Dataset Information

A comparison of the human and chimpanzee olfactory receptor gene repertoires.

ABSTRACT: Olfactory receptor (OR) genes constitute the basis of the sense of smell and are encoded by the largest mammalian gene superfamily, with >1000 members. In humans, but not in mice or dogs, the majority of OR genes have become pseudogenes, suggesting that OR genes in humans evolve under different selection pressures than in other mammals. To explore this further, we compare the OR gene repertoire of human with its closest living evolutionary relative, by taking advantage of the recently sequenced genome of the chimpanzee. In agreement with previous reports based on a small number of ORs, we find that humans have a significantly higher proportion of OR pseudogenes than chimpanzees. Moreover, we can reject the possibility that humans have been accumulating OR pseudogenes at a constant neutral rate since the divergence of human and chimpanzee. The comparison of the two repertoires reveals two chimpanzee-specific OR subfamily expansions and three expansions specific to humans. It also suggests that a subset of OR genes are under positive selection in either the human or the chimpanzee lineage. Thus, although overall there is relaxed constraint on human olfaction relative to chimpanzee, species-specific sensory requirements appear to have shaped the evolution of the functional OR gene repertoires in both species.

SUBMITTER: Gilad Y

PROVIDER: S-EPMC546523 | biostudies-literature | 2005 Feb

REPOSITORIES: biostudies-literature

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A comparison of the human and chimpanzee olfactory receptor gene repertoires.

Gilad Yoav Y Man Orna O Glusman Gustavo G

Genome research 20050201 2

Olfactory receptor (OR) genes constitute the basis of the sense of smell and are encoded by the largest mammalian gene superfamily, with >1000 members. In humans, but not in mice or dogs, the majority of OR genes have become pseudogenes, suggesting that OR genes in humans evolve under different selection pressures than in other mammals. To explore this further, we compare the OR gene repertoire of human with its closest living evolutionary relative, by taking advantage of the recently sequenced ...[more]

PMID: 15687286

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Project description:BACKGROUND: The detection of odorants is mediated by olfactory receptors (ORs). ORs are G-protein coupled receptors that form a remarkably large protein superfamily in vertebrate genomes. We used data that became available through recent sequencing efforts of reptilian and avian genomes to identify the complete OR gene repertoires in a lizard, the green anole (Anolis carolinensis), and in two birds, the chicken (Gallus gallus) and the zebra finch (Taeniopygia guttata). RESULTS: We identified 156 green anole OR genes, including 42 pseudogenes. The OR gene repertoire of the two bird species was substantially larger with 479 and 553 OR gene homologs in the chicken and zebra finch, respectively (including 111 and 221 pseudogenes, respectively). We show that the green anole has a higher fraction of intact OR genes (approximately 72%) compared with the chicken (approximately 66%) and the zebra finch (approximately 38%). We identified a larger number and a substantially higher proportion of intact OR gene homologs in the chicken genome than previously reported (214 versus 82 genes and 66% versus 15%, respectively). Phylogenetic analysis showed that lizard and bird OR gene repertoires consist of group alpha, theta and gamma genes. Interestingly, the vast majority of the avian OR genes are confined to a large expansion of a single branch (the so called gamma-c clade). An analysis of the selective pressure on the paralogous genes of each gamma-c clade revealed that they have been subjected to adaptive evolution. This expansion appears to be bird-specific and not sauropsid-specific, as it is lacking from the lizard genome. The gamma-c expansions of the two birds do not intermix, i.e., they are lineage-specific. Almost all (group gamma-c) OR genes mapped to the unknown chromosome. The remaining OR genes mapped to six homologous chromosomes plus three to four additional chromosomes in the zebra finch and chicken. CONCLUSION: We identified a surprisingly large number of potentially functional avian OR genes. Our data supports recent evidence that avian olfactory ability may be better developed than previously thought. We hypothesize that the radiation of the group gamma-c OR genes in each bird lineage parallels the evolution of specific olfactory sensory functions.

Dataset Information

A comparison of the human and chimpanzee olfactory receptor gene repertoires.

Publications

A comparison of the human and chimpanzee olfactory receptor gene repertoires.

Similar Datasets

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