Scholarly Literature
This is an aggregation of scholarly literature from peer-reviewed journals, bioRxiv , medRxiv and arXiv preprint servers focused on natural and engineered selfish genetic elements and genetic biocontrol. New citations are added as they appear. This content is intended for anyone interested in the scholarly literature on gene drive and genetic biocontrol.
A Wolbachia deubiquitylating enzyme induces cytoplasmic incompatibility
5932Beckmann, J. F., J. A. Ronau and M. Hochstrasser, Nature Microbiology, 2:17007. 2017-03-01 17:45:04.
Wolbachia are obligate intracellular bacteria1 that infect arthropods, including approximately two-thirds of insect species2. Wolbachia manipulate insect reproduction by enhancing their inheritance through the female germline. The most common alteration is cytoplasmic incompatibility (CI)3–5, where eggs from uninfected females fail to develop when fertilized by sperm from Wolbachia-infected males. By contrast, if female and male partners are both infected, embryos are viable. CI is a gene-drive mechanism impacting population structure6 and causing reproductive isolation7, but its molecular mechanism has remained unknown. We show that a Wolbachia deubiquitylating enzyme (DUB) induces CI. The CI-inducing DUB, CidB, cleaves ubiquitin from substrates and is encoded in a two-gene operon, and the other protein, CidA, binds CidB. Binding is strongest between cognate partners in cidA-cidB homologues. In transgenic Drosophila, the cidA-cidB operon mimics CI when sperm introduce it into eggs, and a catalytically inactive DUB does not induce sterility. Toxicity is recapitulated in yeast by CidB alone; this requires DUB activity but is rescued by coexpressed CidA. A paralogous operon involves a putative nuclease (CinB) rather than a DUB. Analogous binding, toxicity and rescue in yeast were observed. These results identify a CI mechanism involving interacting proteins that are secreted into germline cells by Wolbachia, and suggest new methods for insect control.
Daisyfield gene drive systems harness repeated genomic elements as a generational clock to limit spread
13623J. Min, C. Noble, D. Najjar and K. M. Esvelt, bioRxiv, 104877. 2017-02-06 13:30:21.
Here we describe a novel form of gene drive based on the introduction of multiple copies of an engineered ‘daisy’ sequence into repeated elements of the genome. Each introduced copy encodes guide RNAs that target one or more engineered loci carrying the CRISPR nuclease gene and the desired traits. When organisms encoding a drive system are released into the environment, each generation of mating with wild-type organisms will reduce the average number of the guide RNA elements per ‘daisyfield’ organism by half, serving as a generational clock
Dodging silver bullets: good CRISPR gene-drive design is critical for eradicating exotic vertebrates
4063Prowse, TAAC, Phillip; Ross, Joshua V.; Pfitzner, Chandran; Wittmann, Talia A.; Thomas, Paul, Proceedings of the Royal Society B: Biological Sciences, 284:20170799. 2017-01-21 00:00:00.
Self-replicating gene drives that can spread deleterious alleles through animal populations have been promoted as a much needed but controversial ‘silver bullet’ for controlling invasive alien species. Homing-based drives comprise an endonuclease and a guide RNA (gRNA) that are replicated during meiosis via homologous recombination. However, their efficacy for controlling wild populations is threatened by inherent polymorphic resistance and the creation of resistance alleles via non-homologous end-joining (NHEJ)-mediated DNA repair. We used stochastic individual-based models to identify realistic gene-drive strategies capable of eradicating vertebrate pest populations (mice, rats and rabbits) on islands. One popular strategy, a sex-reversing drive that converts heterozygous females into sterile males, failed to spread and required the ongoing deployment of gene-drive carriers to achieve eradication. Under alternative strategies, multiplexed gRNAs could overcome inherent polymorphic resistance and were required for eradication success even when the probability of NHEJ was low. Strategies causing homozygotic embryonic non-viability or homozygotic female sterility produced high probabilities of eradication and were robust to NHEJ-mediated deletion of the DNA sequence between multiplexed endonuclease recognition sites. The latter two strategies also purged the gene drive when eradication failed, therefore posing lower long-term risk should animals escape beyond target islands. Multiplexing gRNAs will be necessary if this technology is to be useful for insular extirpation attempts; however, precise knowledge of homing rates will be required to design low-risk gene drives with high probabilities of eradication success.
How driving endonuclease genes can be used to combat pests and disease vectors
4043Godfray, HCJN, A.; Burt, A., BMC Biology, 15:81. 2017-01-21 00:00:00.
Driving endonuclease genes (DEGs) spread through a population by a non-Mendelian mechanism. In a heterozygote, the protein encoded by a DEG causes a double-strand break in the homologous chromosome opposite to where its gene is inserted and when the break is repaired using the homologue as a template the DEG heterozygote is converted to a homozygote. Some DEGs occur naturally while several classes of endonucleases can be engineered to spread in this way, with CRISPR-Cas9 based systems being particularly flexible. There is great interest in using driving endonuclease genes to impose a genetic load on insects that vector diseases or are economic pests to reduce their population density, or to introduce a beneficial gene such as one that might interrupt disease transmission. This paper reviews both the population genetics and population dynamics of DEGs. It summarises the theory that guides the design of DEG constructs intended to perform different functions. It also reviews the studies that have explored the likelihood of resistance to DEG phenotypes arising, and how this risk may be reduced. The review is intended for a general audience and mathematical details are kept to a minimum.
Is it time for synthetic biodiversity conservation?
4062Piaggio, AJS, G.; Seddon, P. J.; Alphey, L.; Bennett, E. L.; Carlson, R. H.; Friedman, R. M.; Kanavy, D.; Phelan, R.; Redford, K. H.; Rosales, M.; Slobodian, L.; Wheeler, K., Trends in Ecology & Evolution, 32:97-107. 2017-01-20 00:00:00.
Evidence indicates that, despite some critical successes, current conservation approaches are not slowing the overall rate of biodiversity loss. The field of synthetic biology, which is capable of altering natural genomes with extremely precise editing, might offer the potential to resolve some intractable conservation problems (e.g., invasive species or pathogens). However, it is our opinion that there has been insufficient engagement by the conservation community with practitioners of synthetic biology. We contend that rapid, large-scale engagement of these two communities is urgently needed to avoid unintended and deleterious ecological consequences. To this point we describe case studies where synthetic biology is currently being applied to conservation, and we highlight the benefits to conservation biologists from engaging with this emerging technology.
Precaution: Open gene drive research
4042Esvelt, KM, Science, 355:589-590. 2017-01-20 00:00:00.
IN THEIR POLICY Forum “Precaution and governance of emerging technologies” (11 November 2016, p. 710), G. E. Kaebnick and colleagues convincingly assert that precaution is consistent with support for science. However, they overlook one way to improve safety while hastening discovery: Make research open.
Ethical implications of fighting malaria with CRISPR/Cas9
4061Patrão Neves, MD, Christiane, BMJ Global Health, 2:e000396. 2017-01-19 00:00:00.
