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Myelin-associated glycoprotein, a cell adhesion molecule of oligodendrocytes, is phosphorylated in brain
A M Edwards1, M Arquint, P E Braun
1Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Abstract:
Myelin-associated glycoprotein (MAG) has been implicated in the mediation of interactions between oligodendrocytes and neurons during the development of the myelin sheath. Here we show that MAG is phosphorylated in intact myelinating mouse brain primarily at serine residues and to a lesser extent at threonine and tyrosine residues. In vivo, only the larger of the two developmentally regulated MAG isoforms is phosphorylated. MAG can be phosphorylated at tyrosine by the v-fps and v-src protein-tyrosine kinases in vitro and by a kinase endogenous to myelin membrane preparations. MAG phosphorylated in myelin membranes in vitro also contains phosphoserine and phosphothreonine. These observations suggest that phosphorylation of MAG is physiologically significant in regulating oligodendrocyte-neuron interactions.
Insights
Myelin-associated glycoprotein (MAG) phosphorylation occurs in mouse brains, primarily on serine residues. This post-translational modification is vital for regulating neuron-oligodendrocyte interactions during myelin sheath development.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Myelin-associated glycoprotein (MAG) is crucial for oligodendrocyte-neuron interactions during myelin sheath formation.
- Understanding MAG's post-translational modifications is key to elucidating its functional roles.
Purpose of the Study:
- To investigate the phosphorylation status of MAG in vivo and in vitro.
- To identify the specific residues and kinases involved in MAG phosphorylation.
Main Methods:
- Analysis of MAG phosphorylation in intact myelinating mouse brain.
- In vitro phosphorylation assays using myelin membrane preparations and specific kinases (v-fps, v-src).
- Isoform-specific analysis of MAG phosphorylation.
Main Results:
- MAG is primarily phosphorylated at serine residues, with lesser amounts at threonine and tyrosine.
- In vivo, only the larger MAG isoform is phosphorylated.
- Myelin membrane preparations contain endogenous kinases that phosphorylate MAG at tyrosine, serine, and threonine residues.
Conclusions:
- Phosphorylation of MAG is a significant physiological event.
- This modification likely plays a critical role in regulating interactions between oligodendrocytes and neurons.