In this study, we constructed a 3-gRNA homing gene drive system targeting the recessive female fertility gene Tyrosine decarboxylase 2 (Tdc2) in Drosophila suzukii, a notorious fruit pest. Our investigation revealed only a low level of homing in the germline, but feeding octopamine restored the egg-laying defects in Tdc2 mutant females, allowing easier line maintenance than for other suppression drive targets. We tested the effectiveness of a similar system in Drosophila melanogaster and constructed additional split drive systems by introducing promoter-Cas9 transgenes to improve homing efficiency. Our findings show that genetic polymorphisms in wild populations may limit the spread of gene drive alleles, and the position effect profoundly influences Cas9 activity. Furthermore, this study highlights the potential of conditionally rescuing the female infertility caused by the gene drive, offering a valuable tool for the industrial-scale production of gene drive transgenic insects.
Wolbachia symbionts control sex in a parasitoid wasp using a horizontally acquired gene
29885Li C, Li CQ, Chen ZB, Liu BQ, Sun X, Wei KH, Li CY, Luan JB., Current Biology, 2024-05-07 15:55:59.
Host reproduction can be manipulated by bacterial symbionts in various ways. Parthenogenesis induction is the most effective type of reproduction manipulation by symbionts for their transmission. Insect sex is determined by regulation of doublesex (dsx) splicing through transformer2 (tra2) and transformer (tra) interaction. Although parthenogenesis induction by symbionts has been studied since the 1970s, its underlying molecular mechanism is unknown. Here we identify a Wolbachia parthenogenesis-induction feminization factor gene (piff) that targets sex-determining genes and causes female-producing parthenogenesis in the haplodiploid parasitoid Encarsia formosa. We found that Wolbachia elimination repressed expression of female-specific dsx and enhanced expression of male-specific dsx, which led to the production of wasp haploid male offspring. Furthermore, we found that E. formosa tra is truncated and non-functional, and Wolbachia has a functional tra homolog, termed piff, with an insect origin. Wolbachia PIFF can colocalize and interact with wasp TRA2. Moreover, Wolbachia piff has coordinated expression with tra2 and dsx of E. formosa. Our results demonstrate the bacterial symbiont Wolbachia has acquired an insect gene to manipulate the host sex determination cascade and induce parthenogenesis in wasps. This study reveals insect-to-bacteria horizontal gene transfer drives the evolution of animal sex determination systems, elucidating a striking mechanism of insect-microbe symbiosis.
Wolbachia infection-responsive immune genes suppress Plasmodium falciparum infection in Anopheles stephensi
29565Vandana V, Dong S, Sheth T, Sun Q, Wen H, Maldonado A, et al., PLoS Pathogens, 20. 2024-04-25 18:04:55.
Wolbachia, a maternally transmitted symbiotic bacterium of insects, can suppress a variety of human pathogens in mosquitoes, including malaria-causing Plasmodium in the Anopheles vector. However, the mechanistic basis of Wolbachia-mediated Plasmodium suppression in mosquitoes is not well understood. In this study, we compared the midgut and carcass transcriptomes of stably infected Anopheles stephensi with Wolbachia wAlbB to uninfected mosquitoes in order to discover Wolbachia infection-responsive immune genes that may play a role in Wolbachia-mediated anti-Plasmodium activity. We show that wAlbB infection upregulates 10 putative immune genes and downregulates 14 in midguts, while it upregulates 31 putative immune genes and downregulates 15 in carcasses at 24 h after blood-fed feeding, the time at which the Plasmodium ookinetes are traversing the midgut tissue. Only a few of these regulated immune genes were also significantly differentially expressed between Wolbachia-infected and non-infected midguts and carcasses of sugar-fed mosquitoes. Silencing of the Wolbachia infection-responsive immune genes TEP 4, TEP 15, lysozyme C2, CLIPB2, CLIPB4, PGRP-LD and two novel genes (a peritrophin-44-like gene and a macro domain-encoding gene) resulted in a significantly greater permissiveness to P. falciparum infection. These results indicate that Wolbachia infection modulates mosquito immunity and other processes that are likely to decrease Anopheles permissiveness to Plasmodium infection.
Comparing the long-term persistence of different Wolbachia strains after the release of bacteria-carrying mosquitoes
29563Jose L. Orozco-Gonzales, Antone dos Santos Benedito, Daiver Cardona-Salgado et al., Mathematical Biosciences, 372. 2024-04-25 17:59:21.
