Does Paranode Formation and Maintenance Require Partitioning of Neurofascin 155 into Lipid Rafts?

Abstract

Paranodal axoglial junctions in myelinated nerve fibers are essential for efficient action potential conduction and ion channel clustering. We show here that, in the mature CNS, a fraction of the oligodendroglial 155 kDa isoform of neurofascin (NF-155), a major constituent of paranodal junctions, has key biochemical characteristics of a lipid raft-associated protein. However, despite its robust expression, NF-155 is detergent soluble before paranodes form and in purified oligodendrocyte cell cultures. Only during its progressive localization to paranodes is NF-155 (1) associated with detergent-insoluble complexes that float at increasingly lower densities of sucrose and (2) retained in situ after detergent treatment. Finally, mutant animals with disrupted paranodal junctions, including those lacking specific myelin lipids, have significantly reduced levels of raft-associated NF-155. Together, these results suggest that trans interactions between oligodendroglial NF-155 and axonal ligands result in cross-linking, stabilization, and formation of paranodal lipid raft assemblies.

Tumor Suppressor Schwannomin/Merlin Is Critical for the Organization of Schwann Cell Contacts in Peripheral Nerves

“…These observations provide evidence for an important role of schwannomin in the organization and stability of Schwann cells membrane domains. This role may be related to the partitioning of schwannomin in lipid rafts (Stickney et al, 2004), which are important for the segregation of membrane proteins and organization of axoglial contacts (Schafer et al, 2004). …”

Rafts in oligodendrocytes: Evidence and structure–function relationship

“…Recently, it has been shown that NF155 associates with DRMs (rafts) in the CNS and that this association is commensurate with the timing of paranode formation (Schafer et al, 2004). Given the abnormal structure of the paranodal loops in CGT knockout mice (Bosio et al, 1998), it is likely that the correct membrane association of NF155 is important for the stability of the paranodal structure and thus for the integrity of the myelin sheath.…”

“…Mouse OLG 5 DIV CHAPS 20 mM 30 min 4°C 30-days-old rat TX-100 1% 30 min 4°C Kim and Pfeiffer 1999 4-6 weeks old rat TX-100 0.5% 3 min RT Gillespie et al 1989 35-days-old mice TX-100 / CHAPS / Brij 96V / TX-102 1% 30 min 4°C/37°C Taylor et al 2002 2-year-old mice TX-100 2% 30 min 4°C Saravanan et al 2004 TX-100 1% na 4°C Mouse CHAPS 30 mM na 4°C Boyanapalli et al 2005 Rabbit TX-100 1% 16h + 24h 4°C Pereyra et al 1988 Purified myelin Bovine brain E11 -E40 CHAPS 1.5% 30 min 4°C Debruin et al 2005 Primary OLGs 1-2 day old rat brain OLGs 12 DIV TX-100 0.5% 3 min RT Wilson and Brophy 1989 CNP Optic nerve p13, p18, p24 and 2 months old rat TX-100 1% 1h 4°C Maier et al 2005 Primary OLGs premyelinating mouse OLGs TX-100 1% 1h 4°C Schafer et al 2004 TX-100 1% 30 min 4°C Spinal cord Rat (WT or EAE) Lubrol WX 0.5% 30 min 4°C Maier et al 2005 Optic nerve p13, p18, p24 and 2 months old rat TX-100 1% 1h 4°C Schafer et al 2004 35-days-old mice TX-100 / CHAPS / Brij 96V / TX-102 1% 30 min 4°C Taylor et al 2002 Adult mouse brain TX-100 2% 30 min 4°C Krämer et al 1997Krämer et al , 1999 Purified myelin 2-year-old mice TX-100 2% 30 min 4°C Saravanan et al 2004 Mouse OLGs 5/8 DIV TX-100 2% 30 min 4°C Krämer et al 1997Krämer et al , 1999 Primary OLGs Mouse OLG 5 DIV CHAPS 20 mM 30 min 4°C NCAM 120…”

Early events in node of Ranvier formation during myelination and remyelination in the PNS

“…The monoclonal anti-pan Nav channel (K58/35), anti-Nav1.2 (K69/3) and anti-pan neurofascin (L11A/41.6) antibodies have been described previously (Rasband et al, 1999;Boiko et al, 2001;Rasband et al, 2003;Schafer et al, 2004). The polyclonal anti-Nav1.2, anti-Nav1.6 and anti-caspr antibodies have been described previously (Rasband et al, 1999;Boiko et al, 2001;Rasband et al, 2003) and were kindly provided by Dr. James Trimmer.…”

“…Consequently, we have been unable to determine whether the initial clusters of neurofascin consist of NF-155 at developing paranodes and/ or NF-186 at nascent nodes. In the CNS, paranodal proteins, including neurofascin, appear to cluster before localization of nodal proteins (Rasband et al, 1999;Schafer et al, 2004). Therefore, we sought to determine which splice variant of neurofascin is the first to appear at newly forming nodes in the PNS.…”