Defective lymphatic sprouting in nrp2^+/−vegfr3^+/− mice. (A–C) Confocal images of LYVE-1–stained lymph vasculature in the dorsal trunk skin at P0. Note enlarged, poorly branched vessels in nrp2^+/−vegfr3^+/− (B) and nrp2^−/− (C) compared with wild type (A). Several lymphatic tips are present in wild type (A, arrows), none are present in nrp2^+/−vegfr3^+/− (B), and one is present in nrp2^−/− (C, arrow). (D–F) LYVE-1 (green)/phospho–histone H3 (red) DAPI (blue) staining of P0 skin; high magnification views of lymphatic tips are shown. Note filopodial-extending tips composed of several cells in wild type (D), whereas both nrp2^+/−vegfr3^+/− (E) and nrp2^−/− (F) show blunt-ended, enlarged tips devoid of filopodial extensions. (G and H) CD31 staining shows similar patterning of blood vasculature in the skin of mice with the indicated genotypes. A, arteries; V, veins. (I) Dorsal trunk skin at P0 in a nrp2^−/−vegfr3^+/− mouse. Note enlarged lymphatic vessel. (J) Quantification of lymphatic vessel branch points in mice of the indicated genotypes. (K) Replication of LECs. The number of phospho–histone H3 (PH3)-positive nuclei per millimeter squared of LYVE-1–positive vessels was counted. WT, wild type. Error bars indicate SEM. **, P < 0.01; ***, P < 0.001. Bars: (A–C) 200 µm; (D–F) 50 µm; (G–I) 200 µm.