Expression and Secretion of a Soluble Form of Myelin-Associated Glycoprotein (MAG)

Myelin-associated glycoprotein (MAG) was first identified as the major glycoprotein in the central nervous system (CNS) through ³ Hfucose-labeling experiments (1 ). It is expressed on the surface of glial cells of both the CNS and peripheral nervous system (PNS). During development, it is localized throughout the wraps of loose myelin; after compaction, it is restricted to Schmidt-Lanterman incisures, paranodal loops, outer mesaxon, and in particular to the glial-axon interface (2 , 3 ). The protein is thought to play a role in maintaining the periaxonal space. MAG has also been postulated to be involved in glial-neuron adhesion during myelination. This is based on the finding that anti-MAG antibodies inhibit oligodendrocyte-neuron adhesion by 25% (4 ), and that MAG liposomes bind a variety of neuronal cells (5 ). Observations from in vitro myelination cultures also support a role for MAG in Schwann cell adhesion, migration, and elongation along neurites (6 , 7 ).