The effect of 20-hydroxyecdysone and juvenile hormone on transcription and specific gene expression in larval fat body in Galleria

Abstract

The effects of 20-hydroxyecdysone and of juvenile hormone on transcription in fat body were studied in ligated abdomens of day-5 last-instar Galleria mellonella larvae. 20-Hydroxyecdysone stimulated synthesis of both total and poly(A) RNAs while juvenile hormone had no effect on transcription. The stimulatory effect of 20-hydroxyecdysone was observed within 3 h after hormone application and peaked at 6–8 h, at which time the specific activity of total and poly(A) RNAs was double that of controls. Fifteen hours after hormone application the specific activity of poly(A) RNA in treated and control larvae was identical. The specific activity of total RNA, however, remained higher than those of controls even 26 h after hormone treatment. The effect of juvenile hormone and 20-hydroxyecdysone on specific gene expression in these fat body cells was also determined by electrophoretic analysis of the polypeptides synthesized in vitro from the fat body poly(A) RNAs from experimental and control larvae. 20-Hydroxyecdysone induced synthesis of mRNAs that code for 22K and 26K Dalton proteins, which were not detectable in preparations from untreated, Ringers- or juvenile hormone-treated larvae. These mRNAs appeared between 1 and 6 h after hormone treatment and persisted up to 24h. Application of juvenile hormone 4 h before ecdysteroid treatment inhibited ecdysteroid induction of one of the inducible mRNAs.