Genome editing is a new, cheap and versatile technique which has great promise to combat vector-borne diseases. The current ethical debate worldwide is mainly concentrating on the dangers of germline intervention and less so on the potential for fighting vector-borne diseases. ; Gene drive technology has been significantly boosted by the CRISPR/Cas9 gene editing tool which may be able to combat malaria by targeting specific stretches of vector DNA and editing genomes at precise locations, working like a molecular scissors. However, CRISPR/Cas9 is currently not a ‘silver bullet’ and needs further research and consideration of the ethical aspects and consequences of its use.; In September 2016, the UNESCO Chair of Bioethics at the Medical University of Vienna convened a meeting entitled ‘Fighting Malaria with CRISPR/ Cas9: Ethical Implications’, which gathered together infectious disease experts with a focus on malaria, entomologists and ethicists to discuss the advantages and disadvantages of genome editing applied to mosquitoes to fight malaria. ; Although there was no formal consensus, some general conclusions were reached, in particular that any ethical debate needs to involve African stakeholders living in malaria areas and to consider future generations and the environment. The precautionary principle should be taken into account in any discussion, as should be the human cost of doing nothing.
Principles for gene drive research
4041Emerson, CJ, Stephanie; Littler, Katherine; Randazzo, Filippo, Science, 358:1135. 2017-01-19 00:00:00.
The recent outbreak of Zika virus in the Americas renewed attention on the importance of vector-control strategies to fight the many vector-borne diseases that continue to inflict suffering around the world. In 2015, there were ?212 million infections and a death every minute from malaria alone (1). Gene drive technology is being explored as a potentially durable and cost-effective strategy for controlling the transmission of deadly and debilitating vector-borne diseases that affect millions of people worldwide, such as Zika virus and malaria. Additionally, its suitability is being evaluated for various potential applications in conservation biology, including a highly specific and humane method for eliminating invasive species from sensitive ecosystems (2, 3).
Conditions for success of engineered underdominance gene drive systems
4040Edgington, MPA, L. S., Journal of Theoretical Biology, 430:128-140. 2017-01-18 00:00:00.
Engineered underdominance is one of a number of different gene drive strategies that have been proposed for the genetic control of insect vectors of disease. Here we model a two-locus engineered underdominance based gene drive system that is based on the concept of mutually suppressing lethals. In such a system two genetic constructs are introduced, each possessing a lethal element and a suppressor of the lethal at the other locus. Specifically, we formulate and analyse a population genetics model of this system to assess when different combinations of release strategies (i.e. single or multiple releases of both sexes or males only) and genetic systems (i.e. bisex lethal or female-specific lethal elements and different strengths of suppressors) will give population replacement or fail to do so. We anticipate that results presented here will inform the future design of engineered underdominance gene drive systems as well as providing a point of reference regarding release strategies for those looking to test such a system. Our discussion is framed in the context of genetic control of insect vectors of disease. One of several serious threats in this context are Aedes aegypti mosquitoes as they are the primary vectors of dengue viruses. However, results are also applicable to Ae. aegypti as vectors of Zika, yellow fever and chikungunya viruses and also to the control of a number of other insect species and thereby of insect-vectored pathogens.
wtf genes are prolific dual poison-antidote meiotic drivers
4060Nuckolls, NLN, M. A. B.; Eickbush, M. T.; Young, J. M.; Lange, J. J.; Yu, J. S.; Smith, G. R.; Jaspersen, S. L.; Malik, H. S.; Zanders, S. E., eLife, 6:e26033. 2017-01-18 00:00:00.
Meiotic drivers are selfish genes that bias their transmission into gametes, defying Mendelian inheritance. Despite the significant impact of these genomic parasites on evolution and infertility, few meiotic drive loci have been identified or mechanistically characterized. Here, we demonstrate a complex landscape of meiotic drive genes on chromosome 3 of the fission yeasts Schizosaccharomyces kambucha and S. pombe. We identify S. kambucha wtf4 as one of these genes that acts to kill gametes (known as spores in yeast) that do not inherit the gene from heterozygotes. wtf4 utilizes dual, overlapping transcripts to encode both a gamete-killing poison and an antidote to the poison. To enact drive, all gametes are poisoned, whereas only those that inherit wtf4 are rescued by the antidote. Our work suggests that the wtf multigene family proliferated due to meiotic drive and highlights the power of selfish genes to shape genomes, even while imposing tremendous costs to fertility.
Evolutionary dynamics of CRISPR gene drives
4059Noble, CO, Jason; Esvelt, Kevin M.; Church, George M.; Nowak, Martin A., Science Advances, 3:e1601964. 2017-01-17 00:00:00.
The alteration of wild populations has been discussed as a solution to a number of humanity’s most pressing ecological and public health concerns. Enabled by the recent revolution in genome editing, clustered regularly interspaced short palindromic repeats (CRISPR) gene drives—selfish genetic elements that can spread through populations even if they confer no advantage to their host organism—are rapidly emerging as the most promising approach. However, before real-world applications are considered, it is imperative to develop a clear understanding of the outcomes of drive release in nature. Toward this aim, we mathematically study the evolutionary dynamics of CRISPR gene drives. We demonstrate that the emergence of drive-resistant alleles presents a major challenge to previously reported constructs, and we show that an alternative design that selects against resistant alleles could greatly improve evolutionary stability. We discuss all results in the context of CRISPR technology and provide insights that inform the engineering of practical gene drive systems.%U
Impact of mosquito gene drive on malaria elimination in a computational model with explicit spatial and temporal dynamics
4039Eckhoff, PAW, E. A.; Godfray, H. C. J.; Burt, A., Proceedings of the National Academy of Sciences of the United States of America, 114:e255-e264. 2017-01-17 00:00:00.
The renewed effort to eliminate malaria and permanently remove its tremendous burden highlights questions of what combination of tools would be sufficient in various settings and what new tools need to be developed. Gene drive mosquitoes constitute a promising set of tools, with multiple different possible approaches including population replacement with introduced genes limiting malaria transmission, driving-Y chromosomes to collapse a mosquito population, and gene drive disrupting a fertility gene and thereby achieving population suppression or collapse. Each of these approaches has had recent success and advances under laboratory conditions, raising the urgency for understanding how each could be deployed in the real world and the potential impacts of each. New analyses are needed as existing models of gene drive primarily focus on nonseasonal or nonspatial dynamics. We use a mechanistic, spatially explicit, stochastic, individual-based mathematical model to simulate each gene drive approach in a variety of sub-Saharan African settings. Each approach exhibits a broad region of gene construct parameter space with successful elimination of malaria transmission due to the targeted vector species. The introduction of realistic seasonality in vector population dynamics facilitates gene drive success compared with nonseasonal analyses. Spatial simulations illustrate constraints on release timing, frequency, and spatial density in the most challenging settings for construct success. Within its parameter space for success, each gene drive approach provides a tool for malaria elimination unlike anything presently available. Provided potential barriers to success are surmounted, each achieves high efficacy at reducing transmission potential and lower delivery requirements in logistically challenged settings.
