Continuous remodelling of the major filament networks in the cytoskeleton of mammalian cells – actin filaments, microtubules and intermediate filaments (IFs) – is crucial for many cell functions. Actin-filament and microtubule assembly are well understood, but what about IF assembly? The dynamic co-translation model proposes that newly synthesized IF polypeptides integrate at multiple sites throughout the IF network, whereas a second model proposes that non-filamentous IF subunits generated from filaments at specific cellular locations integrate into the IF cytoskeleton in the cell periphery. Rudolf Leube and colleagues (p. 2266) now provide evidence that supports the second model. Using live-cell imaging, photobleaching, photoactivation and quantitative fluorescence measurements in two epithelial cell lines, they show that the assembly of epithelial keratin IFs takes place in the cell periphery and that newly formed filaments are constantly transported towards the perinuclear region. Disassembly of the keratin filaments occurs during this transport, they report, which gives rise to diffusible subunits for another round of peripheral assembly independently of protein biosynthesis. The authors conclude, therefore, that the keratin-filament cycle of assembly and disassembly is a major mechanism of IF plasticity.
- © 2010.