Abstract
Glycoproteins containing O-linked N-acetylglucosamine (O-GlcNAc) are present in axons of Aplysia neurons (Gabel et al., 1989) and among transcription factors and other proteins in the nucleus of eukaryotic cells (Jackson and Tjian, 1988). A recently discovered pathway in neurons transports proteins through the axon and then into the nucleus (Ambron et al., 1992). If any of the axonal O-GlcNAc glycoproteins use this pathway, then the axon and the nucleus will have these glycoproteins in common. We addressed this issue by using galactosyltransferase and UDP-3H-galactose to label and identify the glycoproteins in three regions of Aplysia neurons: axoplasm, extruded from nerves; nuclei, isolated by manual dissection of single neurons; and cytoplasm, obtained after removal of nuclei. At least 21 glycoproteins were labeled by this procedure; several, at 200, 180, 83, 76, and 66 kDa, from the nucleus and axoplasm comigrated after SDS-PAGE. Radiolabeled galactosyl-N-acetylglucosaminitol was released from the glycoproteins by base/borohydride, thereby verifying the presence of O-GlcNAc. Comparison of the 83 kDa glycoprotein from the nucleus and axoplasm revealed that both were soluble, had multiple O-GlcNAcs, and were bound to WGA. Thus, the 83 kDa constituent is a good candidate to use the axonal transport/nuclear import pathway.