The acquisition of competence to respond to ecdysone in Drosophila is transcript specific

Abstract

The steroid hormone ecdysone induces a precise sequence of gene activity in Drosophila melanogaster salivary glands in late third larval instar larvae. The acquisition of competence for this response does not result from a single event or pathway but requires factors that accumulate throughout the instar. Individual transcripts become competent to respond at different times and their expression is differentially affected in ecd 1 , dor 22 and BR-C mutants. The induction of early-late transcripts, originally assumed to necessarily follow early transcripts, is partially independent of early transcript activation. Attempts to inhibit the synthesis of regulatory proteins reveal transcript-specific superinduction effects. Furthermore these inhibitors lead to the induction of βFTZ-F1 and E93 transcripts at levels normally found in prepupal glands. These studies reveal the complexity of the processes underlying the establishment of a hormonal response.