Regulation of Prenatal and Postnatal Protein Synthesis in Mouse Brain

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Abstract
Regulation of protein synthesis during prenatal and postnatal brain development was examined using postmitochondrial supernatant (PMS) fractions and isolated ribosome-pH 5 enzyme systems from fetal, neonatal and adult neural tissue. The rate of polyuridylic acid (poly-U)-dependent protein synthetic activity was inversely proportional to the endogenous rate of protein synthesis in the PMS fractions or ribosomal preparations. Analysis of the kinetics of the poly-U-dependent polypeptide synthesis revealed a lag in the time when certain of the PMS preparations begin to utilize the poly-U template as sole source of mRNA. The lag period was dependent upon the developmental age of the neural tissue used and the Mg2+ concentration of the protein synthesis reaction. Since developmental decrease in the rate of polypeptide synthesis utilizing a poly-U template could not be measured in a purified ribosomal-pH 5 enzyme system, ribosomes were obtained by several isolation techniques to determine if the purification procedure might have affected the ribosomes in some manner by removing a specific protein(s) involved in ribosome-cytosol interactions. At 6 mM Mg2+ the rate of poly-U-dependent protein synthesis was inversely proportional to the rate of endogenous synthesis and depended upon the method used to isolate the ribosomes: microsomes .simeq. Triton X-100-treated < DOC[deoxycholate]-treated < KCl-treated. No age-dependent effect existed with any of the ribosomal preparations. A developmental modulating effect of ribosomal activity apparently exists in PMS preparations which is not found in association with the isolated ribosome-pH 5 enzyme protein synthesizing system.