scholarly journals Can a population targeted by a CRISPR-based homing gene drive be rescued?

2020 ◽  
Author(s):  
Nicolas O. Rode ◽  
Virginie Courtier-Orgogozo ◽  
Florence Débarre
Keyword(s):  
Genetic Control ◽  
Natural Populations ◽  
Genetically Engineered ◽  
Control Technique ◽  
Gene Drive ◽  
Wild Type ◽  
Safety Issues ◽  
Type Population ◽  
Variable Population ◽  
Gene Drives

AbstractCRISPR-based homing gene drive is a genetic control technique aiming to modify or eradicate natural populations. This technique is based on the release of individuals carrying an engineered piece of DNA that can be preferentially inherited by the progeny. Developing countermeasures is important to control the spread of gene drives, should they result in unanticipated damages. One proposed countermeasure is the introduction of individuals carrying a brake construct that targets and inactivates the drive allele but leaves the wild-type allele unaffected. Here we develop models to investigate the efficiency of such brakes. We consider a variable population size and use a combination of analytical and numerical methods to determine the conditions where a brake can prevent the extinction of a population targeted by an eradication drive. We find that a brake is not guaranteed to prevent eradication and that characteristics of both the brake and the drive affect the likelihood of recovering the wild-type population. In particular, brakes that restore fitness are more efficient than brakes that do not. Our model also indicates that threshold-dependent drives (drives that can spread only when introduced above a threshold) are more amenable to control with a brake than drives that can spread from an arbitrary low introduction frequency (threshold-independent drives). Based on our results, we provide practical recommendations and discuss safety issues.Article summary for Issue HighlightsHoming gene drive is a new genetic control technology that aims to spread a genetically engineered DNA construct within natural populations even when it impairs fitness. In case of unanticipated damages, it has been proposed to stop homing gene drives by releasing individuals carrying a genedrive brake; however, the efficiency of such brakes has been little studied. The authors develop a model to investigate the dynamics of a population targeted by a homing drive in absence or in presence of brake. The model provides insights for the design of more efficient brakes and safer gene drives.

scholarly journals Can a Population Targeted by a CRISPR-Based Homing Gene Drive Be Rescued?

2020 ◽  
Vol 10 (9) ◽  
pp. 3403-3415 ◽  
Author(s):  
Nicolas O Rode ◽  
Virginie Courtier-Orgogozo ◽  
Florence Débarre
Keyword(s):  
Natural Populations ◽  
Control Technique ◽  
Gene Drive ◽  
Wild Type ◽  
Safety Issues ◽  
Type Population ◽  
Variable Population ◽  
Gene Drives ◽  
Practical Recommendations ◽  
Variable Population Size

Abstract CRISPR-based homing gene drive is a genetic control technique aiming to modify or eradicate natural populations. This technique is based on the release of individuals carrying an engineered piece of DNA that can be preferentially inherited by the progeny. The development of countermeasures is important to control the spread of gene drives, should they result in unanticipated damages. One proposed countermeasure is the introduction of individuals carrying a brake construct that targets and inactivates the drive allele but leaves the wild-type allele unaffected. Here we develop models to investigate the efficiency of such brakes. We consider a variable population size and use a combination of analytical and numerical methods to determine the conditions where a brake can prevent the extinction of a population targeted by an eradication drive. We find that a brake is not guaranteed to prevent eradication and that characteristics of both the brake and the drive affect the likelihood of recovering the wild-type population. In particular, brakes that restore fitness are more efficient than brakes that do not. Our model also indicates that threshold-dependent drives (drives that can spread only when introduced above a threshold) are more amenable to control with a brake than drives that can spread from an arbitrary low introduction frequency (threshold-independent drives). Based on our results, we provide practical recommendations and discuss safety issues.

scholarly journals Modeling the mutation and reversal of engineered underdominance gene drives

2018 ◽  
Author(s):  
Matthew P. Edgington ◽  
Luke S. Alphey
Keyword(s):  
Genetic Material ◽  
Theoretical Work ◽  
The Other ◽  
Lethal Gene ◽  
Gene Drive ◽  
Loss Of Function ◽  
Wild Type ◽  
Type Population ◽  
Drive Systems ◽  
Gene Drives

AbstractA range of gene drive systems have been proposed that are predicted to increase their frequency and that of associated desirable genetic material even if they confer a fitness cost on individuals carrying them. Engineered underdominance (UD) is such a system and, in one version, is based on the introduction of two independently segregating transgenic constructs each carrying a lethal gene, a suppressor for the lethal at the other locus and a desirable genetic “cargo”. Under this system individuals carrying at least one copy of each construct (or no copies of either) are viable whilst those that possess just one of the transgenic constructs are non-viable. Previous theoretical work has explored various properties of these systems, concluding that they should persist indefinitely in absence of resistance or mutation. Here we study a population genetics model of UD gene drive that relaxes past assumptions by allowing for loss-of-function mutations in each introduced gene. We demonstrate that mutations are likely to cause UD systems to break down, eventually resulting in the elimination of introduced transgenes. We then go on to investigate the potential of releasing “free suppressor” carrying individuals as a new method for reversing UD gene drives and compare this to the release of wild-types; the only previously proposed reversal strategy for UD. This reveals that while free suppressor carrying individuals may represent an inexpensive reversal strategy due to extremely small release requirements, they are not able to return a fully wild-type population as rapidly as the release of wild-types.

