A myelin-related fraction (SN 4) was isolated from forebrain of 17- and 40-day-old rats. Fraction SN 4 was obtained as a supernatant in a slow speed differential centrifugation of a myelin fraction. In contrast to multilamellar myelin fraction, SN 4 consisted of small vesicular profiles of a mixture of single membranes and some triple-layered structures. All typical myelin components were found in the SN 4 fraction from adult rat brain but their relative proportion was different from that of myelin: Wolfgram protein, myelin glycoproteins and 2',3'-cyclic nucleotide 3'-phosphohydrolase were increased, while basic proteins and proteolipid protein were decreased significantly. In contrast, the lipid composition appeared very similar to the one found in myelin. SN 4 from 17-day-old rat brains was essentially similar to that from adults, except that the major myelin glycoprotein was not enriched in comparison to myelin. Developmental changes found in myelin were also present in the SN 4 fraction. The specific radioactivity of the fucose-labeled major myelin glycoprotein was similar in SN 4 and in myelin. The particular composition of fraction SN 4 suggests that this material is not significantly contaminated by non-myelin-related membranes but rather supports the hypothesis that it could be enriched in a membrane representing a zone of transition during the formation of myelin and which is subjected to a remodelling of its protein components.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1976

Hypomyelination in copper-deficient rats. Prenatal and postnatal copper replacement.

Copper deficiency induced by a low copper diet in three generations of rats was associated with substantial reductions in the yield of myelin (56%), brain weight (11%), and body weight (43%) in F2 generation rat pups nursed by their own copper-deficient mothers. The composition of the purified myelin was not different from that of controls in the content of individual proteins, lipids, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) activity, or GM1 ganglioside. The major myelin-associated glycoprotein (mGP) was consistently shifted slightly toward higher apparent molecular weight in the copper-deficient animals. Postnatal copper replacement by a foster mother produced a normal yield of myelin per gram of brain tissue, but failed to reverse the deficiency of brain and body growth. After copper replacement in a copper-deficient mother's diet prior to conception, a subsequent litter showed correction of all abnormalities found in her previous litters. The results suggest that copper is essential for myelin formation and general growth during critical periods in development.

Age Factors↗

PubMed1975

[35-S]sulfate incorporation into myelin glycoproteinsmi=entral nervous system.

The in vivo incorporation of [35-S]sulfate and [3H]fucose into rat brain myelin was investigatedmmost of the 35S in the myelin was in sulfatide, but about 4% was associated with the residual proteins after chloroform/methanol extraction. Polyacrylamide gel electrophoresis of these proteins indicated that the major 35-S-labeled component corresponded to the major fucose-labeled glycoproteinmthe labeling of this predominant glycoprotein with sulfate was more selective than with fucose, since there was relatively little incorporation of sulfate into some of the minor fucose-labeled glycoproteins. There was little or no 35-S associated with proteolipid or basic protein on polyacrylamide gels. The fucose-labeled glycoproteins were converted to glycopeptides by pronase digestion and separated into two major classes by gel filtration on Sephadex-G-50. Only the higher molecular weight class contained significant amounts of 35-S. The association of 35-S with the glycopeptides was not due to binding of sulfatide or free inorganic sulfate. The results indicate that the predominant myelin-associated glycoprotein in rat brain is sulfated.

Animals↗

PubMed1975

[35-S]sulfate incorporation into myelin clycoproteins; II. Peripheral nervous tissue.

The in vivo incorporation of [35-S]sulfate, [3-H]fucose and [3-H]leucine into sciatic nerve myelin was investigatedmpolyacrylamide gel electrophoresis of thr proteins indicated that the 35-S-labeling of proteins occurred almost exclusively in the major myelin protein; A smaller myelin glycoprotein migrating just ahead of the major one was labeled with [3-H]fucose but did not incorporate 35-S to a detectable extent. There was little or no 35-S associated with basic proteins on polyacrylamide gels when the proteins were extracted with chloroform/methanol; Fucose-labeled myelin glycoproteins were converted to glycopeptides by pronase digestion; The glycopeptides gave a single peak on tsephadex G-50 in which the 3-H and 35-S coincided. The association of 35-S with glycopeptides was not caused by binding of sulfatide or free inorganic sulfate. This study shows that the major myelin protein in the sciatic nerve of the rat is glycosylated and sulfated.

Animals↗

PubMed1975

Change in a myelin-associated glycoprotein in rat brain during development: metabolic aspects.

The higher apparent molecular weight of the newly synthesized glycoprotein in immature rat myelin in comparison with that in mature myelin, which was originally demonstrated with radioactive fucose, was also shown by double labeling experiments with radioactive glucosamine or N-acetylmannosamine. In addition, periodic acid-Schiff staining of gels, on which the glycoproteins of mature and immature myelin were electrophoresed separately or mixed together, revealed that the stained glycoprotein in immature myelin had a higher apparent molecular weight. Age studies with radioactive fucose showed that the greatest difference in the apparent molecular weight of the newly synthesized glycoprotein occurred at 12 days. The magnitude of the difference decreased gradually with age until 25 days when the glycoprotein electrophoresed to the same position as that in more mature myelin. Long-term experiments, in which 12- or 13-day-old rats were injected with radioactive fucose and allowed to survive for varying periods of time before myelin isolation, also revealed a gradual decrease with age in the extent of the shift of the glycoprotein toward a higher molecular weight. The possible significance of the developmental change in the glycoprotein for the process of myelin formation is discussed.

Age Factors↗

PubMed1975

Proteins of rat brain myelin in neonatal hypothyroidism.

The amount of myelin and its protein composition was studied in hypothyroid rats during the first 30 days after birth. Although the brain weight was 92% of that in the controls, the yield of myelin in hypothyroid animals was only 60% of that in controls. The protein and glycoprotein ocmposition of the isolated myelin was similar in hypothyroid and control rats. The 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) activity in whole brain from hypothyroid animals was only 60% of the controls and reflected the decrease in myelin formation. In isolated myelin the specific activity of CNP was not different in hypothyroid and control animals with the exception of very immature animals (10 days). The major fucose-labeled glycoprotein in myelin of the hypothyroid rats had a slightly higher apparent molecular weight than that in myelin from age matched controls, probably reflecting a retardation of brain maturation and myelin formation.

Animals↗

PubMed1975

Myelin deficiency in hereditary pituitary dwarfism: a biochemical and morphological study.

Myelin in the central nervous system of 19-day-old Snell's dwarf mice was studied morphologically and biochemically. The number of myelinated axons per unit area in the corticospinal tract and anterior commissure of dwarf mice was significantly decreased. The distribution of myelinated fibers based upon sheath thickness was normal. The yield of isolated myelin was decreased by 56% in the dwarf but its compositions of lipids, proteins, glycoproteins and 2', 3'-cyclic nucleotide 3'-phosphohydrolase activity was nearly equivalent to that of control myelin.

Animals↗

PubMed1975