Activity of VECDp-5′ Int1 in hematopoietic cell differentiation. (A) ES cells were cultured on OP9 for 7 days to induce ECs. Activity of VECDp-5′ Int1 in hemogenic ECs was tested by culturing GFP⁺CD31⁺VECD⁺CD45^- cells on OP9 under appropriate culture conditions for inducing hematopoietic cell lineages. Gr1⁺ granulocytes, Mac1⁺ monocytes, and CD19⁺B220⁺ B lymphocytes were induced from GFP⁺ population, indicating that VECDp-5′ Int1 was active also in hemogenic ECs. GFP expression could not be detected in hematopoietic cell lineages in this culture. (B) GFP expression was measured in the neonatal spleen cells from VECDp-5′ Int1-EGFP transgenic mice after staining with anti-CD45 mAb or anti-VECD mAb. All VECD⁺ cells expressed a high level of GFP. A dull GFP expression was also detected in a low proportion of CD45⁺ cells.