Fig. 4. Immunohistochemistry for epithelial and vascular markers in E18.5 Fgf9^-/- lungs. (A,B) Hematoxylin and Eosin stained sections of the left lobe of control (A) and Fgf9^-/- (B) lungs. Note that fewer generations of conducting airways (i.e. airways without alveolar sacs in their walls) are seen in the Fgf9^-/- lungs compared with controls. (The arrow in A indicates a conducting airway.) Distal aspects of both lungs have similar alveolar duct and alveolar sac structures, which are particularly evident in the less expanded upper regions of the lung sections (leftmost regions of (A,B)). (C,D) Immunohistochemistry for CCSP in lung sections from control (C) and Fgf9^-/- (D) embryos. Fgf9^-/- lung (D) shows normal expression of CCSP in Clara cells in proximal airways. Note the relatively larger diameter of CCSP-positive airways (arrowheads) in Fgf9^-/- versus control lung, indicating reduced branching of conducting airways. (E,F) Immunohistochemistry for SP-C in lung sections from control (E) and Fgf9^-/- (F) embryos. Fgf9^-/- lung (F) shows expression of surfactant in Type II pneumocyte cytoplasm that is comparable with that in the control (E). (G,H) Immunohistochemistry for vWF in lung sections from control (G) and Fgf9^-/- (H) embryos, showing normal staining of large vessels in Fgf9^-/- lung.