Light and electron microscopic radioautographic studies on macromolecular synthesis in amitotic hepatocytes of aging mice.

The problem on cell divisions whether cells proliferate by mitosis or amitosis has been the heated controversy among many biologists since the late 19th century. We confirmed by extensive experiments since the mid 20th century that all the cells proliferated by mitosis not by amitosis but that amitosis actually existed in some glandular cells such as hepatocytes or pancreatic acinar cells which showed only amitotic nuclear divisions without cytoplasmic division producing binucleate cells in several kinds of experimental animals. We further verified that such amitotic cells did not synthesize macromolecular compounds incorporating macromolecular precursors such as 3H-thymidine for DNA, 3H-uridine for RNA or 3H-leucine for proteins. Recent experiments at the end of 20th century using many groups of aging mice, from fetal day 19 to postnatal month 24, injected with such precursors, amitotic cells and resulting binucleate cells in the hepatocytes were detected by electron microscopic radioautography and compared to mononucleate cells. The results demonstrated that only a few hepatocytes showing amitotic nuclear division were found labelled with the 3 precursors demonstrating DNA, RNA and protein synthesis. However, the numbers of silver grains showing incorporations of labelled precursors in respective amitotic cells were very few. It was clarified that the amitotic cells did not synthesize such macromolecules as mononucleate hepatocytes did. On the other hand, more binucleate cells were found than the amitotic cells. DNA synthesis of mononucleate and binucleate hepatocyte nuclei was observed at perinatal stage and disappeared at adult stage. The labeling index of mononucleate hepatocytes was greater than that of binucleate hepatocytes. RNA and protein syntheses in karyoplasm and cytoplasm in both mononucleate and binucleate cells increased from perinatal stage, reaching the maxima at adult stage then decreased to senescent stage. Grain counts revealed that synthesized RNA and proteins were more in binucleate cells than mononucleate cells at respective aging stages.