Mapping mouse hemangioblast maturation from headfold stages

► We resolved the boundaries of mouse hemangioblast maturation at headfold stages. ► HoxB4 and GATA1 are the first markers that distinguish vessel and blood lineages. ► A third population co-expresses both markers, indicating a metastable state. ► We found similar states in rare cells at earliest sites of HSC emergence. ► We formalized our observations using a heuristic Netlogo model.