Figure 1. Hemangioblast versus hemogenic endothelium schematic.

Two proposed models of HSC emergence in the embryo. One model proposes that a specialized bi-potent precursor named the hemangioblast gives rise to both endothelial cells and HSCs. An alternative model proposes that mesoderm gives rise first to endothelium, a small proportion of which can give rise to HSCs. In this schematic, the purple cell represents the subset of hemogenic endothelial cells. The different shades represent heterogeneity within both lineages.