Journal of Neuroscience, Vol 6, 1365-1371, Copyright © 1986 by Society for Neuroscience
Analysis of the carbohydrate composition of axonally transported glycoconjugates in sciatic nerve
CE Hart and JG Wood
Glycosidase enzyme digestion in combination with postembedding lectin
cytochemistry was used to study the carbohydrate composition of axonally
transported glycoproteins. A cold block procedure for the interruption of
axonal transport was employed to increase selectively the population of
anterograde moving components on the proximal side of the transport block.
Electron-microscopic observations revealed that a cold block applied to the
sciatic nerve of an anesthetized rat produced an increase in axonal smooth
membrane vesicles at a site directly proximal to the cold block.
Postembedding lectin cytochemistry of the sciatic nerve demonstrated a
substantial increase in concanavalin A (Con A), wheat germ agglutinin
(WGA), and succinylated WGA binding sites in axons directly proximal to the
cold block. Endoglycosidase H (endo H) digestion prior to lectin
cytochemistry characterized a large population of the axonally transported
Con A binding sites as polymannose and/or hybrid N-linked oligosaccharides
(endo H- susceptible). A distinct population of neuraminidase-resistant WGA
binding sites was also found in axons directly proximal to the transport
block. The concomitant increase in smooth membrane vesicles and lectin
binding sites in axons at the transport block supports the hypothesis that
a system(s) of smooth membrane inside the axon is involved in the transport
of glycoproteins from the cell soma to their cell surface destinations.
Results of glycosidase digestions and lectin cytochemistry experiments
suggest that many of the axonally transported glycoprotein carbohydrates
are polymannose and/or hybrid N-linked oligosaccharides. This observation
is especially interesting in relation to our previous reports, which
indicated that most lectin binding sites on the neuronal cell surface are
composed of complex oligosaccharides.(ABSTRACT TRUNCATED AT 250 WORDS)