Figure 5.

7.5-dpc flk-1^−/− embryos contain hematopoietic progenitors. 7.5-dpc embryos (resulting from flk-1^+/− × +/− matings) were treated with 0.25% collagenase/20% FCS, and cells were then plated in 1% methylcellulose in the presence of insulin (10 ng/ml), erythropoietin (2 units/ml), KL (100 ng/ml), IL-1 (650 units/ml), IL-3 (100 units/ml), granulocyte—macrophage CSF (50 units/ml) and macrophage CSF (100 units/ml) as described. Embryos were genotyped by Southern blot analysis of cultured ectoplacental cone and trophoblast cells (ref. 3; data not shown). Colonies were scored after 7 and 10 days of incubation. Mix, mixed colony; Ery, erythroid colony; M, myeloid/macrophage colony. Results from total eight embryos that are +/+ or +/− and four embryos that are −/− are shown.