This paper proposes a bidimensional modeling framework for Wolbachia invasion, assuming imperfect maternal transmission, incomplete cytoplasmic incompatibility, and direct infection loss due to thermal stress. Our model adapts to various Wolbachia strains and retains all properties of higher-dimensional models. The conditions for the durable coexistence of Wolbachia-carrying and wild mosquitoes are expressed using the model’s parameters in a compact closed form. When the Wolbachia bacterium is locally established, the size of the remanent wild population can be assessed by a direct formula derived from the model. The model was tested for four Wolbachia strains undergoing laboratory and field trials to control mosquito-borne diseases: wMel, wMelPop, wAlbB, and wAu. As all these bacterial strains affect the individual fitness of mosquito hosts differently and exhibit different levels of resistance to temperature variations, the model helped to conclude that: (1) the wMel strain spreads faster in wild mosquito populations; (2) the wMelPop exhibits lower resilience but also guarantees the smallest size of the remanent wild population; (3) the wAlbB strain performs better at higher ambient temperatures than others; (4) the wAu strain is not sustainable and cannot persist in the wild mosquito population despite its resistance to high temperatures.
A naturally isolated symbiotic bacterium suppresses flavivirus transmission by Aedes mosquitoes
29561Liming Zhang et al., Science, 384. 2024-04-25 17:51:54.
Flavivirus diseases are increasing in incidence and prevalence owing to the urban proclivities of its Aedes mosquito vector species. Extirpation of mosquitoes is considered key for the control of several human diseases but often involves toxic chemicals that prompt mosquito resistance. As some biocontrol alternatives look promising in malaria campaigns, Zhang et al. examined the microbiota of Aedes mosquitoes for potential agents to control dengue and Zika virus transmission. The authors isolated a bacterium called Rosenbergiella_YN46 in Aedes albopictus mosquitos. The bacterium was fed to caged mosquitoes to establish stable gut infections, and it was found to prevent the insects from being infected by viruses and blocked viral transmission to mice.
Economic optimization of Wolbachia-infected Aedes aegypti release to prevent dengue
29104Hollingsworth BD, Cho C, Vella M, Roh H, Sass J, Lloyd AL, Brown ZS., Pest Management Science, 2024-04-16 09:30:09.
Dengue virus, primarily transmitted by the Aedes aegypti mosquito, is a major public health concern affecting ≈3.83 billion people worldwide. Recent releases of Wolbachia-transinfected Ae. aegypti in several cities worldwide have shown that it can reduce dengue transmission. However, these releases are costly, and, to date, no framework has been proposed for determining economically optimal release strategies that account for both costs associated with disease risk and releases. We present a flexible stochastic dynamic programming framework for determining optimal release schedules for Wolbachia-transinfected mosquitoes that balances the cost of dengue infection with the costs of rearing and releasing transinfected mosquitoes. Using an ordinary differential equation model of Wolbachia and dengue in a hypothetical city loosely describing areas at risk of new dengue epidemics, we determined that an all-or-nothing release strategy that quickly brings Wolbachia to fixation is often the optimal solution. Based on this, we examined the optimal facility size, finding that it was inelastic with respect to the mosquito population size, with a 100% increase in population size resulting in a 50-67% increase in optimal facility size. Furthermore, we found that these results are robust to mosquito life-history parameters and are mostly determined by the mosquito population size and the fitness costs associated with Wolbachia. These results reinforce that Wolbachia-transinfected mosquitoes can reduce the cost of dengue epidemics. Furthermore, they emphasize the importance of determining the size of the target population and fitness costs associated with Wolbachia before releases occur.
Altering traits and fates of wild populations with Mendelian DNA sequence modifying Allele Sails
29102Michelle L. Johnson, Bruce A. Hay, Maciej Maselko, Nature Communications, 15. 2024-04-16 09:23:41.
Population-scale genome editing can be used to alter the composition or fate of wild populations. One approach to achieving these aims utilizes a synthetic gene drive element—a multi-gene cassette—to bring about an increase in the frequency of an existing allele. However, the use of gene drives is complicated by the multiple scientific, regulatory, and social issues associated with transgene persistence and gene flow. Alternatives in which transgenes are not driven could potentially avoid some of these issues. Here we propose an approach to population scale gene editing using a system we refer to as an Allele Sail. An Allele Sail consists of a genome editor (the Wind) that introduces DNA sequence edits (the Sail) at one or more sites, resulting in progeny that are viable and fertile. The editor, such as a sequence-specific nuclease, or a prime- or base-editor, is inherited in a Mendelian fashion. Meanwhile, the edits it creates experience an arithmetic, Super-Mendelian increase in frequency. We explore this system using agent-based modeling, and identify contexts in which a single, low frequency release of an editor brings edits to a very high frequency. We also identify conditions in which manipulation of sex determination can be used to bring about population suppression. Current regulatory frameworks often distinguish between transgenics as genetically modified organisms (GMOs), and their edited non-transgenic progeny as non-GMO. In this context an Allele Sail provides a path to alter traits and fates of wild populations in ways that may be considered more acceptable.
