Proximal-hCD4 expression marks hemogenic endothelium. (A) FACS analyses of proximal-hCD4, distal-GFP, c-Kit, Tie2, CD34, and CD41 expression in blast colonies day 1 and day 2. (B; Left) FACS analysis of proximal-hCD4 and CD41/distal-GFP expression in populations P1 to P3 sorted from c-Kit+ fraction of day 2 blast culture. (Right) CD41 expression in populations P1 to P3 cultured for 24 hours after sorting in hemogenic endothelium media. (C) FACS analysis of Flk-1 and proximal-hCD4 expression in single neural plate (NP) and head fold (HF) embryos. (D) FACS analysis of proximal-hCD4, distal-GFP, c-Kit, and Tie2 expression in representative HF embryo. (E) FACS analysis of proximal-hCD4 and CD41 expression in single embryos. (F) FACS analysis of CD41 and distal-GFP expression in representative single HF embryo and in yolk sacs from embryos between 5 and 20 sp stages. Numbers indicate percentages of respective populations.