Intermediate filaments

Abstract

Several aspects are discussed of intermediate-filament structure and function. We report primary protein sequences covering the carboxyterminal third of both desmin, the muscle-specific intermediate-filament protein, and vimentin, the intermediate-filament protein often expressed by cells of mesenchymal origin. The results show that the proteins are different gene products but are related in sequence. We then consider the contributions of the 68K, 145K, and 200K components to the neurofilament structure. Reconstitution experiments suggest that the 68K component can self-assemble in vitro and that the 200K component may be responsible for the surface projections often seen on neurofilaments. Immuno-electron microscopy studies of neuronal cytoskeletons support a differing spatial arrangement of the 68K and 220K components. Finally, we summarize some experiments on frozen sections of adult animal and human tissues and on primary and permanent cell lines in culture, using affinity-purified antibodies to each of the five different intermediate-filament types. These experiments, which have also been extended in some cases to pathologic specimens, reinforce the usefulness of antibodies that specifically recognize only one type of filament.