Fig. 1

a Schematic drawing of the genomic edition and HR steps to correct pF508del mutation. After specific cut by ZFNs or TALENs, repair vector is used as a template for homologous recombination and the process generates the P allele, which shows homology arms and position of the primers (P3–4 and P5–6) used for their amplification and detection, with one primer 5’ or 3’ in the genomic region and the other 3’ or 5’ in the terminal repeats of the transposon cassette, respectively. Transposase is then expressed in target cells to eliminate the double selectable marker, which has sequentially selected cells resistant to puromycin which have integrated the donor vector and, from these, cells resistant to Fialuridine which have eliminated the transposon containing the modified Thymidine kinase gene in sequential steps. Primers P1–2 allow for confirmation of the repaired sequence. b Genomic sequence detail of the targeting region, showing the position of the pF508del mutation, ZFN and TALEN target sequences and spacers, silent mutations introduced to avoid retargeting and to create a restriction site to distinguish targeted allele, and TTAA position for the introduction of the PiggyBac double selectable marker. TALEN Transcription activator-like effector nuclease, ZFN Transcription activator-like effector nuclease