A study of proteins from ganglion cells of the goldfish retina

The ganglion cell layer (GCL) is a homogeneous population of neurons obtained from the goldfish retina by microdissection. The pattern of proteins solubilized from GCL and separated by sodium dodecyl sulfatepolyacrylamide gels is quite different from patterns of other retinal layers, and includes ten major polypeptide bands. An electrophoretic doublet at about 59,000 and 53,000 daltons co-migrates with the α and β monomers of tubulin and contributes an estimated 25% of the total neuronal protein. Comparisons of this GCL doublet with purified brain tubulin show identical cyanogen bromide fragments and selective precipitation by antitubulin antibodies. Another prominent GCL polypeptide at 46,000 daltons co-migrates with actin of fish skeletal muscle. This 46,000-dalton protein also contains 3-N-methylhistidine, with a Me-His/His ratio of 1:10, similar to that reported for brain actin. Ten polypeptides of the GCL were identified as major glycoproteins by selective binding of ¹²⁵I-concanavalin A. Major glycosylated elements include α and β monomers of tubulin and another polypeptide of about 43,000 daltons. Axons of ganglion cells outside the retina are surrounded by glia and make up the optic fibers of the visual system. The optic fibers, unlike the GCL, contains three major myelin proteins at 35,000, 23,000, and 14,000 daltons. The 23,000-dalton component is a prominent glycoprotein and binds concanavalin A while the 14,000-dalton component corresponds to a basic myelin protein. Most of the major proteins associated with the GCL or optic fiber are components of the neuronal cytoskeleton or myelin membrane. These identifications allow study of specific proteins during intraaxonal transport and neuronal regeneration within the fish visual system.