EC-specific disruption of Smad2 and Smad3 results in embryonic lethality around E12.5. (A) Genotype analysis of offspring. The exact numbers of the embryos are shown in supplemental Table 1. PN indicates postnatal mice; S2, Smad2; and S3, Smad3. (B) Gross morphology of Smad2^fl/fl;Smad3^+/−;Tie2-Cre (left panel) and EC-Smad2/3KO embryos (right panel) at E10.5. (C-E) Gross morphology of control and EC-Smad2/3KO embryos at E11.5. In panel C, vitelline vessels are clearly visible in the yolk sacs of both the control (left panel) and the EC-Smad2/3KO embryos (right panel), although no blood is detected in the EC-Smad2/3KO embryo. In panel D, embryos lacking both Smad2 and Smad3 exhibit evidence of vasodilatation and diffuse bleeding in the head, trunk, and intersomitic regions. (E) High magnitude view around the umbilical cords reveals avascularity in the EC-Smad2/3KO embryos (right panel). (F) Transverse sections of control and EC-Smad2/3KO embryos at E11.5. EC-Smad2/3KO embryos were sliced at the positions indicated by broken lines of arrows. The sections were then stained with H&E to show profuse bleeding in the ventricles of the brain and the neural tube of EC-Smad2/3KO embryos. In current study, all embryos whose genotype is Smad2^fl/fl;Smad3^−/−;Tie2-Cre show severe hemorrhage at E11.5.