Synaptic localization and neural regulation of an n-acetylgalactosaminyl transferase in skeletal muscle

Abstract

We have previously documented the properties of a ∼ 220-kDa cell surface glycosyltransferase that transfers N-acetylgalactosamine to oligosaccharide chains (Balsamo et al., 1986b). Because N-acetylgalactosamine-terminated carbohydrates are concentrated at the neuromuscular junction (Scott et al., 1988), we assayed skeletal muscle for the presence of the N-acetylgalactosaminyl transferase. Using immunohistochemical methods, we found that the enzyme is localized at neuromuscular junctions on normal adult rat muscle fibers. Biochemical assays confirm that junctional areas are highly enriched in the ∼220-kDa immunoreactive species as well as in enzyme activity associated with the ∼220-kDa species. This restricted distribution is dependent on synaptic integrity, as the enzyme appears extrasynaptically on denervation. These results provide a plausible metabolic basis for the localization of a synapse-specific carbohydrate and demonstrate that the expression of a glycosyltransferase is regulated by synaptic interactions.