Distinct and redundant functions of Esam and VE-cadherin during vascular morphogenesis

The cardiovascular system forms during early embryogenesis and adapts to embryonic growth by sprouting angiogenesis and vascular remodeling. These processes require fine-tuning of cell-cell adhesion to maintain and reestablish endothelial contacts, while allowing cell motility. We have compared the contribution of two endothelial cell specific adhesion proteins - VE-cadherin (VE-cad/Cdh5) and Esama (Endothelial cell-selective adhesion molecule a) - during angiogenic sprouting and blood vessel fusion (anastomosis) in the zebrafish embryo by genetic analyses. Different combinations of mutant alleles can be placed into a phenotypic series with increasing defects in filopodial contact formation. Contact formation in esama mutants appear wild-type like, while esama(-/-); ve-cad(+/-)and ve-cad single mutants exhibit intermediate phenotypes. The lack of both proteins interrupts filopodial interaction completely. Furthermore, double mutants do not form a stable endothelial monolayer, display intrajunctional gaps, dislocalization of Zo-1 and defects in apical-basal polarization. In summary, VE-cadherin and Esama have distinct and redundant functions during blood vessel morphogenesis and both adhesion proteins are central to endothelial cell recognition during anastomosis.