Fig. 7. FGF9 signaling regulates mesenchymal FGF gene expression and signaling. (A,B) Whole-mount in situ hybridization demonstrating upregulated and broad expression of Fgf10 in the sub-mesothelial mesenchyme of E13.5 Fgf9^dox(48) lungs (B) compared with focal expression in control lungs (arrowhead, A). (C,D) Increased Fgf7 expression in both proximal and distal mesenchyme of Fgf9^dox(48) lungs (D) compared with low level mesenchymal expression in control lungs (C). (E,F) Upregulation of Spry2 in epithelium of E11.5 whole lung explant cultures incubated for 48 hours with an FGF9 bead (F) compared with distally restricted expression in BSA controls (E). (G,H) Decreased Spry2 expression in E14.5 Fgf9^–/– lungs (H) compared with controls (G). (I,J) Increased distal and ectopic proximal epithelial expression of Bmp4 in E14.5 Fgf9^dox(48) lungs (J) compared with distally restricted expression in controls (I). (K,L) Comparable Bmp4 expression in E12.5 Fgf9^–/– (L) and control lung epithelium (K), mirroring Fgf10 expression at this time (Colvin et al., 2001). (M,N) Decreased Bmp4 expression in E14.5 Fgf9^–/– lungs (N) compared with controls (M). Bead location in E,F is indicated by orange circles. (A,B) Cranial lobes; (C,D) left lobes; (E,F) left lobes of explant cultures; (G-J,M,N) caudal lobes.