CRISPR/Cas9 gene drives in genetically variable and nonrandomly mating wild populations
4038Drury, DWD, A. L.; Siniard, D. J.; Zentner, G. E.; Wade, M. J., Science Advances, 3:e1601910. 2017-01-16 00:00:00.
Synthetic gene drives based on CRISPR/Cas9 have the potential to control, alter, or suppress populations of crop pests and disease vectors, but it is unclear how they will function in wild populations. Using genetic data from four populations of the flour beetle Tribolium castaneum, we show that most populations harbor genetic variants in Cas9 target sites, some of which would render them immune to drive (ITD). We show that even a rare ITD allele can reduce or eliminate the efficacy of a CRISPR/Cas9-based synthetic gene drive. This effect is equivalent to and accentuated by mild inbreeding, which is a characteristic of many disease-vectoring arthropods. We conclude that designing such drives will require characterization of genetic variability and the mating system within and among targeted populations.
Genetic conflicts: the usual suspects and beyond
4058McLaughlin, RNM, H. S., Journal of Experimental Biology, 220:6-17. 2017-01-16 00:00:00.
Selfishness is pervasive and manifests at all scales of biology, from societies, to individuals, to genetic elements within a genome. The relentless struggle to seek evolutionary advantages drives perpetual cycles of adaptation and counter-adaptation, commonly referred to as Red Queen interactions. In this review, we explore insights gleaned from molecular and genetic studies of such genetic conflicts, both extrinsic (between genomes) and intrinsic (within genomes or cells). We argue that many different characteristics of selfish genetic elements can be distilled into two types of advantages: an over-replication advantage (e.g. mobile genetic elements in genomes) and a transmission distortion advantage (e.g. meiotic drivers in populations). These two general categories may help classify disparate types of selfish genetic elements.
B chromosome in Plantago lagopus Linnaeus, 1753 shows preferential transmission and accumulation through unusual processes
4037Dhar, MKK, G.; Kaul, S., Comparative Cytogenetics, 11:375-391. 2017-01-15 00:00:00.
Plantago lagopus is a diploid (2n = 2x = 12) weed belonging to family Plantaginaceae. We reported a novel B chromosome in this species composed of 5S and 45S ribosomal DNA and other repetitive elements. In the present work, presence of B chromosome(s) was confirmed through FISH on root tip and pollen mother cells. Several experiments were done to determine the transmission of B chromosome through male and female sex tracks. Progenies derived from the reciprocal crosses between plants with (1B) and without (0B) B chromosomes were studied. The frequency of B chromosome bearing plants was significantly higher than expected, in the progeny of 1B female x 0B male. Thus, the B chromosome seems to have preferential transmission through the female sex track, which may be due to meiotic drive. One of the most intriguing aspects of the present study was the recovery of plants having more chromosomes than the standard complement of 12 chromosomes. Such plants were isolated from the progenies of B chromosome carrying plants. The origin of these plants can be explained on the basis of a two step process; formation of unreduced gametes in 1B plants and fusion of unreduced gametes with the normal gametes or other unreduced gametes. Several molecular techniques were used which unequivocally confirmed similar genetic constitution of 1B (parent) and plants with higher number of chromosomes.
Engineering species-like barriers to sexual reproduction
4057Maselko, MH, Stephen C.; Chacón, Jeremy M.; Harcombe, William R.; Smanski, Michael J., Nature Communications, 8:883. 2017-01-15 00:00:00.
Controlling the exchange of genetic information between sexually reproducing populations has applications in agriculture, eradication of disease vectors, control of invasive species, and the safe study of emerging biotechnology applications. Here we introduce an approach to engineer a genetic barrier to sexual reproduction between otherwise compatible populations. Programmable transcription factors drive lethal gene expression in hybrid offspring following undesired mating events. As a proof of concept, we target the ACT1 promoter of the model organism Saccharomyces cerevisiae using a dCas9-based transcriptional activator. Lethal overexpression of actin results from mating this engineered strain with a strain containing the wild-type ACT1 promoter.
Gene drives do not always increase in frequency: from genetic models to risk assessment
4036de Jong, TJ, Journal Fur Verbraucherschutz Und Lebensmittelsicherheit-Journal of Consumer Protection and Food Safety, 12:299-307. 2017-01-14 00:00:00.
Homing genes encode endonucleases that make a double stranded break in the DNA, destroying a target site on the homologous chromosome. When the cell repairs the break the homing allele is copied, converting a heterozygote into a homozygote. This results in gene drive (GD), an overrepresentation of the homing allele in the next generation. GD may propel CRISPR-Cas9 genes and new genes physically coupled to the GD through natural populations. I revisit the population genetic models of GD with the aim of making these models more understandable to non-specialists. What can we learn about risk evaluation from the models? A GD with no or a small effect on fitness (viability) always spreads in the population and goes to fixation. That is provided that no resistance mechanism evolves, for instance due to a mutation in the target site. However, when GDs have a large negative effect on fitness, their spread depends on a threshold or they may not spread at all. The chance of GDs increasing until fixation is much higher in systems with meiotic drive than in systems with embryo conversion. The presence or absence of a meiotic promoter is therefore relevant to take into account in the environmental risk assessment.
Sperm competition suppresses gene drive among experimentally evolving populations of house mice
4056Manser, AL, A. K.; Simmons, L. W.; Firman, R. C., Molecular Ecology, 26:5784-5792. 2017-01-14 00:00:00.
Drive genes are genetic elements that manipulate the 50% ratio of Mendelian inheritance in their own favour, allowing them to rapidly propagate through populations. The action of drive genes is often hidden, making detection and identification inherently difficult. Yet drive genes can have profound evolutionary consequences for the populations that harbour them: most known drivers are detrimental to organismal gamete development, reproduction and survival. In this study, we identified the presence of a well-known drive gene called t haplotype post hoc in eight replicate selection lines of house mice that had been evolving under enforced monandry or polyandry for 20 generations. Previous work on these selection lines reported an increase in sperm competitive ability in males evolving under polyandry. Here, we show that this evolutionary response can be partly attributed to gene drive. We demonstrate that drive-carrying males are substantially compromised in their sperm competitive ability. As a consequence, we found that t frequencies declined significantly in the polyandrous lines while remaining at stable, high levels in the monandrous lines. For the first time in a vertebrate, we thus provide direct experimental evidence that the mating system of a species can have important repercussions on the spread of drive genes over evolutionary relevant timescales. Moreover, our work highlights how the covert action of drive genes can have major, potentially unintended impact on our study systems.
The promise and peril of CRISPR gene drives
4076Zentner, GEW, Michael J. C., Bioessays, 39:1-9. 2017-01-14 00:00:00.
Gene drives are selfish genetic elements that use a variety of mechanisms to ensure they are transmitted to subsequent generations at greater than expected frequencies. Synthetic gene drives based on the clustered regularly interspersed palindromic repeats (CRISPR) genome editing system have been proposed as a way to alter the genetic characteristics of natural populations of organisms relevant to the goals of public health, conservation, and agriculture. Here, we review the principles and potential applications of CRISPR drives, as well as means proposed to prevent their uncontrolled spread. We also focus on recent work suggesting that factors such as natural genetic variation and inbreeding may represent substantial impediments to the propagation of CRISPR drives.
