Characterization of an EcR/USP heterodimer target site that mediates ecdysone responsiveness of the Drosophila Lsp-2 gene
- Cite this article as:
- Antoniewski, C., O'Grady, M.S., Edmondson, R.G. et al. Molec. Gen. Genet. (1995) 249: 545. doi:10.1007/BF00290580
The Larval serum protein-2 gene (Lsp-2) of Drosophila melanogaster is uniquely expressed in the fat body tissue from the beginning of the third instar to the end of adult life. Accumulation of the larval Lsp-2 transcript is enhanced by 20-hydroxyecdysone. To study the molecular basis for ecdysone regulated Lsp-2 activity, deletion mutants of the Lsp-2 5′-flanking region were constructed by fusion to either the Escherichia coli chloramphenicol acetyltransferase (CAT) gene or to an hsp70-lacZ hybrid gene encoding β-galactosidase. Constructs transfected into Drosophila S2/M3 cells were shown to confer transient ecdysone inducibility on the reporter genes. A single functional ecdysone response element (EIRE) was localized at position — 75 relative to the Lsp-2 transcription initiation site. In gel mobility shift assays using fat body nuclear extracts or nuclear receptors synthesized in vitro, a 27-bp sequence harboring the EcRE bound both the Drosophila ecdysone receptor and the Drosophila retinoid-X homologue, Ultraspiracle, in a cooperative manner. Competition experiments indicate that the affinity of the Lsp-2 EcRE for the ecdysone receptor complex is comparable to that of the canonical EcRE of the hsp27 gene and is at least 4-fold greater than that of Fbp1, another fat body-specific Drosophila gene. Our results suggest that structural features of this EcRE determine its ability to induce ecdysone responsiveness at a lower ligand concentration and may form the basis for differential hormone responsiveness within the fat body.