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Oberhofer G, Johnson ML, Ivy T, Antoshechkin I, Hay BA. Cleave and Rescue gamete killers create conditions for gene drive in plants. NATURE PLANTS 2024:10.1038/s41477-024-01701-3. [PMID: 38886522 DOI: 10.1038/s41477-024-01701-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Accepted: 04/16/2024] [Indexed: 06/20/2024]
Abstract
Gene drive elements promote the spread of linked traits and can be used to change the composition or fate of wild populations. Cleave and Rescue (ClvR) drive elements sit at a fixed chromosomal position and include a DNA sequence-modifying enzyme such as Cas9/gRNAs that disrupts endogenous versions of an essential gene and a recoded version of the essential gene resistant to cleavage. ClvR spreads by creating conditions in which those lacking ClvR die because they lack functional versions of the essential gene. Here we demonstrate the essential features of the ClvR gene drive in the plant Arabidopsis thaliana through killing of gametes that fail to inherit a ClvR that targets the essential gene YKT61. Resistant alleles, which can slow or prevent drive, were not observed. Modelling shows plant ClvRs are robust to certain failure modes and can be used to rapidly drive population modification or suppression. Possible applications are discussed.
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Affiliation(s)
- Georg Oberhofer
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Michelle L Johnson
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Tobin Ivy
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Igor Antoshechkin
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Bruce A Hay
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.
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2
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Hernandes N, Qi XM, Bhide S, Brown C, Camm BJ, Baxter SW, Robin C. Acetylcholine esterase of Drosophila melanogaster: a laboratory model to explore insecticide susceptibility gene drives. PEST MANAGEMENT SCIENCE 2024; 80:2950-2964. [PMID: 38344908 DOI: 10.1002/ps.8003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 01/28/2024] [Accepted: 02/12/2024] [Indexed: 03/01/2024]
Abstract
BACKGROUND 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. RESULTS 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 homozygous, 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. CONCLUSIONS 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. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
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Affiliation(s)
- Natalia Hernandes
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Xiaomeng Mollyann Qi
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Soumitra Bhide
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Courtney Brown
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Benjamin J Camm
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Simon W Baxter
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
| | - Charles Robin
- The School of BioSciences, The University of Melbourne, Melbourne, Victoria, Australia
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3
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Zhang S, Champer J. Performance characteristics allow for confinement of a CRISPR toxin-antidote gene drive for population suppression in a reaction-diffusion model. Proc Biol Sci 2024; 291:20240500. [PMID: 38889790 DOI: 10.1098/rspb.2024.0500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 04/26/2024] [Indexed: 06/20/2024] Open
Abstract
Gene drive alleles that can bias their own inheritance could engineer populations for control of disease vectors, invasive species and agricultural pests. There are successful examples of suppression drives and confined modification drives, but developing confined suppression drives has proven more difficult. However, CRISPR-based toxin-antidote dominant embryo (TADE) suppression drive may fill this niche. It works by targeting and disrupting a haplolethal target gene in the germline with its gRNAs while rescuing this target. It also disrupts a female fertility gene by driving insertion or additional gRNAs. Here, we used a reaction-diffusion model to assess drive performance in continuous space, where outcomes can be substantially different from those in panmictic populations. We measured drive wave speed and found that moderate fitness costs or target gene disruption in the early embryo from maternally deposited nuclease can eliminate the drive's ability to form a wave of advance. We assessed the required release size, and finally we investigated migration corridor scenarios. It is often possible for the drive to suppress one population and then persist in the corridor without invading the second population, a potentially desirable outcome. Thus, even imperfect variants of TADE suppression drive may be excellent candidates for confined population suppression.
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Affiliation(s)
- Shijie Zhang
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University , Beijing 100871, People's Republic of China
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University , Beijing 100871, People's Republic of China
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Du J, Chen W, Jia X, Xu X, Yang E, Zhou R, Zhang Y, Metzloff M, Messer PW, Champer J. Germline Cas9 promoters with improved performance for homing gene drive. Nat Commun 2024; 15:4560. [PMID: 38811556 PMCID: PMC11137117 DOI: 10.1038/s41467-024-48874-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Accepted: 05/16/2024] [Indexed: 05/31/2024] Open
Abstract
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.
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Affiliation(s)
- Jie Du
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China.
| | - Weizhe Chen
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China
- School of Life Sciences, Tsinghua University, 100084, Beijing, China
| | - Xihua Jia
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China
| | - Xuejiao Xu
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China
| | - Emily Yang
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
| | - Ruizhi Zhou
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China
| | - Yuqi Zhang
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China
| | - Matt Metzloff
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
| | - Philipp W Messer
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Center for Life Sciences, Peking University, 100871, Beijing, China.
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Hou S, Chen J, Feng R, Xu X, Liang N, Champer J. A homing rescue gene drive with multiplexed gRNAs reaches high frequency in cage populations but generates functional resistance. J Genet Genomics 2024:S1673-8527(24)00070-5. [PMID: 38599514 DOI: 10.1016/j.jgg.2024.04.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 04/02/2024] [Accepted: 04/02/2024] [Indexed: 04/12/2024]
Abstract
CRISPR homing gene drives have considerable potential for managing populations of medically and agriculturally significant insects. They operate by Cas9 cleavage followed by homology-directed repair, copying the drive allele to the wild-type chromosome and thus increasing in frequency and spreading throughout a population. However, resistance alleles formed by end-joining repair pose a significant obstacle. To address this, we create a homing drive targeting the essential hairy gene in Drosophila melanogaster. Nonfunctional resistance alleles are recessive lethal, while drive carriers have a recoded "rescue" version of hairy. The drive inheritance rate is moderate, and multigenerational cage studies show drive spread to 96%-97% of the population. However, the drive does not reach 100% due to the formation of functional resistance alleles, despite using four gRNAs. These alleles have a large deletion but likely utilize an alternate start codon. Thus, revised designs targeting more essential regions of a gene may be necessary to avoid such functional resistance. Replacement of the rescue element's native 3' UTR with a homolog from another species increases drive inheritance by 13%-24%. This was possibly because of reduced homology between the rescue element and surrounding genomic DNA, which could also be an important design consideration for rescue gene drives.
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Affiliation(s)
- Shibo Hou
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Jingheng Chen
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Ruobing Feng
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Xuejiao Xu
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Nan Liang
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Jackson Champer
- Center for Bioinformatics, Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China.
