a, Schematic of lentiviral system for inducible overexpression of Ngn2-2A-eGFP (top). Direct conversion of iPSCs into induced neurons (iNs) by forced expression of an inducible Ngn2 transgene may bypass early NSC-like stages (bottom). b, Representative images of patient-derived iPSC-iNs at different stages in the course of neuronal differentiation. Scale bar 200 μm. Experiments were repeated in all 13 patient lines at 4 different time points. c, Immunocytochemical characterization of iPSC-iNs after two weeks of conversion. Scale bar represents 25 μm. Immunohistochemistry was performed in all 13 patient lines at least once with similar results d, BrdU-labeling experiment with unselected iPSC-iNs during conversion (arrowheads highlight GFP-expressing iPSC-iNs). Scale bar 50 μm. Values represent mean ± s.d.; n=4 independent control cell lines. e, Representative reconstructions of patient-derived iPSC-iNs at the stages indicated in b. Scale bar 100 μm. Experiments were repeated in all 13 patient lines at 4 different time points. Also see Extended Data Figures 8 and 9.