Intermediate Filaments

Abstract

Intermediate filaments are a major constituent of almost all tissues in situ in the body and in cells in culture. They can be recognized by their diameter of 7–11 nm, which is intermediate between that of the 22-nm microtubules and that of the 6-nm microfilaments. They can also be distinguished from microtubules and from actin-containing structures by the use of antibodies to their subunit proteins in immunofluorescence microscopy. Immunologic and biochemical studies of intermediate filaments isolated from different tissues have clearly established in the last 4 years that these filaments can be further subdivided (Table 1) (for review, see Lazarides 1980; Weber and Osborn 1982). Currently, five major types are recognized: (1) the cytokeratins, characteristic of true desmosome-expressing epithelia; (2) the desmin fibers, typical of certain muscle cells; (3) the glial filaments, typical of astrocytes and also of Bermann glia; (4) the neurofilaments, characteristic of neurons; and (5) the vimentin...