Lectin affinity and PAGE analysis of soluble axonally transported glycoconjugates in the rat visual system

Recent reports of the transsynaptic transfer of wheat germ agglutinin (WGA) in several systems are consistent with the hypothesis that WGA binds to endogenous glycoproteins(s) which undergo transsynaptic transfer. Such molecules might be involved in trophic interactions between neurons. Since these hypothetical glycoproteins must be soluble proteins (it is unlikely that integral membrane proteins are exchanged between neurons) this preliminary study of the soluble, axonally transported glycoconjugates of the visual system was undertaken. Soluble, tritium-labeled macromolecules which accumulated in the rat lateral geniculate nucleus (LGN) and visual cortex after intraocular injections of tritiated fucose were studied by lectin affinity chromatography and polyacrylamide gel electrophoresis (PAGE). After correction for hematogenously or cerebrospinal fluid transported label, 9.6% of the radioactivity in the LGN and 17.9% of the radioactivity in the visual cortex was found in the soluble fraction of a phosphate-buffered saline homogenate. In the LGN, 31.3% of the axonally transported soluble label was bound by concanavalin-A (Con-A) agarose. The corresponding figure in the visual cortex was 25.7%. Most (greater than 90%) of the label which did not bind Con-A was soluble in 10% trichloroacetic acid (TCA). Eighty-eight percent of the label which bound Con-A was precipitated by 10% TCA. On 7.5% polyacrylamide SDS reducing gels, the Con-A bound material from either the LGN or the visual cortex migrated as a single peak near the origin of the gel (apparent molecular weight greater than 300,000 Da).(ABSTRACT TRUNCATED AT 250 WORDS)