Genetic and geographic population structure in the malaria vector, Anopheles farauti, provides a candidate system for pioneering confinable gene-drive releases
29098Ambrose, L., Allen, S.L., Iro’ofa, C. et al., Heredity, 2024-04-16 09:13:44.
Indoor insecticide applications are the primary tool for reducing malaria transmission in the Solomon Archipelago, a region where Anopheles farauti is the only common malaria vector. Due to the evolution of behavioural resistance in some An. farauti populations, these applications have become less effective. New malaria control interventions are therefore needed in this region, and gene-drives provide a promising new technology. In considering developing a population-specific (local) gene-drive in An. farauti, we detail the species’ population genetic structure using microsatellites and whole mitogenomes, finding many spatially confined populations both within and between landmasses. This strong population structure suggests that An. farauti would be a useful system for developing a population-specific, confinable gene-drive for field release, where private alleles can be used as Cas9 targets. Previous work on Anopheles gambiae has used the Cardinal gene for the development of a global population replacement gene-drive. We therefore also analyse the Cardinal gene to assess whether it may be a suitable target to engineer a gene-drive for the modification of local An. farauti populations. Despite the extensive population structure observed in An. farauti for microsatellites, only one remote island population from Vanuatu contained fixed and private alleles at the Cardinal locus. Nonetheless, this study provides an initial framework for further population genomic investigations to discover high-frequency private allele targets in localized An. farauti populations. This would enable the development of gene-drive strains for modifying localised populations with minimal chance of escape and may provide a low-risk route to field trial evaluations.
The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses
29088Miranda, L.S.; Rudd, S.R.; Mena, O.; Hudspeth, P.E.; Barboza-Corona, J.E.; Park, H.-W.; Bideshi, D.K., Biology, 13:182. 2024-04-04 09:42:02.
Aedes, Culex, and Anopheles mosquitoes are the most prolific arthropod vectors of viral and parasitic agents of debilitating and lethal diseases in humans and animals. Despite some success in integrated pest management programs to control vectors, mosquito-borne diseases, such as dengue and dengue hemorrhagic fever, yellow fever, chikungunya, West Nile, and Zika, and parasitic diseases, such as malaria, lymphatic filariasis, and river blindness, continue to threaten the health and well-being of half the world’s population, many of whom live in economically and medically challenged societies. The perpetual problem inflicted by vector-borne diseases is compounded by the selection for resistance to synthetic pesticides, globalization, and climate change. The latter appears to be the most significant factor implicated in the geographic expansion of mosquitoes. Here, we present a review of these challenges and highlight traditional vector control strategies that employ synthetic pesticides, and “green” eco-friendly technologies that include SIT, IIT, RIDL, CRISPR/Cas9/Cas13 gene drive systems, and biological control, with an emphasis on Lysinibacillus sphaericus and Bacillus thuringiensis subsp. israelensis (Bti).
Wolbachia Infection through Hybridization to Enhance an Incompatible Insect Technique-Based Suppression of Aedes albopictus in Eastern Spain
29086Cholvi M, Trelis M, Bueno-Marí R, Khoubbane M, Gil R, Marcilla A, Moretti R., Insects, 15. 2024-04-04 09:29:30.
Wolbachia bacteria occur naturally as symbionts of many insect species and are responsible for various phenomena that modify the hosts’ reproductive biology. Among them, cytoplasmic incompatibility (CI) refers to the sterility of eggs produced by crosses between infected males and females that are uninfected or infected by a non-compatible strain of these bacteria. CI can be exploited for vector control by establishing an opportune Wolbachia infection in a laboratory population of a target insect species and then releasing the infected males into the environment as sterilizing agents. In the present work, a suitable Wolbachia strain was introduced into a Spanish population of the Asian tiger mosquito, Aedes albopictus, through hybridization with the laboratory line, ARwP, already tested as an efficient control tool against this vector. The obtained hybrids were compared with the ARwP to ascertain the effects derived from transferring the infection to a different Ae. albopictus population. No significant differences between lines were found regarding survival, female fecundity, and egg fertility. Importantly, the eggs produced by crosses between males of the hybrid lines and unmodified wild females were 99.9% sterile. This result encourages further studies to explore the feasibility of a Wolbachia-based control program against the Asian tiger mosquito in Spain.
Detection and quantification of natural Wolbachia in Aedes aegypti in Metropolitan Manila, Philippines using locally designed primers
29084Reyes JIL, Suzuki T, Suzuki Y, Watanabe K., Frontiers in Cellular and Infection Microbiology, 2024-04-04 09:23:33.
