Epithelial Tonofilaments: Investigating Their Form and Function Using Monoclonal Antibodies

The primary function of intermediate filaments in the organization of the eukaryotic-cell cytoplasm is gen-erally assumed to be a cytoskeletal one, although the evidence for this is so far only circumstantial. Inter-mediate filaments are absent from the early embryo (Jackson et al. 1980), and they can be disrupted in fibroblasts in tissue culture without altering the cell shape (Klymkowsky 1981; Lin and Feramisco 1981). Intermediate filaments appear to be common to all organisms that depend on three-dimensional tissue dif-ferentiation. In view of their characteristic 7- to 11-nm-wide filaments oft~-type helical fiber structure and their physical and chemical stabilities, they appear to con-stitute homologous structures in different cell types. The filament subunit proteins, however, fall into sev-