A critical period of ecdysterone action on sensitive clones of Drosophila cultured in vitro: the maturation of the cells.

Abstract

Ecdysterone-sensitive clones cultured in vitro were isolated from established cell lines of Drosophila melanogaster. The clones FC and 89K are ecdysterone-inducible for two enzymatic activities: acetylcholinesterase and beta-galactosidase. No activity could be detected in untreated cells, whereas after treatment with 50-250 nM ecdysterone, the activity appeared after one day and increased during 3-4 days. We wanted to modulate the response of the cells by varying the conditions of the hormonal stimulus. Mimicking the physiological situation of Drosophila (the ecdysterone peak corresponding to the molts is preceded by low levels) we pretreated the cells with a subthreshold concentration (1-5 nM) for 2 days and then we added the stimulating concentration of 50-250 nM ecdysterone. The enzymatic activities were then detectable within the following hours and the final level of induction was about twice the one of cells without pretreatment. Thus, the continuous presence of a subthreshold concentration of ecdysterone provokes the maturation of the cells which become able to respond to the hormonal stimulus by a quicker and higher enzymatic induction. The cellular maturation seems to be a critical period. It is altosid-sensitive. Altosid (a juvenile hormone analog) abolishes the effects of the ecdysterone-induced maturation.