Distinct roles of ALK1 and VEGFR3 during lymphatic development. (A top) Analysis of lymphatic development in P4 pups after treatment with ALK1Fc (10 mg/kg, P2), VEGFR3Fc (1 mg/kg, P1), or combined ALK1Fc and VEGFR3Fc. Lymphatic development is visualized by LYVE1 staining (red), inset shows a greater magnification image of the honeycomb structure that is disrupted by the treatments. Scale bar represents 500 μm. (Middle) Analysis of podoplanin (green) and LYVE1 (red) expression after ALK1Fc, VEGFR3Fc, or combination treatments. Scale bar represents 250 μm. (Bottom) Analysis of LYVE1 (green) and active Caspase3 (red) expression after ALK1Fc, VEGFR3Fc, and combination treatment. Scale bar represents 250 μm. (B) Analysis of lymphatic development in P8 pups after ALK1Fc (10 mg/kg, P3 and P5), VEGFR3Fc (10 mg/kg, P6 or P7), or combined ALK1Fc and VEGFR3Fc treatment. Lymphatic development is visualized by LYVE1 staining (red). Scale bar represents 250 μm.