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The large isoform of myelin-associated glycoprotein is scarcely expressed in the quaking mouse brain
1Department of Neurology, Niigata University, Japan.
Abstract:
Two polypeptide isoforms of myelin-associated glycoprotein (MAG) with molecular masses of 72 and 67 kDa are produced by alternative splicing of the exon 12 portion. Our previous work has demonstrated that in the quaking mouse brain this alternative splicing is lacking and that the mRNA coding the large MAG isoform (L-MAG) is scarcely expressed, whereas that of small MAG isoform (S-MAG) is overexpressed. In the present study, we prepared antisera specific to the S-MAG and L-MAG amino acid residues, respectively. Immunoblots showed that the L-MAG band was scarcely detectable in the quaking mouse brain, whereas the S-MAG band had an apparently higher molecular mass than in the normal control. Our immunohistochemical study also showed that L-MAG was scarcely stained in the quaking mouse brain. These results seemed to reflect a reduction in content of L-MAG mRNA and abnormal glycosylation in the quaking mouse brain.
Insights
The quaking mouse shows altered expression of myelin-associated glycoprotein (MAG) isoforms. Specifically, large MAG (L-MAG) is reduced, while small MAG (S-MAG) is overexpressed, indicating potential splicing and glycosylation defects.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Myelin-associated glycoprotein (MAG) exists in two isoforms (72 kDa and 67 kDa) generated by alternative splicing of exon 12.
- The quaking mouse model exhibits dysmyelination, with previous studies indicating altered MAG mRNA expression.
Purpose of the Study:
- To investigate the protein expression levels and characteristics of large MAG (L-MAG) and small MAG (S-MAG) isoforms in the quaking mouse brain.
- To elucidate the molecular basis of MAG isoform abnormalities in the quaking mouse.
Main Methods:
- Generation of specific antisera against S-MAG and L-MAG amino acid residues.
- Immunoblot analysis to detect and quantify MAG isoforms in brain tissue.
- Immunohistochemical staining to assess the localization of MAG isoforms in the brain.
Main Results:
- L-MAG protein was barely detectable in the quaking mouse brain, consistent with reduced L-MAG mRNA.
- S-MAG protein in quaking mice exhibited an increased molecular mass compared to normal controls.
- Immunohistochemistry confirmed the scarce presence of L-MAG in the quaking mouse brain.
Conclusions:
- The quaking mouse brain displays a significant reduction in L-MAG protein and an apparent alteration in S-MAG protein size.
- These findings suggest a defect in alternative splicing and potentially abnormal glycosylation of MAG in the quaking mouse model.
- The observed MAG isoform changes likely contribute to the neurological deficits associated with the quaking mutation.