Towards CRISPR/Cas9-based gene drive in the diamondback moth Plutella xylostella

2021 ◽  
Author(s):  
Xuejiao Xu ◽  
Tim Harvey-Samuel ◽  
Hamid Anees Siddiqui ◽  
Joshua Ang ◽  
Michelle E Anderson ◽  
...  
Keyword(s):  
Genetic Control ◽  
Plutella Xylostella ◽  
Control Strategies ◽  
Diamondback Moth ◽  
Regulatory Elements ◽  
Strategy Development ◽  
Gene Drive ◽  
Global Agriculture ◽  
High Level ◽  
Gene Drives

Promising to provide powerful genetic control tools, gene drives have been constructed in multiple dipterans, yeast and mice, for the purposes of population elimination or modification. However, it remains unclear whether these techniques can be applied to lepidopterans. Here, we used endogenous regulatory elements to drive Cas9 and sgRNA expression in the diamondback moth, (Plutella xylostella), and test the first split-drive system in a lepidopteran. The diamondback moth is an economically important global agriculture pest of cruciferous crops and has developed severe resistance to various insecticides, making it a prime candidate for such novel control strategy development. A very high level of somatic editing was observed in Cas9/sgRNA transheterozygotes, although no significant homing was revealed in the subsequent generation. Although heritable, Cas9-medated germline cleavage, as well as maternal and paternal Cas9 deposition was observed, rates were far lower than for somatic cleavage events, indicating robust somatic but limited germline activity of Cas9/sgRNA under the control of selected regulatory elements. Our results provide valuable experience, paving the way for future construction of gene drive-based genetic control strategies in DBM or other lepidopterans.

scholarly journals Spatial gene drives and pushed genetic waves

2017 ◽  
Author(s):  
Hidenori Tanaka ◽  
Howard A. Stone ◽  
David R. Nelson
Keyword(s):  
Reaction Diffusion ◽  
Two Dimensions ◽  
Wild Type Allele ◽  
Gene Drive ◽  
Wild Type ◽  
Wave Regime ◽  
Spatial Spread ◽  
Type Allele ◽  
Reaction Diffusion Model ◽  
Gene Drives

Gene drives have the potential to rapidly replace a harmful wild-type allele with a gene drive allele engineered to have desired functionalities. However, an accidental or premature release of a gene drive construct to the natural environment could damage an ecosystem irreversibly. Thus, it is important to understand the spatiotemporal consequences of the super-Mendelian population genetics prior to potential applications. Here, we employ a reaction-diffusion model for sexually reproducing diploid organisms to study how a locally introduced gene drive allele spreads to replace the wild-type allele, even though it posses a selective disadvantages> 0. Using methods developed by N. Barton and collaborators, we show that socially responsible gene drives require 0.5 <s< 0.697, a rather narrow range. In this “pushed wave” regime, the spatial spreading of gene drives will be initiated only when the initial frequency distribution is above a threshold profile called “critical propagule”, which acts as a safeguard against accidental release. We also study how the spatial spread of the pushed wave can be stopped by making gene drives uniquely vulnerable (“sensitizing drive”) in a way that is harmless for a wild-type allele. Finally, we show that appropriately sensitized drives in two dimensions can be stopped even by imperfect barriers perforated by a series of gaps.

scholarly journals Assessment of a Split Homing Based Gene Drive for Efficient Knockout of Multiple Genes

2019 ◽  
Vol 10 (2) ◽  
pp. 827-837 ◽  
Author(s):  
Nikolay P. Kandul ◽  
Junru Liu ◽  
Anna Buchman ◽  
Valentino M. Gantz ◽  
Ethan Bier ◽  
...  
Keyword(s):  
Disease Transmission ◽  
Target Genes ◽  
High Efficiency ◽  
Population Control ◽  
Natural Populations ◽  
Pathogen Transmission ◽  
Gene Drive ◽  
Guide Rnas ◽  
Cas9 Protein ◽  
Gene Drives

