A major issue in the slow transport of cytoskeletal proteins is the form in which they are transported. We have investigated the possibility that unpolymerized as well as polymerized cytoskeletal proteins can be actively transported in axons. We report the active transport of highly diffusible tubulin oligomers, as well as transport of the less diffusible neurofilament polymers. After injection into the squid giant axon, tubulin was transported in an anterograde direction at an average rate of 2.3 mm/day, whereas neurofilament was moved at 1.1 mm/day. Addition of the metabolic poisons cyanide or dinitrophenol reduced the active transport of both proteins to less than 10% of control values, whereas disruption of microtubules by treatment of the axon with cold in the presence of nocodazole reduced transport of both proteins to ≃20% of control levels. Passive diffusion of these proteins occurred in parallel with transport. The diffusion coefficient of the moving tubulin in axoplasm was 8.6 μ2/s compared with only 0.43 μm2/s for neurofilament. These results suggest that the tubulin was transported in the unpolymerized state and that the neurofilament was transported in the polymerized state by an energy-dependent nocodazole/cold- sensitive transport mechanism.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Sep 28 1999|
- Axoplasmic transport
- Slow axonal transport
ASJC Scopus subject areas