Ultrastructural analysis of Clec-2^−/−, Pdpn^fl/flPGK-Cre, and Pdpn^fl/flNes-Cre microvessels at E11.5 by electron microscopy. In wild-type embryos (^+/+, includes Pdpn^fl/fl littermates; n = 4), endothelial cells enclose a vascular lumen containing a nucleated fetal erythrocyte and are connected by tight junctions (yellow arrowheads). The endothelium is closely associated with surrounding pericyte foot processes and neuro-epithelial cells. In Clec-2^−/− (n = 3), Pdpn^fl/flPGK-Cre (n = 4), and Pdpn^fl/flNes-Cre (n = 4) microvessels, vascular lumens appear expanded, and their surrounding endothelium is enriched in vacuoles. Inter-endothelial junctions remain tightly closed and secured by endothelial cell flaps (yellow arrowheads). Large gaps between the endothelium and overlying pericytes and neuro-epithelial cells are noticeable. NE, neuro-epithelial cell; BV, blood vessel; RBC, nucleated red blood cell; P, pericyte; E, endothelial cell. Original magnification: (left) ×7500; (right) ×15 000. Scale bar, 5 μm.