Neural progenitor cell (NPC) induction was based on a previous report with slight modifications50. The day before the start of induction, hiPSCs (WTiPSCs and p53KDiPSCs) were passaged onto matrigel-coated plates at about 20% confluence and maintained in mTesR overnight. At day 0, culture medium was then switched to Neural Induction Medium 1 (NIM-1: 50% Advanced DMEM/F12 (Invitrogen), 50% Neurobasal (Invitrogen), 1 × N2 (Invitrogen), 1 × B27 (Invitrogen), 2 mM GlutaMAX (Invitrogen) and 10 ng ml−1 hLIF (Millipore), 4 μM CHIR99021 (Cellagentech, premade in 10 mM DMSO solution), 3 μM SB431542 (Cellagentech, premade in 10 mM DMSO solution), 2 μM Dorsomorphin (Sigma) and 0.1 μM Compound E (EMD Chemicals Inc.). Cells were treated with NIM-1 for 2 days, and then switched to Neural Induction Medium 2 (NIM-2: 50% Advanced DMEM/F12, 50% Neurobasal, 1 × N2, 1 × B27, 2 mM GlutaMAX, 10 ng ml−1 hLIF, 4 μM CHIR99021, 3 μM SB431542 and 0.1 μM Compound E) for another 5 days. The cultures were then split onto Matrigel-coated plates with Accumax (Innovative Cell Technologies) and cultured in Neural Stem cell Maintenance
