RAPID MOVEMENTS OF VIMENTIN ON MICROTUBULE TRACKS - KINESIN-DEPENDENTASSEMBLY OF INTERMEDIATE FILAMENT NETWORKS

The assembly and maintenance of an extended intermediate filament (TF) network in fibroblasts requires microtubule (MT) integrity. Using a g reen fluorescent protein-vimentin construct, and spreading BHK-21 cell s as a model system to study IF-MT interactions, we have discovered a novel mechanism involved in the assembly of the vimentin IF cytoskelet on. This entails the rapid, discontinuous, and MT-dependent movement o f IF precursors towards the peripheral regions of the cytoplasm where they appear to assemble into short fibrils. These precursors, or vimen tin dots, move at speeds averaging 0.55 +/- 0.24 mu m/s. The vimentin dots colocalize with MT and their motility is inhibited after treatmen t with nocodazole. Our studies further implicate a conventional kinesi n in the movement of the vimentin dots. The dots colocalize with conve ntional kinesin as shown by indirect immunofluorescence, and IF prepar ations from spreading cells are enriched in kinesin. Furthermore, micr oinjection of kinesin antibodies into spreading cells prevents the ass embly of an extended IF network. These studies provide insights into t he interactions between the IF and MI systems. They also suggest a rol e for conventional kinesin in the distribution of non-membranous prote in cargo, and the local regulation of LF assembly.