Identification of neurotransmitter receptor genes under significantly relaxed selective constraint by orthologous gene comparisons between humans and rodents

Hisakazu Iwama, Takashi Gojobori*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Neurotransmitter receptors (neuroreceptors) are classified into two types, G protein-coupled receptors (GPCRs) and ligand-gated ion channels. The former occupies a small part of the large GPCR superfamily, whereas the latter consists of three superfamilies. In these superfamilies, humans and rodents share almost the same set of neuroreceptor genes. This neuroreceptor gene set is good material to examine the degree of selective constraint exerted on each member gene of a given superfamily. If there are any neuroreceptor genes under the degree of selective constraint that is very different from that of the other member genes, they may have influenced the functional features characteristic of human neural activities. With the aim of identifying such neuroreceptor genes, we collected sequence data of orthologous neuroreceptor genes for humans, mice, and rats by database searches. This data set included ortholog pairs for 141 kinds of neuroreceptor genes, which covered almost the whole set of neuroreceptor genes known to be expressed in the human brain. The degree of selective constraint was estimated by computing the ratio (dN/dS) of the number of nonsynonymous substitutions to that of synonymous substitutions. We found that the dN/dS ratio ranged widely and its distribution fitted a gamma distribution. In particular, we found that four neuroreceptor genes are under the significantly relaxed selective constraint. They are an ionotropic glutamate receptor subunit NMDA-2C, two GABAA receptor subunits, i.e., GABAA-ε and GABAA-θ, and a dopamine receptor D4. Interestingly, these neuroreceptors have been reported to be associated with cognitive abilities such as memory and learning, and responsiveness to novel stimuli. These cognitive abilities can influence the behavioral features of an individual. Thus, it suggests that the relaxed-constraint neuroreceptor genes have evolved, assuring that the nervous system responds to a variety of stimuli with proper flexibility.

Original languageEnglish (US)
Pages (from-to)1891-1901
Number of pages11
JournalMolecular biology and evolution
Issue number11
StatePublished - Nov 2002


  • G protein-coupled receptor (GPCR)
  • Homo sapiens
  • Ligand-gated ion channel (LGIC)
  • Neurotransmitter receptor
  • Ortholog
  • Selective constraint
  • Synonymous substitution

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Molecular Biology
  • Genetics


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