Divergence of T2R chemosensory receptor families in humans, bonobos, and chimpanzees - PubMed (original) (raw)

Comparative Study

. 2004 Oct 12;101(41):14830-4.

doi: 10.1073/pnas.0404894101. Epub 2004 Oct 4.

Affiliations

Comparative Study

Divergence of T2R chemosensory receptor families in humans, bonobos, and chimpanzees

Christopher M Parry et al. Proc Natl Acad Sci U S A. 2004.

Abstract

T2R (Tas2R) genes encode a family of G protein-coupled gustatory receptors, several involved in bitter taste perception. So far, few ligands for these receptors have been identified, and the specificity of most T2Rs is unclear. Differences between individual T2Rs result in altered taste perception in either specificity or sensitivity. All 33 human T2Rs are characterized by significant sequence homology. However, with a total of eight pseudogenes and >83 coding region single-nucleotide polymorphisms, the family displays broad diversity. The underlying variability of individual T2Rs might be the source for personalized taste perception. To test this hypothesis and also to identify T2Rs that possibly function beyond bitter taste, we compared all human T2R genes with those of the closely related primate species Pan paniscus (bonobo) and Pan troglodytes (chimpanzee). The differences identified range from large sequence alterations to nonsynonymous and synonymous changes of single base pairs. In contrast to olfactory receptors, no human-specific loss of the amount of functional genes was observed. Taken together, the results indicate ongoing evolutionary diversification of T2R receptors and a role for T2Rs in dietary adaptation and personalized food uptake.

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Figures

Fig. 1.

Fig. 1.

Cladogram of pseudogenes in hT2R, bT2R, and cT2R DNA. Upon divergence from the common primate ancestor, T2R65PS, PS5, PS3, PS8, PS7, and T2R63PS remained nonfunctional across all species. T2R9 is a pseudogene only in bonobos, whereas T2R62 is a pseudogene only in humans. T2R64 is functional only in bonobos. Moreover, in bonobos, a new T2R with close relation to T2R46 has been identified (not shown; see text). The graph indicates no species-specific loss of T2R function upon primate divergence and instead species-dependent specialization. The cladogram for all T2Rs analyzed is available in Fig. 5, which is published as

supporting information

on the PNAS web site.

Fig. 2.

Fig. 2.

Pseudogenes of selected human, bonobo, and cT2Rs. (A) For hT2R62, an 18-bp indel at position 625 inserts an additional stop codon into the genomic entry that is absent in the database entry. A read through of these two stop codons in both bonobos and chimpanzees converts c/bT2R62 into a functional gene. (B) A read through of the stop codon in hT2R64 leads to a functional gene in bonobos. (C) In bT2R9, deletion of thymidine 431 induces a frame shift, introducing a downstream stop codon.

Fig. 3.

Fig. 3.

C-terminal alterations across species. (A) A single-nucleotide deletion of an adenosine at position 967 of the database hT2R39 leads to a frameshift affecting the subsequent 15 C-terminal amino acids. (B) A SNP at position 955 of T2R7 introduces a stop codon in the database version that is found neither in the human genome nor in the great apes. (C) The bonobo T2R45 has an extended 3′ end to the human ORF. Tryptophan replaces the stop codon found in humans, adding 27 coding base pairs.

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