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Lawler CD, Nuñez AKP, Hernandes N, Bhide S, Lohrey I, Baxter S, Robin C. The haplolethal gene wupA of Drosophila exhibits potential as a target for an X-poisoning gene drive. G3 (BETHESDA, MD.) 2024; 14:jkae025. [PMID: 38306583 PMCID: PMC10989859 DOI: 10.1093/g3journal/jkae025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 06/23/2023] [Accepted: 01/26/2024] [Indexed: 02/04/2024]
Abstract
A synthetic gene drive that targets haplolethal genes on the X chromosome can skew the sex ratio toward males. Like an "X-shredder," it does not involve "homing," and that has advantages including the reduction of gene drive resistance allele formation. We examine this "X-poisoning" strategy by targeting 4 of the 11 known X-linked haplolethal/haplosterile genes of Drosophila melanogaster with CRISPR/Cas9. We find that targeting the wupA gene during spermatogenesis skews the sex ratio so fewer than 14% of progeny are daughters. That is unless we cross the mutagenic males to X^XY female flies that bear attached-X chromosomes, which reverses the inheritance of the poisoned X chromosome so that sons inherit it from their father, in which case only 2% of the progeny are sons. These sex ratio biases suggest that most of the CRISPR/Cas9 mutants we induced in the wupA gene are haplolethal but some are recessive lethal. The males generating wupA mutants do not suffer from reduced fertility; rather, the haplolethal mutants arrest development in the late stages of embryogenesis well after fertilized eggs have been laid. This provides a distinct advantage over genetic manipulation strategies involving sterility which can be countered by the remating of females. We also find that wupA mutants that destroy the nuclear localization signal of shorter isoforms are not haplolethal as long as the open reading frame remains intact. Like D. melanogaster, wupA orthologs of Drosophila suzukii and Anopheles mosquitos are found on X chromosomes making wupA a viable X-poisoning target in multiple species.
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Affiliation(s)
- Clancy D Lawler
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
| | | | - Natalia Hernandes
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
| | - Soumitra Bhide
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
| | - Isabelle Lohrey
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
| | - Simon Baxter
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
| | - Charles Robin
- School of BioSciences, The University of Melbourne, Melbourne 3010, Australia
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Oberhofer G, Johnson ML, Ivy T, Antoshechkin I, Hay BA. Cleave and Rescue gamete killers create conditions for gene drive in plants. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.13.562303. [PMID: 37873352 PMCID: PMC10592828 DOI: 10.1101/2023.10.13.562303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Gene drive elements promote the spread of linked traits, even when their presence confers a fitness cost to carriers, and can be used to change the composition or fate of wild populations. Cleave and Rescue (ClvR) drive elements sit at a fixed chromosomal position and include a DNA sequence-modifying enzyme such as Cas9/gRNAs (the Cleaver/Toxin) that disrupts endogenous versions of an essential gene, and a recoded version of the essential gene resistant to cleavage (the Rescue/Antidote). ClvR spreads by creating conditions in which those lacking ClvR die because they lack functional versions of the essential gene. We demonstrate the essential features of ClvR gene drive in the plant Arabidopsis thaliana through killing of gametes that fail to inherit a ClvR that targets the essential gene YKT61, whose expression is required in male and female gametes for their survival. Resistant (uncleavable but functional) alleles, which can slow or prevent drive, were not observed. Modeling shows plant ClvRs are likely to be robust to certain failure modes and can be used to rapidly drive population modification or suppression. Possible applications in plant breeding, weed control, and conservation are discussed.
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Affiliation(s)
- Georg Oberhofer
- California Institute of Technology. Division of Biology and Biological Engineering. 1200 East California Boulevard, MC156-29, Pasadena, CA 91125
| | - Michelle L. Johnson
- California Institute of Technology. Division of Biology and Biological Engineering. 1200 East California Boulevard, MC156-29, Pasadena, CA 91125
| | - Tobin Ivy
- California Institute of Technology. Division of Biology and Biological Engineering. 1200 East California Boulevard, MC156-29, Pasadena, CA 91125
| | - Igor Antoshechkin
- California Institute of Technology. Division of Biology and Biological Engineering. 1200 East California Boulevard, MC156-29, Pasadena, CA 91125
| | - Bruce A. Hay
- California Institute of Technology. Division of Biology and Biological Engineering. 1200 East California Boulevard, MC156-29, Pasadena, CA 91125
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8
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Kim J, Harris KD, Kim IK, Shemesh S, Messer PW, Greenbaum G. Incorporating ecology into gene drive modelling. Ecol Lett 2023; 26 Suppl 1:S62-S80. [PMID: 37840022 DOI: 10.1111/ele.14194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 02/13/2023] [Accepted: 02/15/2023] [Indexed: 10/17/2023]
Abstract
Gene drive technology, in which fast-spreading engineered drive alleles are introduced into wild populations, represents a promising new tool in the fight against vector-borne diseases, agricultural pests and invasive species. Due to the risks involved, gene drives have so far only been tested in laboratory settings while their population-level behaviour is mainly studied using mathematical and computational models. The spread of a gene drive is a rapid evolutionary process that occurs over timescales similar to many ecological processes. This can potentially generate strong eco-evolutionary feedback that could profoundly affect the dynamics and outcome of a gene drive release. We, therefore, argue for the importance of incorporating ecological features into gene drive models. We describe the key ecological features that could affect gene drive behaviour, such as population structure, life-history, environmental variation and mode of selection. We review previous gene drive modelling efforts and identify areas where further research is needed. As gene drive technology approaches the level of field experimentation, it is crucial to evaluate gene drive dynamics, potential outcomes, and risks realistically by including ecological processes.
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Affiliation(s)
- Jaehee Kim
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
| | - Keith D Harris
- Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Isabel K Kim
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
| | - Shahar Shemesh
- Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Philipp W Messer
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
| | - Gili Greenbaum
- Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Jerusalem, Israel
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James S, Santos M. The Promise and Challenge of Genetic Biocontrol Approaches for Malaria Elimination. Trop Med Infect Dis 2023; 8:201. [PMID: 37104327 PMCID: PMC10140850 DOI: 10.3390/tropicalmed8040201] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 03/15/2023] [Accepted: 03/23/2023] [Indexed: 04/03/2023] Open
Abstract
Malaria remains an ongoing public health challenge, with over 600,000 deaths in 2021, of which approximately 96% occurred in Africa. Despite concerted efforts, the goal of global malaria elimination has stalled in recent years. This has resulted in widespread calls for new control methods. Genetic biocontrol approaches, including those focused on gene-drive-modified mosquitoes (GDMMs), aim to prevent malaria transmission by either reducing the population size of malaria-transmitting mosquitoes or making the mosquitoes less competent to transmit the malaria parasite. The development of both strategies has advanced considerably in recent years, with successful field trials of several biocontrol methods employing live mosquito products and demonstration of the efficacy of GDMMs in insectary-based studies. Live mosquito biocontrol products aim to achieve area-wide control with characteristics that differ substantially from current insecticide-based vector control methods, resulting in some different considerations for approval and implementation. The successful field application of current biocontrol technologies against other pests provides evidence for the promise of these approaches and insights into the development pathway for new malaria control agents. The status of technical development as well as current thinking on the implementation requirements for genetic biocontrol approaches are reviewed, and remaining challenges for public health application in malaria prevention are discussed.
