Abstract
During early embryogenesis, the ectoderm is rapidly subdivided into neural, neural crest and sensory progenitors. How the onset of lineage determinants and the loss of pluripotency markers are temporally and spatially coordinated in vivo is still debated. Here, we identify a crucial role for the transcription factor PRDM1 in the orderly transition from epiblast to defined neural lineages in chick. PRDM1 is initially expressed broadly in the entire epiblast, but becomes gradually restricted as cell fates are specified. We find that PRDM1 is required for the loss of some pluripotency markers and the onset of neural, neural crest and sensory progenitor specifier genes. PRDM1 directly activates their expression by binding to their promoter regions and recruiting the histone demethylase Kdm4a to remove repressive histone marks. However, once neural lineage determinants become expressed, they in turn repress PRDM1, whereas prolonged PRDM1 expression inhibits neural, neural crest and sensory progenitor genes, suggesting that its downregulation is necessary for cells to maintain their identity. Therefore, PRDM1 plays multiple roles during ectodermal cell fate allocation.