The Philippines bears health and economic burden caused by high dengue cases annually. Presently, the Philippines still lack an effective and sustainable vector management. The use of Wolbachia, a maternally transmitted bacterium, that mitigate arbovirus transmission has been recommended. Cytoplasmic incompatibility and viral blocking, two characteristics that make Wolbachia suitable for vector control, depend on infection prevalence and density. There are no current Wolbachia release programs in the Philippines, and studies regarding the safety of this intervention. Here, we screened for Wolbachia in Aedes aegypti collected from Metropolitan Manila, Philippines. We designed location-specific primers for qPCR to test whether this improved Wolbachia detection in Ae. aegypti. We explored if host sex and Wolbachia strain could be potential factors affecting Wolbachia density.
Talking About Gene Drive in Uganda: The Need for Science Communication to Underpin Engagement
29082Hartley, S., Stelmach, A., Opesen, C., Openjuru, G. L., and Neema, S., Science Communication, 2024-04-04 09:15:22.
Uganda may host the world’s first field trials of gene drive mosquitoes for malaria control. Global North discourses pre-suppose African publics have access to information about gene drive and are ready to make decisions about its governance. We explore assumptions about the availability of this information in Uganda. We find a paucity of information available combined with a strong desire for information from lay publics. We discuss these findings in the context of Ugandan information infrastructures and political sensitivities to genetic technologies. If Ugandans are to decide about gene drive, they need independent information about the science to underpin engagement.
Monitoring Aedes populations for arboviruses, Wolbachia, insecticide resistance and its mechanisms in various agroecosystems in Benin
29064S. Ateutchia-Ngouanet, F. Nanfack-Minkeu, K. Mavridis, S. Wanji, M. Demanou, J. Vontas, R. Djouaka, Acta Tropica, 253. 2024-04-02 11:34:55.
The susceptibility of arbovirus vectors to insecticides and the microbiome of Aedes species are understudied in Benin.
Between the lab and the Wild: Establishing the Potential of Gene Drive Mosquitoes for Malaria Control
29055Mäkelin, M., Science as Culture, 2024-04-02 09:42:13.
Malaria control has been one of the defining goals in global health.
Wolbachia strain wAlbB shows favourable characteristics for dengue control use in Aedes aegypti from Burkina Faso
29041Maria Vittoria Mancini, Shivan M. Murdochy, Etienne Bilgo, Thomas H. Ant, Daniel Gingell, Edounou Jacques Gnambani, Anna-Bella Failloux, Abdoulaye Diabate, Steven P. Sinkins, Environmental Microbiology, 26. 2024-03-19 16:46:34.
Dengue represents an increasing public health burden worldwide.
Alpha-mannosidase-2 modulates arbovirus infection in a pathogen- and Wolbachia-specific manner in Aedes aegypti mosquitoes
29035Nadya Urakova, Renuka E. Joseph, Allyn Huntsinger, Vanessa M. Macias, Matthew J. Jones, Leah T. Sigle, Ming Li, Omar S. Akbari, Zhiyong Xi, Konstantinos Lymperopoulos, Richard T. Sayre, Elizabeth A. McGraw, Jason L. Rasgon, Insect Molecular Biology, 2024-03-19 15:50:02.
Multiple Wolbachia strains can block pathogen infection, replication and/or transmission in Aedes aegypti mosquitoes under both laboratory and field conditions.
Prophage proteins alter long noncoding RNA and DNA of developing sperm to induce a paternal-effect lethality
29033Rupinder Kaur et al., Science, 383:1111-1117. 2024-03-19 15:33:59.
Many arthropods carry symbiotic bacteria. Some, including Wolbachia strains, have the capacity to cause male sterility.
Comparative analysis of Wolbachia maternal transmission and localization in host ovaries
29029Michael T.J. Hague, Timothy B. Wheeler, Brandon S. Cooper, bioRxiv, 2024-03-19 13:26:24.
Scientism, trust, value alignment, views of nature, and U.S. public opinion about gene drive mosquitos
31447Evans, J. H., & Schairer, C. E., Public Understanding of Science, 2024-03-12 21:29:22.
Gene drive could be a powerful tool for addressing problems of conservation, agriculture, and human health caused by insect and animal pests but is likely to be controversial as it involves the release of genetically modified organisms. This study examined the social determinants of opinion of gene drive. We asked a representative sample of the U.S. public to respond to a description of a hypothetical application of a gene-drive mosquito to the problem of malaria and examined the relationship of these responses with demographic and ideological beliefs. We found strong general approval for the use of gene-drive mosquitos to address malaria, coinciding with the concern about a possible environmental impact of modified mosquitos and that gene drives represent “too much power over nature.” Among the determinants we measured, respondent acceptance of scientism and trust that scientists are advancing the public’s interest were the greatest predictors of views of gene drive.
