Editing tick genome: Challenges and opportunities

Despite their capacity to acquire and pass on an array of debilitating pathogens, research on ticks has lagged behind other arthropod vectors, such as mosquitoes, largely because of challenges in applying available genetic and molecular tools. CRISPR-Cas9 is transforming non-model organism research; however, successful gene editing has not yet been reported in ticks. Technical challenges for injecting tick embryos to attempt gene editing have further slowed research progress. No heritable insertions have been observed in ticks yet. Successful integration of DNA into the tick genome requires molecular tools such as transposable genetic elements, recombinases, or CRISPR/Cas9. Additionally, functional promoters are needed to drive the expression of transgenes to study gene function and reporter genes as markers of transgenic individuals. We report a successful embryo injection protocol for the black-legged tick, Ixodes scapularis, and the use of this protocol for genome editing with CRISPR-Cas9. We also demonstrate functional endogenous tick promoters for gene knockins. Our results provide innovative tools to the tick research community that are essential for advancing our understanding of the molecular mechanisms governing pathogen transmission by tick vectors and the underlying biology of host-vector-pathogen interactions.