Regulation of prenatal and postnatal protein synthesis in mouse brain

Translational activity of mRNA coding for cytoskeletal brain proteins in newborn and adult mice: a comparative study

Translational activity of mRNA coding for cytoskeletal brain proteins was used to determine the relative abundance of the mRNA in the brains of newborn and adult mice. mRNA was translated in a cell-free system containing rabbit reticulocyte factors. The products of translation were analyzed by two-dimensional gel electrophoresis and characterized by peptide map analysis. Comparison of the products of translation from newborn and from adult brain mRNA shows a 50% decrease in actin and tubulin from newborn to the adult stage. In contrast, the 70 kd neurofilament protein and glial fibrillary acidic protein show a twofold increase in the adult stage. The heat-shock protein HSP70 increases slightly (30%) whereas the brain isozyme of creatine kinase and the heat-shock protein HSP90 are three times as high in adult subjects as in newborns.

Heterogeneity of protein-synthesis initiation factors in developing and aging rat brain

Protein synthesis initiation factors from rat brain were assayed in vitro through the formation of the initiator Met-tRNA X initiation factor 2 X GTP ternary complex. The initiation factor showed different intrinsic activity with increase in age. This difference was elicited by additions of high-salt ribosomal-wash protein to incubation mixtures that were already saturated with protein preparations from brains of older animals. This qualitative difference was further documented by examining the sensitivity of the activities of the initiation factor to spermidine and to temperature. The sensitivity to these effectors varied with age. By fitting an exponential decay model to data from the temperature experiments, it was possible to demonstrate that the preparations of the initiation factor from older brains behaved as a multicomponent system. The brain preparations from older animals contained at least two subpopulations of initiation factor. The fractions of these two gross subclasses varied, inversely one to the other, with age.

Variations in gene expression during development of the rat cerebellum

Prominent variations in the concentration and composition of poly (A)-containing messenger RNA were found to occur during the postnatal development of the rat cerebellum. The concentration of mRNA (microgram/g cerebellar tissue) was determined to be the highest on the tenth postnatal day, at the onset of synaptogenesis. Short non-abundant mRNA chains continuously increase in amount during cerebellar development, while the fraction of long translatable mRNAs decreases. The overall ability of cerebellar mRNA to stimulate the incorporation of [35S]methionine into polypeptides in reticulocyte lysate apparently does not change. The proteins synthesized in vitro by cerebellar mRNA from different developmental stages were therefore analyzed by single and 2-dimensional gel electrophoresis. The diversity of these proteins and the levels of many of them were found to vary with cerebellar development. The newly synthesized brain forms of enolase and creatine kinase were identified by their migration coordinates in the 2-dimensional protein gels, and increase in the abundance of their directing mRNAs was found to accompany the differentiation of cerebellar interneurons. The extent of modification in cerebellar mRNA was determined to be much higher than the consequent changes in the composition of cerebellar proteins. We propose to use the ontogenetic variations in the levels of specific cerebellar mRNA species in normal and malformed cerebellum to identify proteins specific to particular types of cerebellar neurons.

Role of elongation factor 1 in the translational control of rodent brain protein synthesis

The translational control of protein synthesis during early postnatal neural development and aging was examined in the mouse and the rat. The activity of brain elongation factor 1 (bEF-1) was found to decrease exponentially with age and to decline parallel to the age-dependent decrease in total protein synthesis in both rodents. This decrement in bEF-1 activity fell within the range of reported age-related decreases in protein synthesis in in vitro systems. The factor was present in multiple forms; the lighter species predominated in older animals, whereas the young light form apparently disappeared with increasing age, and was replaced by other arising from the heavy form. Elongation factor 1 derived from young brains functioned as a rate-limiting component in polypeptide synthesis in previously saturated adult systems. The data suggest that bEF-1 has an important modulatory effect on total brain protein synthesis.