Effect of inhibiting protein synthesis on axonal transport of membrane glycoproteins in an identified neuron of Aplysia.

Intrasonic injection of L-[3H]fucose into R2, the cholinergic giant neuron in the abdominal ganglion of the marine molluse, Aplysia californica, labeled 5 major glycoprotein membrane components, 3 of which were preferentially exported into the axon. Brief exposure to anisomycin, a potent inhibitor of protein synthesis in Aplysia, almost completely blocked the appearance of [3H]glycoprotein in the axon; but fucosylation of proteins in the cell body was only partially inhibited. Polyacrylamide gel electrophoresis showed that the 5 normal components were present in the cell body of inhibited neurons. Thus, synthesis and insertion of glycoproteins into membranes do not guarantee export from the cell body: presumably completion of transportable organelles requires continuous synthesis of new proteins. Longer exposure before injection resulted in reduced amounts of four of the glycoproteins, but one component continued to be formed. Anisomycin can be used to resolve export of glycoproteins out of the cell body from subsequent movement along the axon. When we exposed R2 to anisomycin after injection, [3H]glycoproteins, which had already entered the axon, were translocated along the axon normally; they were distributed in waves, the most distal moving at 50-60 mm/day.