Model of early hemangioblast commitment. The SCL-independent and -dependent phases are indicated. The BL-CFC is represented as a Flk-1⁺/Brachyury⁺/Scl^- progenitor. In appropriate culture conditions, wild-type (WT) progenitors generate blast colonies composed of the hematopoietic (Hemat), vascular smooth muscle (VSM), and endothelial (endo) lineages. In the absence of SCL, these progenitors fail to generate the hematopoietic and endothelial lineages and give rise to colonies of VSM cells only.