Myelin associated glycoprotein (MAG) is a low abundant component of the myelin sheath and is synthesized by oligodendrocytes and Schwann cells in the central and peripheral nervous system, respectively. MAG is also an adhesion molecule that binds to gangliosides and glycoproteins such as RTN4R and RTN4RL2 to mediate interaction between myelinating cells and neurons, and additionally functions after injury in the CNS to inhibit axon regeneration through the RHO A signaling pathway (reviewed in Schnarr and Lopez, 2009; Mehta et al, 2017; McKerracher and Rosen, 2015).
MAG expression is regulated in part by the binding of EGR2 and SOX10 to elements in the second intron of the gene (LeBlanc et al, 2007; Jang et al, 2006; Jones et al, 2007). Consistent with this, MAG expression is abrogated in EGR2-depleted mice and stimulated by ectopic EGR2 expression (Le et al, 2005; Nagarajan et al, 2001). At the protein level, MAG stability is postively regulated by the adhesion GPCR protein GPR98 (also known as VLGR1). GPR98 signals through G proteins, PKA and PKA to limit MAG ubiquitination and subsequent degradation, although the mechanism remains to be elucidated (Shin et al, 2013; reviewed in Mehta and Piao, 2017).