Acceptability of emergent Aedes aegypti vector control methods in Ponce, Puerto Rico: A qualitative assessment
29010Pérez-Guerra CL, Rosado-Santiago C, Ramos SA, Marrero-Santos KM, González-Zeno G, Partridge SK, et al., PLoS Global Public Health, 2024-03-11 13:41:04.
Aedes aegypti control has been fraught with challenges in Puerto Rico. The government has implemented commonly used vector control methods, but arboviral epidemics still occur. It is necessary to explore new Ae. aegypti control methods. This study aimed to understand the perceptions of community members in Ponce, Puerto Rico about emergent and traditional Ae. aegypti vector control methods and determine their acceptability and support for these methods. We identified the type of information needed to increase support for emergent vector control methods, and the preferred strategies to disseminate this information. Four group discussions were conducted with a total of 32 participants representing eight of the 14 clusters participating in the Communities Organized for the Prevention of Arboviruses (COPA), a project designed to mobilize communities in Ponce, Puerto Rico to prevent diseases transmitted by mosquitoes. Group discussions began with an overview of different methods used for controlling Ae. aegypti mosquitoes. These overviews facilitated participant understanding of the mosquito control methods presented. Use of source reduction, autocidal gravid ovitraps (AGO), and manual application of larvicide for arboviral mosquito control received support from almost all participants. Vector control methods that use more familiar techniques in Puerto Rico such as truck-mounted larvicide spraying (TMLS) and insecticide residual spraying received support from most participants. More than half of participants supported the use of emergent mosquito control methods including Wolbachia suppression, Wolbachia replacement, or genetically modified mosquitoes (GMM). Participants preferred to receive vector control information through house-to-house visits with the distribution of written materials, followed by dissemination of information through traditional (i.e., radio, television) and social media. The detailed information resulting from this study was used to develop messages for a communications campaign to garner future community support. Community acceptance and support are critical for the success of vector control programs using emergent mosquito control methods.
Efficacy of Wolbachia-based mosquito control: Predictions of a spatially discrete mathematical model
29008David Dye, John W. Cain, PLoS One, 19. 2024-03-11 12:43:55.
Wolbachia is an endosymbiont bacterium present in many insect species. When Wolbachia-carrying male Aedes aegypti mosquitoes mate with non-carrier females, their embryos are not viable due to cytoplasmic incompatibility. This phenomenon has been exploited successfully for the purpose of controlling mosquito populations and the spread of mosquito-borne illnesses: Wolbachia carriers are bred and released into the environment. Because Wolbachia is not harmful to humans, this method of mosquito control is regarded as a safer alternative to pesticide spraying. In this article, we introduce a mathematical framework for exploring (i) whether a one-time release of Wolbachia carriers can elicit a sustained presence of carriers near the release site, and (ii) the extent to which spatial propagation of carriers may allow them to establish fixation in other territories. While some prior studies have formulated mosquito dispersal models using advection-reaction-diffusion PDEs, the predictive power of such models requires careful ecological mapping: advection and diffusion coefficients exhibit significant spatial dependence due to heterogeneity of resources and topography. Here, we adopt a courser-grained view, regarding the environment as a network of discrete, diffusively-coupled “habitats”—distinct zones of high mosquito density such as stagnant ponds. We extend two previously published single-habitat mosquito models to multiple habitats, and calculate rates of migration between pairs of habitats using dispersal kernels. Our primary results are quantitative estimates regarding how the success of carrier fixation in one or more habitats is determined by: the number of carriers released, sizes of habitats, distances between habitats, and the rate of migration between habitats. Besides yielding sensible and potentially useful predictions regarding the success of Wolbachia-based control, our framework applies to other approaches (e.g., gene drives) and contexts beyond the realm of insect pest control.
Aedes aegypti Controls Ae. aegypti: SIT and IIT—An Overview
29003Robert L. Aldridge; Seth Gibson; Kenneth J. Linthicum, Journal of the American Mosquito Control Association, 20:32-49. 2024-03-11 12:34:19.
The sterile insect technique (SIT) and the incompatible insect technique (IIT) are emerging and potentially revolutionary tools for controlling Aedes aegypti (L.), a prominent worldwide mosquito vector threat to humans that is notoriously difficult to reduce or eliminate in intervention areas using traditional integrated vector management (IVM) approaches. Here we provide an overview of the discovery, development, and application of SIT and IIT to Ae. aegypti control, and innovations and advances in technology, including transgenics, that could elevate these techniques to a worldwide sustainable solution to Ae. aegypti when combined with other IVM practices.
DENV-1 Titer Impacts Viral Blocking in wMel Aedes aegypti with Brazilian Genetic Background
28991Corrêa-Antônio, Jessica, Mariana R. David, Dinair Couto-Lima, Gabriela Azambuja Garcia, Milan S. G. Keirsebelik, Rafael Maciel-de-Freitas, and Márcio Galvão Pavan., Viruses, 16. 2024-03-11 10:08:24.
