Gene expression profiling indicates that our hiPSC NPCs most resemble cells in the fetal cortical and subcortical forebrain regions (Brennand et al., 2015). NPCs are a replicative population of SOX2-positive and NESTIN-positive cells with the capacity to differentiate to populations comprised of ∼80% neurons (predominantly excitatory) and ∼20% astrocytes (Brennand et al., 2011). Lentiviral transduction of NPCs with doxycycline-inducible human NGN2 rapidly yields excitatory neurons with robust electrical activity and detectable synaptic puncta within 3 weeks (Ho et al., 2016); they can also be differentiated to a population of hiPSC-astrocytes that shares the transcriptional profile and functional characteristics of human fetal astrocytes via a 30-day protocol (TCW et al., 2017). qPCR characterization of hiPSC-derived NPCs, neurons, NGN2 neurons, and astrocytes demonstrated baseline expression of all five SZ-risk genes considered herein, KCTD13, TOAK2, NRXN1, SNAP91, and CLCN3 (Figure S1), prior to dCas9-manipulation.
