Overexpression of Nr2f1b under the fli promoter increases the number of venous cells and endothelial cells per ISV. a-b The number of vein cells was counted in the region beneath ISV 5-15 from 14 wild type or 10 Tg(fli1a:nr2f1b) transient transgenic, overexpressing embryos. The artery is marked by a red bracket, and the vein by a blue bracket. c Uninjected control embryos have 82.5 (± 11.5) cells per vein segment while fli:nr2f1b over-expressing embryos had 100.3 (± 17.7) cells (p = 0.0068; unpaired t-test). d-f The number of cells forming each ISV were determined in wild type control (d) and fli1a: nr2f1b overexpressing embryos (e) at 30 hpf. f The average cells of wild type control is 3.8 ± 0.7 (ISV n = 86) and the average cells of fli:nr2f1b over-expressing embryos is 4.3 ± 0.9 (ISV n = 88). ***refers to p < 0.0005 by an unpaired student's t-test and graphic error bars represent 1 SEM.. Scale bars in a, b, d, e represent 50 μm.