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 sour ce of ecdysteroids; (2) to monitor more accurately the kinetics of ecdyster oid production; and (3) to check for possible relationships between this sy nthetic activity and dynamics of cell division. An insect cell line (IAL-PI D2) established from imaginal discs of the Indian meal moth, Plodia interpu nctella, 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 existe nce of two cell subpopulations that would be able to produce ecdysteroids r hythmically, a minor one that would be cell cycle serum independent populat ion, and a major population that would need serum growth factors to prolife rate and produce ecdysteroids. Qualitative study of the ecdysteroid content of the media clearly showed that ecdysone was the major immunoreactive pro duct, Taken together, our findings clearly show that an insect cell line of epidermal origin is capable of rhythmic autocrine production of ecdysteroi ds. These results support the hypothesis that alternate sites for ecdystero id production in vivo may exist and could play a role in local regulation o f development. We now plan to determine the cellular basis of this rhythmic autocrine activity and to confirm the existence of growth factor-autonomou s cells in the culture as well as the potent role played by ecdysteroids in the cross-talk between various cell subpopulations. Arch, Insect Biochem, Physiol, 44:7-16, 2000. (C) 2000 Wiley-Liss, Inc.