EC-specific gene expression by VECDp-5′ Int1 in ES cell differentiation cultures. The same VECDp-5′ Int1-EGFP ES cell clone as that presented in Figure 2 was cultured on OP9 for inducing differentiation. Undifferentiated ES cells and cells harvested 4 or 7 days after the induction of differentiation were stained with anti-VECD mAb and analyzed by FACS Calibur.