Myelin-associated glycoprotein and its axonal receptors.
Myelin-associated glycoprotein (MAG) is expressed on the innermost myelin membrane wrap, directly apposed to the axon surface. Although it is not required for myelination, MAG enhances long-term axon-myelin stability, helps to structure nodes of Ranvier, and regulates the axon cytoskeleton. In addition to its role in axon-myelin stabilization, MAG inhibits axon regeneration after injury; MAG and a discrete set of other molecules on residual myelin membranes at injury sites actively signal axons to halt elongation. Both the stabilizing and the axon outgrowth inhibitory effects of MAG are mediated by complementary MAG receptors on the axon surface. Two MAG receptor families have been described, sialoglycans (specifically gangliosides GD1a and GT1b) and Nogo receptors (NgRs). Controversies remain about which receptor(s) mediates which of MAG's biological effects. Here we review the findings and challenges in associating MAG's biological effects with specific receptors.
Schnaar
Ronald L
RL
Department of Pharmacology, The Johns Hopkins School of Medicine, 725 N. Wolfe Street, Baltimore, MD 21205, USA. schnaar@jhu.edu
Lopez
Pablo H H
PH
D000818:Animals; D005732:Gangliosides / Q000378:metabolism; D020439:Growth Cones / Q000378:metabolism* / Q000648:ultrastructure; D006131:Growth Inhibitors / Q000378:metabolism*; D006801:Humans; D009185:Myelin Proteins / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism* / Q000648:ultrastructure; D018992:Myelin-Associated Glycoprotein / Q000378:metabolism* / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000378:metabolism* / Q000648:ultrastructure; D000070798:Nogo Proteins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D005732:Gangliosides; D006131:Growth Inhibitors; D009185:Myelin Proteins; D018992:Myelin-Associated Glycoprotein; D000070798:Nogo Proteins; C000603199:RTN4 protein, human; D011956:Receptors, Cell Surface; C021298:ganglioside, GD1a