The Chemical and Neural Control of Insect Metamorphosis

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Insect growth and metamorphosis is controlled primarily by the molting hormone, 20-hydroxyecdysone (20HE), and juvenile hormone (JH) which, when present, prevents metamorphosis. A neuropeptide, eclosion hormone, then triggers ecdysis at the end of each molt. During the next 5 years, this project will focus on the action of these hormones in the context of identified genes in the tobacco hornworm, Manduca sexta, and the fruitfly, Drosophila melanogaster. The particular projects include: 1) The spatial and temporal patterning of ecdysteroid receptors in the epidermis during a larval molt and the larval-pupal transformation and their relationship to the competence of the cells to respond to the hormone. 2) Structural analysis of the gene for insecticyanin, the pigment necessary for adaptive coloration, hormonal regulation of its expression, and factors involved in the bidirectional secretion of this protein. 3) The dual role (induction and repression) of 20HE in determining the timing of expression of gene for dopa decarboxylase, the enzyme necessary for cuticular melanization and hardening after ecdysis. 4) The role of ecdysteroid in the regulation of eclosion hormone gene expression and of these two hormones in the onset of alcohol dehydrogenase gene expression at adult eclosion in Drosophila. These studies will clarify our understanding about how 20HE and JH act together to regulate specific genes during a larval molt and at metamorphosis and how the changing ecdysteroid titer may coordinate the onset of gene expression during a molt. Furthermore, they will define for the first time in a complex system how a neuropeptide and a steroid hormone interact to control specific gene expression. This in-depth knowledge about the mode of action of these critical developmental hormones should also serve as a basis for new approaches to insect control.