Fig. 5. Expression of Sox9 in normal, transgenic and conditional mutant lungs. (A,C,E) Immunohistochemistry for Sox9 in wild-type lungs. Note high expression of Sox9 in undifferentiated distal epithelial cells at E14.5 and E16.5, and downregulation in alveolar epithelium at E18.5 (E,G). In cre(+);Nmyc^flox/flox lungs at E14.5 and E16.5, the number of Sox9-positive cells is greatly reduced (B,D). By contrast, there are numerous Sox9-positive epithelial cells, including small clusters (arrowheads), in the E18.5 Sftpc-NmycEGFP lung (F). (G,H) Double immunohistochemistry for Sox9 and Scgb1a1. Note the sharp junction between proximal and distal domains (arrowhead in G), and low Sox9 expression, in wild-type lung. In transgenic lung (H), note the absence of a clear boundary and the high Sox9 expression, even in bronchiolar regions (br) where Scgb1a1 is expressed. DAPI staining marks nuclei. Scale bars: 50 µm.