• generalized developmental arrest after E9.5

• no embryos survived beyond day E11

• the intersomitic arteries of the embryo also enlarge in E8.5- E9.0 embryos

• loss of alpha-Sma staining in arteries of these mice indicates a failure to recruit arterial smooth muscle cells

• narrowing of the branchial arteries was observed in E8.5 embryos

• narrowing of the rostral dorsal aorta was observed in E 8.5 embryos

• dilation occurred throughout the aorta just distal to the heart and extend to most caudal regions of the E8.5 embryo

• enlargement of adjacent cardinal veins and no evidence of ateriovenus shunts

• abnormal vascular dilation noted at E8.5

• vascular dilation was associated with an increased endothelial proliferation rate

• no difference in vascular apoptosis was observed

• cardiac development is normal prior to the development of vascular defects

• narrowing of the branchial arteries was observed in E8.5 embryos

• embryos retained a primitive yolk sac vascular network

• generalized developmental arrest after E9.5

• narrowing of the branchial arteries was observed in E8.5 embryos