Megakaryocyte potential is derived from hemangioblast precursors. (A) Hemangioblast-derived colony from E7.5 mouse embryo (i). Adherent and nonadherent cells from a hemangioblast-derived colony after 3 days in liquid expansion media (ii). (B) Proplatelet formation of cells differentiated from a hemangioblast-derived colony after 3 days in liquid media (i-ii). (C) PECAM-positive cells (arrowheads) in the adherent cell population after 10 days in liquid expansion media. (D) Primitive erythroid and megakaryocyte colony formation from expanded, nonadherent cells placed into progenitor assays. An EryP-CFC–derived colony contains cells positive for βH1-globin (i) and a Meg-CFC–derived colony contains cells and proplatelet extensions (arrowheads) positive for GP1bβ (ii). (E) Hematopoietic potential of 10 individual hemangioblast colonies expanded in liquid culture. The number of EryP-CFCs, Meg-CFCs, and megakaryocyte cells (meg cells) is shown. Scale bars represent 10 μm.