Two related G protein-coupled receptors: The distribution of GPR7 in rat brain and the absence of GPR8 in rodents

GPR7 and GPR8, orphan G protein-coupled receptor (GPCR) genes, expressed in the brain and periphery share highest sequence identity to each other and significant similarity with opioid and somatostatin receptors. To further o ur knowledge of GPR7's physiological function, we performed in situ hybridi zation analyses of rat brain to reveal specific patterns of expression in t he brain. GPR7 mRNA was found to be discretely localized in areas of the am ygdala, hippocampus, hypothalamus and cortex. We previously reported that G PR7 was highly conserved in both human and rodent orthologs while GPR8 was not found in the rodent [9]. We speculated that GPR8 originated after the d ivergence of the human and rodent. Using primers designed from human GPR8, we isolated lemur GPR8 and subsequently aligned human, monkey, and lemur GP R8 orthologs to design primers recognizing highly conserved regions of GPR8 . Using these primers, orthologs of GPR7 and GPR8 were isolated by the PCR from rabbit, tree shrew, and flying lemur, as well as GPR7 in the rat. Subs equent analysis of the clones obtained demonstrated that both GPR7 and GPR8 sequences were highly conserved amongst the species studied, but a rodent GPR8 was not isolated. The absence of a GPR8 gene in the rodent suggests th at GPR8 originated from gene duplication of GPR7 after the rodent line dive rged from the rabbit, tree shrew, flying lemur, lemur, monkey and human lin es. In addition, the taxonomic distribution of GPR8 is consistent with mole cular studies grouping rabbits with primates, tree shrews and flying lemurs rather than with rodents. (C) 1999 Elsevier Science B.V. All rights reserv ed.