cDNA Cloning of Constitutive Androstane Receptor (CAR) Gene of Japanese Quail

The nuclear receptor class 1 superfamily includes receptors for many biological regulators, such as thyroid hormone, retinoids and vitamin D. These receptors control expression of many genes as heterodimers with 9-cis-retinoic acid receptors (RXRs). The DNA-binding domain of the nuclear receptor class 1 proteins and RXRs bind to the 5’ upstream region of regulated genes. A new orphan nuclear receptor has been isolated by Bases et al.and identified that the expression of the gene is highest in the liver. The receptor, constitutive androstane receptor (CAR), belonging to the nuclear receptor class 1, subfamily I (NR1I3), forms heterodimers with RXR. These bind to retinoic acids-response elements (RAREs). Two androstane metabolites, androstanol and androstenol, were the ligands of CAR. The heterodimer, with these ligands, decrease expression of the target genes. The CAR translocates to the mouse liver nucleus in response to Phenobarbital (PB) and other PB-type inducers. The heterodimer with 1,4-bis[2-(3,5dichlorpyridyloxy)] benzene (TCPOBOP) as a ligand, increases the expression of the cytochrome The constitutive androstane receptor (CAR) belongs to the nuclear receptor class 1, subfamily I (NR1I3). The previous studies suggest the importance of the CAR gene for physiological mechanisms of the vertebrates, especially metabolism of steroid hormones. The present study determines the DNA sequence of a full length cDNA of Japanese quail (Coturnix japonica) CAR by the rapid amplification of cDNA end (RACE) method (Genbank accession No.AB104462). The cDNA consists of 1365bp, which is 25bp longer than chicken CAR (Genbank accession No.AF276753). The A/B domain of the CAR gene was highly variable and the revealed sequence difference between mammals and birds. The fifteen amino acids deletion of mammals CAR and six amino acids insertion of chicken CAR were found in the D domain in comparison to Japanese quail CAR. No insertion or deletion were found in the DNA binding domain (C domain) and the ligand binding domain (E domain) among Japanese quail and other animals. Expression of Japanese quail CAR was detected in duodenum, liver, and kidney using RT-PCR method.