Vascular abnormality in EC-Smad2/3KO embryos at E10.5. (A) Staining of whole embryos at E10.5 with anti–PECAM-1 antibody. The left and right panels show Smad2fl/fl;Smad3+/−;Tie2-Cre and EC-Smad2/3KO embryos, respectively. (B) Staining of yolk sacs at E10.5 with anti–PECAM-1 antibody. The left and right panels show Smad2fl/fl;Smad3+/−;Tie2-Cre and EC-Smad2/3KO embryos, respectively. (C) Transverse sections of embryos at E10.5 including the heart were stained with H&E. DA indicates dorsal aorta; and ACV, anterior cardinal vein. (D) Transverse sections of aortae from E10.5 embryos stained with anti–PECAM-1 (green) and anti-αSMA (red) antibodies. The coverage of ECs with SMCs is shown in yellow. (E) Whole-head staining of embryos at E10.5 with anti–PECAM-1 (green) and antidesmin antibodies (red).