histone H3 (pHH3) was performed on lung sections from adult CCSPrtTA control (n = 3) and CCSPrtTA/tetO-Sox17 (n = 3) mice maintained on Dox for 3 days. Total positive cells were quantified from 21 random fields for morphometric analysis. The average number of pHH3-positive cells per field was increased 4.74-fold in lungs from CCSPrtTA/tetO-Sox17 mice relative to controls. Asterisk indicates statistical significance determined by Student’s t-test (p,0.05). (B) Dual immunofluorescence for Sox17 and pHH3 was performed on lung sections from adult CCSPrtTA/tetO-Sox17 mice maintained on Dox for 3 and 5 days and positive stained cells were quantified from 20 random fields. Phospho-histone H3 was coexpressed in 28% of the Sox17-expressing respiratory epithelial cells. Found at: doi:10.1371/journal.pone.0005711.s001 (0.18 MB TIF) Figure S2 A rare subset of Sox17-induced Sca-1 positive cells coexpress phospho-histone H3. Dual-label immunofluorescence for phospho-histone H3 (pHH3; A) and Sca-1 (B) was performed on lung sections from adult CCSPrtTA/tetO-Sox17 mice maintained on Dox for 5 days. A rare subset of pHH3-positive cells (arrow) colocalized with the Sca-1-expressing cells induced by Sox17 (arrow and arrowhead; B). Nuclei are stained with DAPI. Scale bar, 20 mm. References 1. Wilson M, Koopman P (2002) Matching SOX: partner proteins and co-factors of the SOX family of transcriptional regulators. Curr Opin Genet Dev 12: 441–446. 2. Alexander J, Stainier DY (1999) A molecular pathway leading to endoderm formation in zebrafish. Curr Biol 9: 1147–1157. 3. Clements D, Woodland HR (2000) Changes in embryonic cell fate produced by expression of an endodermal transcription factor, Xsox17. Mech Dev 99: 65–70. 4. Hudson C, Clements D, Friday RV, Stott D, Woodland HR (1997) Xsox17alpha and -beta mediate endoderm formation in Xenopus. Cell 91: 397–405. 5. 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Mol Endocrinol 15: 353–362. PLoS ONE | www.plosone.org 13 May 2009 | Volume 4 | Issue 5 | e5711