The steroid hormone 20-hydroxyecdysone and its EcR/USP receptor are vital during arthropod development for coordinating molting and metamorphosis. Traditionally, little attention has been given to potential post-developmental functions for this hormone signaling system. However, recent studies in Drosophila melanogaster indicate that the hormone and receptor are present and active in adults and that mutations decreasing hormone or receptor levels affect diverse processes such as reproduction, behavior, stress resistance, and lifespan. We review the current state of knowledge regarding adult hormone production and titers and discuss receptor expression and activity in order to identify potential mechanisms which explain the observed mutant phenotypes. Finally, we describe future research directions focused on identifying isoform-specific functions of EcR, distinguishing effects from EcR/USP gene activation and repression, and determining how ecdysone signaling impacts different tissue types.
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