Slow transport in a nerve with embryonic characteristics, the olfactory nerve

The kinetics for slowly transported polypeptides have been examined in intact garfish olfactory nerves. The shape of the slow peak is essentially determined by alpha-and beta-tubulin which are by far the major polypeptides of the entire wave. The proximal area of the peak is similar to the slow component a (Sca) subcomponent defined in other nerves and contains discretely moving neurofilament proteins. The distal peak area, however, is more reminiscent of Scb. The two subcomponents were found to overlap considerably. Traces of polypeptides comigrating with tubulin and actin move far ahead of the slow wave at rates similar to the rate of slow transport measured in growing fibers and to the maximal velocity of axonal elongation. One of the most striking properties of slow transport in this nerve is the difference in the spreading of the various transported polypeptides along the axon, following their release from the perikarya. Labeled tubulin and actin can cover more than 20 cm of nerve; while neurofilament proteins can be found only on a 6 cm segment. Comparisons between slow transport in garfish olfactory axons and other vertebrate nerves indicate that despite major differences, the basic characteristics of slow transport are conserved. The features specific to the olfactory nerve may reflect its specialized properties. The constant turnover of olfactory neurons implies that these cells have an excellent growth potential but a short life span and, therefore, never reach full maturity. It can, therefore, be expected that their molecular composition is reminiscent of that embryonic neurons with a high level of plasticity but a slow stability.