New horizons in cytoskeletal dynamics: transport of intermediate filaments along microtubule tracks.

Until recently, the dynamic properties of intermediate filaments (IF) were attributed primarily to the exchange of subunits between a disassembled pool and polymerized 10nm filaments. During interphase, this subunit exchange process was thought to produce local modifications in IF structure. During cell division, shifts in the equilibrium between subunits and polymers were thought to lead to either the global or regional disassembly of IF networks, thereby facilitating their distribution into daughter cells. Recently, novel structural forms of IF that undergo rapid and directed transport in several cell types were revealed. Time-lapse observations of motile IF structures in different cell systems have also revealed novel insights into the mechanisms underlying the transport of cytoskeletal components throughout the cytoplasm and the molecular basis of the 'crosstalk' between different cytoskeletal systems.