Note: Funding Information: We thank M. Muraro and A. Lyubimova for experimental advice. We also thank the Hubrecht FACS facility, the Hubrecht Single Cell facility, the Hubrecht Imaging facility and the Utrecht Sequencing Facility (USF). This work was supported by a Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) TOP award (NWO-CW 714.016.001) to A.v.O. and by an European Research Council grant (ERC 220-H75001EU/HSCOrigin-309361) and the UMC Utrecht “Regenerative Medicine & Stem Cells” priority research program to C.R. Pax7nGFP mice were kindly provided by S. Tajbakhsh (Institut Pasteur, Paris, France).