Rasip1^−/− mice form vascular lumen with evidence of localized collapse. Transverse sections of DAs from Rasip1^+/− (A-D,I) and Rasip1^−/− (E-H,J) embryos at the indicated somite stage were stained with CD31+CD105 (red) and DAPI (blue). Note that panels C-D,G-H are from adjacent sections, indicating localized collapse of the aorta in Rasip1^−/− embryos. In panel J, note that the left DA collapsed, whereas the right DA was inflated. Scatter plots of DA lumenal areas from serial sections from Rasip1^+/− (HET) and Rasip1^−/− (KO) embryos at 3 to 6 ss (K) and 7 to 10 ss (L). The 20-μm² cutoff line (red) indicates functional blood vessel (or DA) area. Rasip1^−/− DAs display a wider variation of lumenal areas. Each point represents an individual area measurement of a DA section. Scale bars: (A,E) 20 μm; (B-D,F-H) 10 μm; (I-J) 25 μm.