A bigger toolbox: Biotechnology in biodiversity conservation
6012R. T. Corlett, Trends in Biotechnology, 35:55-65. 2017-01-13 20:08:47.
Conservation biology needs a bigger toolbox to meet unprecedented challenges. Genomics, fueled by declining sequencing costs, offers novel tools with increased precision for genetic questions previously answered with a few molecular markers, as well as completely new possibilities. Metabarcoding promises quicker, cheaper, and more accurate assessments of biodiversity in groups that are difficult to assess by traditional methods, while sequencing low-quality DNA extends the range of useable materials to include museum specimens, archeological remains, and environmental samples. Genomic and transcriptomic data can be used to assess the potential of populations to adapt to new challenges. In the near future, gene-editing tools may help endangered species cope with change, while gene drives control unwanted species and help wanted ones. De-extinction has become a serious prospect.
Agricultural pest control with CRISPR-based gene drive: time for public debate: Should we use gene drive for pest control?
4035Courtier?Orgogozo, VM, Baptiste; Boëte, Christophe, EMBO Reports, 18:878-880. 2017-01-13 00:00:00.
Gene drive based on the CRISPR/Cas-9 gene editing system is a powerful technology that promotes the inheritance of the gene drive tool itself via sexual reproduction and can therefore spread quickly through a population. It holds great potential for public health and humanitarian purposes, such as reducing the burden of vector-borne diseases like malaria. Here, we discuss another potential application of CRISPR-based gene drive, namely the control of pest species to increase crop production. We argue that gene drive-based pest control strategies should receive more attention from policymakers and the public given their enormous potential impact on the environment, their easy accessibility, and the current dearth of regulations.
Gene Drive for Mosquito Control: Where Did It Come from and Where Are We Headed?
4055Macias, VMO, J. R.; Rasgon, J. L., International Journal of Environmental Research and Public Health, 14:e1006. 2017-01-13 00:00:00.
Mosquito-borne pathogens place an enormous burden on human health. The existing toolkit is insufficient to support ongoing vector-control efforts towards meeting disease elimination and eradication goals. The perspective that genetic approaches can potentially add a significant set of tools toward mosquito control is not new, but the recent improvements in site-specific gene editing with CRISPR/Cas9 systems have enhanced our ability to both study mosquito biology using reverse genetics and produce genetics-based tools. Cas9-mediated gene-editing is an efficient and adaptable platform for gene drive strategies, which have advantages over innundative release strategies for introgressing desirable suppression and pathogen-blocking genotypes into wild mosquito populations; until recently, an effective gene drive has been largely out of reach. Many considerations will inform the effective use of new genetic tools, including gene drives. Here we review the lengthy history of genetic advances in mosquito biology and discuss both the impact of efficient site-specific gene editing on vector biology and the resulting potential to deploy new genetic tools for the abatement of mosquito-borne disease.
Unintended consequences of 21st century technology for agricultural pest management
4075Young, SL, EMBO reports, 18:1478-1478. 2017-01-13 00:00:00.
Comment on Agricultural pest control with CRISPR-based gene drive: time for public debate by Courtier-Orgogozo et al.
Adaptive risk management of gene drive experiments: Biosafety, biosecurity, and ethics
4054Lunshof, JEB, A., Applied Biosafety, 22:97-103. 2017-01-12 00:00:00.
Emerging technologies in the life sciences call for new models of biosafety risk management. We examine the question of how to; address new developments in the life sciences and biosciences in a bottom-up manner—that is, from the concrete level of; biosafety practice with a focus on the risk management and risk assessment of emerging technologies in the biology laboratory.; We use research on “gene drives” as an example of challenging work with new constructs that have major biosafety implications; for the work in the laboratory and beyond. Gene drives are intended for use in ecosystems and require, at an early stage, the; consideration of potential future biosafety, biosecurity, and societal impact. We argue for an integrative approach, a truly collaborative; model that involves scientists, biosafety officers, institutional leadership, and ethics consultants, with the aim of; maximizing safety as well as scientific progress.
Introduction of a male-harming mitochondrial haplotype via ‘Trojan Females’ achieves population suppression in fruit flies
4074Wolff, JNG, N. J.; Tompkins, D. M.; Dowling, D. K., eLife, 6:e23551. 2017-01-12 00:00:00.
Pests are a global threat to biodiversity, ecosystem function, and human health. Pest control approaches are thus numerous, but their implementation costly, damaging to non-target species, and ineffective at low population densities. The Trojan Female Technique (TFT) is a prospective self-perpetuating control technique that is species-specific and predicted to be effective at low densities. The goal of the TFT is to harness naturally occurring mutations in the mitochondrial genome that impair male fertility while having no effect on females. Here, we provide proof-of-concept for the TFT, by showing that introduction of a male fertility-impairing mtDNA haplotype into replicated populations of Drosophila melanogaster causes numerical population suppression, with the magnitude of effect positively correlated with its frequency at trial inception. Further development of the TFT could lead to establishing a control strategy that overcomes limitations of conventional approaches, with broad applicability to invertebrate and vertebrate species, to control environmental and economic pests.
Novel CRISPR/Cas9 gene drive constructs reveal insights into mechanisms of resistance allele formation and drive efficiency in genetically diverse populations
4034Champer, JR, Riona; Oh, Suh Yeon; Liu, Chen; Liu, Jingxian; Clark, Andrew G.; Messer, Philipp W., PLOS Genetics, 13:e1006796. 2017-01-12 00:00:00.
Author summary Gene drive systems provide a wide array of potential applications, including new strategies for the control of vector-borne diseases. For example, a functioning gene drive system could rapidly spread a genetically modified allele designed to reduce pathogen transmission throughout a vector population. The recently developed CRISPR/Cas9-based gene drive mechanism works by converting wild type alleles to drive alleles in heterozygotes via cleavage and homology-directed repair. However, resistance alleles that are unable to be converted to drive alleles can also be generated during this process, which may pose a major obstacle to the practical use of such gene drives. In our study, we developed two CRISPR/Cas9 gene drive constructs using different promoters and target sites in the model organism Drosophila melanogaster. We observed that these constructs produced resistance alleles at high rates both in the germline and post-fertilization in the embryo. Additionally, conversion efficiency and resistance allele formation rates varied substantially among genetically diverse fly lines. Overall, we conclude that new gene drive approaches will be necessary to reduce the formation of resistance alleles, particularly in genetically diverse natural populations.
A transatlantic perspective on 20 emerging issues in biological engineering
4073Wintle, BCB, C. R.; Rhodes, C.; Molloy, J. C.; Millett, P.; Adam, L.; Breitling, R.; Carlson, R.; Casagrande, R.; Dando, M.; Doubleday, R.; Drexler, E.; Edwards, B.; Ellis, T.; Evans, N. G.; Hammond, R.; Haseloff, J.; Kahl, L.; Kuiken, T.; Lichman, B. R.; Matthewman, C. A.; Napier, J. A.; OhEigeartaigh, S. S.; Patron, N. J.; Perello, E.; Shapira, P.; Tait, J.; Takano, E.; Sutherland, W. J., eLife, 6:21. 2017-01-11 00:00:00.
