Development of Sensory Genomics and Basic Analysis on Taste Bioinformation Technology

味觉是任何动物保持其适当摄食行为的基本感觉。它也为我们建设传统饮食文化和发展尖端食品工业提供了不可或缺的动力。为了清楚地了解这种重要感觉的分子基础，我们利用基因组学对味觉接受和信号传递进行了研究。具体包括1)模型鱼味觉信号传导通路的分析和2)小鼠味觉信号传导通路的分析，结果如下。(1)我们研究了GPCRGPC→G蛋白→PLCbeta2→Trpm5途径，发现味觉信号效应因子PLCbeta2在青冈鱼和斑马鱼以及哺乳动物中都有表达。然后我们揭示了味觉受体，T1RGPCRs和T2R GPCRs，以及TROM5存在于这些鱼以及人类和其他脊椎动物中。有趣的是，T1R2/3接受氨基酸，T1R1/3接受氨基酸，T2Rs接受苦味。我们还尝试将显性负G蛋白连接到PLC启动子上，并成功地构建了一个转基因青竹品味盲突变体。(2)为了研究味觉传递，我们将凝集素、小麦胚凝集素(WGA)与T1R3启动子连接，构建了转基因小鼠，观察了WGA信号在味蕾、初级神经元、GG、NPG和TG以及NST中的变化。观察发现，WGA基因的mRNA和蛋白只在T1R3阳性的细胞中表达，而在其他对苦味和酸味有反应的味觉细胞中没有表达。在GG、NPG甚至NST的部分神经细胞中也观察到WGA信号，从而成功地区分了味觉细胞→味觉神经元→NST传递甜味和指味的神经通路。

Taste is an essential sensation for any animal to keep its appropriate feeding behavior. It has also had an indispensable motivation for us to construct our traditional food cultures and develop sophisticated food industries. To have clear insights into the molecular basis of this important sensation, we have conducted the studies using genomics on taste reception and signaling. In detail, the studies are comprised of 1) analysis of taste signal transmission pathways in model fish and 2) analysis of taste signal transduction pathways in mice, with the following results. (1) We investigates the GPCR→G-protein→PLCbeta2→TRPM5 pathway and found that the taste signal effector, PLCbeta2, was expressed in medaka and zebrafish as well as in mammals. We then revealed that the taste receptors, T1RGPCRs and T2R GPCRs, and TROM5 existed in these fish as well as in humans and other vertebrates. Interestingly enough, the fish received amino acid by T1R2/3 as well as by T1R1/3 and bitter tastants by T2Rs We also tried to ligate the dominant-negative G-protein to the PLC promoter and succeeded to construct a transgenic, taste-blind medaka mutant. (2) For taste transmission studies, we constructed transgenic mice by ligation of the lectin, wheat germ agglutinin (WGA) to the T1R3 promoter, and observed the WGA signaling events in the taste bud, primary neurons, GG, NPG and TG, as well as those in NST. The observation revealed that both the WGA mRNA and the protein were expressed just in the T1R3-positive cells, with no expression in other taste cells responding to bitterness and sourness. The WGA signal was also observed in parts of neurocytes with GG, NPG and even NST, and we thus succeeded to differentially identify the taste cell→taste neuron→NST neuron pathway for sweet and umami-taste transmission.