Biochemical studies of ecdysone control of chromosomal activity

Ecdysone receptors: from the Ashburner model to structural biology

In 1974, Ashburner and colleagues postulated a model to explain the control of the puffing sequence on Drosophila polytene chromosomes initiated by the molting hormone 20-hydroxyecdysone. This model inspired a generation of molecular biologists to clone and characterize elements of the model, thereby providing insights into the control of gene networks by steroids, diatomic gases, and other small molecules. It led to the first cloning of the EcR subunit of the heterodimeric EcR-USP ecdysone receptor. X-ray diffraction studies of the ligand-binding domain of the receptor are elucidating the specificity of receptor-ecdysteroid interactions, the selectivity of some environmentally friendly insecticides, the evolution of the EcR-USP heterodimer, and indeed Ashburner's classical biochemical evidence for the central role of the ecdysone receptor in his model.

Counteraction by 20-hydroxyecdysone of the effect of juvenile hormone on phosphorylation of ribosomal protein S6

Phosphorylation of ribosomal protein S6, induced when the fat body of Sarcophaga peregrina (flesh-fly) larvae was incubated in vitro in the presence of 32P, was found to be suppressed by juvenile hormone. This suppressive effect of juvenile hormone was counteracted by a physiological concentration of 20-hydroxyecdysone. Since 20-hydroxyecdysone is known to induce phosphorylation of S6 in vivo, this reaction was suggested to be regulated by the balance of the effects of ecdysone and juvenile hormone.