Several countries have been using Wolbachia deployments to replace highly competent native Aedes aegypti populations with Wolbachia-carrying mosquitoes with lower susceptibility to arboviruses such as dengue, Zika, and chikungunya. In Rio de Janeiro, Wolbachia deployments started in 2015 and still present a moderate introgression with a modest reduction in dengue cases in humans (38%). Here, we evaluated the vector competence of wild-type and wMel-infected Ae. aegypti with a Brazilian genetic background to investigate whether virus leakage could contribute to the observed outcomes in Brazil. We collected the specimens in three areas of Rio de Janeiro with distinct frequencies of mosquitoes with wMel strain and two areas with wild Ae. aegypti. The mosquitoes were orally exposed to two titers of DENV-1 and the saliva of DENV-1-infected Ae. aegypti was microinjected into wMel-free mosquitoes to check their infectivity. When infected with the high DENV-1 titer, the presence of wMel did not avoid viral infection in mosquitoes’ bodies and saliva but DENV-1-infected wMel mosquitoes produced lower viral loads than wMel-free mosquitoes. On the other hand, wMel mosquitoes infected with the low DENV-1 titer were less susceptible to virus infection than wMel-free mosquitoes, although once infected, wMel and wMel-free mosquitoes exhibited similar viral loads in the body and the saliva. Our results showed viral leakage in 60% of the saliva of wMel mosquitoes with Brazilian background; thus, sustained surveillance is imperative to monitor the presence of other circulating DENV-1 strains capable of overcoming the Wolbachia blocking phenotype, enabling timely implementation of action plans.
Effectiveness evaluation of mosquito suppression strategies on dengue transmission under changing temperature and precipitation
28984Kaihui Liu, Shuanghui Fang, Qiong Li, et al., Acta Tropica, 2024-03-05 20:16:41.
PSRs: Selfish chromosomes that manipulate reproductive development
28974Xinmi Zhang, Patrick M. Ferree, Seminars in Cell and Developmental Biology, 159-160:66-73. 2024-03-05 14:28:18.
B chromosomes are intriguing “selfish” genetic elements, many of which exhibit higher-than-Mendelian transmission. This perspective highlights a group of B chromosomes known as Paternal Sex Ratio chromosomes (PSRs), which are found in several insects with haplo-diploid reproduction. PSRs harshly alter the organism’s reproduction to facilitate their own inheritance. A manifestation of this effect is the conversion of female destined individuals into males. Key to this conversion is the mysterious ability of PSRs to cause elimination of the sperm-inherited half of the genome during zygote formation. Here we discuss how PSRs were discovered, what is known about how they alter paternal chromatin dynamics to cause sex conversion, and how PSR-induced genome elimination is different from other forms of programmed genome elimination in different insects. PSRs also stand out because their DNA sequence compositions differ in remarkable ways from their insect’s essential chromosomes, a characteristic suggestive of interspecies origins. Broadly, we also highlight poorly understood aspects of PSR dynamics that need to be investigated.
Un1Cas12f1 and Cas9 gene drive in HSV1: viruses that ‘infect’ viruses
28972Qiaorui Yao, Zhuangjie Lin, Keyuan Lai, Xianying Zeng, Guanxiong Lei, Tongwen Zhang, Hongsheng Dai, bioRxiv, 2024-03-05 14:11:19.
Synthetic CRISPR-Cas9 gene drive has been developed as a potential tool to control harmful species. However, Cas9 gene drive faces high resistance rate and mitigation strategies developed so far are difficult to implement. Furthermore, studying the resistance to gene drive is time consuming and challenging in higher organisms. We here tackled these two challenges simultaneously by generating Cas9 and Un1Cas12f1 gene drive in a fast-replicating DNA virus, HSV1. We assessed the transmission dynamics and resistance formation through phenotypical staining and next-generation sequencing, and demonstrated that HSV1 supported fast and effective transmission of gene drives, and the Un1Cas12f1 gene drives yielded greater conversion and lower resistance than did the Cas9 gene drives. This positions the Un1Cas12f1 gene drive as a promising alternative, and HSV1 emerges as a dependable and swift platform for gene drive assessment. The gene drive viruses function like pathogens that specifically infect viruses, offering potential applications in attenuating viral infections.
CRISPR-mediated germline mutagenesis for genetic sterilization of Anopheles gambiae males
28970Smidler, A.L., Marrogi, E., Kauffman, J. et al., Scientific Reports, 14. 2024-03-05 13:54:40.
