Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.
J Comp Neurol. 2011 Jun 1;519(8):1616-29. doi: 10.1002/cne.22589.
A comprehensive reevaluation of the G protein alpha subunit genes specifically expressed in taste buds in the tongue epithelium of rodents revealed that Gq and G14 of the Gq class and Gi2 and Ggust (Gt3, also known as gustducin) of the Gi class are expressed in mammalian taste buds. Meanwhile, a database search of fish genomes revealed the absence of a gene encoding an ortholog of the mammalian Ggust gene, which mediates sweet, umami, and bitter taste signals in mammalian taste receptor cells (TRCs). Histochemical screening identified two G protein alpha subunit genes, zfGia and zfG14, expressed in subsets of TRCs in zebrafish. The expression patterns of zfGia and zfG14 in taste buds were mutually exclusive, and the expression of known T1R and T2R genes in zebrafish was restricted to a subset of zfGia-expressing TRCs. These findings highlight the existence of a novel subset of TRCs in zebrafish that is absent in mammals and suggest that unidentified G protein-coupled receptors are expressed in zfG14-expressing TRCs and in zfGia-expressing TRCs where known T1R and T2R genes were not expressed in zebrafish. The existence of not only generalized but also specialized subsets of TRCs may imply a strong connection between the evolution of the peripheral gustatory system and the evolution of particular species.
对舌上皮中专门表达于味蕾的 G 蛋白α亚基基因进行全面重新评估，揭示了 Gq 和 G14 这两个 Gq 家族亚基以及 Gi2 和 Gi 家族的 Ggust（也称为 gustducin）在哺乳动物味蕾中表达。同时，对鱼类基因组的数据库搜索表明，编码哺乳动物 Ggust 基因的同源物的基因缺失，该基因在哺乳动物味觉受体细胞（TRC）中介导甜味、鲜味和苦味信号。组织化学筛选鉴定了两个在斑马鱼 TRC 亚群中表达的 G 蛋白α亚基基因，zfGia 和 zfG14。zfGia 和 zfG14 在味蕾中的表达模式相互排斥，并且在斑马鱼中已知的 T1R 和 T2R 基因的表达局限于 zfGia 表达的 TRC 亚群。这些发现突出了在斑马鱼中存在一种新型的 TRC 亚群，而在哺乳动物中不存在，并表明在 zfG14 表达的 TRC 和在 zfGia 表达的 TRC 中表达了未知的 G 蛋白偶联受体，在这些 TRC 中，已知的 T1R 和 T2R 基因在斑马鱼中未表达。不仅存在一般化的而且存在特化的 TRC 亚群，这可能意味着外周味觉系统的进化与特定物种的进化之间存在紧密联系。
