Clec1b deficiency results in absence of adMYFs, but not defective differentiation of other lung cell types, surfactant secretion, and pulmonary edema. (A) Expression pattern of cell-type-specific markers in E17.5 lung. Lung sections of Clec1b^+/+ and Clec1b^−/− fetuses were stained for markers of AEC1s (aquaporin-5 [Aqp5] and podoplanin [Pdpn]), AEC2s (prosurfactant protein C [ProSPC]), Clara cells (CC10), vascular endothelial cells (CD34), and LECs (Prox1 and Lyve-1) and with DAPI (blue). (B) Transmission electron microscopy images of lamellar bodies in AEC2s (open arrowheads) and secreted surfactants (black arrowheads). (C) Lung wet/dry (W/D) ratio in Clec1b^+/+ and Clec1b^−/− neonates; mean ± SD, n = 7 and 5, Student t test. N.S., not significant. (D) Immunostaining of α-SMA (green) and DAPI (blue) in E16.5/E17.5 distal lung. Arrowheads: bronchial smooth muscle cells, which are not adMYFs. (E) Quantification of α-SMA expression in E17.5 distal lung. α-SMA staining intensity was measured from the lung surface to a depth of 75 μm, as described in the supplemental Materials; mean ± SD, n = 3 each. *P = .0486, **P = .0053, Holm-Sidak test. AL, alveolar sac; BR, bronchiole; LV, lymphatic vessel; M, lung mesothelium; V, vein. Scale bars: 25 μm (A,D); 2 μm (B).