Myelin-Associated Glycoprotein (Siglec-4): A Nervous System Lectin That Regulates Axon-Myelin Stability and Axon Regeneration

Myelin-associated glycoprotein (MAG, Siglec-4) is a multifunctional signaling protein that sits at the critical interface between axons-the thin nerve cell extensions that carry action potentials between nerve cells-and the multilamellar myelin wrap that ensheathes them [1, 2]. Myelin acts not only to insulate but also to nurture axons, to regulate axon cytoarchitecture, and to help direct the local distribution of ion channels required for rapid nerve conduction. MAG plays key signaling roles that stabilize axon-myelin interactions [3, 4], regulate the structure of myelin and axons [5-7], and control axon regeneration after injury [8, 9]. Some of MAG’s functions depend on its lectin activity, which will be described more fully in a subsequent section.