In vivo migration assays using BrdU labelling

E14.5 pregnant wild‐type, Alk ^−/−, Ltk ^−/−, and DKO mice were labeled in vivo by intraperitoneal injections with BrdU (150 μg/g body weight, Sigma‐Aldrich). In some experiments, PPP (20 mg/kg body weight; Girnita et al, ²⁰⁰⁴) or saline (as control) were injected 24 h after BrdU. E17.5 embryos, P2 and P7 pups were sacrificed and brains were fixed in 4% PFA and cryoprotected in 30% (w/v) sucrose at 4°C overnight. Serial cryosections (12 μm) were incubated with anti‐BrdU antibody at 4°C overnight. For quantitation in P2 and P7 mice, BrdU⁺ cells located within each of eight equally sized bins spanning the cortex were counted.