H9 human ES cells (WiCell Research Resources) and iPS cells were expanded in mTeSR1 (Stem Cell Technologies) and passaged as clumps or single cells24. Primary human fetal fibroblasts (HFFs) were isolated from the distal half of the limbs of GW8-10 fetuses obtained from Advanced Bioscience Resources Inc. Primary human postnatal fibroblasts (HPFs) were established from foreskin. Primary mouse cortical cultures and glial monolayer cultures were established as described previously13.
