Origin of endothelial cells and hematopoietic cells [14]. Mesodermal stem cells are the source of hematopoietic stem cells and angioblasts in the developing embryo. The hemangioblast is a precursor to both angioblasts and hematopoietic stem cells. Angioblasts differentiate into endothelial cells. Hematopoietic cells can differentiate into all cell types found in circulating blood