Fig. 1. Defects in lung lobation and maturation in Foxf1^+/- embryos. (A,B) Ventral views of lungs from E18.5 wild-type and Foxf1^+/- fetuses. The mutant lungs (A) are small, pale and have hemorrhagic lesions along the edges (arrowhead). The accessory lobe of the right lung is missing and the remaining lobes are partially fused. (C-F) Hematoxylin and Eosin staining of transversal sections from E18.5 Foxf1^+/- (C,E) and wild-type (D,F) lungs. Low magnification view (C,D) shows the smaller size and denser appearance of the mutant lung. Higher magnification (E,F) reveals that the lax alveolar structure of the wild-type lung is replaced by compact mesenchyme in the Foxf1 mutant. (G-N) Differentiation of epithelial and mesenchymal cells in E18.5 Foxf1^+/- (G,H,K,L) and wild-type (I,J,M,N) lungs. In situ hybridization with probes for Utg (G,I), a marker for Clara cells of the proximal, bronchiolar epithelium, and Sftpc (H,J) expressed in the distal respiratory epithelium. Immunostaining of an endothelial cell marker (K,M; Pecam) and detection of vascular smooth muscle cells by in situ hybridization with a probe for Actvs (L,N). Ac, accessory lobe; Ar, arteriole; Br, bronchiole; Ca, caudal lobe; Cr, cranial lobe; LL, left lung; Me, medial lobe; RL, right lung.