A developmental study of the relationship between the protein components of rat CNS myelin

The relationship between the major and minor protein components of the myelin sheath, and between fractions soluble and insoluble in chloroform methanol has been studied in rat brain between 5 and 60 days of age. The results suggest a continuous sequential buildup of the myelin sheath, in which while the minor protein components form the major proportion of early myelin their contribution is progressively reduced by the addition of myelin specific proteins. Chloroform methanol insoluble myelin is recognisable before the CMS fraction appears. The minor proteins are present in the brain several days before myelination and then appear to migrate into myelin. However, the myelin specific proteins can only be detected shortly before myelination. The results underline previous suggestions that the myelin sheath has a unique protein composition, and suggest that the specific components arise de novo just before they are required. They are not consistent with the supposition that myelin consists of glial cell membrane and are discussed in relation to current views on the myelination process.