Using immunoblot, light and electron immunocytochemistry, we investigated the presence and the localization of polypeptides cross-reacting with the monoclonal antibody CC.310 (mAb CC.310), which is mainly directed against a 175K (K = 10(3) Mr) ciliary rootlet protein. In hypothalamic ependymal cultures, the unique antigen recognized by mAb CC.310 was associated with the Triton X-100-insoluble fraction in these cultures and electrophoretically migrated to these cultures and electrophoretically migrated to 94K. mAb CC.310, which appears to be a very suitable marker for ciliated ependymocytes, allowed us to observe ciliogenesis during the growth of the ependymal cultures, from a single spot in each undifferentiated ependymal cell to a massive labeling in ciliated ependymal cells. In fully differentiated ciliated ependymocytes, mAb CC.310 strongly reacted with fibrous structures corresponding to ciliary rootlets, as confirmed by ultrastructural observations. In addition, a weaker immunostaining was also found along the intercellular junctions, and showed that proteins sharing a common epitope are located in ependymal ciliary rootlets and near adherens-type junctional complexes. Immunofluorescence studies confirmed the presence of positive labeling at the level of junctional complexes between cells in two epithelial lines, HeLa and PtK2, in which mAb CC.310 mainly reacted with one polypeptide of 85K.

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