Ecdysteroids and Integuments in Locusts. In: Hoffmann J, Porchet M, editors. Biosynthesis, Metabolism and Mode of Action of Invertebrate Hormones. Berlin: Springer Berlin Heidelberg; 1984. pp. 234-44. [DOI: 10.1007/978-3-642-69922-1_22]

Rhythmic autocrine activity in cultured insect epidermal cells

It is now well established that ecdysteroids can be produced in insects in the absence of prothoracic glands. In this respect, it has been shown that cells in culture can produce ecdysteroids. Our aims were: (1) to determine whether ecdysteroid target cells of epidermal origin could also be the source of ecdysteroids; (2) to monitor more accurately the kinetics of ecdysteroid production; and (3) to check for possible relationships between this synthetic activity and dynamics of cell division. An insect cell line (IAL-PID2) established from imaginal discs of the Indian meal moth, Plodia interpunctella, with wild-type sensitivity to ecdysteroids was used in our study. Our results showed that the Plodia cell line exhibited autocrine activity. When division of IAL-PID2 cells was synchronized, a rhythmic production of ecdysteroids was observed. However, further experiments indicated that this rhythmicity could be cell autonomous. This led us to anticipate the existence of two cell subpopulations that would be able to produce ecdysteroids rhythmically, a minor one that would be cell cycle serum-independent population, and a major population that would need serum growth factors to proliferate and produce ecdysteroids. Qualitative study of the ecdysteroid content of the media clearly showed that ecdysone was the major immunoreactive product. Taken together, our findings clearly show that an insect cell line of epidermal origin is capable of rhythmic autocrine production of ecdysteroids. These results support the hypothesis that alternate sites for ecdysteroid production in vivo may exist and could play a role in local regulation of development. We now plan to determine the cellular basis of this rhythmic autocrine activity and to confirm the existence of growth factor-autonomous cells in the culture as well as the potent role played by ecdysteroids in the cross-talk between various cell subpopulations.

Roles for insulin and ecdysteroids in differentiation of an insect cell line of epidermal origin

During postembryonic development of insects, molting cycles affect epidermal cells with alternate periods of proliferation and differentiation. Cells of the cell line established from imaginal discs of the Indian meal moth (IAL-PID2) differentiate under the action of the molting hormone, 20-hydroxyecdysone, in a manner that is meaningful in terms of the development of the tissue from which they were derived. In particular, the hormone caused an accumulation of the cells in the G2 phase of their cycle and induced the formation of epithelial-like aggregates and the synthesis of specific proteoglycans. Recent discovery of members of the insulin superfamily in insects and the role of growth factors 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 resumption 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 effect of 20-hydroxyecdysone was reversible, and, prior exposure of the cells to the hormone allowed the cells to complete one cell cycle in serum-free medium. These results suggest that the production of autocrine growth factors induced by ecdysteroids could circumvent the absence of serum. This cell culture model provides potential for further study of interactions between ecdysteroids and growth factor homologs during differentiation of insect epidermal cells.

Insect tissue culture systems: models for study of hormonal control of development

The regulation of growth and development of insects is under endocrine control and involves both juvenile hormones and ecdysteroids. Neuropeptides are master regulators which control the secretion of these hormones. Most experiments in insect endocrinology have been conducted in vivo, but tissue culture methodology is playing an increasing role due to the great interest in simpler model systems for the study of complex processes that occur in vivo. The availability of appropriate media has allowed the culture of a variety of insect organs and cell lines of defined origin which have kept certain properties of the parent tissues. Tissue culture approaches have been useful for studying hormonal control of morphogenetic processes. Cell lines are particularly suited to the study of hormonally regulated mechanisms of macromolecular biosynthesis and gene expression. Thus, the value of in vitro analysis in studies of regulation of hormone production is now recognized. Results obtained from tissue culture allow more precise definition of the hormonal requirements of insect cells and tissues for growth and differentiation and might make possible the discovery of new growth regulators.