Homing based gene drives (HGD) possess the potential to spread linked cargo genes into natural populations and are poised to revolutionize population control of animals. Given that host encoded genes have been identified that are important for pathogen transmission, targeting these genes using guide RNAs as cargo genes linked to drives may provide a robust method to prevent disease transmission. However, effectiveness of the inclusion of additional guide RNAs that target separate genes has not been thoroughly explored. To test this approach, we generated a split-HGD in Drosophila melanogaster that encoded a drive linked effector consisting of a second gRNA engineered to target a separate host-encoded gene, which we term a gRNA-mediated effector (GME). This design enabled us to assess homing and knockout efficiencies of two target genes simultaneously, and also explore the timing and tissue specificity of Cas9 expression on cleavage/homing rates. We demonstrate that inclusion of a GME can result in high efficiency of disruption of both genes during super-Mendelian propagation of split-HGD. Furthermore, both genes were knocked out one generation earlier than expected indicating the robust somatic expression of Cas9 driven by Drosophila germline-limited promoters. We also assess the efficiency of ‘shadow drive’ generated by maternally deposited Cas9 protein and accumulation of drive-induced resistance alleles along multiple generations, and discuss design principles of HGD that could mitigate the accumulation of resistance alleles while incorporating a GME.

scholarly journals RNA-guided gene drives can efficiently and reversibly bias inheritance in wild yeast

2015 ◽  
Author(s):  
James E DiCarlo ◽  
Alejandro Chavez ◽  
Sven L Dietz ◽  
Kevin M Esvelt ◽  
George M Church
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Gene Drive ◽  
Wild Type ◽  
Wild Populations ◽  
Yeast Saccharomyces Cerevisiae ◽  
Wild Yeast ◽  
Successive Generations ◽  
Gene Drives ◽  
General Method ◽  
Made In

Inheritance-biasing “gene drives” may be capable of spreading genomic alterations made in laboratory organisms through wild populations. We previously considered the potential for RNA-guided gene drives based on the versatile CRISPR/Cas9 genome editing system to serve as a general method of altering populations. Here we report molecularly contained gene drive constructs in the yeast Saccharomyces cerevisiae that are typically copied at rates above 99% when mated to wild yeast. We successfully targeted both non-essential and essential genes, showed that the inheritance of an unrelated “cargo” gene could be biased by an adjacent drive, and constructed a drive capable of overwriting and reversing changes made by a previous drive. Our results demonstrate that RNA-guided gene drives are capable of efficiently biasing inheritance when mated to wild-type organisms over successive generations.

scholarly journals Assessment of a split homing based gene drive for efficient knockout of multiple genes

2019 ◽  
Author(s):  
Nikolay P. Kandul ◽  
Junru Liu ◽  
Anna Buchman ◽  
Valentino M. Gantz ◽  
Ethan Bier ◽  
...  
Keyword(s):  
Target Gene ◽  
Tissue Specificity ◽  
Target Genes ◽  
High Efficiency ◽  
Population Control ◽  
Natural Populations ◽  
Pathogen Transmission ◽  
Gene Drive ◽  
Guide Rnas ◽  
Gene Drives

AbstractHoming based gene drives (HGD) possess the potential to spread linked cargo genes into natural populations and are poised to revolutionize population control of animals. Given that host-encoded genes have been identified that are important for pathogen transmission, targeting these genes using guide RNAs as cargo genes linked to drives may provide a robust method to prevent transmission. However, effectiveness of the inclusion of additional guide RNAs that target separate host encoded genes has not been thoroughly explored. To test this approach, here we generated a split-HGD in Drosophila melanogaster that encoded a drive linked effector consisting of a second gRNA engineered to target a separate host encoded gene, which we term a gRNA-mediated effector (GME). This design enabled us to assess homing and knockout efficiencies of two target genes simultaneously, and also explore the timing and tissue specificity of Cas9 expression on cleavage/homing rates. We demonstrate that inclusion of a GME can result in high efficiency of disruption of its target gene during super-Mendelian propagation of split-HGD. However, maternal deposition and embryonic expression of Cas9 resulted in the generation of drive resistant alleles which can accumulate and limit the spread of such a drive. Alternative design principles are discussed that could mitigate the accumulation of resistance alleles while incorporating a GME.

scholarly journals Spatial gene drives and pushed genetic waves

2017 ◽  
Vol 114 (32) ◽  
pp. 8452-8457 ◽  
Author(s):  
Hidenori Tanaka ◽  
Howard A. Stone ◽  
David R. Nelson
Keyword(s):  
Reaction Diffusion ◽  
Two Dimensions ◽  
Wild Type Allele ◽  
Gene Drive ◽  
Wild Type ◽  
Wave Regime ◽  
Spatial Spread ◽  
Type Allele ◽  
Reaction Diffusion Model ◽  
Gene Drives

