Developmental changes in polypeptide composition of, and precursor incorporation into, cellular and subcellular...

Neuronal-enriched and glial-enriched fractions from rat cerebral cortex at 2, 5, 9, 14 and 23 days postnatally, and subcellular fractions from 2, 14 and 46 day old rat were prepared. The polypeptide composition of all fractions was analysed by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis and quantified by densitometry. Fifty-nine polypeptides (mol. wts., 13,200-251,000) were resolved in the cell fractions of which the majority remained unchanged throughout postnatal development. Three polypeptides (mol. wts., 102,000, 56,000, 53,700) were found to increase in amount developmentally in both cellular fractions, the latter two showing a peak in relative amount on day 14 and a subsequent decline. Three polypeptides (mol. wts., 47,000, 28,200, 17,400) were found to be common to the glial-enriched fraction as well as the myelin fraction, and all showed a developmental increase. The neuronal-enriched fraction was found to be enriched in five polypeptides of which one (mol. wt., 51,900) showed a developmental increase after ten days postnatally, the others (mol. wts., 178,700, 142,000, 109,000, 24,000) showing a decrease. In vitro incorporation of [35S]-methionine into the glial-enriched fraction was carried out, and a developmental decline was observed in the labelling of a polypeptide of 42,000 mol. wt.