New horizons in cytoskeletal dynamics: transport of intermediate filamentsalong microtubule tracks

Until recently, the dynamic properties of intermediate filaments (IF) were attributed primarily to the exchange of subunits between a disassembled poo l and polymerized 10 nm 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 wer e thought to lead to either the global or regional disassembly of IF networ ks, thereby facilitating their distribution into daughter cells. Recently, novel structural forms of IF that undergo rapid and directed transport in s everal cell types were revealed. Time-lapse observations of motile IF struc tures in different cell systems have also revealed novel insights into the mechanisms underlying the transport of cytoskeletal components throughout t he cytoplasm and the molecular basis of the 'crosstalk' between different c ytoskeletal systems.