Sox17 and Lung Progenitor Cell Figure 3. Sox17 induces proliferation of respiratory epithelial cells in the adult mouse lung. Immunohistochemistry was performed on lung sections from adult CCSPrtTA control (A–C; G–I) and CCSPrtTA/tetO-Sox17 (D–F; J–L) transgenic mice after treatment with Dox for 1, 3, and 5 days (d). (A–F) Immunostaining shows endogenous expression of Sox17 in endothelial cells and Sox17 transgene expression in bronchioles and alveolar type II cells (D–F). Hyperplastic cell clusters are evident by 5 d (arrow and inset, F). (G–L) Phospho-histone H3 immunostaining shows respiratory epithelial cell proliferation after 3 d of Dox treatment in Sox17 transgenic mice. Proliferative cells were detected in the peripheral lung (K–L; arrow and inset) and bronchioles (K–L; arrowhead). (M–O) Colocalization of Sox17 (M) and phospho-histone H3 (pHH3; N) is shown by dual-label immunofluorescence after 5 d Dox exposure. Nuclei are stained with DAPI (O; blue). Scale bars, 50 mm. doi:10.1371/journal.pone.0005711.g003 PLoS ONE | www.plosone.org 5 May 2009 | Volume 4 | Issue 5 | e5711