β-Catenin Is Not Necessary for Maintenance or Repair of the Bronchiolar Epithelium

Signaling by Wnt/beta-catenin regulates self-renewal of tissue stem cells in the gut and, when activated in the embryonic bronchiolar epithelium, leads to stem cell expansion. We have used transgenic and cell type-specific knockout strategies to determine roles for beta-catenin-regulated gene expression in normal maintenance and repair of the bronchiolar epithelium. Analysis of TOPGal transgene activity detected beta-catenin signaling in the steady-state and repairing bronchiolar epithelium. However, the broad distribution and phenotype of signaling cells precluded establishment of a clear role for beta-catenin in the normal or repairing state. Necessity of beta-catenin signaling was tested through Cre-mediated deletion of Catnb exons 2-6 in airway epithelial cells. Functional knockout of beta-catenin had no impact on expression of Clara cell differentiation markers, mitotic index, or sensitivity of these cells to the Clara cell-specific toxicant, naphthalene. Repair of the naphthalene-injured airway proceeded with establishment of focal regions of beta-catenin-null epithelium. The size of regenerative epithelial units, mitotic index, and restoration of the ciliated cell population did not vary between wild-type and genetically modified mice. Thus, beta-catenin was not necessary for maintenance or efficient repair of the bronchiolar epithelium.