The Apolipoprotein A-I Gene Is Actively Expressed in the Rapidly Myelinating Avian Peripheral Nerve

The expression of the apolipoprotein A-I (apo A-I) gene was investigated in the myelinating sciatic nerve. Hybridization analysis with an apo A-I cDNA probe obtained from a cDNA library of mRNA isolated from rapidly myelinating chick sciatic nerve indicated that apo A-I coding transcripts increase d...

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Bibliographic Details
Published in:The Journal of cell biology 1989-09, Vol.109 (3), p.1245-1256
Main Authors: LeBlanc, Andréa C., Földvári, Marianna, Spencer, David F., Breckenridge, W. Carl, Fenwick, Ray G., Williams, David L., Mezei, Catherine
Format: Article
Language:English
Subjects:
Aging
Animals
Apolipoprotein A-I
Apolipoproteins A - biosynthesis
Apolipoproteins A - genetics
Biological and medical sciences
Chick Embryo
Chickens
Cholesterols
DNA - genetics
DNA - isolation & purification
Fundamental and applied biological sciences. Psychology
Gels
Gene expression
Genes
HDL lipoproteins
Immunohistochemistry
Lipids
Lipoproteins
Lipoproteins, HDL - genetics
Molecular and cellular biology
Molecular genetics
Myelin
Nerve Fibers, Myelinated - metabolism
Nerve Fibers, Myelinated - ultrastructure
Nerves
Organ Culture Techniques
RNA, Messenger - genetics
Schwann cells
Sciatic nerve
Sciatic Nerve - growth & development
Sciatic Nerve - metabolism
Subcellular fractions
Subcellular Fractions - metabolism
Transcription, Genetic
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Summary:The expression of the apolipoprotein A-I (apo A-I) gene was investigated in the myelinating sciatic nerve. Hybridization analysis with an apo A-I cDNA probe obtained from a cDNA library of mRNA isolated from rapidly myelinating chick sciatic nerve indicated that apo A-I coding transcripts increase during development in the chick sciatic nerve in parallel with the increase of myelin lamellae. Substantial apo A-I-like immunoreactivity in chick sciatic nerve homogenates was detected by Western blotting. The amount of antigen increased from the 15-d embryonic stage to 1 d posthatch and then decreased. Two subcellular fractions corresponding to the cytoplasmic compartments were particularly enriched in apo A-I. apo A-I immunoreactivity was also found in highly purified myelin preparations. Immunohistochemical staining provided further evidence for the presence of apo A-I in the endoneurial compartment of the sciatic nerve. Electron microscopic examination of these fractions after negative staining showed the presence of spherical and disc-shaped particles resembling high density lipoproteins. The presence of apo A-I, cholesterol esters, phospholipids, and triacylglycerols in ultracentrifugal fractions corresponding to serum lipoproteins and the behavior of apo A-I on nondenaturing gradient gels implied that apo A-I was associated with lipid. Studies with short-term organ cultures of sciatic nerves from 1-d chicks strengthened the evidence for local synthesis and secretion of apo A-I and apo A-I-containing lipoproteins by this tissue. These results establish that the apo A-I gene is actively expressed in developing sciatic nerve during the period of rapid myelination. These findings support the hypothesis that apo A-I synthesized within the nerve participates in the local transport of lipids used in myelin biosynthesis.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.109.3.1245