Rates of DNA and RNA Synthesis in Various Tissues during a Larval Moult Cycle of Samia cynthia ricini (Lepidoptera)

Abstract

THIS report describes the rates of synthesis of DNA and RNA in various tissues during larval moulting of a silk-moth and examines the control of these processes. The following questions were posed for specific tissues: When during a moult cycle is DNA synthesized ? Is DNA synthesis synchronous in some tissues ? In all tissues ? What proportion of the cells in each tissue engage in DNA synthesis during a moult cycle ? Is DNA synthesis in some tissues under the control of the prothoracic gland hormone, ecdysone ? How does the rate of RNA synthesis in specific tissues change during a moult cycle ? Is RNA synthesis under hormonal control ? Previous investigations of the larval–pupal transformation and of diapausing pupae led us to conclude that “almost all tissues of the pupa require ecdysone for DNA synthesis” whereas “RNA synthesis continues in many tissues when little or no ecdysone is present”^1,2. The present experiments extend these observations and confirm the hypothesis that stimulation of DNA synthesis is a primary effect of ecdysone³.