Taste and smell are two specialized sensory systems that humans and animals use to detect numerous volatile and non-volatile chemical cues in the environment.In the taste system,taste buds are the peripheral organs and can recognize at least five primary taste qualities: sweet,bitter,savory,sour and salt.Physiological studies have demonstrated that different types of taste bud cells display different response profiles to tasting substances,suggesting that these cells may express different gustatory receptors and signal transduction components.To identify these taste signaling components,we set out to isolate individual taste bud cells,amplify and comparatively analyze these single-cell transcriptomes.One of the differentially expressed genes among these transcriptomes was a gene that encodes a novel G protein?subunit,G13.This gene,Gng13,is co-expressed with G1 and G3,and to a lesser extent,with-gustducin in subsets of taste bud cells.Biochemical studies indicated that G13,together with-gustducin and G1 or G3 mediates bitter taste transduction and activates the effector enzyme PLC 2.Its contribution to sweet and savory taste transduction,however,needs to be determined.Gng13 is also expressed in the olfactory epithelium and G13 proteins are abundant both in the cilia of olfactory sensory neurons,where olfactory signal transduction begins,and in the axonal termini,which innervate the next order of neurons in the olfactory bulb.Co-expression data showed that G13 forms a Gdimer with G1.Conditional knockout of Gng13 in mature olfactory sensory neurons resulted in physiological and behavioral anosmia as well as the defects in the olfactory bulb of the mutant mice.Furthermore,the ablation of G13 also reduced the expression level of other signaling molecules including Golf and G1.Unlike in the taste system,however,the G113 dimers effectors in olfactory sensory neurons are still unclear although some evidence suggests its possible roles in epigenetic regulation of gene expression in these neurons.