title: Roles for β-catenin and doxycycline in the regulation of respiratory epithelial cell frequency and function.
abstract: The expression of β-catenin-dependent genes can be increased through the Cre recombinase (Cre)-mediated elimination of the exon 3-encoded sequence. This mutant β-catenin is termed DE3, and promotes the expression of β-catenin-dependent genes. Our previous study used the DE3 model to demonstrate that persistent β-catenin activity inhibited bronchiolar Clara-to-ciliated cell differentiation. The present study was designed to evaluate the roles of β-catenin in regulating the tracheal progenitor cell hierarchy. However, initial experiments demonstrated that the tetracycline-responsive element-Cre transgene (TRE-Cre) was active in the absence of a reverse tetracycline transactivator driver or inducer, doxycycline (Dox). This spurious TRE-Cre transgene activity was not detected using the ROSA26-floxed STOP-LacZ reporter. To determine if the phenotype was a consequence of genotype or treatment with Dox, tracheal and lung specimens were evaluated using quantitative histomorphometric techniques. Analyses of uninduced mice demonstrated a significant effect of genotype on tracheal epithelial cell mass, involving basal, Clara-like cell types. The bronchial and bronchiolar Clara cell mass was also decreased. Paradoxically, an effect on ciliated cell mass was not detected. Activation of the β-catenin reporter transgene TOPGal demonstrated that β-catenin-dependent gene expression led to the genotype-dependent tracheal and bronchiolar phenotype. Comparative analyses of wild-type or keratin 14-rtTA(+/0)/TRE-cre(+/0)/DE3(+/+) mice receiving standard or Dox chow demonstrated an effect of treatment with Dox on basal, Clara-like, and Clara cell masses. We discuss these results in terms of cautionary notes and with regard to alterations of progenitor cell hierarchies in response to low-level injury.
authors.affiliation: Department of Pediatrics, National Jewish Health, Denver, Colorado 80206, USA.
authors.forename: Russell W
authors.initials: RW
authors.lastname: Smith
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Hicks
authors.forename: Susan D
authors.initials: SD
authors.lastname: Reynolds
mesh_terms: D000483:Alleles; D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D004318:Doxycycline / Q000494:pharmacology*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D005838:Genotype; D019426:Integrases; D008297:Male; D051379:Mice; D010641:Phenotype; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D013752:Tetracycline / Q000494:pharmacology; D014132:Trachea / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D015534:Trans-Activators / Q000494:pharmacology; D019076:Transgenes / Q000187:drug effects / Q000235:genetics; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D015534:Trans-Activators; D051176:beta Catenin; C045073:Cre recombinase; D019426:Integrases; D013752:Tetracycline; D004318:Doxycycline