Vimentin: the conundrum of the intermediate filament gene family.

Intermediate filaments are a major component of the "cytoskeleton" of "higher" eukaryotes. These filaments are composed of a number of different, although structurally related, proteins. Different intermediate filament protein genes are expressed in different tissues. Spontaneous and experimentally produced mutations in the intermediate filament genes indicate that these filaments function to enhance the mechanical stability of epidermal and muscle cells. As a result, the use of transgenic mice with "knockout" or dominant negative mutations in IF genes has become an important approach for investigating the significance of IFs in other cell types. However, a knockout mutation of vimentin (-/-), the intermediate filament protein characteristically expressed in cells of mesenchymal origin, results in very subtle phenotypes that are not obviously related to cell fragility. Although experiments with cultured cells have described a variety of discrete changes in cell properties that are associated with vimentin expression or organization, there is no evidence yet that any of these properties are affected in the vimentin-/- mouse.