Figure 2.

Smooth muscle loss from the external muscle layers of the colon of adult, but not newborn, Nup35-mutant mice. A–F: Masson's trichrome staining of the proximal, mid-, and distal colon from 6- to 8-week-old wild-type (A–C) and Nup35^F192L/F192L (D–F) mice. There is a dramatic loss of muscle cells from the circular and longitudinal muscle layers, and replacement by connective tissue (green), in the mid- and distal colon of the mutant mice. There is a less dramatic loss of muscle cells in the proximal colon. The widths of the external muscle layers are indicated by vertical lines. Note greater numbers of surface goblet cells (E and F) and thickened submucosa (F). G and H: High magnification images of circular muscle cells. Although the nuclei (arrows) of WT mice are uniform in appearance (G), many nuclei (arrows) in the remaining smooth muscle cells in the mutant have chromatin condensations (H). I: Pathology grading of distal colon and ileum tissue from three randomly chosen Nup35^+/+ and Nup35^F192L/F192L mice [0 (normal); 7 (severely affected)], which included assessments of the longitudinal and circular muscle layers, the submucosa and mucosa (Table 1). Although the colons of all mutants were graded as severely affected, the ileum was graded normal. J–M: Masson's trichrome (MT; J and K) and hematoxylin and eosin (H&E) (L and M) staining of transverse sections of distal colon from newborn wild-type (+/+, J and L) and Nup35^F192L/F192L (mutant, K and M) mice. There are no detectable differences between the longitudinal muscle layer (LM) and circular muscle layer (CM; double arrow) between mutants and wild-type littermates.