Diversification of bitter taste receptor gene family in western chimpanzees

Tohru Sugawara, Yasuhiro Go, Toshifumi Udono, Naruki Morimura, Masaki Tomonaga, Hirohisa Hirai, Hiroo Imai

Abstract

In mammals, bitter taste is mediated by T2R genes, which belong to the large family of seven transmembrane G protein-coupled receptors. Since T2Rs are directly involved in the interaction between mammals and their dietary sources, it is likely that these genes evolved to reflect species' specific diets during mammalian evolution. Here, we investigated the sequences of all 28 putative functional chimpanzee T2R genes (cT2Rs) in 46 western chimpanzees to compare the intra-species variations in chimpanzees to those already known for all 25 human functional T2R genes (hT2Rs). The numbers of functional genes varied among individuals in western chimpanzees, and most chimpanzees had 2 or 3 more functional genes than humans. Similarly to hT2Rs, cT2Rs showed high nucleotide diversity along with a large number of amino acid substitutions. Comparison of the nucleotide substitution patterns in cT2Rs with those in five cT2R pseudogenes and 14 autosomal intergenic non-coding regions among the same individuals revealed that the evolution of cT2R genes was almost identical to that of putative neutral regions with slight but significantly positive Tajima's D values, suggesting that selective constraint on these genes was relaxed with weak balancing selection. These trends have resulted in the occurrence of various divergent alleles of T2Rs within the western chimpanzee populations, and in heterozygous individuals who might have the ability to taste a broader range of substances.

Keywords

Chimpanzee, Bitter taste receptor, Polymorphism


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