Defective lymphatic valve formation in Bmp9-KO embryos and neonates. (A) WT P0 lymphatic mesenteric collecting vessels were stained for Prox1 (green) and CD31 (red) to allow the discrimination between the different valve maturation stages; arrows point to the valve location; bars, 100 µm. (B-D) Quantitative analysis of valve formation at E18.5, P0, and P4 in WT and Bmp9-KO mice. Values correspond to the number of valves counted on 4 collecting vessels per mesentery; n = 6 (Bmp9-KO) or n = 7 (WT) at E18.5; n = 8 (Bmp9-KO) or n = 9 (WT) at P0; n = 12 (Bmp9-KO) or n = 11 (WT) at P4. ns, not significant. **P ≤ .01, ***P ≤ .001, significantly different from WT pups by unpaired Student t test.