Figure 5. Targeted ablation of Foxl1⁺ mesenchymal cells using the iDTR model causes loss of epithelial proliferation.

(A) Schema for the generation of Foxl1-iDTR mice. Foxl1-Cre mice were crossed to mice carrying a loxP-stop-loxP Simian diphtheria toxin receptor construct in the Rosa26 locus (Rosa^iDTR mice). (B,C) Small intestinal (Jejunum) morphology was assessed by hematoxylin/eosin (H/E) staining of DT-treated control (B) and Foxl1 iDTR mice (C). Note the reduced number and length of intestinal villi. (D) Quantification of small intestinal villus length. (n = 4, in each animal; > 20 villi were evaluated per mouse; ***, P < 0.001). (E,F) Colonic morphology of DT-treated control (E) and Foxl1-iDTR mice (F). Decreased depths of the colonic crypts is apparent in Foxl1-iDTR mice. (G) Quantification of colonic crypt depth. (n = 4, in each animal; >20 crypts were evaluated per mouse; *, P < 0.05). (H,I) Representative immunofluorescence images of small intestinal (jejunum) sections stained for the proliferation marker Ki67 (red) and counterstained with DAPI to label nuclei (blue) of control (H) and Foxl1-iDTR (I) mice. The number of Ki67-positive epithelial cells is dramatically reduced in Foxl1 iDTR mice. (J) Quantification of the number of proliferating cells per crypt unit in the jejunum of DT-treated control and Foxl1 iDTR mice. (n = 20 crypts each) ***, P < 0.001. (K,L) Ki67 labeling (red) overlaid with DAPI to mark nuclei (blue) in the colon of control DT-treated control (K) and Foxl1 iDTR (L) mice. The number of Ki67-positive cells is dramatically reduced in Foxl1 iDTR mice. (M) Quantification of the number of proliferating cells per crypt unit in the colon of DT-treated control and Foxl1 iDTR mice. (n = 20 crypts each) ***, P < 0.001. Scale bars: 100 μm in the small intestine, 50μm in the colon.