Phenotypic changes in embryos lacking endothelial survivin. (A-B) E9.5 embryos were whole-mount stained for CD31 expression, revealing vascular patterning in head and brain. Arborization of vessels was largely intact in both genotypes, but in the tie1-cre/survivin^lox/lox embryos (−/−), vessels were more dilated, often with a “cut-off” appearance (arrow). (C-H) Transverse histologic sections of E10.5 embryos. (C-D) Compared with survivin^lox/lox embryos (+/+), those lacking endothelial survivin (−/−) exhibit notably less intense antithrombomodulin antibody (endothelial-specific) staining of the cardinal vein (cv), which had a discontinuous endothelial border, and was dilated (border shown with red dashed line), congested with blood, and “leaking” nucleated red blood cells into the amniotic space (arrows). da indicates dorsal aorta. (E-F) Higher-power view of transverse section of E10.5 embryos reveal that the cardinal vein endothelium of tie1-cre/survivin^lox/lox embryos is strongly TUNEL positive. (G-H) Prox-1 staining reveals the presence of lymphatic endothelial cells (arrows) emanating from cardinal veins (cv) in both genotypes. Magnifications were the same for paired panels A-B, C-D, E-F, and G-H.