Ecdysterone regulatory elements function as both transcriptional activators and repressors.

Abstract

A synthetic, 23-bp ecdysterone regulatory element (EcRE), derived from the upstream region of the Drosophila melanogaster hsp27 gene, was inserted adjacent to the herpes simplex virus thymidine kinase promoter fused to a bacterial gene for chloramphenicol acetyltransferase (CAT). Hybrid constructs were transfected into Drosophila S3 cells and assayed for ecdysterone-inducible CAT expression. In the absence of ecdysterone a tandem pair of EcREs repressed the high constitutive level of CAT activity found after transfection with the parent reporter plasmid alone. After hormone addition very high levels of CAT activity were observed. Insertion of the EcRE pair 3' of the CAT gene also led to high levels of ecdysterone-induced CAT expression, but the repression of high constitutive levels of CAT activity failed to occur. The EcRE-CAT construct was cotransfected with plasmids containing tandem 10-mers or 40-mers of the EcRE but lacking a reporter gene. These additional EcREs led to a reduced level of ecdysterone-induced CAT activity and to an elevation of basal CAT activity in the absence of hormone. The data suggest that the receptor binds to the EcRE in the absence of hormone, blocking basal transcription from a constitutive promoter. In the presence of ecdysterone, receptor-hormone binding to the EcRE leads to greatly enhanced transcription.

The variety of complexes formed by EcR and Usp nuclear receptors in the nuclei of living cells

“…Both these functions are exhibited in the presence and absence of 20E, respectively (Dobens et al, 1991). Obviously, the nuclear localization of EcR, which according to our data is determined by Usp, is essential in both cases.…”

Direct Repeats Bind the EcR/USP Receptor and Mediate Ecdysteroid Responses in Drosophila melanogaster

“…1) in a head-to-tail orientation into the BamHI site of ptkAT0 (15). The orientation and number of response elements were determined by suitable restriction analysis.…”

Ras signaling modulates activity of the ecdysone receptor EcR during cell migration in the drosophila ovary

“…EcR, which encodes three receptor isoforms that are functionally distinct in some tissues (Yao et al, 1992(Yao et al, , 1993Bender et al, 1993;Thomas et al, 1993), forms heterodimers with the Drosophila RXR homologue USP, encoded by the gene ultraspiracles (usp, Shea et al, 1990;Oro et al, 1992;Henrich et al, 1994). The ecdysone-EcR/USP receptor/ligand complex binds at Ecdysone Response Elements (EcREs) near responsive promoters to coordinate gene expression in diverse tissues (Riddihough and Pelham, 1987;Dobens et al, 1991). During pupariation, EcR initiates the activation of a hierarchy of genes to control complex developmental changes including cuticle formation, tissue apoptosis, and neuronal remodeling (Ashburner et al, 1974;Burtis et al, 1990;DiBello et al, 1991;Riddiford et al, 2000).…”