Germline Cas9 expression yields highly efficient genome engineering in a major worldwide disease vector, <i>Aedes aegypti</i>

The development of CRISPR/Cas9 technologies has dramatically increased the accessibility and efficiency of genome editing in many organisms. In general, in vivo germline expression of Cas9 results in substantially higher activity than embryonic injection. However, no transgenic lines expressing Cas9 have been developed for the major mosquito disease vector <i>Aedes aegypti</i> Here, we describe the generation of multiple stable, transgenic <i>Ae. aegypti</i> strains expressing Cas9 in the germline, resulting in dramatic improvements in both the consistency and efficiency of genome modifications using CRISPR. Using these strains, we disrupted numerous genes important for normal morphological development, and even generated triple mutants from a single injection. We have also managed to increase the rates of homology-directed repair by more than an order of magnitude. Given the exceptional mutagenic efficiency and specificity of the Cas9 strains we engineered, they can be used for high-throughput reverse genetic screens to help functionally annotate the <i>Ae. aegypti</i> genome. Additionally, these strains represent a step toward the development of novel population control technologies targeting <i>Ae. aegypti</i> that rely on Cas9-based gene drives.