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Affiliation(s)
- Stephanie James
- Foundation for the National Institutes of Health, North Bethesda, MD 20852, USA
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10
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Zhu Y, Champer J. Simulations Reveal High Efficiency and Confinement of a Population Suppression CRISPR Toxin-Antidote Gene Drive. ACS Synth Biol 2023; 12:809-819. [PMID: 36825354 DOI: 10.1021/acssynbio.2c00611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
Abstract
Though engineered gene drives hold great promise for spreading through and suppressing populations of disease vectors or invasive species, complications such as resistance alleles and spatial population structure can prevent their success. Additionally, most forms of suppression drives, such as homing drives or driving Y chromosomes, will generally spread uncontrollably between populations with even small levels of migration. The previously proposed CRISPR-based toxin-antidote system called toxin-antidote dominant embryo (TADE) suppression drive could potentially address the issues of confinement and resistance. However, it is a relatively weak form of drive compared to homing drives, which might make it particularly vulnerable to spatial population structure. In this study, we investigate TADE suppression drive using individual-based simulations in a continuous spatial landscape. We find that the drive is actually more confined than in simple models without space, even in its most efficient form with low cleavage rate in embryos from maternally deposited Cas9. Furthermore, the drive performed well in continuous space scenarios if the initial release requirements were met, suppressing the population in a timely manner without being severely affected by chasing, a phenomenon in which wild-type individuals avoid the drive by recolonizing empty areas. At higher embryo cut rates, the drive loses its ability to spread, but a single, widespread release can often still induce rapid population collapse. Thus, if TADE suppression gene drives can be successfully constructed, they may play an important role in control of disease vectors and invasive species when stringent confinement to target populations is desired.
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Affiliation(s)
- Yutong Zhu
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
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11
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Chen J, Xu X, Champer J. Assessment of distant-site rescue elements for CRISPR toxin-antidote gene drives. Front Bioeng Biotechnol 2023; 11:1138702. [PMID: 36860883 PMCID: PMC9968759 DOI: 10.3389/fbioe.2023.1138702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 02/03/2023] [Indexed: 02/15/2023] Open
Abstract
Gene drive is a genetic engineering technology that can enable super-mendelian inheritance of specific alleles, allowing them to spread through a population. New gene drive types have increased flexibility, offering options for confined modification or suppression of target populations. Among the most promising are CRISPR toxin-antidote gene drives, which disrupt essential wild-type genes by targeting them with Cas9/gRNA. This results in their removal, increasing the frequency of the drive. All these drives rely on having an effective rescue element, which consists of a recoded version of the target gene. This rescue element can be at the same site as the target gene, maximizing the chance of efficient rescue, or at a distant site, which allows useful options such as easily disrupting another essential gene or increasing confinement. Previously, we developed a homing rescue drive targeting a haplolethal gene and a toxin-antidote drive targeting a haplosufficient gene. These successful drives had functional rescue elements but suboptimal drive efficiency. Here, we attempted to construct toxin-antidote drives targeting these genes with a distant-site configuration from three loci in Drosophila melanogaster. We found that additional gRNAs increased cut rates to nearly 100%. However, all distant-site rescue elements failed for both target genes. Furthermore, one rescue element with a minimally recoded sequence was used as a template for homology-directed repair for the target gene on a different chromosomal arm, resulting in the formation of functional resistance alleles. Together, these results can inform the design of future CRISPR-based toxin-antidote gene drives.
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Affiliation(s)
- Jingheng Chen
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Xuejiao Xu
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
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12
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Meiborg AB, Faber NR, Taylor BA, Harpur BA, Gorjanc G. The suppressive potential of a gene drive in populations of invasive social wasps is currently limited. Sci Rep 2023; 13:1640. [PMID: 36717606 PMCID: PMC9886928 DOI: 10.1038/s41598-023-28867-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 01/25/2023] [Indexed: 02/01/2023] Open
Abstract
Social insects are very successful invasive species, and the continued increase of global trade and transportation has exacerbated this problem. The yellow-legged hornet, Vespa velutina nigrithorax (henceforth Asian hornet), is drastically expanding its range in Western Europe. As an apex insect predator, this hornet poses a serious threat to the honey bee industry and endemic pollinators. Current suppression methods have proven too inefficient and expensive to limit its spread. Gene drives might be an effective tool to control this species, but their use has not yet been thoroughly investigated in social insects. Here, we built a model that matches the hornet's life history and modelled the effect of different gene drive scenarios on an established invasive population. To test the broader applicability and sensitivity of the model, we also incorporated the invasive European paper wasp Polistes dominula. We find that, due to the haplodiploidy of social hymenopterans, only a gene drive targeting female fertility is promising for population control. Our results show that although a gene drive can suppress a social wasp population, it can only do so under fairly stringent gene drive-specific conditions. This is due to a combination of two factors: first, the large number of surviving offspring that social wasp colonies produce make it possible that, even with very limited formation of resistance alleles, such alleles can quickly spread and rescue the population. Second, due to social wasp life history, infertile individuals do not compete with fertile ones, allowing fertile individuals to maintain a large population size even when drive alleles are widespread. Nevertheless, continued improvements in gene drive technology may make it a promising method for the control of invasive social insects in the future.
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Affiliation(s)
- Adriaan B Meiborg
- HighlanderLab, The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, UK. .,Developmental Biology Unit, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117, Heidelberg, Germany.
| | - Nicky R Faber
- HighlanderLab, The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, UK.,Laboratory of Genetics, Department of Plant Sciences, Wageningen University & Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
| | - Benjamin A Taylor
- Department of Entomology, Purdue University, West Lafayette, IN, 47907, USA
| | - Brock A Harpur
- Department of Entomology, Purdue University, West Lafayette, IN, 47907, USA
| | - Gregor Gorjanc
- HighlanderLab, The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, UK
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13
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Li J, Champer J. Harnessing Wolbachia cytoplasmic incompatibility alleles for confined gene drive: A modeling study. PLoS Genet 2023; 19:e1010591. [PMID: 36689491 PMCID: PMC9894560 DOI: 10.1371/journal.pgen.1010591] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 02/02/2023] [Accepted: 12/21/2022] [Indexed: 01/24/2023] Open
Abstract
Wolbachia are maternally-inherited bacteria, which can spread rapidly in populations by manipulating reproduction. cifA and cifB are genes found in Wolbachia phage that are responsible for cytoplasmic incompatibility, the most common type of Wolbachia reproductive interference. In this phenomenon, no viable offspring are produced when a male with both cifA and cifB (or just cifB in some systems) mates with a female lacking cifA. Utilizing this feature, we propose new types of toxin-antidote gene drives that can be constructed with only these two genes in an insect genome, instead of the whole Wolbachia bacteria. By using both mathematical and simulation models, we found that a drive containing cifA and cifB together creates a confined drive with a moderate to high introduction threshold. When introduced separately, they act as a self-limiting drive. We observed that the performance of these drives is substantially influenced by various ecological parameters and drive characteristics. Extending our models to continuous space, we found that the drive individual release distribution has a critical impact on drive persistence. Our results suggest that these new types of drives based on Wolbachia transgenes are safe and flexible candidates for genetic modification of populations.
