Podoplanin is required in nonhematopoietic cells for blood-lymphatic separation. (A-H) Pdpn^−/− animals exhibit vascular mixing phenotypes identical to those of Slp-76^−/− animals. (A-B) Development of blood-filled lymph sacs in E11.5 Pdpn^−/− embryos. (C-D) Blood-filled cutaneous lymphatics are visible in E14.5 Pdpn^−/− embryos. (E-F) Blood-filled mesenteric lymphatics in Pdpn^−/− neonatal animals (arrows) are shown. (G-H) Histologic evidence of intestinal edema in neonatal animals (double arrows) is shown. Immunostaining for LYVE-1⁺ lymphatic endothelium is shown (A-B,G-H). CV indicates cardinal vein; and LS, lymph sac. (I-K) Blood-filled mesenteric lymphatic vessels arise in lethally irradiated wild-type mice after reconstitution with Slp-76^−/− (K) but not wild-type (I) or Pdpn^−/− (J) donor hematopoietic cells. A indicates artery; V, vein; and L, lymphatic. (L-N) PDPN-Fc fusion protein selectively binds platelets in whole blood. Binding of PDPN-Fc to anuclear platelets vs nucleated blood cells is shown with the use of forward and side scatter (FSC and SSC) on a log scale to discriminate the 2 cell populations (L; gated cell populations are indicated by purple boxes). All PDPN-bound cells express the platelet-specific integrin CD41 (M-N).