CMP-sialic acid, the sole sialosyl donor, is intra-axonally transported

N-Acetyl-D-[6-3H]mannosamine was injected into the 9th dorsal root ganglion of Xenopus laevis and the intra-axonal transport of chloroform/methanol-soluble radioactivity was analyzed using thin-layer chromatography coupled with fluorography. Three radioactive groups were distinct in consecutive segments of the sciatic nerve. The first is due to N-acetyl-D-mannosamine itself which labels the nerve uniformly, but does not seem to migrate within axons. The second group, representing most probably CMP-sialic acid, migrates at about 8 mm/day at 15 degrees C. The third is a species of ganglioside uniquely present in the frog nerve, and this migrates at 1-3 mm/day. Our demonstration of the intra-axonal transport of CMP-sialic acid affords direct support to the contention that sialosylation of the ganglioside can occur in axon terminals.