THE DROSOPHILA E93 GENE FROM THE 93F EARLY PUFF DISPLAYS STAGE-SPECIFIC AND TISSUE-SPECIFIC REGULATION BY 20-HYDROXYECDYSONE

Pulses of ecdysteroids induce dramatic changes in gene expression that direct the early stages of Drosophila metamorphosis. This gene activi ty is reflected by the appearance of early and late puffs in the saliv ary gland polytene chromosomes. Curiously, the early puff genes that h ave been studied to date are induced by both the late larval and prepu pal pulses of ecdysteroids and are expressed in many ecdysteroid targe t tissues, raising the question of how the hormone directs the complex stage- and tissue-specific responses associated with metamorphosis. T n an effort to address this question, we have isolated and characteriz ed the E93 gene responsible for the stage-specific 93F early puff. The E93 mRNA displays no response to ecdysteroids in late larval salivary glands but is directly induced 12 hr later by the prepupal ecdysteroi d pulse, identical to the response of the 93F puff. In tissues other t han the salivary gland, however, E93 displays complex spatial and temp oral regulation. E93 spans at least 55 kb of genomic DNA and encodes a 146-kDa protein that has no matches in the sequence databases, but di splays several characteristics of known Drosophila transcription facto rs. We propose that E93 acts in a stage-specific regulatory hierarchy in the salivary gland to direct its histolysis in response to the prep upal ecdysteroid pulse. (C) 1995 Academic Press, Inc.