Foxm1 in Lung Tumors Figure 1. Conditional deletion of Foxm1 transcription factor in lung epithelial cells. A. Breeding strategy for conditional expression of rtTA in the respiratory epithelium to delete the Foxm1 floxed exons in vivo. Dox-induced expression of Cre-recombinase causes the deletion of exon 4–7 of Foxm1 gene (epFoxm12/2 mice). B–C. Specific expression of Cre in lung epithelium. Lungs from epFoxm12/2 and control Foxm1fl/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 epFoxm12/2 lungs. Cre recombinase was not detected in control Foxm1fl/fl lungs. D. Conditional expression of Cre in lung epithelial cells does not alter the lung morphology. Paraffin sections from Dox-treated epFoxm12/2 and control Foxm1fl/fl lungs were stained with hematoxylin and eosin (H&E). Normal lung alveoli and bronchi were observed in control Foxm1fl/fl and epFoxm12/2 mice. Magnifications: 6200 (B–C) and 650 (D). doi:10.1371/journal.pone.0006609.g001 PLoS ONE | www.plosone.org 3 August 2009 | Volume 4 | Issue 8 | e6609