Host: The Japanese Society of Toxicology
Animals must avoid absorbing toxins. Animals have a sense of bitter taste as a mechanism to avoid ingestion of poisons prior to the absorption. In mammals, the TAS2R family that is expressed in the taste cells of the oral cavity functions as bitter taste receptor proteins, which recognize poisonous substances in food, resulting in neural signals of bitterness. Mammals that have undergone adaptive radiation since the late Cretaceous period have evolved into a variety of dietary species groups. Mammals that rely on plants for diet are more likely to be exposed to toxic plant secondary metabolites. They need to accept a wider range of toxins as bitter. Therefore, plant-eating mammals have dramatically increased the number of TAS2R family genes in their genomes, increasing their repertoire of recognizable toxins. We humans also have one of the largest TAS2R families among all mammals, which is related to the evolution of the arboreal plant-eating primate ancestor of us. This expansion of the TAS2R family is also linked to the evolution of toxic metabolizing enzymes, such as the CYP family expressed in the liver, which has also expanded in plant-eating mammals. Initially, the TAS2R family was discovered as the expressed genes in taste cells of the oral cavity as bitter taste receptors, but subsequent studies have shown functional expression in extraoral tissues, such as the epithelium of the gastrointestinal tract. They may be involved in the regulation of digestion and metabolism, both directly and arthroscopically. Recent developments in next-generation DNA sequencing technology have made it possible to comprehensively examine the genomes and gene expression of many non-model mammalian groups. This presentation will introduce the methodology and findings of comprehensive comparative genomic and gene expression analyses of mammalian groups with diverse dietary habits from the perspective of bitter taste receptor evolution.
