Evidence that all newly synthesized proteins destined for fast axonal transport pass through the Golgi apparatus.

Abstract

Effects of the Na+ ionophore, monensin, were examined on the passage from neuronal cell body to axon of materials undergoing fast intracellular transport. In vitro exposure of bullfrog [Rana catesbeiana] dorsal root ganglia to concentrations of drug < 1.0 .mu.M led to a dose-dependent depression in the amount of fast-transported [3H]leucine- or [3H]glycerol-labeled material appearing in the nerve trunk. Incorporation of either precursor was unaffected. Exposure of a desheathed nerve trunk to similar concentrations of monensin, while ganglia were incubated in drug-free medium, had no effect on transport. With [3H]fucose as precursor, fast transport of labeled glycoproteins was depressed to the same extent as with [3H]leucine; synthesis was unaffected. With [3H]galactose as precursor, an apparent reduction in transport of labeled glycoproteins was accounted for by a marked depression in incorporation. The inference from these findings, that monensin acts to block fast transport at the level of the Golgi apparatus, was supported by ultrastructural examination of the drug-treated neurons. An extensive and selective disruption of Golgi saccules was observed, accompanied by an accumulation of clumped smooth membranous cisternae. Quantitative analyses of 48 individual fast-transported protein species, after separation by 2-dimensional gel electrophoresis, revealed that monensin depresses all proteins to a similar extent. Passage through the Golgi apparatus appears to be an obligatory step in the intracellular routing of materials destined for fast axonal transport.