Volume 133, Issue 6, Pages 1960-1970 (December 2007) Inducible Mouse Model of Chronic Intestinal Pseudo-Obstruction by Smooth Muscle- Specific Inactivation of the SRF Gene  Mathias Mericskay, Jocelyne Blanc, Eva Tritsch, Raphael Moriez, Philippe Aubert, Michel Neunlist, Robert Feil, Zhenlin Li  Gastroenterology  Volume 133, Issue 6, Pages 1960-1970 (December 2007) DOI: 10.1053/j.gastro.2007.09.010 Copyright © 2007 AGA Institute Terms and Conditions

Figure 1 Down-regulation of SRF expression in smooth muscle tissues after tamoxifen injection in the SRFSMKO mutant. (A) Experimental setup for the generation of smooth muscle-specific SRF inactivation (SRFSMKO, see text for details). (B) Real-time RT-PCR analysis of SRF/GAPDH expression ratio in the control and SRF SMKO mice 10 days after tamoxifen injection. Data are expressed as a percentage of the control value ± SEM. *P < .05. (C) Western blot analysis of SRF protein extracted from the urinary bladder and colon 10 days after tamoxifen injection. The 2 major SRF isoforms (arrowheads; 67 kilodaltons, 62 kilodaltons) are down-regulated in the bladder and colon. An additional faint band migrating at 52 kilodaltons (*) is detectable in extracts of both control and mutant bladder. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 2 Intestinal tract dilation in the SRFSMKO mutant. (A and B) Control, macroscopic view after opening of the abdominal cavity and isolated GI tract. (C–F) Two representative mutants showing a dilation of the intestinal tract 19 days after tamoxifen treatment. Arrows in C and E point to dilated small and large intestine, respectively. Arrowhead points to gas in the cecum. Note the dilation of the duodenum down to the jejunum in D and of the cecum and entire colon in F. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 3 Reduction of body weight and food and water intake in the SRFSMKO mutants. Control and mutant mice (n = 6 for each group) were housed in metabolic cages for 24-hour periods at indicated time points. (A) Cumulative body weight variation from days 13 to 18 after tamoxifen treatment. Mean body weight at the beginning of the experiment was 20.8 ± 0.9 g for the controls and 21.4 ± 0.6 g for the mutants (nonsignificant, P > .05). (B and C) Water and food intake over a 24-hour period. (D) Urine production. Differences between controls and mutants were significant, with P < .05 for all points in A–C but not in D. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 4 Stretching and thinning of the intestinal smooth muscle layer in the SRFSMKO mutant. H&E staining of control (A, D, F, and H) and mutant (B, C, E, G, and I) sections. (A–E) Colon. (F–I) Ileum. Note the enlargement of the intestinal lumen in the mutant (C and G) on day 14, loss of intestinal folds in the mutant colon (C), and altered villi in the ileum (arrows) (inset high magnification of a villus showing detached epithelium). (D, E, H, and I) High magnification shows the stretching and thinning of both the longitudinal muscle (LM) and the circular muscle (CM) layers. Asterisk in E shows edematic stroma. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 5 Measure of contractile activity in isolated segments of colon. (A and B) Typical recording showing EFS-mediated contraction in control (A) and relaxation in mutant (B) mice. (C) Area under the curve during EFS stimulation (10 seconds) and for 1 minute after stimulation. n = 5 for each group. (D and E) Typical recording of carbachol dose-response stimulation of contraction in control (D) and mutant (E) mice. (F) Area under the curve as a function of carbachol concentration, measured for 2 minutes after stimulation. □, mutant; ■, control. n = 6 for each group. *P < .05. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 6 Down-regulation of SRF target genes in smooth muscle tissues. (A) Real-time RT-PCR analysis of SRF target gene expression 10 days after tamoxifen treatment. Data are expressed as a percentage of the mean control value ± SEM. All values in mutants were significantly different from the mean control, with P < .05. (B) Western blot analysis of protein extracts from the colon at days 13 and 19. Antibodies are indicated on the left. Co, control; Mu, mutant. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 7 Immunohistochemistry of dilated bowel after SRF inactivation. (A, C, E, and G) Sf/Sf control. (B, D, F, and H) SRFSMKO mutant. (A–F) Transverse colon on day 14. (G–H) Ileum on day 10. (A) SRF-positive nuclei (brown) are present in smooth muscle cells of the longitudinal and circular muscle layer (lm, cm, respectively), mesenteric vessels (mv), and muscularis mucosa (mm) in the tissues expressing α-SMA (C) and desmin (E). (B) In the mutant, only a few SRF-positive nuclei are present in the muscle layers (arrowheads). Scattered SRFPos cells are present in the stroma (asterisks). α-SMA (D) and desmin (F) are down-regulated in the thin muscularis propria and muscularis mucosa. (G–H) SM-MHC immunostaining. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions

Figure 8 Down-regulation of F/G actin ratio in the smooth muscles of the colon. Confocal images of control (A, C, and E) and mutant (B, D, and H) frozen sections 10 days after tamoxifen treatment. Phalloidin-TRITC (red) labels F-actin, DNAse-Alexa488 (green) labels G-actin, and DAPI (blue) labels nuclei. Note the lower intensity of the phalloidin-TRITC signal in the mutant smooth muscle cells (B) than in control cells (A). The intensity of the epithelial F-actin cortical network staining is identical for both sections (arrows). The G-actin signal is slightly lower in mutant (C) than in control (D) SMCs. The F/G actin ratio, as visualized in overlap panels (E and F), is lower in the mutant. mm, muscularis mucosa; lm, longitudinal muscle layer; cm, circular muscle layer; mv, mesenteric vessels. Gastroenterology 2007 133, 1960-1970DOI: (10.1053/j.gastro.2007.09.010) Copyright © 2007 AGA Institute Terms and Conditions