Sorted cells were either cultured in neurobasal medium (Invitrogen, Carlsbad, CA) with B27 supplement (20 ml/ml; Invitrogen), Glutamax (10 ml/ml; Invitrogen), fibroblast growth factor 2 (20 ng/ml; Peprotech, Rocky Hill, NJ), epidermal growth factor (20 ng ml; Peprotech) or transferred to DMEM supplemented with 10% fetal calf serum (FCS) and 1% glutamine and grown on cover slips in 24 well plates.