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

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 si ngle event or pathway but requires factors that accumulate throughout the i nstar. Individual transcripts become competent to respond at different time s 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 tra nscript activation. Attempts to inhibit the synthesis of regulatory protein s reveal transcript specific superinduction effects. Furthermore these inhi bitors lead to the induction of beta FTZ-F1 and E93 transcripts at levels n ormally found in prepupal glands. These studies reveal the complexity of th e processes underlying the establishment of a hormonal response. (C) 1999 E lsevier Science ireland Ltd. All rights reserved.