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Affiliation(s)
- Jiahe Li
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
- * E-mail:
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14
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Sun H, Bu LA, Su SC, Guo D, Gao CF, Wu SF. Knockout of the odorant receptor co-receptor, orco, impairs feeding, mating and egg-laying behavior in the fall armyworm Spodoptera frugiperda. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2023; 152:103889. [PMID: 36493964 DOI: 10.1016/j.ibmb.2022.103889] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 11/30/2022] [Accepted: 12/02/2022] [Indexed: 06/17/2023]
Abstract
The olfactory transduction system of insects is involved in multiple behavioral processes such as foraging, mating, and egg-laying behavior. In the insect olfactory receptor neurons (ORNs), the odorant receptor co-receptor (Orco) is an obligatory component that is required for dimerization with odorant receptors (ORs) to form a ligand-gated ion channel complex. The ORs/Orco heteromeric complex plays a crucial role in insect olfaction. To explore the function of OR-mediated olfaction in the physiological behavior of the fall armyworm, Spodoptera frugiperda, we applied CRISPR/Cas9 genome editing to mutate its Orco gene and constructed a homozygous mutant strain of Orco (Orco-/-) by genetic crosses. Electroantennogram (EAG) analysis showed that the responses of Orco-/- male moths to two universal sex pheromones, Z9-14: Ac and Z7-12: Ac, were abolished. We found that Orco-/- males cannot successfully mate with female moths. An oviposition preference assay confirmed that Orco-/- female moths had a reduced preference for the optimal host plant maize. A larval feeding assay revealed that the time for Orco-/- larvae to locate the food source was significantly longer than in the wild-type. Overall, in the absence of Orco, the OR-dependent olfactory behavior was impaired in both larval and adult stages. Our results confirm that Orco is essential for multiple behavioral processes related to olfaction in the fall armyworm.
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Affiliation(s)
- Hao Sun
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China
| | - Ling-Ao Bu
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China
| | - Shao-Cong Su
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China
| | - Di Guo
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China
| | - Cong-Fen Gao
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China
| | - Shun-Fan Wu
- College of Plant Protection, Nanjing Agricultural University, State & Local Joint Engineering Research Center of Green Pesticide Invention and Application, Weigang Road 1, Nanjing, 210095, Jiangsu, China.
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15
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Geci R, Willis K, Burt A. Gene drive designs for efficient and localisable population suppression using Y-linked editors. PLoS Genet 2022; 18:e1010550. [PMID: 36574454 PMCID: PMC9829173 DOI: 10.1371/journal.pgen.1010550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Revised: 01/09/2023] [Accepted: 11/29/2022] [Indexed: 12/28/2022] Open
Abstract
The sterile insect technique (SIT) has been successful in controlling some pest species but is not practicable for many others due to the large number of individuals that need to be reared and released. Previous computer modelling has demonstrated that the release of males carrying a Y-linked editor that kills or sterilises female descendants could be orders of magnitude more efficient than SIT while still remaining spatially restricted, particularly if combined with an autosomal sex distorter. In principle, further gains in efficiency could be achieved by using a self-propagating double drive design, in which each of the two components (the Y-linked editor and the sex ratio distorter) boosted the transmission of the other. To better understand the expected dynamics and impact of releasing constructs of this new design we have analysed a deterministic population genetic and population dynamic model. Our modelling demonstrates that this design can suppress a population from very low release rates, with no invasion threshold. Importantly, the design can work even if homing rates are low and sex chromosomes are silenced at meiosis, potentially expanding the range of species amenable to such control. Moreover, the predicted dynamics and impacts can be exquisitely sensitive to relatively small (e.g., 25%) changes in allele frequencies in the target population, which could be exploited for sequence-based population targeting. Analysis of published Anopheles gambiae genome sequences indicates that even for weakly differentiated populations with an FST of 0.02 there may be thousands of suitably differentiated genomic sites that could be used to restrict the spread and impact of a release. Our proposed design, which extends an already promising development pathway based on Y-linked editors, is therefore a potentially useful addition to the menu of options for genetic biocontrol.
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Affiliation(s)
- René Geci
- Dept. of Life Sciences, Imperial College London, Silwood Park, United Kingdom
| | - Katie Willis
- Dept. of Life Sciences, Imperial College London, Silwood Park, United Kingdom
| | - Austin Burt
- Dept. of Life Sciences, Imperial College London, Silwood Park, United Kingdom
- * E-mail:
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16
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Abstract
Spore killers are specific genetic elements in fungi that kill sexual spores that do not contain them. A range of studies in the last few years have provided the long-awaited first insights into the molecular mechanistic aspects of spore killing in different fungal models, including both yeast-forming and filamentous Ascomycota. Here we describe these recent advances, focusing on the wtf system in the fission yeast Schizosaccharomyces pombe; the Sk spore killers of Neurospora species; and two spore-killer systems in Podospora anserina, Spok and [Het-s]. The spore killers appear thus far mechanistically unrelated. They can involve large genomic rearrangements but most often rely on the action of just a single gene. Data gathered so far show that the protein domains involved in the killing and resistance processes differ among the systems and are not homologous. The emerging picture sketched by these studies is thus one of great mechanistic and evolutionary diversity of elements that cheat during meiosis and are thereby preferentially inherited over sexual generations.
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Affiliation(s)
- Sven J Saupe
- Institut de Biochimie et de Génétique Cellulaire, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France;
| | - Hanna Johannesson
- Department of Organismal Biology, Uppsala University, Uppsala, Sweden;
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17
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Finney M, Romanowski J, Adelman ZN. Strategies to improve homology-based repair outcomes following CRISPR-based gene editing in mosquitoes: lessons in how to keep any repair disruptions local. Virol J 2022; 19:128. [PMID: 35908059 PMCID: PMC9338592 DOI: 10.1186/s12985-022-01859-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 07/18/2022] [Indexed: 11/10/2022] Open
Abstract
Programmable gene editing systems such as CRISPR-Cas have made mosquito genome engineering more practical and accessible, catalyzing the development of cutting-edge genetic methods of disease vector control. This progress, however, has been limited by the low efficiency of homology-directed repair (HDR)-based sequence integration at DNA double-strand breaks (DSBs) and a lack of understanding about DSB repair in mosquitoes. Innovative efforts to optimize HDR sequence integration by inhibiting non-homologous end joining or promoting HDR have been performed in mammalian systems, however many of these approaches have not been applied to mosquitoes. Here, we review some of the most relevant steps of DNA DSB repair choice and highlight promising approaches that influence this choice to enhance HDR in the context of mosquito gene editing.
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Affiliation(s)
- Micaela Finney
- Department of Entomology, Texas A&M University, 329A Minnie Belle Heep Center, 370 Olsen Blvd, College Station, TX, 77843, USA
| | - Joseph Romanowski
- Department of Entomology, Texas A&M University, 329A Minnie Belle Heep Center, 370 Olsen Blvd, College Station, TX, 77843, USA
| | - Zach N Adelman
- Department of Entomology, Texas A&M University, 329A Minnie Belle Heep Center, 370 Olsen Blvd, College Station, TX, 77843, USA.
