Abstract
Mitochondrial gene expression has been investigated in synaptic endings from rat cerebral cortex isolated at various stages during the postnatal development and maturation of the animal. The pattern of the mitochondrial translation products labeled in vitro in rat brain synaptosomes revealed some distinctive features when compared with the pattern observed in a rat fibroblast cell line, the most remarkable being the apparent absence of labeling of the ND5 product. This absence contrasted with the presence in synaptosomes of an amount of ND5 mRNA comparable with that found in the rat fibroblast cell line. The rate of mitochondrial protein synthesis per unit amount of mtDNA in brain synaptosomes showed a characteristic reproducible burst at 10-13 days after birth, thereafter declining sharply in the 3rd week to reach a level that remained constant over a 2-year period. The postnatal burst of mitochondrial protein synthesis coincided with a sharp increase in cytochrome c oxidase activity, pointing to a phase of rapid assembly of respiratory complexes. A comparison of the levels of mitochondrial mRNAs with the corresponding rates of protein synthesis during the animal development and maturation showed a lack of correlation. These observations, together with the apparent lack of translation of the ND5 mRNA, indicate that translational control plays a major role in the regulation of gene expression in rat brain synaptic mitochondria.
Highlights
Mitochondrial gene expression has been investigated level of translation in specialized cells
The rat was used as an expersynaptosomes revealed some distinctive features when imental system because of the facility of obtaining fresh compared with the pattern observed in a rat fibroblast cell line, the most remarkable being the apparent absence of labeling of the ND5 product
This absence contrasted with the presence in synaptosomes of an amount of ND5 mRNA comparablewith that found in the rat fibroblast cell line
Summary
A comparisonof the levels of mitochondrialmRNAs with the correspondingrates of protein synthesis during the animal development and maturation showed a lack of correlation These observations, together with the apparent lack of translation of the ND5 mRNA, indicate that translational control plays a major rolein the regulation of geneexpressionin rat brain synaptic mitochondria. Nerve terminals creates the problem of a continuous supply of nuclear coded components to the peripheral organelles or possibly of a recycling of the organelles to thecell body,with intriguing implications from the point ofviewof regulation of gene expression In another context, it can be expected that increased knowledge concerning the energetic metabolism that supports synaptic function will help in understanding the mechanism of this function. A comparison of the rates of mitochondrial protein synthesiswith the steady state levels of the mRNAs has shown that translational control plays an important role in gene expression in neuronal mitochondria
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