Aging changes of intramitochondrial nucleic acid synthesis, both DNA and RNA, in hepatocytes of several groups of litter mate mice at various ages, from fetal day 19, to postnatal newborn day 1, 3, juvenile day 7, 14, adult month 1, 6, senile year 1 and 2, were studied by means of electron microscopic radioautography. After the injections with either 3H-thymidine or 3H-uridine, the liver tissues were taken out, fixed, processed for radioautography and observed by electron microscopy. From the results, it was found that some of the mitochondria in the hepatocytes were labeled with silver grains showing either DNA or RNA syntheses. Quantitative analysis revealed that the numbers of mitochondria in the hepatocytes increased from the prenatal day to postnatal month 6, reaching the maximum, then decreased to year 2. On the other hand, the intramitochondrial labeling indices with silver grains showing DNA synthesis and grain counts showing RNA synthesis increased from prenatal day to postnatal newborn, juvenile and adult month 1, reaching the maxima, then decreased to senile year 1 to 2. These results indicate the aging changes of both DNA and RNA syntheses and suggest the aging changes of gene expressions in hepatocyte mitochondria.
Buy this Article