TAK1 is important for vascular development independent of suppression of TNF-induced cell death. (A) Percentages of viable TAK1^ecko, TAB1^ecko, and TAB2^ecko embryos in a wild-type or Tnfr1^−/− background are shown. PN indicates postnatal. (B-C) Whole-mount PECAM-1 staining of control TNFR1^−/− (Tak1^flox/floxTnfr1^−/−) and TAK1^ecko TNFR1^−/− (Tie2-Cre Tak1^flox/floxTnfr1^−/−) embryos at E11.5 (B) and yolk sacs at E12.5 (C). Photos show representative specimens from 5 embryos. Vessel lengths, branch points, and the number of sprouts were determined in 3 randomly chosen areas from 3 different yolk sacs (graphs). Sprouts were defined as endothelial protrusions from the vascular loops that did not branch or fuse with other vessels. Data are shown as means ± SD (n = 3). Scale bar indicates 200 μm in embryos, 80 μm in yolk sacs. **P < .01; *P < .05.