CRISPR/Cas9-mediated genome engineering and the promise of designer flies on demand.

The CRISPR/Cas9 system has attracted significant attention for its potential to transform genome engineering. We and others have recently shown that the RNA-guided Cas9 nuclease can be employed to engineer the Drosophila genome, and that these modifications are efficiently transmitted through the germline. A single targeting RNA can guide Cas9 to a specific genomic sequence where it induces double-strand breaks that, when imperfectly repaired, yield mutations. We have also demonstrated that 2 targeting RNAs can be used to generate large defined deletions and that Cas9 can catalyze gene replacement by homologous recombination. Zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) have shown similar promise in Drosophila. However, the ease of producing targeting RNAs over the generation of unique sequence-directed nucleases to guide site-specific modifications makes the CRISPR/Cas9 system an appealingly accessible method for genome editing. From the initial planning stages, engineered flies can be obtained within a month. Here we highlight the variety of genome modifications facilitated by the CRISPR/Cas9 system along with key considerations for starting your own CRISPR genome engineering project.