Differential expression of MAG isoforms during development.
The myelin-associated glycoproteins (MAG) mediate the cell interactions of oligodendrocytes and Schwann cells with axons that are myelinated. MAG exists in two developmentally regulated isoforms: large MAG (L-MAG) and small MAG (S-MAG). In this paper, we have studied the tissue-specific and developmentally regulated alternative splicing of these isoforms using monospecific antibodies that recognize epitopes common to both isoforms or that are present only on L-MAG. In the central nervous system (CNS), L-MAG is the major form synthesized early in development, and it persists as a significant proportion of the MAG present in the adult. In the peripheral nervous system (PNS), L-MAG is expressed at modest levels during development; it is virtually absent in the adult. Thus, the expression of L-MAG is not limited to the CNS, as was formerly believed, suggesting that it plays a common role during the early stages of myelin formation by both oligodendrocytes and Schwann cells. In both the CNS and PNS, S-MAG is the predominant isoform in the adult. A higher-molecular-weight form of MAG is present in the PNS at low abundance, that is developmentally regulated, and appears to be a glycosylation variant. An analysis of the carbohydrate residues on MAG demonstrates that it contains both N-linked and O-linked sugars that could be modulated during development. These results suggest a possible mechanism for the regulation of MAG function during myelinogenesis via the expression of alternative isoforms and carbohydrate modifications.
Pedraza
L
L
Department of Cell Biology, New York University Medical School 10016.
Frey
A B
AB
Hempstead
B L
BL
Colman
D R
DR
Salzer
J L
JL
D000818:Animals; D000831:Animals, Newborn; D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity; D001933:Brain Stem / Q000254:growth & development / Q000378:metabolism; D015151:Immunoblotting; D007536:Isomerism; D009185:Myelin Proteins / Q000276:immunology / Q000378:metabolism*; D018992:Myelin-Associated Glycoprotein; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D012584:Sciatic Nerve / Q000254:growth & development / Q000378:metabolism
D000906:Antibodies; D009185:Myelin Proteins; D018992:Myelin-Associated Glycoprotein; D009844:Oligosaccharides