S1PR1 regulates dermal LV development in a VEGFR3-independent manner. The dorsal skin of E16.5 embryos was dissected and analyzed by whole-mount IHC with anti-PROX1 antibody. The developing LVs were identified by the presence of PROX1^hi clusters (arrowheads). Statistics: n = 5 for control embryos; n = 4 for each mutant genotype, respectively. Each dot represents one animal on the graph. The graphs were plotted as mean ± SD. One-way ANOVA was performed for the statistical analysis. ***P < 0.001; ****P < 0.0001.