Molecular cloning of the orphanin FQ receptor gene and differential tissueexpression of splice variants in rat

Pharmacological and receptor-ligand binding studies of the cloned orphanin FQ (OFQ) receptor suggest that multiple forms of this receptor may exist. T o further characterize the OFQ receptor (OFQR), we attempted to isolate the gene encoding this receptor in rat. The OFQR gene exceeds 10 kb in length and contains six exons ranging from 34 to 524 bp that are interrupted by fi ve introns. The ATG translation initiation codon is located in exon, and th e open reading frame consists of 1283 bp. Primer extension analysis of the gene revealed two major transcription initiation sites: one in the 5 ' Rank ing region and the other in intron 1. The rat OFQR gene appeared to be alte rnatively spliced to yield multiple mRNAs. Four splice variants deleted for exon 1 were expressed only in brain. In contrast, five isoforms containing exon 1 were expressed in various tissues, such as brain, testes, and gastr ointestinal tract. These data suggest that unique regions in intron 1 and i n the 5 ' flanking region of the OFQR gene contribute to the regulation of its expression in different tissues. (C) 2001 Elsevier Science B.V. All rig hts reserved.