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Association of TAG-1 with Caspr2 is essential for the molecular organization of juxtaparanodal regions of myelinated fibers.

Traka M, Goutebroze L, Denisenko N, Bessa M, Nifli A, Havaki S, Iwakura Y, Fukamauchi F, Watanabe K, Soliven B, Girault JA, Karagogeos D - J. Cell Biol. (2003)

Bottom Line: Myelination results in a highly segregated distribution of axonal membrane proteins at nodes of Ranvier.In the absence of TAG-1, axonal Caspr2 did not accumulate at juxtaparanodes, and the normal enrichment of shaker-type K+ channels in these regions was severely disrupted, in the central and peripheral nervous systems.This complex is analogous to that described previously at paranodes, suggesting that similar molecules are crucial for different types of axo-glial interactions.

View Article: PubMed Central - PubMed

Affiliation: Department of Basic Science, University of Crete Medical School, Heraklion 71110, Crete, Greece.

ABSTRACT
Myelination results in a highly segregated distribution of axonal membrane proteins at nodes of Ranvier. Here, we show the role in this process of TAG-1, a glycosyl-phosphatidyl-inositol-anchored cell adhesion molecule. In the absence of TAG-1, axonal Caspr2 did not accumulate at juxtaparanodes, and the normal enrichment of shaker-type K+ channels in these regions was severely disrupted, in the central and peripheral nervous systems. In contrast, the localization of protein 4.1B, an axoplasmic partner of Caspr2, was only moderately altered. TAG-1, which is expressed in both neurons and glia, was able to associate in cis with Caspr2 and in trans with itself. Thus, a tripartite intercellular protein complex, comprised of these two proteins, appears critical for axo-glial contacts at juxtaparanodes. This complex is analogous to that described previously at paranodes, suggesting that similar molecules are crucial for different types of axo-glial interactions.

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Expression levels of juxtaparanodal proteins in central myelinated fibers of TAG-1 knockout mice. Expression levels of (A) TAG-1, (B) Caspr2, and (C) Kv1.1 potassium channels in 2-mo-old wild-type (+/+) and TAG-1 mutant mice (−/−) were examined by IB analysis of optic nerve extracts (top). Protein levels were quantified (three mice in each group) using actin (bottom) in each sample for normalization: Caspr2 levels in mutant mice were 84 ± 2% of wild-type (mean ± SD); Kv1.1 86-kD band; 129± 22%; and 70-kD band 193 ± 21%. The position of molecular mass markers (kD) is indicated.
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fig3: Expression levels of juxtaparanodal proteins in central myelinated fibers of TAG-1 knockout mice. Expression levels of (A) TAG-1, (B) Caspr2, and (C) Kv1.1 potassium channels in 2-mo-old wild-type (+/+) and TAG-1 mutant mice (−/−) were examined by IB analysis of optic nerve extracts (top). Protein levels were quantified (three mice in each group) using actin (bottom) in each sample for normalization: Caspr2 levels in mutant mice were 84 ± 2% of wild-type (mean ± SD); Kv1.1 86-kD band; 129± 22%; and 70-kD band 193 ± 21%. The position of molecular mass markers (kD) is indicated.

Mentions: The dramatic alterations of Caspr2 and Kv1.1-IR in juxtaparanodal regions raised the possibility that TAG-1 might control either their expression levels or their enrichment in these regions. To address this question we measured the levels of these proteins by immunoblot (IB) of optic nerve extracts. In the mutants, as expected, no TAG-1 immunoreactive band was observed (Fig. 3 A), whereas Caspr2 levels were virtually unchanged (Fig. 3 B). Kv1.1 antibodies revealed a doublet (Fig. 3 C), which may correspond to the 86-kD mature, and 70-kD immature forms of these channels (Manganas and Trimmer, 2000). In mutant mice, the lower immunoreactive band was markedly increased, whereas the upper band was not significantly altered (Fig. 3 C). Thus, the biochemical measurements demonstrated that the dramatic alterations in Caspr2 and Kv1.1 channels in TAG-1 mutant mice did not result from defects in their expression but rather from the lack of concentration of these proteins in juxtaparanodal regions, presumably below IF detection levels.


