Endocrine Regulation of the Ecdysteroid Cascade During Insect Metamorphosis

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9817339RiddifordMetamorphosis involves a spectacular change of form such as the transformation of a caterpillar into a lovely butterfly. Dr. Riddiford seeks to understand the cellular and molecular basis of the hormonal regulation of the complex series of events necessary for this transformation to occur in a coordinated manner at the right time. In insects the growth of the larva requires periodic molts of its cuticular exoskeleton which are initiated and coordinated by the steroid hormone ecdysone acting on the epidermis which makes the culticle in the presence of a second hormone juvenile hormone. Metamorphosis occurs when ecdysone acts in the absence of juvenile hormone, causing changes in the epidermis that lead to a new type of cuticle and the differentiation of imaginal (adult) discs and processor cells to form new adult structures. Dr. Riddiford will utilize antibodies to the isoforms of the ecdysone receptor and its partner ultraspiracle and of the early ecdysteroid-induced transcription factors and when necessary, in situ hybridization analysis of the RNAs, to study differences in epidermal cell response to the circulating ecdysteroids in the presence of juvenile hormone during a larval molt and in its absence during metamorphosis of the tobacco hornworm, Manduca sexta. These responses will be compared to those in the imaginal cells which mainly proliferate during larval life, then become committed for metamorphosis early in the final larval stage to elucidate the mechanism whereby these two different types of cells respond to the same hormonal milieu. Dr. Riddiford will also develop a method of selectively deleting one of the ecdysone receptors or the induced transcription factors in the epidermis when it is responding to ecdysteroid in vitro and then in the animal so as to assay the functional roles of these various factors in causing both new cuticle formation during the molts and the cellular switches necessary for metamorphosis. These studies will provide deeper insight into how the two major ecdysteroids, ecdysone and 20-hydroxyecdysone, initiate and coordinate the cellular responses during a molt and during the switching of the epidermal cell fate that is the hallmark of metamorphosis and how juvenile hormone directs ecdysteroid action to prevent metamorphosis. The basic knowledge gained also may lead to new selective approaches to insect control.