Fig. 1.

Embryonic lung mesenchymal deletion of Apc induced ectopic activation of Wnt/Ctnnb1 signaling. a Induced Cre expression specifically in embryonic lung mesenchyme by a Tbx4 lung enhancer-driven Tet-On system was verified in an mT-mG reporter mouse lung (Tbx4-rtTA/TetO-Cre/mT-mG) one day after Dox administration (E10.5-E11.5). mG (green) was only expressed when upstream floxed-mT (red) was deleted by the induced Cre. b Lung specificity of Apc gene knockout at E11.5. Fetuses with different tail DNA genotypes were listed, and the heterozygous (lane 7) and homozygous (lane 8) deletions of floxed (fx)-exon 14 (ΔE14) were confirmed in lung tissue genomic DNAs. Leakage of Apc gene deletion in fetal lung was not detected in the absence of Dox induction (lane 9). c Truncation of Apc mRNA transcript in Apc conditional knockout lungs was verified by RT-PCR at E11.5. d Ectopic activation of Wnt/Ctnnb1 signaling in embryonic lung mesenchyme was detected by accumulated non-phospho (active) Ctnnb1 in both cytoplasm and nucleus of mesenchymal cells. Epithelial airway is highlighted with dashed line. e-f Increased Wnt canonical signaling activity in lung tissue was also verified by elevated Axin2 expression using real-time PCR (e; n = 5 in each group, *P < 0.05) and immunofluorescence staining (f)