Fig. 5. The effect of endoglin deletion on in vitro vascular sprout formation in differentiating EBs. (A) FACS analyses of day 6 Eng^+/+ and Eng^-/- EBs for VE-cadherin/FLK-1 (top) and VE-cadherin/TIE-2 (bottom). Fluorescence intensity for VE-cadherin is indicated on the y axis and for FLK-1 or TIE-2 on the x axis. (B) Percentage of EBs in each of the four classes of vascular sprout development in Eng^+/+, Eng^+/- and Eng^-/- ES cells. Categories: I, no sprout formation; II, few sprouts; III, many sprouts but no network; and IV, many sprouts with network. Error bars indicate standard deviations from two independent experiments performed in duplicate. ^*, P<0.0001 versus controls (+/+ and +/-) on category IV. (C) Morphologic aspect of sprouting in Eng^+/- (upper panels) and Eng^-/- (lower panels) EBs.