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The raft-associated protein MAL is required for maintenance of proper axon--glia interactions in the central nervous system.

Schaeren-Wiemers N, Bonnet A, Erb M, Erne B, Bartsch U, Kern F, Mantei N, Sherman D, Suter U - J. Cell Biol. (2004)

Bottom Line: These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered.Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts.Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.

View Article: PubMed Central - PubMed

Affiliation: Neurobiology, Department of Research, University Hospital Basel, 4056 Basel, Switzerland. Nicole.Schaeren-Wiemers@unibas.ch

ABSTRACT
The myelin and lymphocyte protein (MAL) is a tetraspan raft-associated proteolipid predominantly expressed by oligodendrocytes and Schwann cells. We show that genetic ablation of mal resulted in cytoplasmic inclusions within compact myelin, paranodal loops that are everted away from the axon, and disorganized transverse bands at the paranode--axon interface in the adult central nervous system. These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered. Initial formation of paranodal regions appeared normal, but abnormalities became detectable when MAL started to be expressed. Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts. Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.

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MAL deficiency leads to reduced expression and dispersed localization of Caspr, Kv1.2, and NF155 at the node of Ranvier. Confocal localization on longitudinally sectioned optic nerves from 3-mo-old WT (left column) and KO (right column) mice for Caspr (A and B, green; C–F, red), NaCh (A, B, and insets in E and F; red), Kv1.2 (C and D, blue), and NF155 (E and F, green). Note the strong reduction of Caspr and Kv1.2 clusters in KO mice (B and D), whereas the distribution of NaCh was not altered. Inset in D: dispersed distribution of Caspr in mal-deficient paranodes, eventually extending beyond juxtaparanodally located Kv1.2 (arrowhead; asterisk; node). However, Kv1.2 (inset in D, open arrow) was never detected within paranodes. NF155 (E and F, green) and Caspr (E and F, red) showed strong overlap (arrowheads point to pairs of clusters) in the paranodes of WT, but were barely detectable in KO mice (inset). Bars, 20 μm.
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fig5: MAL deficiency leads to reduced expression and dispersed localization of Caspr, Kv1.2, and NF155 at the node of Ranvier. Confocal localization on longitudinally sectioned optic nerves from 3-mo-old WT (left column) and KO (right column) mice for Caspr (A and B, green; C–F, red), NaCh (A, B, and insets in E and F; red), Kv1.2 (C and D, blue), and NF155 (E and F, green). Note the strong reduction of Caspr and Kv1.2 clusters in KO mice (B and D), whereas the distribution of NaCh was not altered. Inset in D: dispersed distribution of Caspr in mal-deficient paranodes, eventually extending beyond juxtaparanodally located Kv1.2 (arrowhead; asterisk; node). However, Kv1.2 (inset in D, open arrow) was never detected within paranodes. NF155 (E and F, green) and Caspr (E and F, red) showed strong overlap (arrowheads point to pairs of clusters) in the paranodes of WT, but were barely detectable in KO mice (inset). Bars, 20 μm.

Mentions: Because axoglial contact controls local differentiation of myelinated axons, we performed confocal analyses to determine the localization of nodal (e.g., sodium channel [NaCh]), paranodal (e.g., Caspr and neurofascin 155 [NF155]), and juxtaparanodal (e.g., Kv1.2) proteins. Immunofluorescence analysis of optic nerve sections from adult KO showed a strong reduction in the number of Caspr-positive paranodes as well as in the intensity of the Caspr labeling (Fig. 5 B, overview) when compared with WT animals (Fig. 5 A, overview). Moreover, analysis of the few remaining Caspr-positive paranodes at higher magnification revealed a diffuse distribution of Caspr (Fig. 5 B inset, open arrow). Immunofluorescence analysis of Kv1.2 in the juxtaparanodal membrane also revealed a reduction in staining intensity and in the number of positive juxtaparanodes, as well as some lateral diffusion in KO mice (Fig. 5 D). The number of nodes, indicated by tight clusters of NaCh, was not altered in the mutant (Fig. 5 B). Quantification of the number of Caspr clusters in the paranode and of Kv1.2 clusters in the juxtaparanode revealed a reduction of 70–90% and ∼70%, respectively, in KO mice (Fig. 6 A). The number of NaCh clusters was similar in WT and KO mice. Immunofluorescence analysis of NF155, which colocalized with Caspr in WT animals (Fig. 5 E, arrowheads), revealed a similarly strong reduction in staining intensity as observed for Caspr, and was barely detectable in KO mice (Fig. 5 F, overview and inset).


The raft-associated protein MAL is required for maintenance of proper axon--glia interactions in the central nervous system.

