Intermediate filaments — Heterogenous expression pattern and modulation: Can their role in structure and function of the cell be ascertained?

Summary— Intermediate filaments (IFs), a group of highly heterogenous proteins grouped on the basis of their size, are expressed almost ubiquitously and specifically. Earlier, IFs were considered to play a major role in maintaining cell shape along with other cytoskeletal elements, however, the multitude of IFs are unlikely to have a single function. Evolution pattern of IFs reveals presence of simple IFs in a wide range of cells in lower vertebrates whereas structurally complex IFs have specific distribution in higher vertebrates, implicating they may have evolved later in need to perform specialized functions. There could be functions common to various IFs, but some IFs may have very specific functions. Functional capabilities could also be a result of the various dynamic modifications displayed by IFs under influence of different intrinsic and extrinsic factors. Functions assigned to the IFs in the literature range from providing a passive skeletal support to the cells to involvement in macromolecular biosynthesis, signal transduction and control of gene expression. In this review, we have attempted to outline the possible functional roles that IFs may play in resting. and actively dividing and differentiating cells.