Association of TAG-1 with Caspr2 is essential for the molecular organization of juxtaparanodal regions of myelinated fibers.

Traka M, Goutebroze L, Denisenko N, Bessa M, Nifli A, Havaki S, Iwakura Y, Fukamauchi F, Watanabe K, Soliven B, Girault JA, Karagogeos D - J. Cell Biol. (2003)

Expression levels of juxtaparanodal proteins in central myelinated fibers of TAG-1 knockout mice. Expression levels of (A) TAG-1, (B) Caspr2, and (C) Kv1.1 potassium channels in 2-mo-old wild-type (+/+) and TAG-1 mutant mice (−/−) were examined by IB analysis of optic nerve extracts (top). Protein levels were quantified (three mice in each group) using actin (bottom) in each sample for normalization: Caspr2 levels in mutant mice were 84 ± 2% of wild-type (mean ± SD); Kv1.1 86-kD band; 129± 22%; and 70-kD band 193 ± 21%. The position of molecular mass markers (kD) is indicated.
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Related In: Results  -  Collection

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fig3: Expression levels of juxtaparanodal proteins in central myelinated fibers of TAG-1 knockout mice. Expression levels of (A) TAG-1, (B) Caspr2, and (C) Kv1.1 potassium channels in 2-mo-old wild-type (+/+) and TAG-1 mutant mice (−/−) were examined by IB analysis of optic nerve extracts (top). Protein levels were quantified (three mice in each group) using actin (bottom) in each sample for normalization: Caspr2 levels in mutant mice were 84 ± 2% of wild-type (mean ± SD); Kv1.1 86-kD band; 129± 22%; and 70-kD band 193 ± 21%. The position of molecular mass markers (kD) is indicated.
Mentions: The dramatic alterations of Caspr2 and Kv1.1-IR in juxtaparanodal regions raised the possibility that TAG-1 might control either their expression levels or their enrichment in these regions. To address this question we measured the levels of these proteins by immunoblot (IB) of optic nerve extracts. In the mutants, as expected, no TAG-1 immunoreactive band was observed (Fig. 3 A), whereas Caspr2 levels were virtually unchanged (Fig. 3 B). Kv1.1 antibodies revealed a doublet (Fig. 3 C), which may correspond to the 86-kD mature, and 70-kD immature forms of these channels (Manganas and Trimmer, 2000). In mutant mice, the lower immunoreactive band was markedly increased, whereas the upper band was not significantly altered (Fig. 3 C). Thus, the biochemical measurements demonstrated that the dramatic alterations in Caspr2 and Kv1.1 channels in TAG-1 mutant mice did not result from defects in their expression but rather from the lack of concentration of these proteins in juxtaparanodal regions, presumably below IF detection levels.

Bottom Line: Myelination results in a highly segregated distribution of axonal membrane proteins at nodes of Ranvier.In the absence of TAG-1, axonal Caspr2 did not accumulate at juxtaparanodes, and the normal enrichment of shaker-type K+ channels in these regions was severely disrupted, in the central and peripheral nervous systems.This complex is analogous to that described previously at paranodes, suggesting that similar molecules are crucial for different types of axo-glial interactions.

View Article: PubMed Central - PubMed

Affiliation: Department of Basic Science, University of Crete Medical School, Heraklion 71110, Crete, Greece.

ABSTRACT
Myelination results in a highly segregated distribution of axonal membrane proteins at nodes of Ranvier. Here, we show the role in this process of TAG-1, a glycosyl-phosphatidyl-inositol-anchored cell adhesion molecule. In the absence of TAG-1, axonal Caspr2 did not accumulate at juxtaparanodes, and the normal enrichment of shaker-type K+ channels in these regions was severely disrupted, in the central and peripheral nervous systems. In contrast, the localization of protein 4.1B, an axoplasmic partner of Caspr2, was only moderately altered. TAG-1, which is expressed in both neurons and glia, was able to associate in cis with Caspr2 and in trans with itself. Thus, a tripartite intercellular protein complex, comprised of these two proteins, appears critical for axo-glial contacts at juxtaparanodes. This complex is analogous to that described previously at paranodes, suggesting that similar molecules are crucial for different types of axo-glial interactions.

Show MeSH
Related in: MedlinePlus