Advances in biological engineering are likely to have substantial impacts on global society. To explore these potential impacts we ran a horizon scanning exercise to capture a range of perspectives on the opportunities and risks presented by biological engineering. We first identified 70 potential issues, and then used an iterative process to prioritise 20 issues that we considered to be emerging, to have potential global impact, and to be relatively unknown outside the field of biological engineering. The issues identified may be of interest to researchers, businesses and policy makers in sectors such as health, energy, agriculture and the environment.
Gene Drive 101: A Basic Guidance Resource for Biosafety Professionals
4053Krishnan, PG, David, Applied Biosafety, 22:181-184. 2017-01-11 00:00:00.
Biosafety risk assessment and containment framework strategies for research involving gene drives pose a challenge, as there are no published guidelines or regulatory information yet written specifically addressing biosafety and gene drive use. Since the risk is more at an ecologic population level than an individual risk to the researcher, this further confounds the typical risk assessment process, which traditionally places emphasis on evaluating biosafety risks to the user and how the agent is spread among permissible hosts. We also realize that many of the publications currently available for gene drive biosafety are written with the assumption that readers have a good grasp of molecular biology and genetics. We have good reason to believe that this assumption is neither correct nor justified among all biosafety professionals. Our goal here is to create a resource that would offer a basic primer on gene drive technology while providing enough resources to start the risk assessment process of a gene drive proposal. We developed several questions and answers that we believe will make tackling the biosafety aspects of a gene proposal less formidable.
Teilhard de Chardin’s oeuvre within an ongoing discussion of a gene drive release for public health reasons
4033Cartolovni, A, Life Sciences, Society and Policy, 13:18. 2017-01-11 00:00:00.
Within the domain of public health, vector-borne diseases are among the most vehemently discussed issues. Recent scientific breakthroughs in genome editing technology provided a solution to this issue in the form of a gene drive that might decrease and even eradicate vector-borne diseases. Gene drives are engineered, and designed genes that can break typical inheritance rules and be passed to almost all of the carrier’s offspring. This genome editing and gene drive technology has become a powerful tool for ecological and environmental engineering, through which man can manipulate his surroundings, adjusting it to himself and directly mastering evolution and the ecosystem. Although the gene drive technology has been perceived as promising in the public health domain, ecological implications of its use are not to be underestimated. The primary aim of this paper is to overcome the ongoing discussion which mostly focuses on whether priority should be given to the environment or to public health, and to find an adequate answer and solution. In this quest to find the proper answer and solution, Pierre Teilhard de Chardin’s thought might be useful, especially his concepts of the biosphere and the noosphere which may provide some clarifications as to why we are at the moment so cautious with gene drive technology and how we need to move towards a better common future on earth.
A pooled sequencing approach identifies a candidate meiotic driver in Drosophila
4072Wei, KHCR, H. M.; Rathnam, C.; Lee, J.; Lin, D. A. N.; Ji, S. Q.; Mason, J. M.; Clark, A. G.; Barbash, D. A., Genetics, 206:451-465. 2017-01-10 00:00:00.
Meiotic drive occurs when a selfish element increases its transmission frequency above the Mendelian ratio by hijacking the asymmetric divisions of female meiosis. Meiotic drive causes genomic conflict and potentially has a major impact on genome evolution, but only a few drive loci of large effect have been described. New methods to reliably detect meiotic drive are therefore needed, particularly for discovering moderate-strength drivers that are likely to be more prevalent in natural populations than strong drivers. Here, we report an efficient method that uses sequencing of large pools of backcross (BC1) progeny to test for deviations from Mendelian segregation genome-wide with single-nucleotide polymorphisms (SNPs) that distinguish the parental strains. We show that meiotic drive can be detected by a characteristic pattern of decay in distortion of SNP frequencies, caused by recombination unlinking the driver from distal loci. We further show that control crosses allow allele-frequency distortion caused by meiotic drive to be distinguished from distortion resulting from developmental effects. We used this approach to test whether chromosomes with extreme telomere-length differences segregate at Mendelian ratios, as telomeric regions are a potential hotspot for meiotic drive due to their roles in meiotic segregation and multiple observations of high rates of telomere sequence evolution. Using four different pairings of long and short telomere strains, we find no evidence that extreme telomere-length variation causes meiotic drive in Drosophila. However, we identify one candidate meiotic driver in a centromere-linked region that shows an similar to 8% increase in transmission frequency, corresponding to a similar to 54: 46 segregation ratio. Our results show that candidate meiotic drivers of moderate strength can be readily detected and localized in pools of BC1 progeny.
Recommendations for Laboratory Containment and Management of Gene Drive Systems in Arthropods
4032Benedict, MQB, Austin; Capurro, Margareth L.; De Barro, Paul; Handler, Alfred M.; Hayes, Keith R.; Marshall, John M.; Tabachnick, Walter J.; Adelman, Zach N., Vector-Borne and Zoonotic Diseases, 18:2-13. 2017-01-10 00:00:00.
Versatile molecular tools for creating driving transgenes and other invasive genetic factors present regulatory, ethical, and environmental challenges that should be addressed to ensure their safe use. In this article, we discuss driving transgenes and invasive genetic factors that can potentially spread after their introduction into a small proportion of individuals in a population. The potential of invasive genetic factors to increase their number in natural populations presents challenges that require additional safety measures not provided by previous recommendations regarding accidental release of arthropods. In addition to providing physical containment, invasive genetic factors require greater attention to strain management, including their distribution and identity confirmation. In this study, we focus on insects containing such factors with recommendations for investigators who are creating them, institutional biosafety committees charged with ensuring safety, funding agencies providing support, those managing insectaries handling these materials who are responsible for containment, and other persons who will be receiving insects?transgenic or not?from these facilities. We give specific examples of efforts to modify mosquitoes for mosquito-borne disease control, but similar considerations are relevant to other arthropods that are important to human health, the environment, and agriculture.; Versatile molecular tools for creating driving transgenes and other invasive genetic factors present regulatory, ethical, and environmental challenges that should be addressed to ensure their safe use. In this article, we discuss driving transgenes and invasive genetic factors that can potentially spread after their introduction into a small proportion of individuals in a population. The potential of invasive genetic factors to increase their number in natural populations presents challenges that require additional safety measures not provided by previous recommendations regarding accidental release of arthropods. In addition to providing physical containment, invasive genetic factors require greater attention to strain management, including their distribution and identity confirmation. In this study, we focus on insects containing such factors with recommendations for investigators who are creating them, institutional biosafety committees charged with ensuring safety, funding agencies providing support, those managing insectaries handling these materials who are responsible for containment, and other persons who will be receiving insects?transgenic or not?from these facilities. We give specific examples of efforts to modify mosquitoes for mosquito-borne disease control, but similar considerations are relevant to other arthropods that are important to human health, the environment, and agriculture.
