DNA Synthesis in the Tracheae of Aging Mice by Light and Electron Microscopic Radioautography

Abstract

The present study was undertaken to elucidate the age-related changes of DNA synthesis and morphology of tracheal cells in aging mice by light and electron microscopic radioautography. The tracheae of 8 groups of mice from fetal day 18 to 2 years after birth were labeled with ³H-thymidine in vitro. The results demonstrated that the DNA syntheses and morphology of tracheal cells in aging mice changed due to aging. The radioautographic examinations revealed that the DNA syntheses of the nonciliated and basal cells reached their maxima on fetal day 18, then fell from postnatal 3 das onwards. The activity of DNA synthesis of ciliated cell was very low in the fetal stage. Ciliated cells could not synthesize DNA and proliferate in the postnatal stage, which were derived by the division and transformation of basal cells. On the other hand, the DNA synthesis of chondrocytes was the highest on embryonic day 18, and rapidly declined on postnatal day 3. The chondrocytes lost the ability of synthesizing DNA at 2 months after birth. The DNA syntheses of other cells (including fibroblasts, smooth muscle and glandular cells) were the highest on fetal day 18 and fell markedly on the third day after birth. They increased again at 1 week, then decreased progressively due to aging.