20-HYDROXYECDYSONE IS REQUIRED FOR, AND NEGATIVELY REGULATES, TRANSCRIPTION OF DROSOPHILA PUPAL CUTICLE PROTEIN GENES

Transcripts of ecdysone-dependent genes (EDGs) accumulate in isolated imaginal discs within 8 hr after exposure to a pulse of the steroid hormone 20-hydroxyecdysone (20-HE; 1 μg/ml for 6 hr) but not in discs cultured in the continuous presence or absence of the hormone. Sequence analyses show that two of the EDGs are members of gene families encoding insect cuticle proteins. We conclude that a third EDG encodes a cuticle protein because the conceptual glycine-rich protein contains sequence motifs similar to those found in insect egg shell proteins and vertebrate cytokeratins and because expression of this gene is limited to tissues that deposit the pupal cuticle. Nuclear run-on assays show that the hormone-dependent expression of each of these EDGs is due to transcriptional regulation. Readdition of hormone to imaginal discs actively synthesizing the EDG messages causes rapid repression of EDG transcription. Thus, 20-HE acts as both a positive and a negative regulator of EDG transcription. Sequences in the promoter regions of two of the EDGs are similar to an ecdysone response element and may play a role in negative regulation. © 1991.