Hemangioblasts derived from scl^RER/RER ES cells produce hematopoietic cells. (A) Steps involved in the BL-CFC colony assay. MeC indicates methylcellulose. (B) Representative blast colonies from wild-type (scl^Wt/Wt) and mutant (scl^RER/RER) EB cells (left and right) and secondary EB from scl^−/− cells (middle; original magnification, ×200). (C) Frequency of blast colonies (Blast), transitional colonies (Trans), and secondary EBs (EBs) in scl^Wt/Wt, scl^−/−, and scl^RER/RER cultures. Error bars indicate plus or minus 1 SD from 5 independent experiments. (D) When replated on Matrigel-coated wells, blast colonies gave rise to hematopoietic (cells in suspension) and endothelial (adherent cells) compartments (left and right). In contrast, the scl^−/− EBs only gave rise to adherent cells and a core of cells (middle; original magnification, ×100). (E) The hematopoietic cells shown in panel D (left and right) were replated in methylcellulose. Primitive erythroid (Pery; original magnification, ×200) and myeloid (original magnification, ×40) colonies were observed.