X chromosome drive in a widespread Palearctic woodland fly, Drosophila testacea
4052Keais, GLH, M. A.; Gowen, B. E.; Perlman, S. J., Journal of Evolutionary Biology, 30:1185-1194. 2017-01-10 00:00:00.
Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals and insects. Here, we report a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. We show that males carrying the driving X (SR males) sire 80-100% female offspring and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. We find that the majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, we demonstrate that the driving X is present in wild populations at a frequency of similar to 10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hot spot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.
Evaluating strategies for reversing CRISPR-Cas9 gene drives
4071Vella, MRG, Christian E.; Lloyd, Alun L.; Gould, Fred, Scientific Reports, 7:11038. 2017-01-09 00:00:00.
A gene drive biases inheritance of a gene so that it increases in frequency within a population even when the gene confers no fitness benefit. There has been renewed interest in environmental releases of engineered gene drives due to recent proof of principle experiments with the CRISPR-Cas9 system as a drive mechanism. Release of modified organisms, however, is controversial, especially when the drive mechanism could theoretically alter all individuals of a species. Thus, it is desirable to have countermeasures to reverse a drive if a problem arises. Several genetic mechanisms for limiting or eliminating gene drives have been proposed and/or developed, including synthetic resistance, reversal drives, and immunizing reversal drives. While predictions about efficacy of these mechanisms have been optimistic, we lack detailed analyses of their expected dynamics. We develop a discrete time model for population genetics of a drive and proposed genetic countermeasures. Efficacy of drive reversal varies between countermeasures. For some parameter values, the model predicts unexpected behavior including polymorphic equilibria and oscillatory dynamics. The timing and number of released individuals containing a genetic countermeasure can substantially impact outcomes. The choice among countermeasures by researchers and regulators will depend on specific goals and population parameters of target populations.
Requirements for Driving Antipathogen Effector Genes into Populations of Disease Vectors by Homing
4031Beaghton, AH, Andrew; Nolan, Tony; Crisanti, Andrea; Godfray, H. Charles J.; Burt, Austin, Genetics, 205:1587-1596. 2017-01-09 00:00:00.
There is a need for new interventions against the ongoing burden of vector-borne diseases such as malaria and dengue. One suggestion has been to develop genes encoding effector molecules that block parasite development within the vector, and then use the nuclease-based homing reaction as a form of gene drive to spread those genes through target populations. If the effector gene reduces the fitness of the mosquito and does not contribute to the drive, then loss-of-function mutations in the effector will eventually replace functional copies, but protection may nonetheless persist sufficiently long to provide a public health benefit. Here, we present a quantitative model allowing one to predict the duration of protection as a function of the probabilities of different molecular processes during the homing reaction, various fitness effects, and the efficacy of the effector in blocking transmission. Factors that increase the duration of protection include reducing the frequency of pre-existing resistant alleles, the probability of nonrecombinational DNA repair, the probability of homing-associated loss of the effector, the fitness costs of the nuclease and effector, and the completeness of parasite blocking. For target species that extend over an area much larger than the typical dispersal distance, the duration of protection is expected to be highest at the release site, and decrease away from there, eventually falling to zero, as effector-less drive constructs replace effector-containing ones. We also model an alternative strategy of using the nuclease to target an essential gene, and then linking the effector to a sequence that restores the essential function and is resistant to the nuclease. Depending upon parameter values, this approach can prolong the duration of protection. Our models highlight the key design criteria needed to achieve a desired level of public health benefit.%U http://www.genetics.org/content/genetics/205/4/1587.full.pdf
Sry gene drive for rodent control: Reply to Gemmell and Tompkins
4051Kanavy, DS, M., Trends in Ecology & Evolution, 32:315-316. 2017-01-09 00:00:00.
We would like to thank Gemmell and Tompkins for their interest and comments onthe articlebyPiaggioet al. [1].Theissues raised by Gemmell and Tompkins [2] are very pertinent, and they correctly identified that the format of the article did not lend itself to a comprehensive discussion of the ideas of using gene drives in mice. The method being considered in the Piaggio et al. article is to utilize a naturally occurring t-allele transgene (Tg) to sex-bias amouse population, causing it to crash. Inserting the sex-determining region on the Y chromosome (Sry) into the Tg allows biased inheritance where the majority of the offspring born are phenotypically male.
Eradicating Mosquitoes? The promise and peril of gene drive technologies.
4050Jun, B-O, Eubios Journal of Asian and International Bioethics, 27:113-116. 2017-01-08 00:00:00.
This paper discusses the ethical issues associated with genetic modification of mosquito species that are human disease vectors. The Oxitec genetically changed mosquito—a variant of a species called Aedes aegypti, OX513A, is taken as an example. The benefits and risks are discussed, and questions need to be discussed in public prior to release of this gene drive system
Evolution of Resistance Against CRISPR/Cas9 Gene Drive
4070Unckless, RLC, A. G.; Messer, P. W., Genetics, 205:827-841. 2017-01-08 00:00:00.
CRISPR/Cas9 gene drive (CGD) promises to be a highly adaptable approach for spreading genetically engineered alleles throughout a species, even if those alleles impair reproductive success. CGD has been shown to be effective in laboratory crosses of insects, yet it remains unclear to what extent potential resistance mechanisms will affect the dynamics of this process in large natural populations. Here we develop a comprehensive population genetic framework for modeling CGD dynamics, which incorporates potential resistance mechanisms as well as random genetic drift. Using this framework, we calculate the probability that resistance against CGD evolves from standing genetic variation, de novo mutation of wild-type alleles, or cleavage repair by nonhomologous end joining (NHEJ)-a likely by-product of CGD itself. We show that resistance to standard CGD approaches should evolve almost inevitably in most natural populations, unless repair of CGD-induced cleavage via NHEJ can be effectively suppressed, or resistance costs are on par with those of the driver. The key factor determining the probability that resistance evolves is the overall rate at which resistance alleles arise at the population level by mutation or NHEJ. By contrast, the conversion efficiency of the driver, its fitness cost, and its introduction frequency have only minor impact. Our results shed light on strategies that could facilitate the engineering of drivers with lower resistance potential, and motivate the possibility to embrace resistance as a possible mechanism for controlling a CGD approach. This study highlights the need for careful modeling of the population dynamics of CGD prior to the actual release of a driver construct into the wild.
Vector control with driving Y chromosomes: modelling the evolution of resistance
4030Beaghton, AB, P. J.; Burt, A., Malaria Journal, 16:286. 2017-01-08 00:00:00.
