Numerous strategies exist for genome editing using CRISPR, predominantly differing in the method of delivery of the Cas9 and guide RNA components. Inducible Cas9 transgenes (Gonzalez et al. 2014), DNA plasmids (Ding et al. 2013a, b; Kwart et al. 2017; Merkert et al. 2014; Miyaoka et al. 2016, 2014; Yang et al. 2013) or Cas9 ribonucleoprotein (RNP) complexes (Kim et al. 2014; Liang et al. 2015; Lin et al. 2014; Richardson et al. 2016) have all been successful in introducing targeted mutations in hiPS cells (reviewed in more detail in Merkert and Martin 2016; Santos et al. 2016). The choice of system depends on multiple factors including the importance of off-targeting, the type of repair necessary (single nucleotide changes or indel mutations) and prior knowledge of optimal delivery methods into a particular cell line. However, our preference is for delivery of RNPs composed of recombinant, bacterially expressed Cas9 protein and synthetic RNA oligos corresponding to the CRISPR RNA (crRNA) and trans-activating CRISPR RNA (tracrRNA) components of the system. This has many advantages over other systems since the RNP complex is
