Effects of steroids on insulin signaling in a growing insect tissue

Our interest is focused on the long‐term effects of a steroid hormone, ecdysone, on the insulin pathway in Manduca sexta (tobacco hornworm caterpillars). In insects and higher vertebrates, the insulin pathway plays a key role in growth and development. The insulin receptor induces signaling within a cell using a variety of downstream kinases, transcription factors, and other proteins. Growth in the wing discs of Manduca larvae seems to be similar to that in vertebrates in that a positive feedback system is present between ecdysone and the insulin pathway. The mechanism by which this occurs is not known. To begin to investigate this system, and hence understand the cellular basis of growth in this tissue, we have focused on the effects of ecdysone on the insulin signaling system by testing and measuring insulin receptor transcription levels, as well as the presence of downstream insulin‐signaling proteins. This work will have implications for understanding the regulation of insect development, as well as possible effects of steroids on insulin signaling in higher organisms.