Molecular cloning of an ecdysone receptor (B1 isoform) homologue from the silkworm, Bombyx mori, and its mRNA expression during wing disc development

We reported the isolation and sequence of a clone encoding a putative ecdysone receptor B1 isoform of the silkworm, Bombyx mori. The predicted open reading frame encoded 543 amino acids, with 51%, 95% and 71% identities with the Drosophila melanogaster ecdysone receptor B1 isoform in the N terminal A/B region, DNA binding domain (C region) and ligand binding domain (E region), respectively. A single 6.2 kb message for the EcR gene was abundant in wing discs and fat bodies at the onset of metamorphosis. At the same stage, however, no or a tiny amount of mRNA was shown in posterior or middle silk glands, respectively. During the final instar, the mRNA expression in wing discs was maximal on the day of wandering. These data suggest the transcription of the Bombyx EcR gene is regulated in tissue specific and stage-specific manner during metamorphosis.