Vascular defects in Snai1-cko embryos. (a-d) PECAM-1 immunostained E8.5 littermate control (a) and Snai1-cko (b-d) embryos. (d) Higher magnification view of the dorsal region of a different embryo showing endothelial cell aggregates (arrow). (e, f) VE-cadherin immunostained E8.5 control (e) and Snai1-cko (f) embryos. Asterisks indicate discontinuous vessels, and arrows point to isolated aggregates of PECAM-1 positive cells.