Fast transport of neurofilament protein along microtubules in squid axoplasm

Using squid axoplasm as a model system, we have visualized the fast transpo rt of non-filamentous neurofilament protein particles along axonal microtub ules. This: transport occurs at speeds of 0.5-1.0 mum/second and the majori ty of neurofilament particles stain with kinesin antibody, These observatio ns demonstrate, for the first time, that fast (0.5-1.0 mum/second) transpor t of neurofilament proteins occurs along microtubules. In addition, our stu dies suggest that neurofilament protein can be transported as non-membrane bound, nonfilamentous subunits along axons, and that the transport is kines in-dependent, Microtubule-based fast transport might therefore provide a me chanism for the distribution and turnover of neurofilament, and perhaps oth er cytoskeletal proteins, throughout neurons.