Ecdysone and RNA synthesis in target tissues

Abstract

The action of ecdysone on RNA synthesis of the integument of blowfly larvae and on isolated nuclei from fat-body cells is described. Ecdysone induces in the integument the enzyme DOPA-decarboxylase, which is involved in the tanning process of the cuticle. Using inhibitors of RNA and protein synthesis, we concluded that de novo synthesis of enzyme protein dependent on the presence of newly synthesized RNA is involved in the induction process. Ecdysone stimulates, within 1 hr after administration, nuclear RNA synthesis involving both rapidly labeled DNA-like, as well as ribosomal RNA. After 3 hr, an increased specific activity of heterogeneously sedimenting (4–18 S) RNA of the cytoplasm is also observed. By acrylamide gel electrophoresis and double labeling techniques not only quantitative but also qualitative differences in the RNA synthesized after hormone action were detected. In the system of isolated fat-body nuclei, ecdysone as well as juvenile hormone stimulates RNA synthesis, whereas the presence of both hormones leads only to slight effects. The stimulation is independent of the ionic composition of the medium and is dependent, particularly in regard to the effects of juvenile hormone, on the developmental stage of the larvae from which the nuclei were isolated. Molecular DNA RNA hybridization shows that new species of RNA are induced by the hormones and suggests that some of the genes affected by ecdysone may also be affected by juvenile hormone.