Proposed models for etsrp function within the anterior lateral mesoderm. (A) Etsrp induces scl in the hemangioblast cells, which give rise to both vascular endothelial and myeloid precursors. As hemangioblasts divide, etsrp expression becomes restricted to endothelial cells where it is both necessary and sufficient for vasculogenesis. (B) Alternatively, there are 2 separate pools of etsrp-expressing endothelial and myeloid precursors. As the cells initiate myeloid marker expression, they down-regulate etsrp expression.