Ganglioside localization on myelinated nerve fibres by cholera toxin binding

Abstract

Summary G_M1 ganglioside has been localized on the surfaces of myelinated, peripheral nerve fibres by using immunofluorescence to detect cholera toxin receptors. Unfixed, mouse sciatic nerves were teased into individual, intact fibres in order to expose their extracellular surfaces. Cholera toxin binding sites were abundant at all nodes of Ranvier; they were scarce on the internodal fibre surfaces. The nodal receptors were resistant to various degradative enzymes, including trypsin and proteinase K. Proteases did not unmask receptors on the internodal surfaces. Exogenous G_M1 successfully competed for the toxin binding sites on the fibres. From this evidence and the specificity of cholera toxin binding, we conclude that G_M1 ganglioside is abundantly present on the membrane surfaces of peripheral nodes of Ranvier and is not present on the internodal Schwann cell surfaces in an appreciable amount. The patterns of fluorescence within the node suggest that the axon and Schwann cell structures are sites where G_M1 is localized. Treatment of the teased fibres withVibrio cholerae neuraminidase, which is known to reduce polysialogangliosides to the monosialoganglioside G_m1, induced cholera toxin binding on the internodal Schwann cell surfaces. The induced receptors, as well as their precursors, were resistant to trypsin and proteinase K. We conclude that the internodal Schwann cell surface is rich in an unidentified polysialoganglioside(s) that can be converted to G_M1 by neuraminidase.