Intermediate filaments are dynamic and motile elements of cellular architecture

Recent evidence showing that intermediate filaments (IFs) are dynamic, motile elements of the cytoskeletal repertoire of vertebrate cells has overturned the long-standing view that they simply form static `space filling' cytoplasmic networks. In fact, many types of IF are now known to engage in a remarkable array of movements that are closely associated with their assembly, disassembly and subcellular organization. Some of these motile properties are intrinsic to IFs and others are attributable to molecular crosstalk with either microtubules or actin-containing microfilaments. This crosstalk is, to a large extent, mediated by molecular motors, including conventional kinesin and cytoplasmic dynein. These motors are responsible for the high-speed delivery of nonfilamentous IF precursors and short filaments to specific regions of the cytoplasm, where they assemble into long IFs. Interestingly, the patterns and speeds of IF movements vary in different cell types and even within different regions of the same cell. These differences in motility may be related to their interactions with different types of molecular motor and/or other factors, such as IF-associated proteins.