Figure 2.

Features of the myelination process. (A) Sequential stages of oligodendrocyte maturation. Specific markers for differentiation status of the oligodendrocyte lineage. Differentiation into mature oligodendrocytes is associated with acquisition of myelin-related proteins. (B) Myelin sheath organization in the CNS. Myelinating glial cells, oligodendrocytes in the CNS form the myelin sheath by enwrapping axons. Myelinated axon regions are interrupted by non-myelinated regions (nodes of Ranvier). Myelinated axons have four distinct domains: node (N), paranode (PN), juxtaparanode (JXP) and internode (INT). Nodes of Ranvier are regions of concentrated sodium channels that form between two internodes. Adjacent to the nodes of Ranvier are the paranode and the juxtaparanode. All four domains have characteristic proteins (see upper inset). At the nodes of Ranvier, Neurofascin 186 (Nf-186) supports the clustering of Na⁺ channels. The nodal Na⁺ channels are separated from the juxtaparanodal K⁺ channels via the paranode, where Neurofascin 155 (Nf-155) binds tightly to the axonal complex of Contactin and Contactin-associated protein (Caspr). CNP, an abundant cytoplasmic myelin protein, is predominantly found at the paranode. At the juxtaparanode, clustered K⁺ channels are associated to Caspr-2 and Contactin-2.