Fig. 3. Normal distal and proximal differentiation in E18.5 Fgf9-/- lungs. (A-D) Toluidine Blue stained plastic sections of control (A,C) and Fgf9-/- (B,D) lungs showing normal differentiation of distal (A,B) and proximal (C,D) epithelium. (A,B) Sections of control (A) and Fgf9-/- (B) distal lung showing similar epithelial structure between alveolar sac airspaces. Surfactant (s) is seen in airways in A,B. Note that capillaries (white arrows) are present and similarly located within surrounding tissue in A,B. Differentiating epithelial cells display characteristic vacuolization due to loss of glycogen during section processing (black arrows in A,B). (C,D) Sections of proximal airway in control (C) and Fgf9-/- (D) lungs show similar epithelial architecture. Normal appearing ciliated cells (arrowheads) and Clara cells (arrows) are seen in control (C) and Fgf9-/- (D) sections. (E-L) Transmission electron micrographs of E18.5 control and Fgf9-/- lungs. (E,F) Control (E) and Fgf9-/- (F) lung capillaries showing the gas diffusion barrier between airspace (a) and blood (b). (G,H) Higher power views of the diffusion barrier in control (G) and Fgf9-/- (H) lungs, demonstrating normal close apposition of endothelial cell processes (e) and Type I pneumocyte processes (p), separated by basement membrane (asterisks). (I) A Type II pneumocyte from a control lung showing lamellar bodies (asterisk). (J) A Type II pneumocyte from an Fgf9-/- lung showing lamellar bodies (asterisk) and surface microvilli (arrowhead). (K) Transmission electron microscopy of the surface of an Fgf9-/- lung showing the basement membrane (arrowheads) beneath and a long microvillus (arrow) on the surface of a pleural mesothelial cell. (L) Transmission electron micrograph of the surface of an Fgf9-/- lung showing a tight junction (arrowheads) between two pleural mesothelial cells. (The tight junction is the extended s-shaped region of close apposition between the plasma membranes of neighboring pleural cells.) Scale bars: 1.1 µm in E,F; 0.15 µm in G,H; 0.5 µm in I,J; 0.28 µm in K; 0.22-µm in L.
