Plates were coated with Matrigel (BD biosciences, #354230) prior to thawing NPCs. A 1 mg aliquot of Matrigel was thawed for every two plates, by resuspending Matrigel in 24 ml of ice-cold DMEM (ThermoFisher Scientific, #10566-016) and rapidly adding 2 ml of this cold mixture to each well of a 6-well plate. Plates were incubated at 37 °C (for at least 1 h, typically overnight).
