DIFFERENT ORGANIZATION OF INTERMEDIATE FILAMENTS IN COLUMNAR CELLS OFRAT LARGE INTESTINAL-MUCOSA AS REVEALED BY CONFOCAL LASER-SCANNING MICROSCOPY AND QUICK-FREEZING AND DEEP-ETCHING METHOD

The relationship between cell differentiation and ultrastructural chan ges of intermediate filaments (IF) was studied in columnar cells of la rge intestinal mucosa of rats by confocal laser scanning microscopy an d quick-freezing and deep-etching method. A feature of the IF in immat ure columnar cells was minibundle formation with prominent branching, which organized the meshwork structures. The minibundles, which appear ed to be formed by the attachment of two or more IF in side-to-side fa shion, were loosely distributed throughout the cytoplasm. In contrast, in mature columnar cells, the IF were densely distributed under the t erminal web in the cytoplasm and beneath the upper part of the lateral membrane regions, whereas the other areas of the cytoplasm contained only a small number of IF. Minibundle formation was not observed, and the branching was rarely identified. The changes in the distribution a nd density of IF, which are expressed in specific areas of mature colu mnar cells, apparently represent a characteristic of intracellular dif ferentiation. It is suggested that the dissociation of minibundled IF, which was often observed in the immature columnar cells, is an import ant step in the acquisition of functional polarity in cells of this ty pe.