Haematopoietic stem cell induction by somite-derived endothelial cells controlled by meox1

A new somite compartment, called the endotome, that contributes to the formation of the embryonic dorsal aorta by providing endothelial progenitors is identified here; endotome-derived endothelial progenitors, whose formation is regulated by the activity of the meox1 gene, induce haematopoietic stem cell formation upon colonization of the nascent dorsal aorta.