Fig. 1. Morphological and histological analysis of Fgf9^-/- lungs. (A,B) Anterior views of gross dissections of uninflated control (A) and Fgf9^-/- (B) lungs at E18.5. The Fgf9^-/- lung is smaller but contains the same lobes as the control. Arrowhead in B indicates the accessory lobe. (C,D) Sagittal sections of the right side of the thoracic cavity at similar levels from E14.5 control (C) and Fgf9^-/- (D) embryos. The control lung (lu) fills the thoracic cavity while the Fgf9^-/- lung does not. A dilated cardiac atrium (a) is observed adjacent to the Fgf9^-/- lung (D). An intact diaphragm (arrowheads) is seen just superior to the liver (li) in both C,D. (E,F) High power views of the caudal part of the right lower lobe of grossly dissected E12.5 control (E) and Fgf9^-/- (F) lungs. Note the lack of mesenchyme and the reduced branching complexity in the Fgf9^-/- lung relative to the control. (G,H) High-power views of the left lobe of grossly dissected E12.5 control (G) and Fgf9^-/- (H) lungs. Epithelial buds in the Fgf9^-/- lung (arrow in H) appear dilated and have less adjacent mesenchyme than comparably located epithelial buds in the control lung (arrow in G). In addition, a control lung bud (arrow in G) is branching into two buds, while the corresponding Fgf9^-/- bud (arrow in H) is not branching. (I,J) Sagittal sections of E11.5 lungs showing similar appearance of control (I) and Fgf9^-/- (J) samples. (K,L) E13.5 lung sections showing reduced mesenchyme in Fgf9^-/- (L) compared with control lung (K). Small diameter airways are more prevalent in control lung (arrow in K) than in Fgf9^-/- lung. (I-L) are shown at the same magnification. m, mesenchyme; r, ribs; asterisks indicate future airspaces within epithelial branches.