Fig. 3. Histology and mesenchymal differentiation in Fgf9^dox(48) developing lungs. (A,B) Hematoxylin and Eosin stained sections showed increased size and mesenchymal area in E11.5 Fgf9^dox(48) lungs (B). (C,D) Tie2-lacZ staining for endothelial cells in E12.5 Fgf9^dox(48) lungs showing a multi-layered vascular network extending into the expanded mesenchyme (D), in contrast to a single layer of endothelial cells in wild-type controls (C). (E,F) Anti-PECAM immunohistochemistry confirmed an extended domain of blood vessels in E13.5 Fgf9^dox(48) lungs (F). (G,H) Increased luminal space, fewer epithelial airways and a wide band of mesenchyme separating epithelial ducts was found in E14.5 Fgf9^dox(48) lungs (H). (I,J) Smooth muscle actin (SMA) staining in proximal sub-epithelial mesenchyme adjacent to airways (a) is absent in E14.5 Fgf9^dox(48) lungs (arrow, J). SMA was still found adjacent to blood vessels (bv). C, D and G-J are left lobes; E and F are cranial lobes.