Electron microscopic radioautographic study on the nucleic acids and protein syntheses in the aging mouse testis

The ultrastructural difference between³H-thymidine labeled and unlabeled germ cells in mouse testis was observed by electron microscopic radio-autography. The RNA and protein syntheses in the seminiferous tubules of aging mice were also studied using³H-uridine and leucine radioautography. At embryonic day 19, the Sertoli cells and myoid cells labeled with³H-thymidine were often observed. The gonocytes labeled with³H-thymidine that were not rich in cell organelles appeared from the early postnatal stage. The silver grains were located mainly over the nuclei of labeled gonocytes, but a few were over the mitochondria. The labeling index of spermatogonia for³H-thymidine rapidly increased from 2 weeks on, and stayed relatively constant until old age. The labeling indices of the other two kinds of cells, i.e., Sertoli and myoid cells, decreased to low levels with aging, while these cells continued RNA and protein syntheses through aging, as detected by the incorporation of³H-leucine and uridine.