Paranodal proteins

Paranodal proteins other than tetraspan proteins. The... 

Dupree JL, Girault JA, Popko B (1999) Axo-glial interactions regulate the locaUzation of axonal paranodal proteins. J Cell Biol 147 1145—1152... 

CD9 is a well-characterized hematopoietic tetraspan protein that has been shown to be present in CNS and PNS myelin, although it is present at higher levels in PNS myelin. In other cells, it is involved in integrin signaling and cell adhesion and motility. It is expressed at late stages of myelination and in the CNS is primarily found in paranodal junctions [34]. While compact CNS myelin is apparently normal in CD9-null animals, the paranodal loops are often disconnected from axonal membranes, and the transverse bands of the paranodal loops are lost. In the PNS, in addition to altered paranodes, hypermy-elination occurs. Thus, this tetraspan protein appears to act primarily at paranodes, where it is crucial for normal paranodal junctions. 

Ishibashi, T., Ding, L., Ikenaka, K. et al. Tetraspanin protein CD9 is a novel paranodal component regulating paranodal junctional formation. /. Neurosci. 24, 96-102, 2004. 

A third myelin inhibitory protein, OMgp, is a GPI-linked protein expressed by oligodendrocytes [18], OMgp is a relatively minor component of myelin, believed to be localized to the paranodal loops, next to the node of Ranvier. OMgp contains a leucine-rich repeat (LRR) domain and a C-terminal domain with serine/threonine repeats. Like MAG, OMgp is also found in the PNS. Like Nogo, OMgp is also expressed in adult neurons. 

The node ofRanvier, paranodal junctions and the adjacent juxtaparanodal regions each contain distinct protein complexes. Each of these membrane domains contains a specific set of cell adhesion molecules that are stabilized and retained through interactions with cytoskeletal and scaffolding proteins. These in turn recruit and stabilize the appropriate channels (Coman et al., 2005 Simons and Trajkovic, 2006). 

Myelin basic proteins (MBP). Basic proteins are abundant both in CNS and PNS myelin, where they are associated with negatively charged lipids. They are assumed to be involved in myelin compaction on the cytoplasmic side of the membrane bilayer. A spontaneous MBP mutant, the shiverer mouse, is devoid of the major dense line of myelin in the CNS (Dupouey et al., 1979). Another such mutant, the Long Evans Shaker (LES) rat, shows major changes in spinal cord white matter, with dispersed labeling of Kvl.l and Kvl.2 K+ channel subunits as well as of Caspr, a molecule normally confined to paranodes along LES rat spinal axons (Eftekharpour et al, 2005). 

As noted in the preceding section, Cx32 is a ubiquitous protein that is also found in CNS myelin. Its presence in Schwann cells was discovered when Cx32 mutations were associated with Charcot-Marie-Tooth disease of the CMTX type. CMTX is an X-linked demyelinating neuropathy. The molecule is located in the paranodes. There are subtle anomalies of the myelin sheath and the Ranvier node (Hahn et al.,... 

Proteins and Specific Lipids of the Node of Ranvier and the Paranodal and Juxtaparanodal Areas... 

The myelin protein cyclic nucleotide phosphodiesterase (CNP) is required for maintenance of axon-glia interactions at the node of Ranvier. It also maintains the integrity of the paranodes (Rasband et al., 2005). 

Ishibashi T, Dakin KA, Stevens B, Lee PR, Kozlov SV, Stewart CL, Fields RD (2006) Astrocytes promote myeRnation in response to electrical impulses. Neuron 49 823-832 Ishibashi T, Ding L, Ikenaka K, Inoue Y, Miyado K, Mekada E, Baba H (2004) Tetiaspanin protein CD9 is a novel paianodal component regulating paranodal junctional formation. J Neurosci 24 96-102... 

NG2 expressed by a variety of immature glia in the CNS including ohgodendrocyte progenitor cells, paranodal astrocytes and perisynaptic glia. The protein has a large extracellular domain with tw o LNS/Lam G domains at the N-terminus and a short intracellular tail with a PDZ-recognition domain at the C-terminus. 

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