Changes in the composition of labeled protein transported in motor axons during their regeneration

Labeled proteins transported in rat sciatic nerve axons after application of L-(35S) methionine to motoneuron cell bodies were characterized by SDS0poly-acrylamide gel electrophoresis. During nerve regeneration following a crush injury, changes were observed in the composition of the fast-transported proteins. The major change was an increase in relative amount of a 18,000-dalton poly-peptide (S2). Less dramatic changes occurred in a 66,000-dalton polypeptide (N) which also increased, and in a 13,000-dalton polypeptide (T) which decreased. The increase in S2 and N was significant by three days after injury and all changes were maximal between 7 and 14 days. A return to normal proportions was reached between 21 and 42 days. It is concluded that axonal injury produces, among its other effects, an alteration in the proportions of proteins transported into the axon. It remains to be determined whether these changes are prerequisites for axonal regeneration, or facilitate regeneration, or are incidental to it.