Fig. 5. A subset of small intestinal mesenchymal cells showed a robust response to Fgf9 and expressed Tgfβ inhibitors. Sections of E18.5 small intestines from (A,D-H) control and (B) Fgf9^-/- embryos stained with antisera directed against p-Erk1/2 (green) and co-stained with antisera against (D) Pecam-1, (E) CD45, (F) BrdU, (G) Fst and (H) Fstl1 (in D-H, co-staining is in red). In all panels, the mesenchyme at the base of a single villus is shown. The broken white lines indicate the epithelial-mesenchymal boundaries. The green arrows indicate high p-Erk1/2 positive mesenchymal cells near the base of villi. The red arrows indicate mesenchymal cells that do not colocalize with p-Erk1/2 cells for a given marker (e.g. CD45, Pecam1 and BrdU). The yellow arrows denote mesenchymal cells that colocalize with a given marker (e.g. Fst and Fstl1). (C) Quantification of the mean percentage (±s.d.) of mesenchymal cells with detectable p-Erk in control and Fgf9^-/- embryos. The double asterisks indicate a statistically significant difference when comparing Fgf9^-/- embryos with controls, as determined by Student's t-test (P<0.01). Scale bars: 10 µm.