Cloning and developmental expression of Choristoneura hormone receptor 3, an ecdysone-inducible gene and a member of the steroid hormone receptor superfamily.

Degenerate oligonucleotides and cDNA converted from Choristoneura fumiferana embryonic RNA were used in a polymerase chain reaction (PCR) procedure to isolate a 683 bp cDNA fragment. Comparison of the deduced amino acid sequence of this cDNA fragment showed that it was a region of an MHR3-like gene from C. fumeferana; we therefore named it Choristoneura hormone receptor 3 (CHR3). This CHR3 cDNA fragment was used as a probe to screen a C. fumiferana embryonic cDNA library. Twenty clones were isolated and two overlapping clones were sequenced. The longest open reading frame of CHR3 cDNA codes for 546 amino acids. The deduced amino acid sequence of this open reading frame contained all five regions typical of a steroid hormone nuclear receptor. The C domain showed the highest identity to Manduca hormone receptor 3 (MHR3), Drosophila hormone receptor 3 (DHR3) and Galleria hormone receptor 3 (GHR3). The A/B, D and E domains also showed significant amino acid similarity with MHR3, DHR3 and GHR3. The 683 bp CHR3 cDNA probe detected two mRNAs of 3.8 and 4.5 kb present during the ecdysteroid peaks for embryonic, larval, pupal and adult molts but were not detected during the intermolt periods. In sixth instar larvae, the 3.8 and 4.5 kb mRNA were detected in the epidermis, fat body and midgut tissues and the maximum expression was observed during the prepupal peak of ecdysteroids in the hemolymph. CHR3 mRNA was induced in 20-hydroxyecdysone treated CF-203 cells as well as in the midgut, fat body and epidermis of larvae that were fed the non-steroidal molting hormone agonist, RH-5992. In vitro transcription and translation of the CHR3 cDNA yielded a 61 kDa protein that bound to the retinoid related orphan receptor response element.