hiPSC forebrain NPCs were derived from the three controls as described previously74. These samples were selected irrespective of their genotypes for the FURIN-eQTL SCZ-risk variant at SNP rs4702, with two being heterozygous G/A and the third homozygous risk G/G. Incubation with Collagenase (1 mg/ml in DMEM) at 37°C for 1–2 hours lifted colonies, which were transferred to a nonadherent plate (Corning). Embryoid Bodies (EBs) were grown in suspension with dual-SMAD inhibition (0.1mM LDN193189 (Stemgent) and 10mM SB431542 (Tocris)) N2/B27 media (DMEM/F12-Glutamax (Invitrogen), 1× N2 (Invitrogen), 1X B27 (Invitrogen)). 7-day-old EBs were plated in N2/B27 media with 1 µg/ml Laminin (Invitrogen) onto poly-ornithine/Laminin-coated plates. Neural rosettes were harvested from 14-day-old EBs using Neural Rosette Selection Reagent (STEMdiff™) for 60 minutes at 37°C before being plated in NPC media (DMEM/F12, 1× N2, 1× B27-RA (Invitrogen), 1 µg/ml Laminin and 20 ng/ml FGF2 on poly-ornithine/laminin-coated plates.
