Fig. 3. Fgf9 signals through mesenchymal receptors to drive small intestine development/elongation. (A) Section of an E14.5 Dermo1-cre; Rosa26R small intestine stained with X-Gal. The epithelium, mesenchyme and muscularis propria are indicated. Blue staining showed regions of Dermo1-cre activity in all cells in the mesenchyme and muscularis propria. The epithelial compartment showed no detectable staining. (B) Section of an E18.5 Dermo1-cre; Rosa26R small intestine stained with anti-β-galactosidase and anti-Pecam (red, top) or CD45 (red, bottom). Both cells show colocalization of punctuate β-galactosidase with the cell lineage markers. No detectable β-galactosidase staining was detected in the epithelium. (C) PCR products of DNA that was procured from the epithelium and mesenchyme of control and DCR1R2 E18.5 small intestines. The recombined alleles of Fgfr1 and Fgfr2 were detected in the mesenchyme of DCR1R2 mice but not in the epithelium. PCR of vimentin is shown as a control for the isolation of the DNA. (D) Quantification of the means of the small intestinal lengths (±s.d. normalized to wild-type length; n=4-5 mice/group) in mice with loss of mesenchymal Fgfr1 (DCR1), Fgfr2 (DCR2), and both Fgfr1 and Fgfr2 (DCR1R2). Loss of both Fgfrs was additive. Two asterisks indicate statistically significant differences when comparing any two groups (Student's t-test, P<0.01). (E) Quantification of S-phase cells in three cellular compartments (intervillus epithelium, mesenchyme and muscularis propria) of E18.5 control and DCR1R2 small intestines. Mean±s.d. for each group is plotted. Statistically significant differences in the means are denoted by an asterisk (P<0.05 by Student's t-test). Scale bars: 10 µm in A; 5 µm in B.