Comparison of the synthesis and axonal transport of fucosylated glycoproteins by intact and regenerating sensory neurons in the frog

Abstract

Peripheral nerve regeneration requires a reorganization of neuronal synthesis and axonal transport to replace the degenerating axon. This study examines the time course, the extent and the molecular components which comprise the observed increases in protein fucosylation and fast axonal transport of fucosylated proteins in regenerating frog peripheral nerves. The in vitro spinal ganglia-sciatic nerve preparation used in these experiments allowed comparisons to be made between axotomized and intact neurons from the same animal, incubated in the same [³H]fucose-containing solution, and subjected to the same axonal transport conditions. Thus, we were able to show that the fucosylation of constituent proteins increased in axotomized neurons without an increase in the membrane transport of fucose or neuronal protein synthesis. An increase in the amount of newly fucosylated protein conveyed by fast transport preceded the apparent increase in neuronal synthesis by approximately 3 days. The increase in anterograde transport was initiated just subsequent to a transient increase in retrograde or ‘turnaround’ transport, suggesting a possible association between the two responses. The protein (distinguished on the basis of molecular weight) undergoing the most pronounced increase in fucosylation in the cell body was different from that in the nerve, but there was no evidence for the production of novel glycoproteins. The data indicate that protein fucosylation increases significantly in regenerating neurons and that an increase in the incorporation of newly fucosylated protein into the fast axonal transport system precedes an increase in synthesis. The increase in transport of fucosylated protein may be one of the earliest responses directed toward the generation of a new axon.