ROLES FOR INSULIN AND ECDYSTEROIDS IN DIFFERENTIATION OF AN INSECT-CELL LINE OF EPIDERMAL ORIGIN

During postembryonic development of insects, molting cycles affect epi dermal cells with alternate periods of proliferation and differentiati on, Cells of the cell line established from imaginal discs of the Indi an meal moth (IAL-PID2) differentiate under the action of the molting hormone, 20-hydroxyecdysone, in a manner that is meaningful in terms o f the development of the tissue from which they were derived. In parti cular, the hormone caused an accumulation of the cells in the G2 phase of their cycle and induced the formation of epithelial-like aggregate s and the synthesis of specific proteoglycans. Recent discovery of mem bers of the insulin superfamily in insects and the role of growth fact ors played by this family of molecules in vertebrates led us to check for their potential effects on IAL-PID2 cell cycle regulation. On the one hand, our results showed that insulin was involved in partial resu mption of the cell cycle after an arrest caused by serum deprivation, but that other growth factors present in fetal calf serum were needed for full completion of mitosis. On the other hand, the cytostatic effe ct of 20-hydroxyecdysone was reversible, and, prior exposure of the ce lls to the hormone allowed the cells to complete one cell cycle in ser um-free medium. These results suggest that the production of autocrine growth factors induced by ecdysteroids could circumvent the absence o f serum. This cell culture model provides potential for further study of interactions between ecdysteroids and growth factor homologs during differentiation of insect epidermal cells.