Localization of Phospholipid Synthesis to Schwann Cells and Axons

Authors

  • Robert M. Gould,

    Corresponding author
    1. Department of Pathological Biochemistry, Institute for Basic Research in Developmental Disabilities, Staten Island, New York, U.S.A.
      Address correspondence and reprint requests to Dr. R. M. Gould at Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, U.S.A.
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  • John Holshek,

    1. Department of Pathological Biochemistry, Institute for Basic Research in Developmental Disabilities, Staten Island, New York, U.S.A.
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  • Wayne Silverman,

    1. Department of Psychology, New York State Office of Mental Retardation and Developmental Disabilities, Institute for Basic Research in Developmental Disabilities, Staten Island, New York, U.S.A.
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  • Warren D. Spivack

    1. Department of Pathological Biochemistry, Institute for Basic Research in Developmental Disabilities, Staten Island, New York, U.S.A.
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Address correspondence and reprint requests to Dr. R. M. Gould at Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, U.S.A.

Abstract

Abstract: Quantitative electron microscopic autoradiography was used to detect and characterize endoneurial sites of lipid synthesis in mouse sciatic nerve. Six tritiated phospholipid precursors (choline, serine, methionine, inositol, glyc-erol, and ethanolamine) and a protein precursor (proline) were individually injected into exposed nerves and after 2 h the mice were perfused with buffered aldehyde. The labeled segments of nerve were prepared for autoradiography with procedures that selectively remove nonincorporated precursors and other aqueous metabolites, while preserving nerve lipids (and proteins). At both the light and electron microscope levels, the major site of phospholipid and protein synthesis was the crescent-shaped perinuclear cytoplasm of my-elinating Schwann cells. Other internodal Schwann cell cytoplasm, including that in surface channels, Schmidt-Lanterman incisures, and paranodal regions, was less well labeled than the perinuclear region. Newly formed proteins were selectively located in the Schwann cell nucleus. Lipid and protein formation was also detected in unmyelinated fiber bundles and in endoneurial and perineurial cells. Tritiated inositol was selectively incorporated into phospholip-ids in both myelinated axons and unmyelinated fibers. Like inositol, glycerol incorporation appeared particularly active in unmyelinated fibers. Quantitative autoradiographic analyses substantiated the following points: (1) myelinating Schwann cells dominate phospholipid and protein synthesis, (2) myelinated axons selectively incorporate tritiated inositol, (3) phospholipid precursors label myelin sheaths and myelinated axons better than proline.

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