Abstract
BackgroundSensing bitter tastes is crucial for many animals because it can prevent them from ingesting harmful foods. This process is mainly mediated by the bitter taste receptors (T2R), which are largely expressed in the taste buds. Previous studies have identified some T2R gene repertoires, and marked variation in repertoire size has been noted among species. However, the mechanisms underlying the evolution of vertebrate T2R genes remain poorly understood.ResultsTo better understand the evolutionary pattern of these genes, we identified 16 T2R gene repertoires based on the high coverage genome sequences of vertebrates and studied the evolutionary changes in the number of T2R genes during birth-and-death evolution using the reconciled-tree method. We found that the number of T2R genes and the fraction of pseudogenes vary extensively among species. Based on the results of phylogenetic analysis, we showed that T2R gene families in teleost fishes are more diverse than those in tetrapods. In addition to the independent gene expansions in teleost fishes, frogs and mammals, lineage-specific gene duplications were also detected in lizards. Furthermore, extensive gains and losses of T2R genes were detected in each lineage during their evolution, resulting in widely differing T2R gene repertoires.ConclusionThese results further support the hypotheses that T2R gene repertoires are closely related to the dietary habits of different species and that birth-and-death evolution is associated with adaptations to dietary changes.
Highlights
Sensing bitter tastes is crucial for many animals because it can prevent them from ingesting harmful foods
bitter taste receptor (T2R) genes belong to one type of G-protein-coupled receptors (GPCR) which are characterized by their seven conserved transmembrane regions [8]
We have identified the T2R gene repertories of the rhesus macaque (Macaca mulatta), horse (Equus caballus), platypus (Ornithorhynchus anatinus), lizard (Anolis carolinensis) and stickleback (Gasterosteus aculeatus) for the first time; Table 1 shows the number of T2R genes identified for these species
Summary
Sensing bitter tastes is crucial for many animals because it can prevent them from ingesting harmful foods. Taste perception refers to sensations triggered by taste buds on the surface of the tongue, which sense sweet, salty, sour, bitter and umami flavors. Most taste sensations are triggered via receptor-based sensors expressed in different taste-cell types [4,5,6] Among these chemical senses, bitter tastes are important because many poisonous substances tend to be bitter, and bitter taste perception can allow animals to detect and avoid toxins in food [7]. Bitter tastes are important because many poisonous substances tend to be bitter, and bitter taste perception can allow animals to detect and avoid toxins in food [7] This process is mainly mediated by bitter taste receptors (T2R) which are encoded by T2R genes. T2R genes contain an average of 300 codons, and there are no introns in their coding regions, making them easy to (page number not for citation purposes)
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