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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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Onset of paranodal alterations correlates with MAL expression. Immunohistochemical analysis of sagittal brain sections for PLP (A–D), MAL (E–H), and confocal localization analyses of NaCh (I–M, red) and Caspr (I–M, green) on consecutive tissue sections in WT (A–I and L) and KO mice (K and M). At P16 in WT mice, myelination had already started in the corpus callosum as seen by PLP expression (A, arrows demarcate the border between corpus callosum and hippocampus), but MAL is not detectable yet (E). Clustering of Caspr in paranodes is normal in KO mice (K, top), whereas in the cerebellum myelination is more advanced, as seen by MAL expression (F); the immunofluorescent signal for Caspr is reduced (K, bottom). In contrast, at P23 MAL expression starts in corpus callosum (G, arrow) and Caspr is strongly reduced in paranodes of KO mice (M). PLP expression in KO mice occurred normally (not depicted), comparable to WT mice (C, arrow). Quantification of the confocal localization analyses of NaCh, Caspr, and NF in corpus callosum and cerebellum at P16 (N) and P23 (O). Immunofluorescent particles larger than 0.7 μm3 were quantified in two WT and KO mice. Note that at P16, total amounts of Caspr were reduced in cerebellum of KO mice, but not in corpus callosum; no differences were observed for NaCh. Error bars: SD from two animals per age and tissue area. At P23, strong reduction of Caspr and NF was observed in cerebellum as well in corpus callosum. For quantification, the pan-NF antiserum was used, which recognizes the 186 (nodal) and 155 (paranodal) isoforms; therefore, the residual amounts of NF-immunofluorescent intensity can be attributed to the nodal 186 isoform, which did not show differences between WT and KO mice (not depicted). wm, white matter; gcl, granule cell layer; CA1, pyramidal cell layer (hippocampus); cc, corpus callosum.
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fig7: Onset of paranodal alterations correlates with MAL expression. Immunohistochemical analysis of sagittal brain sections for PLP (A–D), MAL (E–H), and confocal localization analyses of NaCh (I–M, red) and Caspr (I–M, green) on consecutive tissue sections in WT (A–I and L) and KO mice (K and M). At P16 in WT mice, myelination had already started in the corpus callosum as seen by PLP expression (A, arrows demarcate the border between corpus callosum and hippocampus), but MAL is not detectable yet (E). Clustering of Caspr in paranodes is normal in KO mice (K, top), whereas in the cerebellum myelination is more advanced, as seen by MAL expression (F); the immunofluorescent signal for Caspr is reduced (K, bottom). In contrast, at P23 MAL expression starts in corpus callosum (G, arrow) and Caspr is strongly reduced in paranodes of KO mice (M). PLP expression in KO mice occurred normally (not depicted), comparable to WT mice (C, arrow). Quantification of the confocal localization analyses of NaCh, Caspr, and NF in corpus callosum and cerebellum at P16 (N) and P23 (O). Immunofluorescent particles larger than 0.7 μm3 were quantified in two WT and KO mice. Note that at P16, total amounts of Caspr were reduced in cerebellum of KO mice, but not in corpus callosum; no differences were observed for NaCh. Error bars: SD from two animals per age and tissue area. At P23, strong reduction of Caspr and NF was observed in cerebellum as well in corpus callosum. For quantification, the pan-NF antiserum was used, which recognizes the 186 (nodal) and 155 (paranodal) isoforms; therefore, the residual amounts of NF-immunofluorescent intensity can be attributed to the nodal 186 isoform, which did not show differences between WT and KO mice (not depicted). wm, white matter; gcl, granule cell layer; CA1, pyramidal cell layer (hippocampus); cc, corpus callosum.

Mentions: To examine further whether the paranodal abnormalities observed in mal-deficient mice result from the inability of these fibers to establish normal axoglial contacts during development or are the result of later disassembly of the paranodal junction, we compared the distribution of paranodal components between WT and KO mice at different postnatal ages. Immunohistochemical analysis of mice at P16 revealed that in the cerebellum, myelinated fibers expressed proteolipid protein (PLP) as well as MAL (Fig. 7, B and F). In contrast, in the corpus callosum, myelinated fibers expressed PLP (Fig. 7 A, arrows), but do not yet MAL (Fig. 7 E). Immunofluorescence analysis of Caspr showed paranodal clustering in the corpus callosum of P16 WT as well as in KO animals (Fig. 7, I and K; top), suggesting that during development Caspr clustering occurred normally in the KO. In contrast, at this age, myelination and node formation in the cerebellum was more advanced, as indicated by the higher number of NaCh and Caspr clusters (Fig. 7 N). However, in the cerebellum of P16 KO mice, Caspr was already dispersed and the immunofluorescence signal was weaker (Fig. 7 K, bottom) than in age-matched WT mice (Fig. 7 I). Quantification of Caspr clusters showed a reduction in the cerebellum of P16 KO mice, whereas in the corpus callosum no difference between WT and KO could be detected (Fig. 7 N). At P23, beside PLP, MAL was also expressed in the corpus callosum (Fig. 7, C and G, respectively) and cerebellum (Fig. 7, D and H), and a reduced number of Caspr as well as NF155 clusters was observed in both brain regions (Fig. 7 O). At this age, a dispersed Caspr immunofluorescence was also apparent in paranodes of the corpus callosum of KO mice (Fig. 7 M).


