POU5F1 and infection: Infection of human iPS cells with lentivirus expressing Cas9-sgRNA followed by puromycin selection for guide expression did not alter expression of key transcriptional markers of pluripotency, POU5F1, Nanog or Sox2 (Fig. 2a, Supplementary Fig. 2) or iPS cell proliferation rate (Fig. 2b, Supplementary Fig. 2) relative to uninfected cells.