(A through D) Histological analysis of E9.5 wild-type (A and C) and CBP homozygous (B and D) mutant embryos stained with anti-PECAM antibody and counter-stained with hematoxylin. Open neural tube (arrow in B), disoriented posterior branch of primary head vein (arrowheads in B), and decreased numbers of blood cells in dorsal aorta (da; stars in A and B) were observed in the head region of CBP homozygous mutant embryos. In the trunk, lack of sprouting vessels from the dorsal aorta or umbilical vein (uv) in parietal mesoderm (arrowheads in C) and a decrease in PECAM-1⁺endothelial cells in the omphalomesenteric artery (oa) and dorsal aorta (arrows in D) were observed in CBP homozygous mutant embryos. Note ectopic blood cells in hindgut diverticulum (hd) and coelomic cavity (cc) in CBP homozygous mutant embryos (stars in D). Scale bar indicates 50 μm.