Schaeren-Wiemers N, Bonnet A, Erb M, Erne B, Bartsch U, Kern F, Mantei N, Sherman D, Suter U - J. Cell Biol. (2004)

MAL deficiency leads to reduced expression and dispersed localization of Caspr, Kv1.2, and NF155 at the node of Ranvier. Confocal localization on longitudinally sectioned optic nerves from 3-mo-old WT (left column) and KO (right column) mice for Caspr (A and B, green; C–F, red), NaCh (A, B, and insets in E and F; red), Kv1.2 (C and D, blue), and NF155 (E and F, green). Note the strong reduction of Caspr and Kv1.2 clusters in KO mice (B and D), whereas the distribution of NaCh was not altered. Inset in D: dispersed distribution of Caspr in mal-deficient paranodes, eventually extending beyond juxtaparanodally located Kv1.2 (arrowhead; asterisk; node). However, Kv1.2 (inset in D, open arrow) was never detected within paranodes. NF155 (E and F, green) and Caspr (E and F, red) showed strong overlap (arrowheads point to pairs of clusters) in the paranodes of WT, but were barely detectable in KO mice (inset). Bars, 20 μm.
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fig5: MAL deficiency leads to reduced expression and dispersed localization of Caspr, Kv1.2, and NF155 at the node of Ranvier. Confocal localization on longitudinally sectioned optic nerves from 3-mo-old WT (left column) and KO (right column) mice for Caspr (A and B, green; C–F, red), NaCh (A, B, and insets in E and F; red), Kv1.2 (C and D, blue), and NF155 (E and F, green). Note the strong reduction of Caspr and Kv1.2 clusters in KO mice (B and D), whereas the distribution of NaCh was not altered. Inset in D: dispersed distribution of Caspr in mal-deficient paranodes, eventually extending beyond juxtaparanodally located Kv1.2 (arrowhead; asterisk; node). However, Kv1.2 (inset in D, open arrow) was never detected within paranodes. NF155 (E and F, green) and Caspr (E and F, red) showed strong overlap (arrowheads point to pairs of clusters) in the paranodes of WT, but were barely detectable in KO mice (inset). Bars, 20 μm.
Mentions: Because axoglial contact controls local differentiation of myelinated axons, we performed confocal analyses to determine the localization of nodal (e.g., sodium channel [NaCh]), paranodal (e.g., Caspr and neurofascin 155 [NF155]), and juxtaparanodal (e.g., Kv1.2) proteins. Immunofluorescence analysis of optic nerve sections from adult KO showed a strong reduction in the number of Caspr-positive paranodes as well as in the intensity of the Caspr labeling (Fig. 5 B, overview) when compared with WT animals (Fig. 5 A, overview). Moreover, analysis of the few remaining Caspr-positive paranodes at higher magnification revealed a diffuse distribution of Caspr (Fig. 5 B inset, open arrow). Immunofluorescence analysis of Kv1.2 in the juxtaparanodal membrane also revealed a reduction in staining intensity and in the number of positive juxtaparanodes, as well as some lateral diffusion in KO mice (Fig. 5 D). The number of nodes, indicated by tight clusters of NaCh, was not altered in the mutant (Fig. 5 B). Quantification of the number of Caspr clusters in the paranode and of Kv1.2 clusters in the juxtaparanode revealed a reduction of 70–90% and ∼70%, respectively, in KO mice (Fig. 6 A). The number of NaCh clusters was similar in WT and KO mice. Immunofluorescence analysis of NF155, which colocalized with Caspr in WT animals (Fig. 5 E, arrowheads), revealed a similarly strong reduction in staining intensity as observed for Caspr, and was barely detectable in KO mice (Fig. 5 F, overview and inset).

Bottom Line: These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered.Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts.Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.

View Article: PubMed Central - PubMed

Affiliation: Neurobiology, Department of Research, University Hospital Basel, 4056 Basel, Switzerland. Nicole.Schaeren-Wiemers@unibas.ch

ABSTRACT
The myelin and lymphocyte protein (MAL) is a tetraspan raft-associated proteolipid predominantly expressed by oligodendrocytes and Schwann cells. We show that genetic ablation of mal resulted in cytoplasmic inclusions within compact myelin, paranodal loops that are everted away from the axon, and disorganized transverse bands at the paranode--axon interface in the adult central nervous system. These structural changes were accompanied by a marked reduction of contactin-associated protein/paranodin, neurofascin 155 (NF155), and the potassium channel Kv1.2, whereas nodal clusters of sodium channels were unaltered. Initial formation of paranodal regions appeared normal, but abnormalities became detectable when MAL started to be expressed. Biochemical analysis revealed reduced myelin-associated glycoprotein, myelin basic protein, and NF155 protein levels in myelin and myelin-derived rafts. Our results demonstrate a critical role for MAL in the maintenance of central nervous system paranodes, likely by controlling the trafficking and/or sorting of NF155 and other membrane components in oligodendrocytes.

Show MeSH
Related in: MedlinePlus