Initial events of vasculogenesis including the formation of nascent endothelial tubes are not dependent on VE-cadherin activity. (A-D) Confocal images of PECAM-immunolabeled 7.8-dpc allantoides cultured for 18 hours. (A-B) Cultured allantoides that were either untreated (A) or treated with BV13 monoclonal antibody (24 μg IgG/mL; B) for 18 hours. (C) An allantois that was exposed to BV13 for the first 9 hours of culture and then cultured for 9 hours in the absence of BV13. (D) An allantois that was cultured in the absence of BV13 for 9 hours and then cultured for 9 hours in the presence of BV13. Comparison of panels A and C demonstrates that the presence of the BV13 antibody had no discernible effect on de novo blood vessel formation. In contrast, following BV13 treatment, the blood vessels formed in the first 9 hours of culture (C) disassemble, forming disconnected clusters of PECAM⁺ cells (D). Bars equal 100 μm.