Rapid spread of insecticide resistance among anopheline mosquitoes threatens malaria elimination efforts, necessitating development of alternative vector control technologies. Sterile insect technique (SIT) has been successfully implemented in multiple insect pests to suppress field populations by the release of large numbers of sterile males, yet it has proven difficult to adapt to Anopheles vectors. Here we outline adaptation of a CRISPR-based genetic sterilization system to selectively ablate male sperm cells in the malaria mosquito Anopheles gambiae. We achieve robust mosaic biallelic mutagenesis of zero population growth (zpg, a gene essential for differentiation of germ cells) in F1 individuals after intercrossing a germline-expressing Cas9 transgenic line to a line expressing zpg-targeting gRNAs. Approximately 95% of mutagenized males display complete genetic sterilization, and cause similarly high levels of infertility in their female mates. Using a fluorescence reporter that allows detection of the germline leads to a 100% accurate selection of spermless males, improving the system. These males cause a striking reduction in mosquito population size when released at field-like frequencies in competition cages against wild type males. These findings demonstrate that such a genetic system could be adopted for SIT against important malaria vectors.
Efficacy of Wolbachia-mediated sterility to reduce the incidence of dengue: a synthetic control study in Singapore
28940Jue Tao Lim, Somya Bansal*, Chee Seng Chong*, Borame Dickens, Youming Ng, Lu Deng, Caleb Lee, Li Yun Tan, Grace Chain, Pei Ma, Shuzhen Sim, Cheong Huat Tan, Alex R Cook, Lee Ching Ng, The Lancet Microbe, 2024-02-27 18:18:52.
Our study comprised an at-risk population of 607 872 individuals living in intervention sites and 3 894 544 individuals living in control sites. Interventions demonstrated up to 77·28% (121/156, 95% CI 75·81–78·58) intervention efficacy despite incomplete coverage across all towns until EW 26, 2022. Intervention efficacies increased as release coverage increased across all intervention sites. Releases led to 2242 (95% CI 2092–2391) fewer cases per 100 000 people in intervention sites during the study period. Secondary analysis showed that these intervention effects were replicated across all age groups and both sexes for intervention sites.
Acetylcholine esterase of Drosophila melanogaster: a laboratory model to explore insecticide susceptibility gene drives
28938Hernandes, N., Qi, X.M., Bhide, S., Brown, C., Camm, B.J., Baxter, S.W. and Robin, C., Pest Management Science, 2024-02-27 18:08:08.
One of the proposed applications of gene drives has been to revert pesticide resistant mutations back to the ancestral susceptible state. Insecticides that have become ineffective because of the rise of resistance could have reinvigorated utility and be used to suppress pest populations again, perhaps at lower application doses. We have created a laboratory model for susceptibility gene drives that replaces field-selected resistant variants of the acetylcholine esterase (Ace) locus of Drosophila melanogaster with ancestral susceptible variants. We constructed a CRISPR/Cas9 homing drive and found that homing occurred in many genetic backgrounds with varying efficiencies. While the drive itself could not be homozygosed, it converted resistant alleles into susceptible ones and produced recessive lethal alleles that could suppress populations. Our studies provided evidence for two distinct classes of Gene Drive Resistance (GDR): rather than being mediated by the conventional Non-Homologous End-joining (NHEJ) pathway, one seemed to involve short homologous repair and the other was defined by genetic background. Additionally, we used simulations to explore a distinct application of susceptibility drives; the use of chemicals to prevent the spread of synthetic gene drives into protected areas. Insecticide susceptibility gene drives could be useful tools to control pest insects however problems with particularities of target loci and GDR will need to be overcome for them to be effective. Furthermore, realistic patterns of pest dispersal and high insecticide exposure rates would be required if susceptibility were to be useful as a ‘safety-switch’ to prevent the unwanted spread of gene drives.
Introduction of Aedes aegypti mosquitoes carrying wAlbB Wolbachia sharply decreases dengue incidence in disease hotspots
28927AA Hoffmann, NW Ahmad, WM Keong, CY Ling, NA Ahmad, N. Golding, N. Tierney, J. Jelip, PW Putit, N Mohktar, SS Sandhu, LS Ming, et al., iScience, 2024-02-27 16:48:03.
Partial replacement of resident Aedes aegypti mosquitoes with introduced mosquitoes carrying certain strains of inherited Wolbachia symbionts can result in transmission blocking of dengue and other viruses of public health importance. Wolbachia strain wAlbB is an effective transmission blocker and stable at high temperatures, making it particularly suitable for hot tropical climates. Following trial field releases in Malaysia, releases using wAlbB Ae. aegypti have become operationalized by the Malaysian health authorities. We report here on an average reduction in dengue fever of 62.4% (confidence intervals 50–71%) in 20 releases sites when compared to 76 control sites in high-rise residential areas. Importantly the level of dengue reduction increased with Wolbachia frequency, with 75.8% reduction (61–87%) estimated at 100% Wolbachia frequency. These findings indicate large impacts of wAlbB Wolbachia invasions on dengue fever incidence in an operational setting, with incidence expected to further decrease as wider areas are invaded.
