Isoform-Specific Quantification of Human Bitter Taste Receptor Transcripts Using Real-Time PCR Analysis

Bitter taste receptors (TAS2Rs) are expressed by oral cavity cells in mammals and classically function as sensors for bitter compounds. There are 25 functional isoforms of human TAS2Rs, with individual bitter ligands. Each human TAS2R isoform is distributed in several tissues, such as the airway epithelia and gastrointestinal tract, and plays an important role in physiological functions. However, quantification of each isoform is difficult because of highly homologous sequences between some TAS2R isoforms. Therefore, differentiating the isoforms by their expression levels is suitable for clarifying the tissue-specific effects of bitter compounds. In this study, we developed a real-time quantitative PCR (qPCR) method to determine the expression of each TAS2R isoform. Using plasmid standards harboring each isoform, we confirmed that the current assay can quantify the gene expression of each isoform, with negligible interference from other isoforms. In addition, our methods can successfully discriminate between the mRNA expression of each isoform in human cell lines and tissues. Therefore, this qPCR method can successfully quantify the mRNA level of each TAS2R isoform. This method will contribute to a better understanding of the molecular mechanisms underlying the TAS2R ligand-activated signal transduction.