Abstract
Because radioactive precursors can be injected directly into the cell body or axon of R2, a giant, identified neuron of the Aplysia abdominal ganglion, it was possible to show that glycolipid is synthesized in the cell body, inserted into membranes along with glycoprotein, and then exported into the axon within organelles that are moved by fast axonal transport. After intrasomatic injection of N-[3H]-acetyl-D- galactosamine, five major 3H-glycolipids were identified using thin layer polysilicic acid glass fiber chromatography. At least two of the lipids are negatively charged. Analysis of 32P-labeled lipid from the abdominal ganglion revealed the presence of 2-aminoethylphosphonate, indicating that these polar substances are sphingophosphonoglycolipids. The major 3H-glycolipids synthesized in R2 are similar to a family of phospholipids isolated from the skin of A. kurodai, previously characterized by Araki et al. (Araki, S., Y. Komai, and M. Satake (1980) Biochem J. 87: 503–510). Since sialic acid is absent in Aplysia as in other invertebrates, these polar glycolipids may function like gangliosides in vertebrates. The polar 3H-glycolipids are synthesized and incorporated into intracytoplasmic membranes solely in the cell body. Direct injection of the labeled sugar into the axon revealed no local synthesis or exchange of glycolipid. Moreover, there was no indication for transfer from glial cells into axoplasm. Although the incorporation of N-[3H]-acetyl-D-galactosamine into glycolipid is not affected by anisomycin, an effective inhibitor of protein synthesis, the export into the axon of membranes containing the newly synthesized lipid is completely blocked by the drug.(ABSTRACT TRUNCATED AT 250 WORDS)
