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 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.
LeBlanc
A C
AC
Department of Neurology, Mayo Clinic, Rochester, Minnesota 55905.
Földvári
M
M
Spencer
D F
DF
Breckenridge
W C
WC
Fenwick
R G
RG
Williams
D L
DL
Mezei
C
C
D000375:Aging; D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000096:biosynthesis / Q000235:genetics*; D002642:Chick Embryo; D002645:Chickens; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005796:Genes; D007150:Immunohistochemistry; D008075:Lipoproteins, HDL / Q000235:genetics*; D009413:Nerve Fibers, Myelinated / Q000378:metabolism* / Q000648:ultrastructure; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000235:genetics*; D012584:Sciatic Nerve / Q000254:growth & development* / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D012333:RNA, Messenger; D004247:DNA