Electron microscopic radioautographic study on nucleic acid synthesis in amitotic hepatocytes of the aging mouse

Twenty groups of aging mice, each consisting of three individuals from fetal day 19 to postnatal month 24, were injected with either (3)H-thymidine or (3)H-uridine. The mice were killed 1 h and the livers processed for light and electron microscopic radioautography. On radioautograms obtained from each animal, amitotic nuclear divisions and resulting binucleate hepatocytes were detected and compared to mononucleate hepatocytes. From the results, it was demonstrated that only a few hepatocytes showing amitotic nuclear division were found labeled with the two precursors demonstrating DNA and RNA synthesis. However, there were very few silver grains showing incorporation of labeled precursors in respective amitotic cells. It was clarified that the amitotic cells did not synthesize such macromolecules as mononucleate hepatocytes did. On the other hand, the binucleate cells were found more often than the amitotic cells. DNA synthesis of binucleate hepatocyte nuclei was observed at the perinatal stage but disappeared at the adult stage. RNA syntheses in karyoplasm and cytoplasm in both mononucleate and binucleate cells significantly increased from the perinatal stage, reaching the maxima at the adult stage, then significantly decreased to the senescent stage. Grain counts revealed that RNA was synthesized significantly more in binucleate cells than in mononucleate cells at the respective aging stages.