Relative Expression Levels of Taste Receptors in Murine Tongue Papillae

Objectives: The transduction of sweet, bitter, and umami tastes are triggered by taste receptors, the family of G protein-coupled receptors. Taste receptors consist of type I (T1Rs) and type II taste receptors (T2Rs). T1Rs include three kinds of proteins and different heterodimers of them transduce sweet or umami taste. T2Rs are 35 kinds in mouse and transduce bitter taste. Various strains of experimental mouse show different taste sensitivities. DBA2 mouse that are sensitive to bitter substances were employed, which may provide more detailed insight of expression pattern of various bitter taste receptors. Tongue has 4 kinds of papillae including fungiform (FU), foliate (FO) and circumvallate papillae (CV). Taste sensitivities among these papillae are different, the reason is not clear. This study was designed to find the clue of area difference of taste thresholds.
Methods: Male DBA2 mice, 42-60 days old, were used. Massinger RNAs were extracted from the tongue epithelial tissues including FU, FO and CV. RT-qPCRs were performed to determine expression levels of mRNAs of taste receptors.
Results: All three T1Rs were expressed in FU, FO and CV, and relative expression levels of T1Rs were different. The expression levels of T2Rs were higher in FO or CV than in FU. Results of qPCR revealed that expression levels of tas2r108 and tas2r137 were highest in all tested papillae.
Conclusions: The different physiological functions of papillae may due to the different expression levels and patterns of taste receptors in three papillae, which suggest that physiological functions of papillae may be different. Additional studies, such as in situ hybridization or taste receptor cell activity recording, might elucidate the detailed physiological functions in tongue papillae.