Short-term effects of crustecdysone (20-hydroxyecdysone) on protein and RNA synthesis in third instar larvae of Calliphora

Abstract

The effect of exogenous crustecdysone (20-hydroxyecdysone) on protein and RNA synthesis in body wall and fat body of third instar larvae of Calliphora stygia has been investigated in vivo. The effect of injury resulting from the injection and handling technique has been separated from responses to the hormone. Protein synthesis in body wall is most sensitive to crustecdysone in larvae aged 7 to 8 days, somewhat before the level of endogenous moulting hormone rises. Protein synthesis in fat body is stimulated over a wider age range. The time-course of the hormone effect on protein synthesis in 7 to 8 day larvae is similar in body wall and fat body, and is quantitatively the same for either ecdysone or crustecdysone. There is an initial depression of protein synthesis 1 hr after injection of hormone, followed by a burst of protein synthesis at 4 hr which is substantially over at 6 hr. The effect of crustecdysone on protein synthesis in body wall from treated 7 to 8 day larvae is proportional to the logarithm of the dose over the range 0·002 to 0·2 μg/larva. The response of protein synthesis in fat body to increasing dose in this range is slight. Gross RNA synthesis in body wall from 7–8 day larvae is greatly stimulated 2 hr after injection of crustecdysone but approximates control levels by 4 hr. An initial depression in gross RNA synthesis is apparent at 2 hr in fat body preparations from the same animals, but by 4 hr RNA synthesis shows marked enhancement above the control levels. A study of 3H-uridine incorporation into subcellular fractions from body wall and fat body shows that synthesis in nuclear, microsomal, and soluble RNA components is affected by the hormone, but at different times and to varying degrees.