: The introduction of new malaria control interventions has often led to the evolution of resistance, both of the parasite to new drugs and of the mosquito vector to new insecticides, compromising the efficacy of the interventions. Recent progress in molecular and population biology raises the possibility of new genetic-based interventions, and the potential for resistance to evolve against these should be considered. Here, population modelling is used to determine the main factors affecting the likelihood that resistance will evolve against a synthetic, nuclease-based driving Y chromosome that produces a male-biased sex ratio. Methods: A combination of deterministic differential equation models and stochastic analyses involving branching processes and Gillespie simulations is utilized to assess the probability that resistance evolves against a driving Y that otherwise is strong enough to eliminate the target population. The model considers resistance due to changes at the target site such that they are no longer cleaved by the nuclease, and due to trans-acting autosomal suppressor alleles. Results: The probability that resistance evolves increases with the mutation rate and the intrinsic rate of increase of the population, and decreases with the strength of drive and any pleiotropic fitness costs of the resistant allele. In seasonally varying environments, the time of release can also affect the probability of resistance evolving. Trans-acting suppressor alleles are more likely to suffer stochastic loss at low frequencies than target site resistant alleles. Conclusions: As with any other intervention, there is a risk that resistance will evolve to new genetic approaches to vector control, and steps should be taken to minimize this probability. Two design features that should help in this regard are to reduce the rate at which resistant mutations arise, and to target sequences such that if they do arise, they impose a significant fitness cost on the mosquito.
A large gene family in fission yeast encodes spore killers that subvert Mendel’s law
4049Hu, WJ, Z. D.; Suo, F.; Zheng, J. X.; He, W. Z.; Du, L. L., eLife, 6:e28567. 2017-01-07 00:00:00.
Spore killers in fungi are selfish genetic elements that distort Mendelian segregation in their favor. It remains unclear how many species harbor them and how diverse their mechanisms are. Here, we discover two spore killers from a natural isolate of the fission yeast Schizosaccharomyces pombe. Both killers belong to the previously uncharacterized wtf gene family with 25 members in the reference genome. These two killers act in strain-background-independent and genome-location-independent manners to perturb the maturation of spores not inheriting them. Spores carrying one killer are protected from its killing effect but not that of the other killer. The killing and protecting activities can be uncoupled by mutation. The numbers and sequences of wtf genes vary considerably between S. pombe isolates, indicating rapid divergence. We propose that wtf genes contribute to the extensive intraspecific reproductive isolation in S. pombe, and represent ideal models for understanding how segregation-distorting elements act and evolve.
New Weapons in the Toad Toolkit: A Review of Methods to Control and Mitigate the Biodiversity Impacts of Invasive Cane Toads (Rhinella Marina)
4069Tingley, RW-F, Georgia; Schwarzkopf, Lin; Greenlees, Matthew J.; Phillips, Benjamin L.; Brown, Gregory; Clulow, Simon; Webb, Jonathan; Capon, Robert; Sheppard, Andy; Strive, Tanja; Tizard, Mark; Shine, Richard, The Quarterly Review of Biology, 92:123-149. 2017-01-07 00:00:00.
Our best hope of developing innovative methods to combat invasive species is likely to come from the study of high-profile invaders that have attracted intensive research not only into control, but also basic biology. Here we illustrate that point by reviewing current thinking about novel ways to control one of the world?s most well-studied invasions: that of the cane toad in Australia. Recently developed methods for population suppression include more effective traps based on the toad?s acoustic and pheromonal biology. New tools for containing spread include surveillance technologies (e.g., eDNA sampling and automated call detectors), as well as landscape-level barriers that exploit the toad?s vulnerability to desiccation?a strategy that could be significantly enhanced through the introduction of sedentary, range-core genotypes ahead of the invasion front. New methods to reduce the ecological impacts of toads include conditioned taste aversion in free-ranging predators, gene banking, and targeted gene flow. Lastly, recent advances in gene editing and gene drive technology hold the promise of modifying toad phenotypes in ways that may facilitate control or buffer impact. Synergies between these approaches hold great promise for novel and more effective means to combat the toad invasion and its consequent impacts on biodiversity.
B Chromosomes – A matter of chromosome drive
4048Houben, A, Frontiers in Plant Science, 8:210. 2017-01-06 00:00:00.
B chromosomes are supernumerary chromosomes which are often preferentially inherited, deviating from usual Mendelian segregation. The balance between the so-called chromosome drive and the negative effects that the presence of Bs applies on the fitness of their host determines the frequency of Bs in a particular population. Drive is the key for understanding most B chromosomes. Drive occurs in many ways at pre-meiotic, meiotic or post-meiotic divisions, but the molecular mechanism remains unclear. The cellular mechanism of drive is reviewed based on the findings obtained for the B chromosomes of rye, maize and other species. How novel analytical tools will expand our ability to uncover the biology of B chromosome drive is discussed.
Spatial gene drives and pushed genetic waves
4068Tanaka, HS, Howard A.; Nelson, David R., Proceedings of the National Academy of Sciences of the United States of America, 114:8452. 2017-01-06 00:00:00.
Gene constructs introduced into natural environments have been proposed to solve various ecological problems. The CRISPR-Cas9 technology greatly facilitates construction of gene drives that allow desired traits to rapidly replace wild types, even if these convey a selective growth rate disadvantage s > 0. However, accidental release of a gene drive could damage ecosystems irreversibly. We have modeled the spatial spread of gene drives and find a preferred range of selective disadvantages, 0.5 < s < 0.697. In this regime, gene drives spread but only when a nucleus exceeds a critical size and intensity. By making gene drives uniquely susceptible to a compound, their advance can be stopped in two dimensions by finite-width barriers, even when interrupted by gaps.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 disadvantage s > 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.
Towards the genetic control of invasive species
4047Harvey-Samuel, TA, T.; Alphey, L., Biological Invasions, 19:1683-1703. 2017-01-05 00:00:00.
Invasive species remain one of the greatest threats to global biodiversity. Their control would be enhanced through the development of more effective and sustainable pest management strategies. Recently, a novel form of genetic pest management (GPM) has been developed in which the mating behaviour of insect pests is exploited to introduce genetically engineered DNA sequences into wild conspecific populations. These 'transgenes' work in one or more ways to reduce the damage caused by a particular pest, for example reducing its density, or its ability to vector disease. Although currently being developed for use against economically important insect pests, these technologies would be highly appropriate for application against invasive species that threaten biodiversity. Importantly, these technologies have begun to advance in scope beyond insects to vertebrates, which include some of the world's worst invasives. Here we review the current state of this rapidly progressing field and, using an established set of eradication criteria, discuss the characteristics which make GPM technologies suitable for application against invasive pests.
Results from the Workshop “Problem Formulation for the Use of Gene Drive in Mosquitoes”
4066Roberts, ADA, P. P.; Okumu, F.; Quemada, H.; Savadogo, M.; Singh, J. A.; James, S., American Journal of Tropical Medicine and Hygiene, 96:530-533. 2017-01-04 00:00:00.
Reducing the incidence of malaria has been a public health priority for nearly a century. New technologies and associated vector control strategies play an important role in the prospect of sustained reductions. The development of the CRISPR/Cas9 gene editing system has generated new possibilities for the use of gene-drive constructs to reduce or alter vector populations to reduce malaria incidence. However, before these technologies can be developed and exploited, it will be necessary to understand and assess the likelihood of any potential harms to humans or the environment. To begin this process, the Foundation for the National Institutes of Health and the International Life Sciences Institute Research Foundation organized an expert workshop to consider the potential risks related to the use of gene drives in Anopheles gambiae for malaria control in Africa. The resulting discussion yielded a series of consensus points that are reported here.
