Desmosomes--dual junctional principles of intra- and supracellular order in epithelial differentiation and tissue formation.

The cells of most normal and malignantly growing tissues are connected by "adhering junctions", i.e. distinct sites of "homotypic" contact between the plasma membranes of two cells of the same or a similar kind, associated on the cytoplasmic side by a dense plaque at which often bundles of cytoskeletal filaments anchor. Of the various types of adhering junctions desmosomes are characteristic of epithelia and carcinomas but also occur in some other cell types. Their molecular components have recently been identified and characterized by cDNA-cloning and sequencing. Unexpectedly, the molecular complement of desmosomes has been found to show certain differences in different epithelia, with particularly complex patterns in stratified squamous epithelia as well as in tumors and cultured cell lines derived therefrom. In addition, molecular principles important in the assembly of desmosomes and in the specific anchorage of intermediate-sized filaments (IFs) at desmosomal plaques have been elucidated. The possible value of cell type-specific isoforms of desmosomal components as markers for the subtyping of carcinomas and the role of desmosomal cadherins during invasion and metastasis of carcinomas are discussed.