H9 human ES cells (WiCell Research Resources) were expanded in mTeSR1 (Stem Cell Technologies). The generation and characterization of the iPS cells used in this study will be published elsewhere (Sebastiano & Wernig). The day before infection, cells were treated with accutase and seeded as single cells in 3.5 cm tissue culture dishes on matrigel in mTeSR1 containing 2 µM Thiazovivin (Bio Vision)24. To inhibit the growth of uninfected ES cells and select for post-mitotic neurons, we added 4 µM Cytosine β-d-arabinofuranoside (Ara-C) to the media 48 hours after dox addition. Primary human fetal fibroblasts were isolated from the distal half of the limbs of 8–10 week old fetuses (Advanced Bioscience Resources Inc.). The tissue was dissociated after trypsin digestion and plated in MEF media (DMEM high glucose, calf serum, sodium pyruvate, non-essential amino acids, penicillin/streptomycin and β-mercaptoethanol). Primary human postnatal fibroblasts (HPFs) were established from dissociated foreskin tissue derived from 1–3 day-old newborns. Before being used for experiments, primary fibroblast cells were passaged for at least 3 times. Primary mouse cortical cultures and glial monolayer cultures were established as
