title: Adaptive evolution of MRG, a neuron-specific gene family implicated in nociception.
abstract: The MRG gene family (also known as SNSR) belongs to the G-protein-coupled receptor (GPCR) superfamily, is expressed specifically in nociceptive neurons, and is implicated in the modulation of nociception. Here, we show that Ka/Ks (the ratio between nonsynonymous and synonymous substitution rates) displays distinct profiles along the coding regions of MRG, with peaks (Ka/Ks>1) corresponding to extracellular domains, and valleys (Ka/Ks<1) corresponding to transmembrane and cytoplasmic domains. The extracellular domains are also characterized by a significant excess of radical amino acid changes. Statistical analysis shows that positive selection is by far the most suitable model to account for the nucleotide substitution patterns in MRG. Together, these results demonstrate that the extracellular domains of the MRG receptor family, which presumably partake in ligand binding, have experienced strong positive selection. Such selection is likely directed at altering the sensitivity and/or selectivity of nociceptive neurons to aversive stimuli. Thus, our finding suggests pain perception as an aspect of the nervous system that may have experienced a surprising level of adaptive evolution.
authors.affiliation: Howard Hughes Medical Institute and Department of Human Genetics, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Sun Shim
authors.initials: SS
authors.lastname: Choi
authors.forename: Bruce T
authors.initials: BT
authors.lastname: Lahn
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D002352:Carrier Proteins; D030541:Databases, Genetic; D019143:Evolution, Molecular; D000071438:Fatty Acid-Binding Protein 7; D005796:Genes / Q000235:genetics / Q000502:physiology; D016147:Genes, Tumor Suppressor; D006801:Humans; D008251:Macaca / Q000235:genetics; D051379:Mice; D005810:Multigene Family / Q000235:genetics*; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D009928:Organ Specificity / Q000235:genetics; D017288:Pain Threshold / Q000502:physiology*; D010802:Phylogeny; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000502:physiology; D012641:Selection, Genetic; D025521:Tumor Suppressor Proteins
chemical_list: D002352:Carrier Proteins; C107608:FABP7 protein, human; D000071438:Fatty Acid-Binding Protein 7; D043562:Receptors, G-Protein-Coupled; D025521:Tumor Suppressor Proteins