Cloning and characterization of CcEcR

In order to understand the role that 20‐hydroxyecdysone plays during development of the Mediterranean fruit fly Ceratitis capitata (medfly), a major agricultural pest, we have cloned a Ceratitis ecdysone receptor (CcEcR) and studied its expression and its binding properties to an ecdysone response element. Using the conserved DNA binding region of the Drosophila melanogaster ecdysone receptor (DmEcR) B1 cDNA as a probe, we isolated a medfly cDNA clone containing the coding region, a part of the 5′‐untranslated region and the complete 3′‐untranslated region of a CcEcR. The deduced CcEcR polypeptide contained all five domains typical of a nuclear receptor. Alignment comparisons and phylogenetic analyses indicated that CcEcR most closely resembled the B1 isoform of DmEcR and Lucilia cuprina EcR homolog (LcEcR) relative to all other known ecdysone receptors. In situ hybridization analysis showed that the CcEcR gene is mapped in the region 53B of the 4R chromosome arm, while Northern hybridization analysis showed that CcEcR transcripts have a size of approximately 8 kb. Significant levels of CcEcR transcripts were detected in eggs, middle and late embryos, late third instar larvae and middle prepupae. The levels of the CcEcR transcripts during the other larval stages as well as during pupal and adult stages were much lower, while during the early stages of embryogenesis were very low. Electrophoretic mobility shift assays indicated that CcEcR binds specifically to the Drosophila hsp27 ecdysone response element as a heterodimer with Drosophila USP, the product of the ultraspiracle gene. Our structural and biochemical data suggest that CcEcR is the functional homolog of the B1 isoform of DmEcR.