Conditional deletion of Foxm1 transcription factor in lung epithelial cells.

<p>A. Breeding strategy for conditional expression of rtTA in the respiratory epithelium to delete the <i>Foxm1</i> floxed exons <i>in vivo</i>. Dox-induced expression of Cre-recombinase causes the deletion of exon 4–7 of Foxm1 gene (<i>epFoxm1^−/−</i> mice). B–C. Specific expression of Cre in lung epithelium. Lungs from <i>epFoxm1^−/−</i> and control <i>Foxm1</i>^fl/fl mice, that were given Dox in water for 4 weeks, were fixed, paraffin-embedded, sectioned, and stained with Cre antibody (dark brown nuclei) and then counterstained with nuclear fast red (red nuclei). Cre expression was observed in type II lung epithelial cells (B) and Clara cells (C), but not in mesenchymal cells of Dox-treated <i>epFoxm1^−/−</i> lungs. Cre recombinase was not detected in control <i>Foxm1^fl/fl</i> lungs. D. Conditional expression of Cre in lung epithelial cells does not alter the lung morphology. Paraffin sections from Dox-treated <i>epFoxm1^−/−</i> and control <i>Foxm1^fl/fl</i> lungs were stained with hematoxylin and eosin (H&E). Normal lung alveoli and bronchi were observed in control <i>Foxm1</i>^fl/fl and <i>epFoxm1^−/−</i> mice. Magnifications: ×200 (B–C) and ×50 (D).