hemangioblast
The first hematopoietic and endothelial precursors arise from extra-embryonic mesoderm and differentiate to form the blood islands in the yolk sac of the early embryo.
The close spatial and temporal development of these lineages within the blood islands provided the basis for the hypothesis that they arise from a common progenitor, the hemangioblast.
Indirect evidence supporting the hemangioblast concept came from studies demonstrating that a large number of genes are expressed by both hematopoietic and endothelial lineages and that some of these genes are essential for both blood cell and vascular development.
Direct demonstration for the existence of a progenitor with hemangioblast properties has been provided by experiments using a model system based on the in vitro differentiation potential of embryonic stem (ES) cells.
See also
hematopoietic development