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Endocytic depletion of L-MAG from CNS myelin in quaking mice.
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MedLine Citation:
PMID:  8557747     Owner:  NLM     Status:  MEDLINE    
Quaking is an autosomal recessive hypo/dysmyelinating mutant mouse which has a 1-Mbp deletion on chromosome 17. The mutation exhibits pleiotrophy and does not include genes encoding characterized myelin proteins. The levels of the 67-kD isoform of the myelin-associated glycoprotein (S-MAG) relative to those of the 72-kD isoform (L-MAG) are increased in the quaking CNS, but not in other dysmyelinating mutants. Abnormal expression of MAG isoforms in quaking may result from altered transcription of the MAG gene or from abnormal sorting, transport, or targeting of L-MAG or S-MAG. To test these hypotheses, we have determined the distribution of L-MAG and S-MAG in cervical spinal cord of 7-, 14-, 21-, 28-, and 35-d-old quaking mice. In 7-d-old quaking and control spinal cord, L- and S-MAG was detectable in periaxonal regions of myelinated fibers and in the perinuclear cytoplasm of oligodendrocytes. Between 7 and 35 d, L-MAG was removed from the periaxonal membrane of quaking but not control mice. Compared to control mice, a significant increase in MAG labeling of endosomes occurred within oligodendrocyte cytoplasm of 35-d-old quaking mice. S-MAG remained in periaxonal membranes of both quaking and control mice. Analysis of the cytoplasmic domain of L-MAG identifies amino acid motifs at tyrosine 35 and tyrosine 65 which meet the criteria for "tyrosine internalization signals" that direct transmembrane glycoproteins into the endocytic pathway. These results establish that L-MAG is selectively removed from the periaxonal membrane of CNS-myelinated fibers by receptor-mediated endocytosis. The loss of L-MAG from quaking periaxonal membranes results from increased endocytosis of L-MAG and possibly a decrease in L-MAG production.
L Bö; R H Quarles; N Fujita; Z Bartoszewicz; S Sato; B D Trapp
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of cell biology     Volume:  131     ISSN:  0021-9525     ISO Abbreviation:  J. Cell Biol.     Publication Date:  1995 Dec 
Date Detail:
Created Date:  1996-02-26     Completed Date:  1996-02-26     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  0375356     Medline TA:  J Cell Biol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1811-20     Citation Subset:  IM    
Department of Neurosciences, Cleveland Clinic Foundation, Ohio 44195, USA.
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MeSH Terms
Amino Acid Sequence
Antibody Specificity
Axons / chemistry,  ultrastructure
Endocytosis / physiology*
Mice, Quaking / physiology*
Microscopy, Confocal
Molecular Sequence Data
Myelin Proteolipid Protein / analysis,  immunology
Myelin Sheath / chemistry*
Myelin-Associated Glycoprotein / analysis*,  immunology,  metabolism
Spinal Cord / chemistry
Subcellular Fractions / chemistry
Grant Support
Reg. No./Substance:
0/Myelin Proteolipid Protein; 0/Myelin-Associated Glycoprotein

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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Journal Information
Journal ID (nlm-ta): J Cell Biol
ISSN: 0021-9525
ISSN: 1540-8140
Publisher: The Rockefeller University Press
Article Information
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Print publication date: Day: 2 Month: 12 Year: 1995
Volume: 131 Issue: 6
First Page: 1811 Last Page: 1820
ID: 2120655
Publisher Id: 96134030
PubMed Id: 8557747

Endocytic depletion of L-MAG from CNS myelin in quaking mice

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