University College London (UCL) scientists report that a unique source of stem cells in blood helps to build blood vessels in the growing embryo. They say their study (“ Erythro-myeloid progenitors contribute endothelial cells to blood vessels ”) in Nature changes scientific understanding of how blood vessels are made and brings researchers  one step closer to using stem cells to grow new blood vessels and repair damaged ones.

“The earliest blood vessels in mammalian embryos are formed when endothelial cells differentiate from angioblasts and coalesce into tubular networks. Thereafter, the endothelium is thought to expand solely by proliferation of pre-existing endothelial cells. Here we show that a complementary source of endothelial cells is recruited into pre-existing vasculature after differentiation from the earliest precursors of erythrocytes, megakaryocytes and macrophages, the erythro-myeloid progenitors (EMPs) that are born in the yolk sac. A first wave of EMPs contributes endothelial cells to the yolk sac endothelium, …