MAINTENANCE OF CELL-TYPE-SPECIFIC CYTOSKELETAL CHARACTER IN EPITHELIAL-CELLS OUT OF EPITHELIAL CONTEXT - CYTOKERATINS AND OTHER CYTOSKELETAL PROTEINS IN THE RESTS OF MALASSEZ OF THE PERIODONTAL-LIGAMENT

We have determined the patterns of synthesis of cytokeratins and other epithelial marker proteins in the ''rests of Malassez'' of the period ontium of rabbits and humans, by immunofluorescence microscopy of cryo sections prepared from fixed and decalcified rabbit teeth with attache d ligament or from manually isolated human periodontal ligaments. Prot eins of the major cell structures characterizing epithelial differenti ation are present in Malassez cells: a complex set of cytokeratins as well as desmosomal, hemidesmosomal and basal lamina proteins. In addit ion, we have shown these cytoskeletal and extracellular matrix structu res by electron microscopy. The cytokeratin complement of Malassez cel ls was found to be highly complex, as 8 of the total of 20 known epith elial cytokeratins were detected (nos. 5, 7, 8, 14, 15, 17, 18, 19). T his pattern, together with the presence of the desmosomal cadherins Ds g2 and Dsc2 and the cytoplasmic desmosome plaque-associated protein pl akophilin 1, indicates that the cells of the rests of Malassez are der ived from the basal cell layer of a stratified squamous epithelium rat her than from simple epithelial or neuroendocrine epithelial cells. Ou r observations show that Malassez cells retain the major characteristi cs of epithelial cells throughout their differentiation from the root sheath epithelium into the rests of Malassez, even though the surface location and the polar tissue architecture that typify epithelia are l ost during this process. From this study we further conclude that the specific cytoskeletal complement of the Malassez cells represents an i ntrinsic gene expression program that neither depends on nor causes th e formation of a stratified epithelium. We also compare the specific c ytoskeletal features of Malassez cells with those of other persisting epithelial residues and discuss the potential value of these findings in relation to the histogenesis and diagnostic classification of denta l and periodontal cysts and tumors.