VCAM1 and VE-cadherin expression in control and Snai1-cko allantois explants. (a-d) VCAM1-immunostained allantois explants derived from littermate control (a, b) and Snai1-cko (c, d) embryos plated on fibronectin. (b) Higher magnification of a control explant showing that VCAM positive cells are more abundant in the periphery of the explant. In Snai1-cko mutant explants, fewer VCAM1-positive cells are observed, but these cells also tend to localize to the periphery of the explant. (e, f) VE-cadherin-immunostained allantois explants derived from E8.5 control (e) and Snai1-cko (f) embryos. Scale bar (a, c-f): 100 μm, (b) 50 μm.