Fig. 2. Fgf9 regulates mesenchymal fibroblast proliferation. (A) Hematoxylin and Eosin stained section (left) and color-coded cartoon (right) showing micro-anatomical regions of a control E18.5 small intestine. (B) Immunohistochemistry of BrdU stained sections of control (left) and Fgf9^-/- (right) E18.5 proximal small intestines. The broken red lines indicate the boundaries between the epithelium, mesenchyme and muscle layers. (C) Quantification of the means (±s.d.) of the proportion of S-phase cells (as indicated by BrdU incorporation) in the epithelium, mesenchyme and muscularis propria for E14.5, E16.5 and E18.5 for control and Fgf9^-/- embryos. Statistically significant differences between the two groups (n=4 embryos/group) were determined by a Student's t-test (^**P<0.01; ^*P<0.05). (D) Quantification of the mean percent BrdU incorporation (±s.d.) in fibroblasts (prolyl 4-hydroxylase positive) and endothelial cells (Pecam1 positive) from the mesenchyme of E18.5 control and Fgf9^-/- small intestines. Statistically significant differences between the two groups were determined by comparison of SEMs using Student's t-test; ^**P<0.01; n=4 mice/group). Scale bars: 30 µm.