The impact of CRISPR–Cas9 on target identification and validation

•Cas9 has utility across gene editing especially for rapid knock-out (KO) generation.•The D10A nickase mutant may boost rates of homologous recombination.•The infrastructure developed for shRNA can be redeployed in sgRNA drop out screens.•sgRNA KO screens may overcome many of the issues with large-scale shRNA screens.•Cas9 enables rapid gene editing in vivo: KO animals can be made in a few months. The addition of an RNA-guided nuclease, Cas9, to the gene editing toolbox has increased the accessibility of gene editing technologies by greatly simplifying the design of editing reagents. Only a single 75–100 nucleotide RNA is required to guide Cas9 to the target gene of interest, which has meant that the established infrastructure of short-hairpin RNA interference screen could be readily adapted to genome-wide knock out screens. Cas9-based editing technology should streamline the generation of animal and cell-line models, make the generation of activity-dead mutations in target validation routine, and enable the discovery of a new generation of targets across therapeutic areas.