Endothelial-specific TAK1 deficiency impairs vascular development. (A) Whole-mount colorimetric PECAM-1 staining of control (Tak1^flox/flox) and TAK1^ecko (Tie2-Cre Tak1^flox/flox) embryos at E10.5 (color images). Pictures are representative of 6 independent litters (n = 10). Black arrow indicates truncated vessel. Whole-mount fluorescent PECAM-1 staining of control (Tak1^flox/flox) and TAK1^ecko (Tie2-Cre Tak1^flox/flox) are also shown (black and white images). Areas indicated in lower-magnification images are shown at a higher magnification. Arrows indicate sprouting vessels. Scale bar indicates 200 μm. (B) Whole-mount PECAM-1 staining of control (Tak1^flox/flox) and TAK1^ecko (Tie2-Cre Tak1^flox/flox) yolk sacs at E10.5. Vessel lengths and branch points were determined in 3 randomly chosen areas from 3 different yolk sacs (graphs). Data are shown as means ± SD (n = 3). ***P < .001; **P < .01.