Cytokeratin expression in epithelial cells isolated from the crypt and villus regions of the rodent small intestine.

Many physiological and structural features of epithelium in the small intestine are regulated during their transit from the crypt base to the villus tip. This crypt-villus axis is an important model for the study of the regulation of cell proliferation and differentiation. We have investigated the expression of cytokeratins in purified epithelial cells from the proliferative (crypt) and differentiated (villus) regions of this tissue. Three polypeptides were identified (cytokeratins 8, 18 and 19) as well as a fourth, 46 kDa polypeptide with similar electrophoretic characteristics to the recently identified cytokeratin 20. The distribution of these molecules was found to vary along the crypt-villus axis, with cytokeratin 18 being restricted to the proliferative crypt and cytokeratins 8 and 19 demonstrating more uniform distributions. The 46 kDa component was found to be expressed predominantly within the villus epithelium. Although there is no substantial evidence of a direct role for cytokeratins in the process of epithelial differentiation, these data suggest that differential expression of cytokeratins is associated with changes in intestinal epithelial differentiation.