Lee D K, Nguyen T, Porter C A, Cheng R, George S R, O'Dowd B F
Department of Pharmacology, University of Toronto, Medical Sciences Building, 8 Taddle Creek Rd. Rm. 4353, Toronto, Ontario, Canada.
Brain Res Mol Brain Res. 1999 Jul 23;71(1):96-103. doi: 10.1016/s0169-328x(99)00171-0.
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 our knowledge of GPR7's physiological function, we performed in situ hybridization analyses of rat brain to reveal specific patterns of expression in the brain. GPR7 mRNA was found to be discretely localized in areas of the amygdala, hippocampus, hypothalamus and cortex. We previously reported that GPR7 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 divergence of the human and rodent. Using primers designed from human GPR8, we isolated lemur GPR8 and subsequently aligned human, monkey, and lemur GPR8 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. Subsequent 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 that GPR8 originated from gene duplication of GPR7 after the rodent line diverged from the rabbit, tree shrew, flying lemur, lemur, monkey and human lines. In addition, the taxonomic distribution of GPR8 is consistent with molecular studies grouping rabbits with primates, tree shrews and flying lemurs rather than with rodents.
GPR7和GPR8是孤儿G蛋白偶联受体（GPCR）基因，在大脑和外周组织中表达，它们彼此之间具有最高的序列同一性，并且与阿片受体和生长抑素受体具有显著的相似性。为了进一步了解GPR7的生理功能，我们对大鼠大脑进行了原位杂交分析，以揭示其在大脑中的特定表达模式。发现GPR7 mRNA离散地定位在杏仁核、海马体、下丘脑和皮质区域。我们之前报道过，GPR7在人类和啮齿动物直系同源物中高度保守，而在啮齿动物中未发现GPR8[9]。我们推测GPR8起源于人类和啮齿动物分化之后。利用从人类GPR8设计的引物，我们分离出了狐猴GPR8，随后将人类、猴子和狐猴的GPR8直系同源物进行比对，以设计识别GPR8高度保守区域的引物。使用这些引物，通过PCR从兔子、树鼩、鼯猴以及大鼠中分离出了GPR7和GPR8的直系同源物。对获得的克隆进行的后续分析表明，在所研究的物种中，GPR7和GPR8序列都高度保守，但未分离出啮齿动物的GPR8。啮齿动物中不存在GPR8基因，这表明GPR8起源于啮齿动物谱系与兔子、树鼩、鼯猴、狐猴、猴子和人类谱系分化之后GPR7的基因复制。此外，GPR8的分类分布与将兔子与灵长类动物、树鼩和鼯猴归为一类而不是与啮齿动物归为一类的分子研究结果一致。
