RNA synthesis in liver and heart of growing and adult mice

Abstract

Cells of liver and heart of 12-day-old mice actively synthesize DNA, whereas in 5-month-old mice, the rate of DNA synthesis in these two organs is reduced to a negligible level. Livers and hearts of 12-day- and 5-month-old mice were therefore compared in order to determine differences in some aspects of RNA synthesis. RNA synthesis was studied by determining nucleic acid concentration, incorporation in vivo of radioactive cytidine into whole cells and into subcellular fractions, the size of the endogenous cytidine pool, RNA turnover over a period of 30 days, the effect of actinomycin D and sucrose gradient analysis of phenol-extracted RNA. The rate of synthesis of rapidly-labeled RNA was higher in 12-day-old than in 5-month-old tissues (50 % higher in liver and 2.4 times higher in heart). The specific activity of the cytidine precursor pool was doubled in the adult tissues. In addition, the turnover of RNA was decreased in the adult heart, and the concentration of RNA per cell in the adult liver was almost twice the amount found in growing liver. Other parameters of RNA synthesis were substantially similar in growing and adult livers an hearts.