Fig. 3. Deletion of Klf5 disrupts lung morphogenesis. (A-H) Lung sections were prepared from the fetus at E15.5 (A,B) and E18.5 (C-H), and were stained with a guinea pig anti-mouse KLF5 polyclonal antibody (A-F) or pancytokeratin (G,H), which outlined the epithelial cells. Nuclear staining of KLF5 was observed in epithelial cells lining the conducting and peripheral airways in control (A,C) and Klf5^/+ (E) mice. Staining was absent or decreased in Klf5^/ mice (B,D,F). Morphological changes in the lungs of Klf5^/ mice were not observed at E15.5 (A versus B). At E18.5, lung morphology was markedly perturbed in Klf5^/ mice (D,F,H), note the thickened walls of the mutant saccules, compared with Klf5^+/+ (C,G) and Klf5^/+ mice (E). Squamous epithelial cells (arrow) were rarely observed in the lungs of Klf5^/ mice (H), compared with controls (G). Scale bars: 50 µm.