Engineered Reciprocal Chromosome Translocations Drive High Threshold, Reversible Population Replacement in Drosophila

Gene editing technologies and applications for insects

Initially discovered in bacteria, CRISPR-based genome editing endonucleases have proven remarkably amenable for adaptation to insects. To date, these endonucleases have been utilized in a plethora of both model and non-model insects including diverse flies, bees, beetles, butterflies, moths, and grasshoppers, to name a few, thereby revolutionizing functional genomics of insects. In addition to basic genome editing, they have also been invaluable for advanced genome engineering and synthetic biology applications. Here we explore the recent genome editing advancements in insects for generating site-specific genomic mutations, insertions, deletions, as well as more advanced applications such as Homology Assisted Genome Knock-in (HACK), potential to utilize DNA base editing, generating predictable reciprocal chromosomal translocations, and development gene drives to control the fate of wild populations.

Gene drives in our future: challenges of and opportunities for using a self-sustaining technology in pest and vector management

Gene drives are systems of biased inheritance that enhance the likelihood a sequence of DNA passes between generations through sexual reproduction and potentially throughout a local population and ultimately all connected populations of a species. Gaps in our knowledge of gene drive systems prompted the US National Institutes of Health (NIH) and the Foundation for the NIH to ask the US National Academies of Sciences, Engineering, and Medicine (NASEM) to convene an expert panel to provide an independent, objective examination of what we know about gene drive systems. The report, "Gene drives on the horizon: Advancing science, navigating uncertainty, and aligning research with public values," outlines our understanding of the science, ethics, public engagement, governance, and risk assessment pertaining to gene drive research. Researchers have studied naturally occurring gene drive systems for more than a century. While CRISPR/Cas9 was not the first molecular tool considered to create an engineered gene drive, the advent of the CRISPR/Cas9 technology for gene editing gave a renewed impetus to developing gene drives in the laboratory for eventual release in the field. Recent experiments demonstrate that a CRISPR/Cas9-based gene drive can spread a targeted gene throughout nearly all of laboratory populations of yeast, fruit flies, or mosquitoes. Applying this basic science, there are proposals to use gene drive modified organisms to address such things as eradication of insect-borne infectious diseases and conservation of threatened and endangered species. Gene drives could potentially support agriculture by reversing pesticide and herbicide resistance in insects and weeds, and by control of damaging, invasive species. A major recommendation of the NASEM report is that there is insufficient evidence at this time to support release of gene-drive modified organisms into the environment. Importantly, the committee also recognized that the potential benefits of gene drives for basic and applied research are significant and justify proceeding with laboratory research and controlled field trials. This review summarizes highlights of the NASEM report with its focus on using the CRISPR/Cas9 genome-editing technology to develop gene drive modified organisms.

Can CRISPR-Based Gene Drive Be Confined in the Wild? A Question for Molecular and Population Biology

The recent discovery of CRISPR and its application as a gene editing tool has enabled a range of gene drive systems to be engineered with greater ease. In order for the benefits of this technology to be realized, in some circumstances drive systems should be developed that are capable of both spreading into populations to achieve their desired impact and being recalled in the event of unwanted consequences or public disfavor. We review the performance of three broad categories of drive systems at achieving these goals: threshold-dependent drives, homing-based drive and remediation systems, and temporally self-limiting systems such as daisy-chain drives.

Gene Drive: Evolved and Synthetic

Drive is a process of accelerated inheritance from one generation to the next that allows some genes to spread rapidly through populations even if they do not contribute to-or indeed even if they detract from-organismal survival and reproduction. Genetic elements that can spread by drive include gametic and zygotic killers, meiotic drivers, homing endonuclease genes, B chromosomes, and transposable elements. The fact that gene drive can lead to the spread of fitness-reducing traits (including lethality and sterility) makes it an attractive process to consider exploiting to control disease vectors and other pests. There are a number of efforts to develop synthetic gene drive systems, particularly focused on the mosquito-borne diseases that continue to plague us.

Conditions for success of engineered underdominance gene drive systems

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.