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18
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Yang E, Metzloff M, Langmüller AM, Xu X, Clark AG, Messer PW, Champer J. A homing suppression gene drive with multiplexed gRNAs maintains high drive conversion efficiency and avoids functional resistance alleles. G3 (BETHESDA, MD.) 2022; 12:jkac081. [PMID: 35394026 PMCID: PMC9157102 DOI: 10.1093/g3journal/jkac081] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Accepted: 03/30/2022] [Indexed: 11/14/2022]
Abstract
Gene drives are engineered alleles that can bias inheritance in their favor, allowing them to spread throughout a population. They could potentially be used to modify or suppress pest populations, such as mosquitoes that spread diseases. CRISPR/Cas9 homing drives, which copy themselves by homology-directed repair in drive/wild-type heterozygotes, are a powerful form of gene drive, but they are vulnerable to resistance alleles that preserve the function of their target gene. Such resistance alleles can prevent successful population suppression. Here, we constructed a homing suppression drive in Drosophila melanogaster that utilized multiplexed gRNAs to inhibit the formation of functional resistance alleles in its female fertility target gene. The selected gRNA target sites were close together, preventing reduction in drive conversion efficiency. The construct reached a moderate equilibrium frequency in cage populations without apparent formation of resistance alleles. However, a moderate fitness cost prevented elimination of the cage population, showing the importance of using highly efficient drives in a suppression strategy, even if resistance can be addressed. Nevertheless, our results experimentally demonstrate the viability of the multiplexed gRNAs strategy in homing suppression gene drives.
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Affiliation(s)
- Emily Yang
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Matthew Metzloff
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Anna M Langmüller
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Institut für Populationsgenetik, Vetmeduni Vienna, 1210 Wien, Austria
- Vienna Graduate School of Population Genetics, 1210 Wien, Austria
| | - Xuejiao Xu
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Andrew G Clark
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Philipp W Messer
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
| | - Jackson Champer
- Department of Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
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19
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Metzloff M, Yang E, Dhole S, Clark AG, Messer PW, Champer J. Experimental demonstration of tethered gene drive systems for confined population modification or suppression. BMC Biol 2022; 20:119. [PMID: 35606745 PMCID: PMC9128227 DOI: 10.1186/s12915-022-01292-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 04/11/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Homing gene drives hold great promise for the genetic control of natural populations. However, current homing systems are capable of spreading uncontrollably between populations connected by even marginal levels of migration. This could represent a substantial sociopolitical barrier to the testing or deployment of such drives and may generally be undesirable when the objective is only local population control, such as suppression of an invasive species outside of its native range. Tethered drive systems, in which a locally confined gene drive provides the CRISPR nuclease needed for a homing drive, could provide a solution to this problem, offering the power of a homing drive and confinement of the supporting drive. RESULTS Here, we demonstrate the engineering of a tethered drive system in Drosophila, using a regionally confined CRISPR Toxin-Antidote Recessive Embryo (TARE) drive to support modification and suppression homing drives. Each drive was able to bias inheritance in its favor, and the TARE drive was shown to spread only when released above a threshold frequency in experimental cage populations. After the TARE drive had established in the population, it facilitated the spread of a subsequently released split homing modification drive (to all individuals in the cage) and of a homing suppression drive (to its equilibrium frequency). CONCLUSIONS Our results show that the tethered drive strategy is a viable and easily engineered option for providing confinement of homing drives to target populations.
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Affiliation(s)
- Matthew Metzloff
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Emily Yang
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Sumit Dhole
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, 27695, USA
| | - Andrew G Clark
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Philipp W Messer
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA
| | - Jackson Champer
- Department of Computational Biology, Cornell University, Ithaca, NY, 14853, USA.
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA.
- Present Address: Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China.
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20
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Liu Y, Champer J. Modelling homing suppression gene drive in haplodiploid organisms. Proc Biol Sci 2022; 289:20220320. [PMID: 35414240 PMCID: PMC9006016 DOI: 10.1098/rspb.2022.0320] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Accepted: 03/21/2022] [Indexed: 01/13/2023] Open
Abstract
Gene drives have shown great promise for suppression of pest populations. These engineered alleles can function by a variety of mechanisms, but the most common is the CRISPR homing drive, which converts wild-type alleles to drive alleles in the germline of heterozygotes. Some potential target species are haplodiploid, in which males develop from unfertilized eggs and thus have only one copy of each chromosome. This prevents drive conversion, a substantial disadvantage compared to diploids where drive conversion can take place in both sexes. Here, we study homing suppression gene drives in haplodiploids and find that a drive targeting a female fertility gene could still be successful. However, such drives are less powerful than in diploids and suffer more from functional resistance alleles. They are substantially more vulnerable to high resistance allele formation in the embryo owing to maternally deposited Cas9 and guide RNA and also to somatic cleavage activity. Examining spatial models where organisms move over a continuous landscape, we find that haplodiploid suppression drives surprisingly perform nearly as well as in diploids, possibly owing to their ability to spread further before inducing strong suppression. Together, these results indicate that gene drive can potentially be used to effectively suppress haplodiploid populations.
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Affiliation(s)
- Yiran Liu
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871 People's Republic of China
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871 People's Republic of China
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21
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Wang GH, Du J, Chu CY, Madhav M, Hughes GL, Champer J. Symbionts and gene drive: two strategies to combat vector-borne disease. Trends Genet 2022; 38:708-723. [PMID: 35314082 DOI: 10.1016/j.tig.2022.02.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 02/24/2022] [Accepted: 02/24/2022] [Indexed: 01/26/2023]
Abstract
Mosquitoes bring global health problems by transmitting parasites and viruses such as malaria and dengue. Unfortunately, current insecticide-based control strategies are only moderately effective because of high cost and resistance. Thus, scalable, sustainable, and cost-effective strategies are needed for mosquito-borne disease control. Symbiont-based and genome engineering-based approaches provide new tools that show promise for meeting these criteria, enabling modification or suppression approaches. Symbiotic bacteria like Wolbachia are maternally inherited and manipulate mosquito host reproduction to enhance their vertical transmission. Genome engineering-based gene drive methods, in which mosquitoes are genetically altered to spread drive alleles throughout wild populations, are also proving to be a potentially powerful approach in the laboratory. Here, we review the latest developments in both symbionts and gene drive-based methods. We describe some notable similarities, as well as distinctions and obstacles, relating to these promising technologies.
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Affiliation(s)
- Guan-Hong Wang
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
| | - Jie Du
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Chen Yi Chu
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Mukund Madhav
- Departments of Vector Biology and Tropical Disease Biology, Centre for Neglected Tropical Disease, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK
| | - Grant L Hughes
- Departments of Vector Biology and Tropical Disease Biology, Centre for Neglected Tropical Disease, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK
| | - Jackson Champer
- Center for Bioinformatics, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China.
