Abstract: Ecdysteroids, the steroid hormones, play a crucial role in coordinating molting, metamorphosis and reproduction in insects. The action of ecdysteroids, mainly 20-hydroxyecdysone (20E), is mediated by their binding to the ecdysone receptor (EcR), which requires a heterodimeric partner, ultraspiracle protein (USP). Upon binding the ligand, the EcR-USP heterodimer binds to a DNA ecdysone response element (EcRE) that is located in the promoter region of a series of ecdysteroid-responsive genes and thereafter triggers the expression of a cascade of genes involved in regulating some key developmental events in insects. The EcR has been an important target in designing new, environmentally safe insecticides against pest species. The differences in the ligand binding domains (LBD) of EcRs from insects belonging to different orders can be exploited to discover order-specific insecticides. The EcR also has been used to develop inducible gene switches for efficient regulation of foreign genes in applications such as gene therapy, protein production and functional genomics. The structural and function characteristics of EcRs, the mode of molecular action of ecdysteroid (PonA) and diacylhydrazine (BYI06830) with EcR/USP respectively, and EcR-based screening assays and gene switches were reviewed in this article.

Key words: Ecdysteroid receptor (EcR), ultraspiracle protein (USP), ligand binding domain, genetic cascade, screening assays, gene switch