Intermediate filaments: versatile building blocks of cell structure.

Cytoskeletal intermediate filaments (IF) are organized into a dynamic nanofibrillar complex that extends throughout mammalian cells. This organization is ideally suited to their roles as response elements in the subcellular transduction of mechanical perturbations initiated at cell surfaces. IF also provide a scaffold for other types of signal transduction that together with molecular motors ferries signaling molecules from the cell periphery to the nucleus. Recent insights into their assembly highlight the importance of co-translation of their precursors, the hierarchical organization of their subunits in the formation of unit-length filaments (ULF) and the linkage of ULF into mature apolar IF. Analyses by atomic force microscopy reveal that mature IF are flexible and can be stretched to over 300% of their length without breaking, suggesting that intrafilament subunits can slide past one another when exposed to mechanical stress and strain. IF also play a role in the organization of organelles by modulating their motility and providing anchorage sites within the cytoplasm.