Mucous cells and cell migration in the mouse duodenal epithelium

The distribution of mucous cells in the mouse duodenum was used to determine whether or not intestinal epithelial cells move as a sheet during their migration from crypts to villi. The experiments took advantage of the probable symmetry of mucous-cell divisions (symmetry in the sense that each mucous-cell division produces two mucous cells). Since approximately 50% of newly formed mucous cells are derived from mucous-cell divisions, at least 50% of newly formed mucous cells in the crypt should be found in mucous-cell pairs. It follows that if the epithelium moves as a firmly interconnected sheet, at least 50% of mucous cells found in the villus should also be in pairs. On the other hand, if a significant amount of cell mixing occurs during migration, the pairing tendency of mucous cells would be lost. Mucous-cell pairing was determined by two independent methods: 1) direct observation of mucous-cell pairs and 2) the application of Poisson statistics to the mucous-cell distribution to determine a "pairing tendency." We found that in the crypt at least 75-80% of newly formed mucous cells occur in pairs, while in all regions of the villus (base, middle, and top) mucous cells are distributed randomly. These results strongly indicate the existence of a significant amount of cell mixing in the epithelium at some point between the site of mucous-cell formation in the crypts and the villus base. Since the mucous-cell population was randomly distributed in all regions of the villus we were unable to determine whether or not additional cell mixing occurs in the villus epithelium.