Towards best-practice approaches for CRISPR/Cas9 gene engineering

In recent years, CRISPR has evolved from \"the curious sequence of unknown biological function\" into a functional genome editing tool. The CRISPR/Cas9 technology is now delivering novel genetic models for fundamental research, drug screening, therapy development, rapid diagnostics and transcriptional modulation. Despite the apparent simplicity of the CRISPR/Cas9 system, the outcome of a genome editing experiment can be substantially impacted by technical parameters as well as biological considerations. Here, we present guidelines and tools to optimize CRISPR/Cas9 genome targeting efficiency and specificity. The nature of the target locus, the design of the single guide RNA and the choice of the delivery method should all be carefully considered prior to a genome editing experiment. Different methods can also be used to detect off-target cleavages and decrease the risk of unwanted mutations. Together, these optimized tools and proper controls are essential to the assessment of CRISPR/Cas9 genome editing experiments.