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22
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Beaghton PJ, Burt A. Gene drives and population persistence vs elimination: The impact of spatial structure and inbreeding at low density. Theor Popul Biol 2022; 145:109-125. [PMID: 35247370 DOI: 10.1016/j.tpb.2022.02.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 02/15/2022] [Accepted: 02/22/2022] [Indexed: 11/26/2022]
Abstract
Synthetic gene drive constructs are being developed to control disease vectors, invasive species, and other pest species. In a well-mixed random mating population a sufficiently strong gene drive is expected to eliminate a target population, but it is not clear whether the same is true when spatial processes play a role. In species with an appropriate biology it is possible that drive-induced reductions in density might lead to increased inbreeding, reducing the efficacy of drive, eventually leading to suppression rather than elimination, regardless of how strong the drive is. To investigate this question we analyse a series of explicitly solvable stochastic models considering a range of scenarios for the relative timing of mating, reproduction, and dispersal and analyse the impact of two different types of gene drive, a Driving Y chromosome and a homing construct targeting an essential gene. We find in all cases a sufficiently strong Driving Y will go to fixation and the population will be eliminated, except in the one life history scenario (reproduction and mating in patches followed by dispersal) where low density leads to increased inbreeding, in which case the population persists indefinitely, tending to either a stable equilibrium or a limit cycle. These dynamics arise because Driving Y males have reduced mating success, particularly at low densities, due to having fewer sisters to mate with. Increased inbreeding at low densities can also prevent a homing construct from eliminating a population. For both types of drive, if there is strong inbreeding depression, then the population cannot be rescued by inbreeding and it is eliminated. These results highlight the potentially critical role that low-density-induced inbreeding and inbreeding depression (and, by extension, other sources of Allee effects) can have on the eventual impact of a gene drive on a target population.
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Affiliation(s)
- P J Beaghton
- Institute for Security Science and Technology, South Kensington Campus, Imperial College London, London, UK; Department of Computing, South Kensington Campus, Imperial College London, London, UK.
| | - Austin Burt
- Department of Life Sciences, Silwood Park Campus, Imperial College London, Ascot, UK
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23
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Oberhofer G, Ivy T, Hay BA. Gene drive that results in addiction to a temperature-sensitive version of an essential gene triggers population collapse in Drosophila. Proc Natl Acad Sci U S A 2021; 118:e2107413118. [PMID: 34845012 PMCID: PMC8670509 DOI: 10.1073/pnas.2107413118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2021] [Indexed: 12/15/2022] Open
Abstract
One strategy for population suppression seeks to use gene drive to spread genes that confer conditional lethality or sterility, providing a way of combining population modification with suppression. Stimuli of potential interest could be introduced by humans, such as an otherwise benign virus or chemical, or occur naturally on a seasonal basis, such as a change in temperature. Cleave and Rescue (ClvR) selfish genetic elements use Cas9 and guide RNAs (gRNAs) to disrupt endogenous versions of an essential gene while also including a Rescue version of the essential gene resistant to disruption. ClvR spreads by creating loss-of-function alleles of the essential gene that select against those lacking it, resulting in populations in which the Rescue provides the only source of essential gene function. As a consequence, if function of the Rescue, a kind of Trojan horse now omnipresent in a population, is condition dependent, so too will be the survival of that population. To test this idea, we created a ClvR in Drosophila in which Rescue activity of an essential gene, dribble, requires splicing of a temperature-sensitive intein (TS-ClvRdbe ). This element spreads to transgene fixation at 23 °C, but when populations now dependent on Ts-ClvRdbe are shifted to 29 °C, death and sterility result in a rapid population crash. These results show that conditional population elimination can be achieved. A similar logic, in which Rescue activity is conditional, could also be used in homing-based drive and to bring about suppression and/or killing of specific individuals in response to other stimuli.
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Affiliation(s)
- Georg Oberhofer
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Tobin Ivy
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Bruce A Hay
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125
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24
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Adelman ZN, Kojin BB. Malaria-Resistant Mosquitoes (Diptera: Culicidae); The Principle is Proven, But Will the Effectors Be Effective? JOURNAL OF MEDICAL ENTOMOLOGY 2021; 58:1997-2005. [PMID: 34018548 DOI: 10.1093/jme/tjab090] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Indexed: 06/12/2023]
Abstract
Over the last few decades, a substantial number of anti-malarial effector genes have been evaluated for their ability to block parasite infection in the mosquito vector. While many of these approaches have yielded significant effects on either parasite intensity or prevalence of infection, just a few have been able to completely block transmission. Additionally, many approaches, while effective against the parasite, also disrupt or alter important aspects of mosquito physiology, leading to corresponding changes in lifespan, reproduction, and immunity. As the most promising approaches move towards field-based evaluation, questions of effector gene robustness and durability move to the forefront. In this forum piece, we critically evaluate past effector gene approaches with an eye towards developing a deeper pipeline to augment the current best candidates.
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Affiliation(s)
- Zach N Adelman
- Department of Entomology and AgriLife Research, Texas A&M University, College Station, TX, USA
| | - Bianca B Kojin
- Department of Entomology and AgriLife Research, Texas A&M University, College Station, TX, USA
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25
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Devos Y, Mumford JD, Bonsall MB, Glandorf DCM, Quemada HD. Risk management recommendations for environmental releases of gene drive modified insects. Biotechnol Adv 2021; 54:107807. [PMID: 34314837 DOI: 10.1016/j.biotechadv.2021.107807] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2021] [Revised: 07/01/2021] [Accepted: 07/21/2021] [Indexed: 12/18/2022]
Abstract
The ability to engineer gene drives (genetic elements that bias their own inheritance) has sparked enthusiasm and concerns. Engineered gene drives could potentially be used to address long-standing challenges in the control of insect disease vectors, agricultural pests and invasive species, or help to rescue endangered species. However, risk concerns and uncertainty associated with potential environmental release of gene drive modified insects (GDMIs) have led some stakeholders to call for a global moratorium on such releases or the application of other strict precautionary measures to mitigate perceived risk assessment and risk management challenges. Instead, we provide recommendations that may help to improve the relevance of risk assessment and risk management frameworks for environmental releases of GDMIs. These recommendations include: (1) developing additional and more practical risk assessment guidance to ensure appropriate levels of safety; (2) making policy goals and regulatory decision-making criteria operational for use in risk assessment so that what constitutes harm is clearly defined; (3) ensuring a more dynamic interplay between risk assessment and risk management to manage uncertainty through closely interlinked pre-release modelling and post-release monitoring; (4) considering potential risks against potential benefits, and comparing them with those of alternative actions to account for a wider (management) context; and (5) implementing a modular, phased approach to authorisations for incremental acceptance and management of risks and uncertainty. Along with providing stakeholder engagement opportunities in the risk analysis process, the recommendations proposed may enable risk managers to make choices that are more proportionate and adaptive to potential risks, uncertainty and benefits of GDMI applications, and socially robust.
