Total RNA from iPSCs, EBs or neurons was extracted with Trizol (Invitrogen, 15596-0926), ±5 μg of UltraPure glycogen (Thermo Fisher Scientific, Waltham, MA, USA) to enhance RNA recovery. RNA was treated with DNase (Thermo Fisher Scientific) and reverse transcribed (Superscript III, Invitrogen) using random nonamers. The cDNA was then used in PCR (primers in Supplementary Table 1B).