Protein synthesis in cells isolated from the developing rat cerebellum

The rate of protein synthesis was estimated in structurally preserved perikaryal preparations from 8-day-old rat cerebellum under conditions which overcome the problems of intracellular compartmentation. The rates were lower than the in vivo estimates at comparable ages, but they were of similar magnitude, and very much higher than previous estimates on isolated cells. Protein synthesis rate depended on the cell type. When expressed per cell the rank order in the preparations enriched in the indicated classes of cells was: Purkinje cells > astrocytes > granule cells in the S, G2 and M phase of the cell cycle > granule cells in G1 and G0. However, after normalizing the results for size differences between cell types, by expressing the rates in terms of unit protein or as a percentage replacement of the protein bound amino acid, astrocytes and replicating granule cells displayed greater rates than the Purkinje cells. The resolution of labelled proteins using SDS-PAGE indicated marked differences in the rate of synthesis of particular proteins. The results were consistent with the view that certain polypeptides are uniquely expressed in particular cell classes.