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Affiliation(s)
- Yann Devos
- Scientific Committee and Emerging Risk (SCER) Unit, European Food Safety Authority (EFSA), Parma, Italy.
| | - John D Mumford
- Centre for Environmental Policy, Imperial College London, Ascot, United Kingdom
| | | | - Debora C M Glandorf
- National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands
| | - Hector D Quemada
- Department of Biological Sciences, Western Michigan University, Kalamazoo, MI, United States
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26
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Devos Y, Mumford JD, Bonsall MB, Camargo AM, Firbank LG, Glandorf DCM, Nogué F, Paraskevopoulos K, Wimmer EA. Potential use of gene drive modified insects against disease vectors, agricultural pests and invasive species poses new challenges for risk assessment. Crit Rev Biotechnol 2021; 42:254-270. [PMID: 34167401 DOI: 10.1080/07388551.2021.1933891] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Potential future application of engineered gene drives (GDs), which bias their own inheritance and can spread genetic modifications in wild target populations, has sparked both enthusiasm and concern. Engineered GDs in insects could potentially be used to address long-standing challenges in control of disease vectors, agricultural pests and invasive species, or help to rescue endangered species, and thus provide important public benefits. However, there are concerns that the deliberate environmental release of GD modified insects may pose different or new harms to animal and human health and the wider environment, and raise novel challenges for risk assessment. Risk assessors, risk managers, developers, potential applicants and other stakeholders at many levels are currently discussing whether there is a need to develop new or additional risk assessment guidance for the environmental release of GD modified organisms, including insects. Developing new or additional guidance that is useful and practical is a challenge, especially at an international level, as risk assessors, risk managers and many other stakeholders have different, often contrasting, opinions and perspectives toward the environmental release of GD modified organisms, and on the adequacy of current risk assessment frameworks for such organisms. Here, we offer recommendations to overcome some of the challenges associated with the potential future development of new or additional risk assessment guidance for GD modified insects and provide considerations on areas where further risk assessment guidance may be required.
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Affiliation(s)
- Yann Devos
- GMO Unit, European Food Safety Authority (EFSA), Parma, Italy
| | - John D Mumford
- Centre for Environmental Policy, Imperial College London, Ascot, UK
| | | | - Ana M Camargo
- GMO Unit, European Food Safety Authority (EFSA), Parma, Italy
| | | | - Debora C M Glandorf
- National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands
| | - Fabien Nogué
- Institut Jean-Pierre Bourgin, INRAE, AgroParisTech, Université Paris-Saclay, Versailles, France
| | | | - Ernst A Wimmer
- Johann Friedrich Blumenbach Institute of Zoology and Anthropology, GZMB, Georg August University, Göttingen, Germany
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27
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Willis K, Burt A. Double drives and private alleles for localised population genetic control. PLoS Genet 2021; 17:e1009333. [PMID: 33755671 PMCID: PMC8018619 DOI: 10.1371/journal.pgen.1009333] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 04/02/2021] [Accepted: 03/07/2021] [Indexed: 12/12/2022] Open
Abstract
Synthetic gene drive constructs could, in principle, provide the basis for highly efficient interventions to control disease vectors and other pest species. This efficiency derives in part from leveraging natural processes of dispersal and gene flow to spread the construct and its impacts from one population to another. However, sometimes (for example, with invasive species) only specific populations are in need of control, and impacts on non-target populations would be undesirable. Many gene drive designs use nucleases that recognise and cleave specific genomic sequences, and one way to restrict their spread would be to exploit sequence differences between target and non-target populations. In this paper we propose and model a series of low threshold double drive designs for population suppression, each consisting of two constructs, one imposing a reproductive load on the population and the other inserted into a differentiated locus and controlling the drive of the first. Simple deterministic, discrete-generation computer simulations are used to assess the alternative designs. We find that the simplest double drive designs are significantly more robust to pre-existing cleavage resistance at the differentiated locus than single drive designs, and that more complex designs incorporating sex ratio distortion can be more efficient still, even allowing for successful control when the differentiated locus is neutral and there is up to 50% pre-existing resistance in the target population. Similar designs can also be used for population replacement, with similar benefits. A population genomic analysis of CRISPR PAM sites in island and mainland populations of the malaria mosquito Anopheles gambiae indicates that the differentiation needed for our methods to work can exist in nature. Double drives should be considered when efficient but localised population genetic control is needed and there is some genetic differentiation between target and non-target populations.
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Affiliation(s)
- Katie Willis
- Department of Life Sciences, Imperial College London, Silwood Park, Ascot, United Kingdom
| | - Austin Burt
- Department of Life Sciences, Imperial College London, Silwood Park, Ascot, United Kingdom
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Oberhofer G, Ivy T, Hay BA. Split versions of Cleave and Rescue selfish genetic elements for measured self limiting gene drive. PLoS Genet 2021; 17:e1009385. [PMID: 33600432 PMCID: PMC7951863 DOI: 10.1371/journal.pgen.1009385] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 03/11/2021] [Accepted: 01/28/2021] [Indexed: 12/26/2022] Open
Abstract
Gene drive elements promote the spread of linked traits, providing methods for changing the composition or fate of wild populations. Drive mechanisms that are self-limiting are attractive because they allow control over the duration and extent of trait spread in time and space, and are reversible through natural selection as drive wanes. Self-sustaining Cleave and Rescue (ClvR) elements include a DNA sequence-modifying enzyme such as Cas9/gRNAs that disrupts endogenous versions of an essential gene, a tightly linked recoded version of the essential gene resistant to cleavage (the Rescue), and a Cargo. ClvR spreads by creating loss-of-function (LOF) conditions in which those without ClvR die because they lack functional copies of the essential gene. We use modeling to show that when the Rescue-Cargo and one or both components required for LOF allele creation (Cas9 and gRNA) reside at different locations (split ClvR), drive of Rescue-Cargo is self-limiting due to a progressive decrease in Cas9 frequency, and thus opportunities for creation of LOF alleles, as spread occurs. Importantly, drive strength and duration can be extended in a measured manner-which is still self-limiting-by moving the two components close enough to each other that they experience some degree of linkage. With linkage, Cas9 transiently experiences drive by hitchhiking with Rescue-Cargo until linkage disequilibrium between the two disappears, a function of recombination frequency and number of generations, creating a novel point of control. We implement split ClvR in Drosophila, with key elements on different chromosomes. Cargo/Rescue/gRNAs spreads to high frequency in a Cas9-dependent manner, while the frequency of Cas9 decreases. These observations show that measured, transient drive, coupled with a loss of future drive potential, can be achieved using the simple toolkit that make up ClvR elements-Cas9 and gRNAs and a Rescue/Cargo.
