Enhancer activity of the 5′ half of the first intron of the vecd gene in ES cell differentiation cultures. The first intron of the VECD gene was split into 4-kbp 5′ (5′ Int1) and 4.5-kbp 3′ (3′ Int1) fragments, and their enhancer activity was assessed by using the EGFP gene driven by 2.8-kbp 5′ flanking region of the VECD gene (VECDp). ES cell clones harboring VECDp-egfp, VECDp-5′ Int1-EGFP, or VECDp-3′ Int1-egfp were established and induced to differentiate into ECs. GFP expression in the cells in each culture were assessed after staining with anti-VECD mAb and were analyzed using FACS Vantage. Each panel represents the result of clones that showed the highest GFP expression level among each group.