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Biochemical demonstration of the myelin-associated glycoprotein in the peripheral nervous system
Abstract:
Recent immunocytochemical studies indicated that the myelin-associated glycoprotein (MAG) is localized in the periaxonal region of central nervous system (CNS) and peripheral nervous system (PNS) myelin sheaths but previous biochemical studies had not demonstrated the presence of MAG in peripheral nerve. The glycoproteins in rat sciatic nerves were heavily labeled by injection of [3H]fucose in order to re-examine whether MAG could be detected chemically in peripheral nerve. Myelin and a myelin-related fraction, W1, were isolated from the nerves. Labeled glycoproteins in the PNS fractions were extracted by the lithium diiodosalicylate (LIS)-phenol procedure, and the extracts were treated with antiserum prepared to CNS MAG in a double antibody precipitation. This resulted in the immune precipitation of a single [3H]fucose-labeled glycoprotein with electrophoretic mobility very similar to that of [14C]fucose-labeled MAG from rat brain. A sensitive peptide mapping procedure involving iodination with Bolton-Hunter reagent and autoradiography was used to compare the peptide maps generated by limited proteolysis from this PNS component and CNS MAG. The peptide maps produced by three distinct proteases were virtually identical for the two glycoproteins, showing that the PNS glycoprotein is MAG. The MAG in the PNS myelin and W1 fractions was also demonstrated by Coomassie blue and periodic acid-Schiff staining of gels on which the whole LIS-phenol extracts were electrophoresed, and densitometric scanning of the gels indicated that both fractions contained substantially less MAG than purified rat brain myelin. The presence of MAG in the periaxonal region of both peripheral and central myelin sheaths is consistent with a similar involvement of this glycoprotein in axon-sheath cell interactions in the PNS and CNS.
Insights
This study chemically confirms the presence of myelin-associated glycoprotein (MAG) in peripheral nerves. These findings support MAG
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Immunocytochemistry localized myelin-associated glycoprotein (MAG) to the periaxonal region of central nervous system (CNS) and peripheral nervous system (PNS) myelin.
- Previous biochemical studies had not confirmed MAG's presence in peripheral nerves.
Purpose of the Study:
- To biochemically detect and characterize myelin-associated glycoprotein (MAG) in peripheral nerves.
- To compare peripheral MAG with central nervous system (CNS) MAG.
Main Methods:
- Rat sciatic nerves were labeled with [3H]fucose.
- Myelin and myelin-related fractions (W1) were isolated.
- MAG was detected using antiserum, double antibody precipitation, peptide mapping, and gel electrophoresis.
Main Results:
- A [3H]fucose-labeled glycoprotein from PNS fractions precipitated with anti-CNS MAG antiserum.
- Peptide mapping revealed identical peptide maps between the PNS glycoprotein and CNS MAG.
- MAG was detected in PNS myelin and W1 fractions, though at lower levels than in rat brain myelin.
Conclusions:
- The PNS glycoprotein is confirmed to be myelin-associated glycoprotein (MAG).
- The presence of MAG in both CNS and PNS myelin suggests a conserved role in axon-sheath interactions.