(A–D) Confocal optics displaying individual nuclei of endothelial cells in the dorsal aorta (A,B stained with efnb2 antibody, the posterior cardinal vein and intersomitic vessels in wild-type embryos [Tg(fli:EGFP-nuc)] at 36 hpf (A) and 72 hpf (C),as compared to the increased endothelial nuclei in enlarged cardinal veins in smo mutants [smohi1640/smohi1640;Tg(fli:EGFP-nuc)] at 36 hpf (B) and 72 hpf (D). (E) Bar chart depicting number of arterial and venous cells in wild-type embryos compared to smo mutants. At 36 hpf, arterial cell number: 19.2± 1.7 (WT), 0 (smo); Venous cell number: 43.2±1.3 (WT), 60.3±2.4 (smo). At 72 hpf, arterial cell number: 20.2±1.3 (WT), 0 (smo); Venous cell number: 54±1.6 (WT), 66.8±3.4 (smo). Endothelial cells were counted from 12 lateral sections derived from 6 wild-type embryos and 6 smo mutants. Each section covers four segment lengths of intersomitic vessels along the dorsal aorta and the postertior cardinal vein in the middle trunk above the yolk extension region. a: aorta. v: vein.