Tissue-dependent expression of bitter receptor TAS2R38 mRNA.

TAS2R38 is a human bitter receptor gene with a common but inactive allele; people homozygous for the inactive form cannot perceive low concentrations of certain bitter compounds. The frequency of the inactive and active form of this receptor is nearly equal in many human populations, and heterozygotes with one copy of the active form and one copy of the inactive form have the most common diplotype. However, even though they have the same genotype, heterozygotes differ markedly in their perception of bitterness, perhaps in part because of differences in TAS2R38 mRNA expression. Other tissues express this receptor too, including the nasal sinuses, where it contributes to pathogen defense. We therefore wondered whether heterozygous people had a similar wide range of TAS2R38 mRNA in sinonasal tissue and whether those with higher TAS2R38 mRNA expression in taste tissue were similarly high-expressers in nasal tissue. To that end, we measured gene expression by qPCR in taste and sinonasal tissue and found that expression abundance in one tissue was not related to the other. We confirmed the independence of expression in other tissues pairs expressing TAS2R38 mRNA, such as pancreas and small intestine, using autopsy data from the Genotype-Tissue Expression (GTEx) project (although people with high expression of TAS2R38 mRNA in colon also tended to have higher expression in the small intestine). Thus, taste tissue TAS2R38 mRNA expression among heterozygotes is unlikely to predict expression in other tissues, perhaps reflecting tissue-dependent function, and hence regulation, of this protein.