Abnormal lymphatic development in double-heterozygous nrp2^+/−vegfr3^+/− mice. (A) X-gal staining (blue) of E13.5 vegfr3^+/− (left) and double-heterozygous nrp2^+/−vegfr3^+/− (right) littermate embryos. (B) expression levels of lymphatic marker genes as measured by quantitative PCR in RNA isolated from hearts of wild-type and double-heterozygote nrp2^+/−vegfr2^+/− and nrp2^+/−vegfr3^+/− mice. Values significantly different from wild-type mice (*, P > 0.05; **, P > 0.001) by Student’s t test are shown. Error bars indicate SEM. (C and D) Higher magnification of heads of embryos shown in A. Note numerous lymphatic vessel sprouts in vegfr3^+/− (black arrows) and fewer enlarged lymph vessel sprouts in nrp2^+/−vegfr3^+/− (red arrows). e, eye; *, ear. (E and F) Transverse section through the neck of E13.5 embryos double stained with X-gal (blue) and CD-31 (brown). Note similar development of CD-31–positive arteries, veins, and skin capillaries (arrowheads) in vegfr3^+/− (E) and nrp2^+/−vegfr3^+/− (F). Note enlarged jugular lymph sacs (asterisks) in nrp2^+/−vegfr3^+/− (F) compared with vegfr3^+/− (E). Lymph vessels sprouting from the lymph sac toward the skin are less numerous in nrp2^+/−vegfr3^+/− compared with vegfr3^+/− (arrows). A, arteries; V, veins; NT, neural tube; Vt, vertebra. Bars: (A) 1.4 mm; (C and D) 0.8 mm; (E and F) 150 µm.