P-Sp of E9.5 VEGFR-3–deficient embryos and wild-type littermates were cultured on OP9 cells for 10 days. Nonadherent cells were then assayed for hematopoietic colonies in a methylcellulose medium. The number of hematopoietic colonies were scored after 7 days of culture. Total cell numbers of colonies (>40 cells) per one explant were obtained from 3 independent experiments and expressed as the means ± SEM (n = 4). Methylcellulose culture was performed in the presence of IL-3 (200 U/mL), stem cell factor (50 ng/mL), and EPO (2 U/mL).