Temporal profiles of nuclear receptor gene expression reveal coordinate transcriptional responses during Drosophila development.

The recent completion of the Drosophila genome sequence revealed 21 members of the nuclear receptor superfamily. Many of these genes are transcriptionally regulated by the steroid hormone ecdysone and play a role during the onset of metamorphosis, including the EcR/USP ecdysone receptor heterodimer. As a first step toward a genomic analysis of this gene family, we have characterized the temporal patterns of expression for all detectable nuclear receptor transcripts throughout major ecdysone-regulated developmental transitions in the life cycle: embryogenesis, a larval molt, puparium formation, and the prepupal-pupal transition. We find an unexpected close temporal relationship between DHR3, E75B, and betaFTZ-F1 expression after each major ecdysone pulse examined, reflecting the known cross-regulatory interactions of these genes in prepupae and suggesting that they act together at other stages in the life cycle. In addition, E75A, E78B, and DHR4 are expressed in a reproducible manner with DHR3, E75B, and betaFTZ-F1, suggesting that they intersect with this regulatory cascade. Finally, we find that known ecdysone-inducible primary-response transcripts are coordinately induced at times when the ecdysteroid titer is low, implying the existence of novel, as yet uncharacterized, temporal signals in Drosophila.