Glial polypeptides transferred into the squid giant axon.

The proteins synthesized by the glial sheath of an isolated segment of squid giant axon and by the cell bodies of the giant axon in the isolated stellate ganglion were labeled by incubation in the presence of [3H]leucine. The axoplasm, which contained labeled proteins transferred from the glial sheath, was separated from the sheath by mechanical extrusion. The labeled proteins in the axoplasm, the empty sheath and the stellate ganglion were analyzed and compared by one- and two-dimensional polyacrylamide gel electrophoresis. Over 80 glial polypeptides were found to be selectively transferred into the axoplasm and many of these were distinct from stellate ganglion polypeptides which presumably could be supplied to the axon via axonal transport. Three of the more highly labeled transferred glial polypeptides (TGPs) were actin, a fodrin-like polypeptide and a polypeptide we have named traversin. Our observations, considered in the context of other reports, suggest that the squid axon receives a large number of polypeptides from its surrounding glia either by phagocytozing glial cell process that project into it or via cytoplasmic channels between adaxonal glia and the axon. These TGPs may help the axon survive unfavorable conditions.