Expression of Galpha14 in sweet-transducing taste cells of the posterior tongue

By RT-PCR, Gα14 is expressed strongly and in a taste selective manner in posterior (vallate and foliate), but not anterior (fungiform and palate) taste fields. Gαq and Gα11, although detectable, are not expressed in a taste-selective fashion. Further, expression of Gα14 mRNA is limited to Type II/Receptor cells in taste buds. Immunocytochemistry on vallate papillae using a broad Gαq family antiserum reveals specific staining only in Type II taste cells (i.e. those expressing TrpM5 and PLCβ2). This staining persists in Gαq knockout mice and immunostaining with a Gα11-specific antiserum shows no immunoreactivity in taste buds. Taken together, these data show that Gα14 is the dominant Gαq family member detected. Immunoreactivity for Gα14 strongly correlates with expression of T1R3, the taste receptor subunit present in taste cells responsive to either umami or sweet. Single cell gene expression profiling confirms a tight correlation between the expression of Gα14 and both T1R2 and T1R3, the receptor combination that forms sweet taste receptors.Gα14 is co-expressed with the sweet taste receptor in posterior tongue, although not in anterior tongue. Thus, sweet taste transduction may rely on different downstream transduction elements in posterior and anterior taste fields.Taste buds, the end-organs for gustation, detect and respond to a variety of macronutrient and aversive compounds to generate taste perception. Compounds that evoke bitter taste bind to one or more G protein coupled receptors (GPCRs) of the T2R family of taste receptors [1-3]. Amino acids and compounds that elicit umami taste bind to a variety of GPCRs including metabotropic glutamate receptors, mGluR4 and mGluR1, and the heterodimeric taste receptor, T1R1+T1R3 [4-7]. Sugars and a variety of other sweeteners bind to the heterodimeric receptor, T1R2+T1R3[5,8]. Most of these various taste GPCRs appear to all couple to a common transduction pathway that includes the heterotrimeric G protein subunits, Gβ3 an