Magp1 is not required for specifying or maintaining the expression of markers for vascular endothelium and smooth muscles. In situ hybridization was conducted to analyze the expression of vascular markers. Expression of flk1 in a wild-type embryo (A-B) and an magp1 MO–injected embryo (C-D) at 31 hours after fertilization. Cross-sections of panels B and D revealed normal expression levels of flk1 in the endothelium lining the dilated caudal vein of magp1 morphant embryos (frequency with dilated caudal vein: 68% ± 7%; N = 47). Expression of sm22a in a wild-type embryo (E-F) and an magp1 MO–injected embryo (G-H) at 31 hours after fertilization. Cross-sections of panels F and H revealed that magp1 morphant embryos displayed normal expression levels of sm22a surrounding the dilated caudal vein (frequency with dilated caudal vein: 78% ± 10%; N = 34). Arrows indicate the dilated caudal veins in magp1 morphant embryos. Lines in panels A, C, E, and G indicate levels of sections in panels B, D, F, and H, respectively. (A-H) Original magnifications, 10 ×.