Gene drive and resilience through renewal with next generation <i>Cleave and Rescue</i> selfish genetic elements.

Abstract

Gene drive-based strategies for modifying populations face the problem that genes encoding cargo and the drive mechanism are subject to separation, mutational inactivation, and loss of efficacy. Resilience, an ability to respond to these eventualities in ways that restore population modification with functional genes, is needed for long-term success. Here, we show that resilience can be achieved through cycles of population modification with "<i>Cleave and Rescue</i>" (<i>ClvR</i>) selfish genetic elements. <i>ClvR</i> comprises a DNA sequence-modifying enzyme such as Cas9/gRNAs that disrupts endogenous versions of an essential gene and a recoded version of the essential gene resistant to cleavage. <i>ClvR</i> spreads by creating conditions in which those lacking <i>ClvR</i> die because they lack functional versions of the essential gene. Cycles of modification can, in principle, be carried out if two <i>ClvR</i> elements targeting different essential genes are located at the same genomic position, and one of them, <i>ClvR</i>ⁿ⁺¹, carries a <i>Rescue</i> transgene from an earlier element, <i>ClvR</i>ⁿ<i>ClvR</i>ⁿ⁺¹ should spread within a population of <i>ClvR</i>ⁿ, while also bringing about a decrease in its frequency. To test this hypothesis, we first show that multiple <i>ClvR</i>s, each targeting a different essential gene, function when located at a common chromosomal position in <i>Drosophila</i> We then show that when several of these also carry the <i>Rescue</i> from a different <i>ClvR</i>, they spread to transgene fixation in populations fixed for the latter and at its expense. Therefore, genetic modifications of populations can be overwritten with new content, providing an ongoing point of control.