The creation and selection of mutations resistant to a gene drive over multiple generations in the malaria mosquito
4046Hammond, AMK, Kyros; Bruttini, Marco; North, Ace; Galizi, Roberto; Karlsson, Xenia; Kranjc, Nace; Carpi, Francesco M.; D’Aurizio, Romina; Crisanti, Andrea; Nolan, Tony, PLOS Genetics, 13:e1007039. 2017-01-04 00:00:00.
Gene drives are selfish genetic elements that are able to bias their own inheritance among offspring. Starting from very low frequencies they can rapidly invade a population in just a few generations, even when imposing a fitness cost. Gene drives based on the precise DNA cutting enzyme CRISPR have been shown recently to be highly efficient at copying themselves from one chromosome to the other during the process of gamete formation in mosquitoes, resulting in transmission to 99% of offspring instead of the 50% expected for a single gene copy. One proposed use for CRISPR-based gene drives is in the control of mosquitoes by designing the gene drive to target mosquito genes involved in fertility, thereby reducing their overall reproductive output and leading to population suppression. Like any intervention designed to suppress a population these gene drives are expected to select for mutations in the mosquito that are resistant to the drive and restore fertility to mosquitoes. We have analyzed the origin and selection of resistant alleles in caged populations of mosquitoes initiated with a gene drive construct targeting a female fertility gene. We find the selected alleles are in-frame insertions and deletions that are resistant to cleavage and restore female fertility. Our findings allow us to improve predictions on gene drive behaviour and to make concrete recommendations on how to improve future gene drive designs by decreasing the likelihood that they generate resistance.
Advances in vector control science: Rear-and-release strategies show promise… but don’t forget the basics
4065Ritchie, SAJ, B. J., Journal of Infectious Diseases, 215:S103-S108. 2017-01-03 00:00:00.
Both chikungunya and Zika viruses have recently swept from Africa across the Pacific to the Americas, causing major outbreaks of disease in humans. In the meantime, dengue epidemics continue throughout the tropics. Traditional vector control programs based on strategies from 1950s and 1960s have been relatively ineffective in combating recent epidemics. In response, new methods involving the rearing and releasing of large numbers of mosquitoes to eliminate or modify local Aedes populations are being developed, with several currently conducting field releases in high-risk countries. These advances, include the release of Wolbachia-infected Aedes aegypti and Aedes albopictus, for either its virus-blocking capabilities, sterilization by cytoplasmic incompatibility, or both; the release of Aedes carrying dominant lethal genes, such as the OX513A strain of A. aegypti; and other emerging techniques, such as advancing gene-drive technologies, are summarized, as well as current stages of development and primary operational and regulatory hurdles. Although these technologies show great promise, none are ready for widespread rollout for cities of millions of people. Thus, efforts should be made to avoid methods such as space sprays that have failed and improve existing technologies to increase their efficacy.
CRISPR-based gene drive in agriculture will face technical and governance challenges
4045Gutzmann, NE, Johanna E.; Barnes, Jessica Cavin; Baltzegar, Jennifer; Jones, Michael S.; Sudweeks, Jayce, EMBO reports, 18:1479-1480. 2017-01-03 00:00:00.
Comment on "Agricultural pest control with CRISPR-based gene drive: time for public debate" by Courtier-Orgogozo et al.
CRISPR/Cas9 gene drive: Growing pains for a new technology
4064Reed, FA, Genetics, 205:1037-1039. 2017-01-02 00:00:00.
In this commentary, Floyd Reed discusses Unckless et al. (2017),; “Evolution of resistance against CRISPR/Cas9 gene drive,”; which was published in the February issue of GENETICS.
Potential of gene drives with genome editing to increase genetic gain in livestock breeding programs
4044Gonen, SJ, J.; Gorjanc, G.; Mileham, A. J.; Whitelaw, C. B. A.; Hickey, J. M., Genetics Selection Evolution, 49:14. 2017-01-02 00:00:00.
This paper uses simulation to explore how gene drives can increase genetic gain in livestock breeding programs. Gene drives are naturally occurring phenomena that cause a mutation on one chromosome to copy itself onto its homologous chromosome. Methods: We simulated nine different breeding and editing scenarios with a common overall structure. Each scenario began with 21 generations of selection, followed by 20 generations of selection based on true breeding values where the breeder used selection alone, selection in combination with genome editing, or selection with genome editing and gene drives. In the scenarios that used gene drives, we varied the probability of successfully incorporating the gene drive. For each scenario, we evaluated genetic gain, genetic variance (sigma(2)(A)), rate of change in inbreeding (Delta F), number of distinct quantitative trait nucleotides (QTN) edited, rate of increase in favourable allele frequencies of edited QTN and the time to fix favourable alleles. Results: Gene drives enhanced the benefits of genome editing in seven ways: (1) they amplified the increase in genetic gain brought about by genome editing; (2) they amplified the rate of increase in the frequency of favourable alleles and reduced the time it took to fix them; (3) they enabled more rapid targeting of QTN with lesser effect for genome editing; (4) they distributed fixed editing resources across a larger number of distinct QTN across generations; (5) they focussed editing on a smaller number of QTN within a given generation; (6) they reduced the level of inbreeding when editing a subset of the sires; and (7) they increased the efficiency of converting genetic variation into genetic gain. Conclusions: Genome editing in livestock breeding results in short-, medium- and long-term increases in genetic gain. The increase in genetic gain occurs because editing increases the frequency of favourable alleles in the population. Gene drives accelerate the increase in allele frequency caused by editing, which results in even higher genetic gain over a shorter period of time with no impact on inbreeding.
The End of the GMO? Genome Editing, Gene Drives and New Frontiers of Plant Technology
15368K. L. Hefferon and R. J. Herring, Review of Agrarian Studies, 7. 2017-01-01 21:40:33.
mprovements to agriculture will constitute one of the world’s greatest challenges in the coming century. Political and social controversies, as well as complications of plant breeding, intellectual property, and regulation, have compromised the promised impact of genetically engineered – typically transgenic – crops designated as “GMOs.” Genome editing is a new suite of molecular tools for assisting biologists identify genes that control agronomic traits such as drought tolerance and pest resistance, as well as to elucidate how expression of these genes is intertwined within the functional framework of the cell. This technology has recently gained momentum for its ability to accelerate the crop breeding process in an unprecedented fashion and expand the range of crop varieties with improved precision and lower costs. This review explains the basic concepts and provides examples of how genome editing could help address the United Nation’s Sustainable Development Goals with respect to food, agriculture, and medicine. It concludes with a discussion of the potential social impact of genome editing and gene drive. These effects are contingent on the resolution of novel ethical and regulatory challenges that add new layers of complexity to societal questions of appropriate technology, in agriculture and beyond. We expect these questions to replace the irresolvable GMO debate.
