Single-cell expression profiling on Type II cells. A: mRNA was purified from 21 individual PLCβ2-GFP cells and two GFP negative cells (# 12 and # 23) and reverse transcribed. Each cDNA was divided into 7 individual tubes and was used to assay the expression of three Gα subunits (Gαgus, Gαq, Gα14), sweet receptor subunits (T1R2, T1R3) and TrpM5. β-actin served as a positive control for all samples. All PLCβ2-GFP positive cells displayed PCR product for TrpM5. In contrast, the Gα subunits and sweet receptors were expressed in only a fraction of PLCβ2-GFP cells. B. Venn diagram showing co-localization patterns based on the single cell RT-PCR analysis and previous studies on T2R localization patterns . T2Rs do not co-localize with T1Rs and in the vallate papilla, always co-localize with Gα Gustducin. In our single cell RT-PCR study, all T1R2+T1R3 (sweet receptor) expressing taste cells express Gα14. A subset of these also express Gαq. The sweet receptive cells are themselves a subset of the Type II (receptor) taste cells identified by expression of PLCβ2 and TrpM5. Another set of TrpM5/PLCβ2-expressing cells express the T2R family of bitter receptors. These T2R-expressing cells invariably express GαGustducin .
Tizzano et al. BMC Neuroscience 2008 9:110 doi:10.1186/1471-2202-9-110