Studies on multiple hormonal regulation of insectdevelopment by endocrine perturbation

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In insects, a steroid hormone, 20-hydroxyecdysone (20E), plays important roles in the regulation of developmental transitions by initiating signaling cascades via the ecdysone receptor (EcR). Although 20E has been well characterized as the molting hormone, its precursor ecdysone (E) has been considered to be a relatively inactive compound because it has little or no effect on classic EcR mediated responses. I elucidate that not only 20E but also E is essential for the regulation of developmental timing in Drosophila melanogaster. I also explored a system in which ecdysteroid level is reduced by ectopic expression of an inactivating enzyme. By using the system, I find that developmental fate of second instar larva is converted to pupariation instead of molting to third instar at a low level of ecdysteroid. Further, I characterized 3-oxo steroids as components of the ecdysteroid biosynthetic pathway.