Cleave and Rescue, a novel selfish genetic element and general strategy for gene drive.

Abstract

There is great interest in being able to spread beneficial traits throughout wild populations in ways that are self-sustaining. Here, we describe a chromosomal selfish genetic element, <i>CleaveR</i> [Cleave and Rescue (<i>ClvR</i>)], able to achieve this goal. <i>ClvR</i> comprises two linked chromosomal components. One, germline-expressed Cas9 and guide RNAs (gRNAs)-the Cleaver-cleaves and thereby disrupts endogenous copies of a gene whose product is essential. The other, a recoded version of the essential gene resistant to cleavage and gene conversion with cleaved copies-the Rescue-provides essential gene function. <i>ClvR</i> enhances its transmission, and that of linked genes, by creating conditions in which progeny lacking <i>ClvR</i> die because they have no functional copies of the essential gene. In contrast, those who inherit <i>ClvR</i> survive, resulting in an increase in <i>ClvR</i> frequency. <i>ClvR</i> is predicted to spread to fixation under diverse conditions. To test these predictions, we generated a <i>ClvR</i> element in <i>Drosophila melanogaster</i><i>ClvR</i>^tko is located on chromosome 3 and uses Cas9 and four gRNAs to disrupt <i>melanogaster technical knockout</i> (<i>tko</i>), an X-linked essential gene. Rescue activity is provided by <i>tko</i> from <i>Drosophila virilis</i><i>ClvR</i>^tko results in germline and maternal carryover-dependent inactivation of <i>melanogaster tko</i> (>99% per generation); lethality caused by this loss is rescued by the <i>virilis</i> transgene; <i>ClvR</i>^tko activities are robust to genetic diversity in strains from five continents; and uncleavable but functional <i>melanogaster tko</i> alleles were not observed. Finally, <i>ClvR</i>^tko spreads to transgene fixation. The simplicity of <i>ClvR</i> suggests it may be useful for altering populations in diverse species.