@article{metzloff_yang_dhole_clark_messer_champer_2022, title={Experimental demonstration of tethered gene drive systems for confined population modification or suppression}, volume={20}, ISSN={["1741-7007"]}, DOI={10.1186/s12915-022-01292-5}, abstractNote={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. }, number={1}, journal={BMC BIOLOGY}, author={Metzloff, Matthew and Yang, Emily and Dhole, Sumit and Clark, Andrew G. and Messer, Philipp W. and Champer, Jackson}, year={2022}, month={May} } @article{dhole_lloyd_gould_2020, title={Gene Drive Dynamics in Natural Populations: The Importance of Density Dependence, Space, and Sex}, volume={51}, ISSN={["1545-2069"]}, DOI={10.1146/annurev-ecolsys-031120-101013}, abstractNote={ 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. }, number={1}, journal={ANNUAL REVIEW OF ECOLOGY, EVOLUTION, AND SYSTEMATICS, VOL 51, 2020}, author={Dhole, Sumit and Lloyd, Alun L. and Gould, Fred}, year={2020}, pages={505–531} } @article{sudweeks_hollingsworth_blondel_campbell_dhole_eisemann_edwards_godwin_howald_oh_et al._2019, title={Locally Fixed Alleles: A method to localize gene drive to island populations}, volume={9}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-019-51994-0}, abstractNote={AbstractInvasive species pose a major threat to biodiversity on islands. While successes have been achieved using traditional removal methods, such as toxicants aimed at rodents, these approaches have limitations and various off-target effects on island ecosystems. Gene drive technologies designed to eliminate a population provide an alternative approach, but the potential for drive-bearing individuals to escape from the target release area and impact populations elsewhere is a major concern. Here we propose the “Locally Fixed Alleles” approach as a novel means for localizing elimination by a drive to an island population that exhibits significant genetic isolation from neighboring populations. Our approach is based on the assumption that in small island populations of rodents, genetic drift will lead to alleles at multiple genomic loci becoming fixed. In contrast, multiple alleles are likely to be maintained in larger populations on mainlands. Utilizing the high degree of genetic specificity achievable using homing drives, for example based on the CRISPR/Cas9 system, our approach aims at employing one or more locally fixed alleles as the target for a gene drive on a particular island. Using mathematical modeling, we explore the feasibility of this approach and the degree of localization that can be achieved. We show that across a wide range of parameter values, escape of the drive to a neighboring population in which the target allele is not fixed will at most lead to modest transient suppression of the non-target population. While the main focus of this paper is on elimination of a rodent pest from an island, we also discuss the utility of the locally fixed allele approach for the goals of population suppression or population replacement. Our analysis also provides a threshold condition for the ability of a gene drive to invade a partially resistant population.}, journal={SCIENTIFIC REPORTS}, author={Sudweeks, Jaye and Hollingsworth, Brandon and Blondel, Dimitri V and Campbell, Karl J. and Dhole, Sumit and Eisemann, John D. and Edwards, Owain and Godwin, John and Howald, Gregg R. and Oh, Kevin P. and et al.}, year={2019}, month={Nov} } @article{gould_dhole_lloyd_2019, title={Pest management by genetic addiction}, volume={116}, ISSN={["0027-8424"]}, url={http://dx.doi.org/10.1073/pnas.1901886116}, DOI={10.1073/pnas.1901886116}, abstractNote={In the PNAS article “Cleave and Rescue, a novel selfish genetic element and general strategy for gene drive,” Oberhofer et al. (1) describe an exciting new mechanism for enabling a transgenic sequence to increase in frequency within a sexually reproducing population, even if the transgenic sequence causes individuals bearing it to have somewhat lower fitness than those without it. The authors liken the mechanism to the “gene addiction” that can maintain a useless plasmid in a bacterium. The work of Oberhofer et al. (1) adds substantially to a growing field within genetic engineering, often termed gene drive research, in which selfish genetic elements overcome the rules of Mendelian inheritance and push transgenes into a population. While no engineered gene drives have been released into wild populations, that is the ultimate goal, and both the technical and cultural roads toward that goal have been tortuous at times. Gene drive projects are categorized based on having one of two aims. The first is to physically link a desirable gene to a gene drive mechanism and engineer both into a viable strain of the target organism. If individuals of the strain are released into a sexually reproducing field population of that species, the DNA sequence of the drive mechanism is predicted to increase in frequency in the population and the linked, desirable gene should “hitchhike” along with it. If the population is a mosquito that transmits dengue virus, the desirable gene could be one that codes for an RNA interference molecule targeted to prevent the virus from replicating in the mosquito—thus interfering with its transmission to a person whom the mosquito subsequently bites. Projects with the second aim are designed to suppress or eliminate a pest species, be it a mosquito, rat, roach, or crop pest. Here, the gene drive mechanism itself or … [↵][1]1To whom correspondence should be addressed. Email: fred_gould{at}ncsu.edu. [1]: #xref-corresp-1-1}, number={13}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Gould, Fred and Dhole, Sumit and Lloyd, Alun L.}, year={2019}, month={Mar}, pages={5849–5851} } @article{dhole_lloyd_gould_2019, title={Tethered homing gene drives: A new design for spatially restricted population replacement and suppression}, volume={12}, ISSN={["1752-4571"]}, url={http://dx.doi.org/10.1111/eva.12827}, DOI={10.1111/eva.12827}, abstractNote={AbstractOptimism regarding potential epidemiological and conservation applications of modern gene drives is tempered by concern about the possibility of unintended spread of engineered organisms beyond the target population. In response, several novel gene drive approaches have been proposed that can, under certain conditions, locally alter characteristics of a population. One challenge for these gene drives is the difficulty of achieving high levels of localized population suppression without very large releases in the face of gene flow. We present a new gene drive system, tethered homing (TH), with improved capacity for both localization and population suppression. The TH drive is based on driving a payload gene using a homing construct that is anchored to a spatially restricted gene drive. We use a proof‐of‐concept mathematical model to show the dynamics of a TH drive that uses engineered underdominance as an anchor. This system is composed of a split homing drive and a two‐locus engineered underdominance drive linked to one part of the split drive (the Cas endonuclease). We use simple population genetic simulations to show that the tethered homing technique can offer improved localized spread of costly transgenic payload genes. Additionally, the TH system offers the ability to gradually adjust the genetic load in a population after the initial alteration, with minimal additional release effort. We discuss potential solutions for improving localization and the feasibility of creating TH drive systems. Further research with models that include additional biological details will be needed to better understand how TH drives would behave in natural populations, but the preliminary results shown here suggest that tethered homing drives can be a useful addition to the repertoire of localized gene drives.}, number={8}, journal={EVOLUTIONARY APPLICATIONS}, author={Dhole, Sumit and Lloyd, Alun L. and Gould, Fred}, year={2019}, month={Sep}, pages={1688–1702} }