The morphology and phenotype of transgenic lungs. (a) Control E18.5 lung and (b) transgenic lung, with normal-appearing tracheae and lobulation pattern. Sections of (c) wild-type lung, and (d,e) two transgenic lungs, after staining with hematoxylin and eosin. Expression of the transgene is detected by in situ hybridization with a probe for rabbit β-globin intron in (f) wild-type and (g) transgenic lung. Cell proliferation was assayed by immunostaining for incorporated 5-bromo-2-deoxyuridine (BrdU) in (h) control and (i) transgenic lung. The insets show typical bronchiolar epithelium. Quantitation showed a 10-fold higher ratio of labeled to unlabeled nuclei in the transgenic embryos (see Additional data file 1, Figure S2). Thin sections (500 nm) of (j) control and (k) transgenic lung, after staining with ethylene blue, reveal a uniform, cuboidal/columnar epithelium in the transgenic sample. Electron microscopy shows the ultrastructural morphology of (l) wild-type lung shows typical alveolar type II cells, secreted surfactant protein (SP) and a red blood cell in a capillary (RBC). (m) Transgenic lung shows cuboidal cells with microvilli (M) and stored glycogen (G). Scale bar, 200 μm (c,d,e); 50 μm (f-i). 20 μm (j,k); magnification in the original films is 3,200×.