Figure 3.

Increased lung epithelial Yap signaling is responsible for basal cell expansion. (A,B) In control E18.5 fetuses, non-phosphorylated (nuclear, active) Yap is present in small clusters of distal lung cells (A) and phosphorylated (cytosolic, non-active) Yap is widely present (B). (C) In E18.5 TO lung, non-phosphorylated Yap is present more homogenously throughout the lung and can be detected more in nuclei than in control, with denser abundance of nuclear-Yap-containing cells round airways. (D) In TO lung, phosphorylated Yap is less abundant than in control lung. (E,F) PCR of lung homogenates showed increased levels of connective tissue growth factor (CTGF) (E) and p63 (F). Both are Yap target genes. Comparison is by Welch's t-test. (G) Mice with hemizygous deletion of lung epithelial cell Yap at baseline (n = 9) and after TO (n = 5) showed similar numbers of basal cells to wild-type (WT) mice. Lung epithelial cell-specific deletion of Yap without TO (n = 4) or with TO (n = 5) both had basal cell frequencies comparable to control hemizygous and WT mice. *p < 0.05, **p < 0.01 by Holm–Sidak post-hoc test. (H,I) Compared to wild-type (H), mice with conditional deletion of Yap from the lung epithelium (I) had reduced abundance of basal cells as assessed by nerve growth factor receptor (NGFR) immunohistochemistry. Scale bars, 500 and 100 μm. (A′), Magnified Image of A; (C′), Magnified Image of C; (H′), Magnified Image of H; (I′), Magnified Image of I.