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Affiliation(s)
- Georg Oberhofer
- California Institute of Technology, Pasadena, California, United States of America
| | - Tobin Ivy
- California Institute of Technology, Pasadena, California, United States of America
| | - Bruce A. Hay
- California Institute of Technology, Pasadena, California, United States of America
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29
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Champer J, Kim IK, Champer SE, Clark AG, Messer PW. Suppression gene drive in continuous space can result in unstable persistence of both drive and wild-type alleles. Mol Ecol 2021; 30:1086-1101. [PMID: 33404162 DOI: 10.1111/mec.15788] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 12/23/2020] [Indexed: 12/31/2022]
Abstract
Rapid evolutionary processes can produce drastically different outcomes when studied in panmictic population models vs. spatial models. One such process is gene drive, which describes the spread of "selfish" genetic elements through a population. Engineered gene drives are being considered for the suppression of disease vectors or invasive species. While laboratory experiments and modelling in panmictic populations have shown that such drives can rapidly eliminate a population, it remains unclear if these results translate to natural environments where individuals inhabit a continuous landscape. Using spatially explicit simulations, we show that the release of a suppression drive can result in what we term "chasing" dynamics, in which wild-type individuals recolonize areas where the drive has locally eliminated the population. Despite the drive subsequently reconquering these areas, complete population suppression often fails to occur or is substantially delayed. This increases the likelihood that the drive is lost or that resistance evolves. We analyse how chasing dynamics are influenced by the type of drive, its efficiency, fitness costs, and ecological factors such as the maximal growth rate of the population and levels of dispersal and inbreeding. We find that chasing is more common for lower efficiency drives when dispersal is low and that some drive mechanisms are substantially more prone to chasing behaviour than others. Our results demonstrate that the population dynamics of suppression gene drives are determined by a complex interplay of genetic and ecological factors, highlighting the need for realistic spatial modelling to predict the outcome of drive releases in natural populations.
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Affiliation(s)
- Jackson Champer
- Department of Computational Biology, Cornell University, Ithaca, New York, USA.,Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA
| | - Isabel K Kim
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
| | - Samuel E Champer
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
| | - Andrew G Clark
- Department of Computational Biology, Cornell University, Ithaca, New York, USA.,Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA
| | - Philipp W Messer
- Department of Computational Biology, Cornell University, Ithaca, New York, USA
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30
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Devos Y, Bonsall MB, Firbank LG, Mumford J, Nogué F, Wimmer EA. Gene Drive-Modified Organisms: Developing Practical Risk Assessment Guidance. Trends Biotechnol 2020; 39:853-856. [PMID: 33342557 DOI: 10.1016/j.tibtech.2020.11.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 11/24/2020] [Accepted: 11/25/2020] [Indexed: 12/23/2022]
Abstract
Risk assessors, risk managers, developers, potential applicants, and other stakeholders at many levels discuss the need for new or further risk assessment guidance for deliberate environmental releases of gene drive-modified organisms. However, preparing useful and practical guidance entails challenges, to which we offer recommendations based on our experience drafting guidance.
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Affiliation(s)
- Yann Devos
- GMO Unit, European Food Safety Authority (EFSA), Parma, Italy.
| | | | | | - John Mumford
- Centre for Environmental Policy, Imperial College London, Ascot, UK
| | - Fabien Nogué
- Institut Jean-Pierre Bourgin, INRAE, AgroParisTech, Université Paris-Saclay, Versailles, France
| | - Ernst A Wimmer
- Johann Friedrich Blumenbach Institute of Zoology and Anthropology, GZMB, Georg August University, Göttingen, Germany
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Naegeli H, Bresson J, Dalmay T, Dewhurst IC, Epstein MM, Guerche P, Hejatko J, Moreno FJ, Mullins E, Nogué F, Rostoks N, Sánchez Serrano JJ, Savoini G, Veromann E, Veronesi F, Bonsall MB, Mumford J, Wimmer EA, Devos Y, Paraskevopoulos K, Firbank LG. Adequacy and sufficiency evaluation of existing EFSA guidelines for the molecular characterisation, environmental risk assessment and post-market environmental monitoring of genetically modified insects containing engineered gene drives. EFSA J 2020; 18:e06297. [PMID: 33209154 PMCID: PMC7658669 DOI: 10.2903/j.efsa.2020.6297] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Advances in molecular and synthetic biology are enabling the engineering of gene drives in insects for disease vector/pest control. Engineered gene drives (that bias their own inheritance) can be designed either to suppress interbreeding target populations or modify them with a new genotype. Depending on the engineered gene drive system, theoretically, a genetic modification of interest could spread through target populations and persist indefinitely, or be restricted in its spread or persistence. While research on engineered gene drives and their applications in insects is advancing at a fast pace, it will take several years for technological developments to move to practical applications for deliberate release into the environment. Some gene drive modified insects (GDMIs) have been tested experimentally in the laboratory, but none has been assessed in small-scale confined field trials or in open release trials as yet. There is concern that the deliberate release of GDMIs in the environment may have possible irreversible and unintended consequences. As a proactive measure, the European Food Safety Authority (EFSA) has been requested by the European Commission to review whether its previously published guidelines for the risk assessment of genetically modified animals (EFSA, 2012 and 2013), including insects (GMIs), are adequate and sufficient for GDMIs, primarily disease vectors, agricultural pests and invasive species, for deliberate release into the environment. Under this mandate, EFSA was not requested to develop risk assessment guidelines for GDMIs. In this Scientific Opinion, the Panel on Genetically Modified Organisms (GMO) concludes that EFSA's guidelines are adequate, but insufficient for the molecular characterisation (MC), environmental risk assessment (ERA) and post-market environmental monitoring (PMEM) of GDMIs. While the MC,ERA and PMEM of GDMIs can build on the existing risk assessment framework for GMIs that do not contain engineered gene drives, there are specific areas where further guidance is needed for GDMIs.
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32
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Dhole S, Lloyd AL, Gould F. Gene Drive Dynamics in Natural Populations: The Importance of Density Dependence, Space, and Sex. ANNUAL REVIEW OF ECOLOGY, EVOLUTION, AND SYSTEMATICS 2020; 51:505-531. [PMID: 34366722 PMCID: PMC8340601 DOI: 10.1146/annurev-ecolsys-031120-101013] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The spread of synthetic gene drives is often discussed in the context of panmictic populations connected by gene flow and described with simple deterministic models. Under such assumptions, an entire species could be altered by releasing a single individual carrying an invasive gene drive, such as a standard homing drive. While this remains a theoretical possibility, gene drive spread in natural populations is more complex and merits a more realistic assessment. The fate of any gene drive released in a population would be inextricably linked to the population's ecology. Given the uncertainty often involved in ecological assessment of natural populations, understanding the sensitivity of gene drive spread to important ecological factors is critical. Here we review how different forms of density dependence, spatial heterogeneity, and mating behaviors can impact the spread of self-sustaining gene drives. We highlight specific aspects of gene drive dynamics and the target populations that need further research.
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Affiliation(s)
- Sumit Dhole
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, North Carolina 27695, USA
| | - Alun L Lloyd
- Biomathematics Graduate Program and Department of Mathematics, North Carolina State University, Raleigh, North Carolina 27695-8213, USA
- Genetic Engineering and Society Center, North Carolina State University, Raleigh, North Carolina 27695-7565, USA
| | - Fred Gould
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, North Carolina 27695, USA
- Genetic Engineering and Society Center, North Carolina State University, Raleigh, North Carolina 27695-7565, USA
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