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)

Onset of paranodal alterations correlates with MAL expression. Immunohistochemical analysis of sagittal brain sections for PLP (A–D), MAL (E–H), and confocal localization analyses of NaCh (I–M, red) and Caspr (I–M, green) on consecutive tissue sections in WT (A–I and L) and KO mice (K and M). At P16 in WT mice, myelination had already started in the corpus callosum as seen by PLP expression (A, arrows demarcate the border between corpus callosum and hippocampus), but MAL is not detectable yet (E). Clustering of Caspr in paranodes is normal in KO mice (K, top), whereas in the cerebellum myelination is more advanced, as seen by MAL expression (F); the immunofluorescent signal for Caspr is reduced (K, bottom). In contrast, at P23 MAL expression starts in corpus callosum (G, arrow) and Caspr is strongly reduced in paranodes of KO mice (M). PLP expression in KO mice occurred normally (not depicted), comparable to WT mice (C, arrow). Quantification of the confocal localization analyses of NaCh, Caspr, and NF in corpus callosum and cerebellum at P16 (N) and P23 (O). Immunofluorescent particles larger than 0.7 μm3 were quantified in two WT and KO mice. Note that at P16, total amounts of Caspr were reduced in cerebellum of KO mice, but not in corpus callosum; no differences were observed for NaCh. Error bars: SD from two animals per age and tissue area. At P23, strong reduction of Caspr and NF was observed in cerebellum as well in corpus callosum. For quantification, the pan-NF antiserum was used, which recognizes the 186 (nodal) and 155 (paranodal) isoforms; therefore, the residual amounts of NF-immunofluorescent intensity can be attributed to the nodal 186 isoform, which did not show differences between WT and KO mice (not depicted). wm, white matter; gcl, granule cell layer; CA1, pyramidal cell layer (hippocampus); cc, corpus callosum.
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fig7: Onset of paranodal alterations correlates with MAL expression. Immunohistochemical analysis of sagittal brain sections for PLP (A–D), MAL (E–H), and confocal localization analyses of NaCh (I–M, red) and Caspr (I–M, green) on consecutive tissue sections in WT (A–I and L) and KO mice (K and M). At P16 in WT mice, myelination had already started in the corpus callosum as seen by PLP expression (A, arrows demarcate the border between corpus callosum and hippocampus), but MAL is not detectable yet (E). Clustering of Caspr in paranodes is normal in KO mice (K, top), whereas in the cerebellum myelination is more advanced, as seen by MAL expression (F); the immunofluorescent signal for Caspr is reduced (K, bottom). In contrast, at P23 MAL expression starts in corpus callosum (G, arrow) and Caspr is strongly reduced in paranodes of KO mice (M). PLP expression in KO mice occurred normally (not depicted), comparable to WT mice (C, arrow). Quantification of the confocal localization analyses of NaCh, Caspr, and NF in corpus callosum and cerebellum at P16 (N) and P23 (O). Immunofluorescent particles larger than 0.7 μm3 were quantified in two WT and KO mice. Note that at P16, total amounts of Caspr were reduced in cerebellum of KO mice, but not in corpus callosum; no differences were observed for NaCh. Error bars: SD from two animals per age and tissue area. At P23, strong reduction of Caspr and NF was observed in cerebellum as well in corpus callosum. For quantification, the pan-NF antiserum was used, which recognizes the 186 (nodal) and 155 (paranodal) isoforms; therefore, the residual amounts of NF-immunofluorescent intensity can be attributed to the nodal 186 isoform, which did not show differences between WT and KO mice (not depicted). wm, white matter; gcl, granule cell layer; CA1, pyramidal cell layer (hippocampus); cc, corpus callosum.
Mentions: To examine further whether the paranodal abnormalities observed in mal-deficient mice result from the inability of these fibers to establish normal axoglial contacts during development or are the result of later disassembly of the paranodal junction, we compared the distribution of paranodal components between WT and KO mice at different postnatal ages. Immunohistochemical analysis of mice at P16 revealed that in the cerebellum, myelinated fibers expressed proteolipid protein (PLP) as well as MAL (Fig. 7, B and F). In contrast, in the corpus callosum, myelinated fibers expressed PLP (Fig. 7 A, arrows), but do not yet MAL (Fig. 7 E). Immunofluorescence analysis of Caspr showed paranodal clustering in the corpus callosum of P16 WT as well as in KO animals (Fig. 7, I and K; top), suggesting that during development Caspr clustering occurred normally in the KO. In contrast, at this age, myelination and node formation in the cerebellum was more advanced, as indicated by the higher number of NaCh and Caspr clusters (Fig. 7 N). However, in the cerebellum of P16 KO mice, Caspr was already dispersed and the immunofluorescence signal was weaker (Fig. 7 K, bottom) than in age-matched WT mice (Fig. 7 I). Quantification of Caspr clusters showed a reduction in the cerebellum of P16 KO mice, whereas in the corpus callosum no difference between WT and KO could be detected (Fig. 7 N). At P23, beside PLP, MAL was also expressed in the corpus callosum (Fig. 7, C and G, respectively) and cerebellum (Fig. 7, D and H), and a reduced number of Caspr as well as NF155 clusters was observed in both brain regions (Fig. 7 O). At this age, a dispersed Caspr immunofluorescence was also apparent in paranodes of the corpus callosum of KO mice (Fig. 7 M).

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