At day 14 cells were detached with Accutase (75 ml/cm2; GIBCO), resuspended in B27 media (Neurobasal supplemented with 1% B27 without vitamin A (GIBCO), 2 mM L-glutamine and 0.2% penicillin/streptomycin Y27632 (10 μM), BDNF (20 ng/ml; R&D), and L-ascorbic acid (0.2 mM; Sigma) containing RY27632 (10 μM) and Draq7 (1:1000, BD Bioscience) and strained with a 70μm (BD Bioscience) filter. Gating parameters were determined by side and forward scatter to eliminate debris and aggregated cells. The GFP-positive gates were set using untransduced fbNPCs. The sorting gates and strategies were validated via reanalysis of sorted cells (> 95% purity cut-off). 200.000 GFP-positive/Draq7-negative cells were collected per sample, spun down at 400g for 5 min and snap frozen on dry ice. Cell pellets were kept at −80°C until RNA was isolated.