Gene drives have the potential to rapidly replace a harmful wild-type allele with a gene drive allele engineered to have desired functionalities. However, an accidental or premature release of a gene drive construct to the natural environment could damage an ecosystem irreversibly. Thus, it is important to understand the spatiotemporal consequences of the super-Mendelian population genetics before potential applications. Here, we use a reaction–diffusion model for sexually reproducing diploid organisms to study how a locally introduced gene drive allele spreads to replace the wild-type allele, although it possesses a selective disadvantages> 0. Using methods developed by Barton and collaborators, we show that socially responsible gene drives require 0.5 <s< 0.697, a rather narrow range. In this “pushed wave” regime, the spatial spreading of gene drives will be initiated only when the initial frequency distribution is above a threshold profile called “critical propagule,” which acts as a safeguard against accidental release. We also study how the spatial spread of the pushed wave can be stopped by making gene drives uniquely vulnerable (“sensitizing drive”) in a way that is harmless for a wild-type allele. Finally, we show that appropriately sensitized drives in two dimensions can be stopped, even by imperfect barriers perforated by a series of gaps.

scholarly journals Suppression gene drive in continuous space can result in unstable persistence of both drive and wild-type alleles

2019 ◽  
Author(s):  
Jackson Champer ◽  
Isabel Kim ◽  
Samuel E. Champer ◽  
Andrew G. Clark ◽  
Philipp W. Messer
Keyword(s):  
Natural Populations ◽  
Spatial Models ◽  
Ecological Factors ◽  
Natural Environments ◽  
Gene Drive ◽  
Wild Type ◽  
Lower Efficiency ◽  
Continuous Space ◽  
Selfish Genetic Elements ◽  
Drive Systems

ABSTRACTRapid evolutionary processes can produce drastically different outcomes when studied in panmictic population models versus spatial models where the rate of evolution is limited by dispersal. One such process is gene drive, which allows “selfish” genetic elements to quickly spread through a population. Engineered gene drive systems are being considered as a means for suppressing disease vector populations or invasive species. While laboratory experiments and modeling in panmictic populations have shown that such drives can rapidly eliminate a population, it is not yet clear how well these results translate to natural environments where individuals inhabit a continuous landscape. Using spatially explicit simulations, we show that instead of population elimination, release of a suppression drive can result in what we term “chasing” dynamics. This describes a condition in which wild-type individuals quickly recolonize areas where the drive has locally eliminated the population. Despite the drive subsequently chasing the wild-type allele into these newly re-colonized areas, complete population suppression often fails or is substantially delayed. This delay increases the likelihood that the drive becomes lost or that resistance evolves. We systematically analyze how chasing dynamics are influenced by the type of drive, its efficiency, fitness costs, as well as ecological and demographic factors such as the maximal growth rate of the population, the migration rate, and the level of inbreeding. We find that chasing is generally more common for lower efficiency drives and in populations with low dispersal. However, we further find that some drive mechanisms are substantially more prone to chasing behavior 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 modeling to predict the outcome of drive releases in natural populations.

scholarly journals Mathematical modeling of self-contained CRISPR gene drive reversal systems

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Matthew G. Heffel ◽  
Gregory C. Finnigan
Keyword(s):  
Mendelian Inheritance ◽  
Ecological Systems ◽  
Mathematical Work ◽  
Gene Drive ◽  
Key Species ◽  
Type Population ◽  
Reversal Mechanism ◽  
Drive Systems ◽  
External Stimuli ◽  
Gene Drives

AbstractThere is a critical need for further research into methods to control biological populations. Numerous challenges to agriculture, ecological systems, and human health could be mitigated by the targeted reduction and management of key species (e.g. pests, parasites, and vectors for pathogens). The discovery and adaptation of the CRISPR/Cas editing platform co-opted from bacteria has provided a mechanism for a means to alter an entire population. A CRISPR-based gene drive system can allow for the forced propagation of a genetic element that bypasses Mendelian inheritance which can be used to bias sex determination, install exogenous information, or remove endogenous DNA within an entire species. Laboratory studies have demonstrated the potency by which gene drives can operate within insects and other organisms. However, continued research and eventual application face serious opposition regarding issues of policy, biosafety, effectiveness, and reversal. Previous mathematical work has suggested the use of modified gene drive designs that are limited in spread such as daisy chain or underdominance drives. However, no system has yet been proposed that allows for an inducible reversal mechanism without requiring the introduction of additional individuals. Here, we study gene drive effectiveness, fitness, and inducible drive systems that could respond to external stimuli expanding from a previous frequency-based population model. We find that programmed modification during gene drive propagation could serve as a potent safeguard to either slow or completely reverse drive systems and allow for a return to the original wild-type population.

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