Genome editing in pests: basic science to applications
28908Chen, X., Palli, S.R., Journal of Pest Science, 2024-02-20 15:39:21.
Recent developments in sequencing technologies produced enormous data on gene sequences and the identity of genes in many pest insects and disease vectors. However, the function of many of these genes is unknown. Functional genomics studies to uncover gene function in pest insects are urgently needed. RNA interference methods could be used in some insects but not most due to their variable efficiency among insect pests. Recently developed clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system of genome editing method is being developed for use in many insect pests. This technology has already been demonstrated to function in more than 40 insect pest species from seven orders and has contributed to advances in pest biology and the development of improved pest management methods. This review summarizes recent results of CRISPR/Cas9 technology developments and their contributions to advancing the basic and applied science of insect pests and disease vectors.
Deep orange gene editing triggers temperature-sensitive lethal phenotypes in Ceratitis capitata
28906Sollazzo, G., Nikolouli, K., Gouvi, G. et al., BMC Biotechnology, 24. 2024-02-20 15:24:38.
The Mediterranean fruit fly, Ceratitis capitata, is a significant agricultural pest managed through area-wide integrated pest management (AW-IPM) including a sterile insect technique (SIT) component. Male-only releases increase the efficiency and cost-effectiveness of SIT programs, which can be achieved through the development of genetic sexing strains (GSS). The most successful GSS developed to date is the C. capitata VIENNA 8 GSS, constructed using classical genetic approaches and an irradiation-induced translocation with two selectable markers: the white pupae (wp) and temperature-sensitive lethal (tsl) genes. However, currently used methods for selecting suitable markers and inducing translocations are stochastic and non-specific, resulting in a laborious and time-consuming process. Recent efforts have focused on identifying the gene(s) and the causal mutation(s) for suitable phenotypes, such as wp and tsl, which could be used as selectable markers for developing a generic approach for constructing GSS. The wp gene was recently identified, and efforts have been initiated to identify the tsl gene. This study investigates Ceratitis capitata deep orange (Ccdor) as a tsl candidate gene and its potential to induce tsl phenotypes. An integrated approach based on cytogenetics, genomics, bioinformatics, and gene editing was used to characterize the Ccdor. Its location was confirmed on the right arm of chromosome 5 in the putative tsl genomic region. Knock-out of Ccdor using CRISPR/Cas9-NHEJ and targeting the fourth exon resulted in lethality at mid- and late-pupal stage, while the successful application of CRISPR HDR introducing a point mutation on the sixth exon resulted in the establishment of the desired strain and two additional strains (dor 12del and dor 51dup), all of them expressing tsl phenotypes and presenting no (or minimal) fitness cost when reared at 25 °C. One of the strains exhibited complete lethality when embryos were exposed at 36 °C. Gene editing of the deep orange gene in Ceratitis capitata resulted in the establishment of temperature-sensitive lethal mutant strains. The induced mutations did not significantly affect the rearing efficiency of the strains. As deep orange is a highly conserved gene, these data suggest that it can be considered a target for the development of tsl mutations which could potentially be used to develop novel genetic sexing strains in insect pests and disease vectors.
Meiotic drive against chromosome fusions in butterfly hybrids
28892Jesper Boman, Christer Wiklund, Roger Vila, Niclas Backström, bioRxiv, 2024-02-13 21:18:38.
Species frequently differ in karyotype, but heterokaryotypic individuals may suffer from reduced fitness. Chromosomal rearrangements like fissions and fusions can thus serve as a mechanism for speciation between incipient lineages but their evolution poses a paradox. How does underdominant rearrangements evolve? One solution is the fixation of underdominant chromosomal rearrangements through genetic drift. However, this requires small and isolated populations. Fixation is more likely if a novel rearrangement is favored by a transmission bias, such as meiotic drive. Here, we investigate transmission ratio distortion in hybrids between two wood white (Leptidea sinapis) butterfly populations with extensive karyotype differences. Using data from two different crossing experiments, we uncover a transmission bias favoring the fused state at chromosome with unknown polarization in one experiment and a transmission bias favoring the unfused state of derived fusions in both experiments. The latter result support a scenario where chromosome fusions can fix in populations despite counteracting effects of meiotic drive. This means that meiotic drive not only can promote runaway chromosome number evolution and speciation, but also that this transmission bias can be a conservative force acting against karyotypic change and the evolution of reproductive isolation. Based on our results, we suggest a mechanistic model for why derived fusions may be opposed by meiotic drive and discuss factors contributing to karyotype evolution in Lepidoptera.
