Sox17 and Lung Progenitor Cell Figure 2. Prolonged expression of Sox17 results in formation of bronchiolar-like structures in the alveoli. Adult CCSPrtTA/tetO-Sox17 transgenic mice were maintained on Dox for 12 months. (A) H&E staining shows the presence of bronchiolar-like sheets of cells in the peripheral lung. Arrowhead indicates the pleural surface. (B–D) Immunostaining for Sox17 (B), Foxj1 (C), and CCSP (D) was performed on lung sections. The Sox17- induced bronchiolar-like structures contained cells expressing proximal airway markers CCSP and Foxj1. (E–H) Immunofluorescent staining for CCSP (E), proSP-C (F), and Sca-1 (G). The bronchiolar-like structures (dotted outline) contained cells that express Sca-1 and subsets of cells expressing CCSP or proSP-C. Arrowheads demark CCSP-expressing cells in the bronchiolar epithelium and the arrow indicates normal proSP-C expression in a type II cell. Nuclei are stained with DAPI (H; blue) Scale bars, 50 mm. doi:10.1371/journal.pone.0005711.g002 PLoS ONE | www.plosone.org 4 May 2009 | Volume 4 | Issue 5 | e5711