Pdpn on LECs partners with platelet Clec-2 for lung development. (A) Pdpn expression (green) in wild-type and AEC-, luMC-, and LEC-specific Pdpn-deficient lungs (Shh-EGFPCre, Wt1-EGFPCre, and Tie2-Cre, respectively). Lyve-1 (magenta) and DAPI (blue) were co-stained with Pdpn to visualize lymphatic vessels and nuclei. (B) Neonatal lethality in tissue-specific Pdpn-deficient mice. *P = .0000, Fisher’s exact test. (C) Ventral views of E17.5 whole lung. (D) Immunostaining of α-SMA (green) and DAPI (blue) in E17.5 distal lung. (E) Quantification of α-SMA expression in E17.5 distal lung. The asterisk indicates the group in which α-SMA expression was significantly lower than that in the other 3 groups; mean ± SD, n = 3 each. *P < .0001, Holm-Sidak test. (F) Whole-mount immunohistochemistry of Wt1 (magenta) or GFP (magenta) and Pdpn (green) in luMCs. GFP staining was performed only in Wt1-EGFPCre, Pdpn^fl/fl luMCs because this strain is heterozygous for the Wt1 gene, and therefore the intensity of Wt1 staining in these mice was indistinct from that in other strains. Pdpn was not detected in Wt1-EGFPCre, Pdpn^fl/fl luMCs, as Pdpn was deleted by Wt1-EGFPCre. A, artery; AL, alveolar sac; BR, bronchiole; LV, lymphatic vessel; M, lung mesothelium. Scale bars: 25 μm (A, D, and F); 1 mm (C).