Mouse lungs were inflated and fixed in 2% paraformaldehyde, dehydrated in a series of increasing ethanol concentration washes, embedded in paraffin and sectioned. Antibodies used were anti-SM22α (goat anti-SM22α 1:200 Abcam), GFP (goat anti-GFP 1:100 Abcam, rabbit anti-GFP 1:100 Molecular Probe), Scgb1a1 (goat anti-Scgb1a1 1:20 Santa Cruz), SPC (rabbit-anti SPC 1:500 Chemicon), Pdgfrα (rabbit anti-Pdgfrα 1:50 Cell Signaling), Pdgfrβ (rabbit anti-Pdgfrβ 1:100 Cell Signaling), vimentin (rabbit anti-vimentin 1:100 Santa Crux), collagen type1 (rabbit anti-Col1 1:500 Abcam), Ki67 (rabbit anti-Ki67 1:50 Abcam), PCNA (mouse anti-PCNA 1:50 Biocare), PO4-Histone H3 (mouse anti-PO4-Histone H3 1:200 Cell Signaling), TubbIV (mouse anti-TubbIV 1:20 Biogenex), S100A4 (rabbit anti-S100A4 1:200 Abcam). LacZ staining of lungs was performed as previously described8 (link). The slide was imaged on a Zeiss LSM 710 confocal microscope and analyzed in ImageJ software.