The careful evaluation of food is important for survival throughout the animal kingdom, and specialized chemoreceptors have evolved to recognize nutrients, minerals, acids, and many toxins. Vertebrate bitter taste, mediated by the taste receptor type 2 (T2R) family, warns against potentially toxic compounds. During evolution T2R receptors appear first in bony fish, but the functional properties of bony fish T2R receptors are mostly unknown. We performed a phylogenetic analysis showing the “living fossil” coelacanth (Latimeria chalumnae) and zebrafish (Danio rerio) to possess T2R repertoires typical for early-diverged species in the lobe-finned and the ray-finned clade, respectively. Receptors from these two species were selected for heterologous expression assays using a diverse panel of bitter substances. Remarkably, the ligand profile of the most basal coelacanth receptor, T2R01, is identical to that of its ortholog in zebrafish, consistent with functional conservation across >400 Myr of separate evolution. The second coelacanth receptor deorphaned, T2R02, is activated by steroid hormones and bile acids, evolutionary old molecules that are potentially endogenously synthesized agonists for extraoral T2Rs. For zebrafish, we report the presence of both specialized and promiscuous T2R receptors. Moreover, we identified an antagonist for one of the zebrafish receptors suggesting that bitter antagonism contributed to shape this receptor family throughout evolution.

中文翻译：

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T2R 基因进化的根源：腔棘鱼和斑马鱼苦味受体的识别谱

仔细评估食物对于整个动物王国的生存很重要，并且专门的化学感受器已经进化到可以识别营养物质、矿物质、酸和许多毒素。由 2 型味觉受体 (T2R) 家族介导的脊椎动物苦味对潜在的有毒化合物发出警告。在进化过程中，T2R 受体首先出现在硬骨鱼中，但硬骨鱼 T2R 受体的功能特性大多未知。我们进行了系统发育分析，显示了“活化石”腔棘鱼 ( Latimeria chalumnae ) 和斑马鱼 ( Danio rerio) 分别拥有叶鳍和射线鳍进化枝中早期分化物种的典型 T2R 库。使用多种苦味物质选择来自这两个物种的受体用于异源表达测定。值得注意的是，最基础的腔棘鱼受体 T2R01 的配体谱与其在斑马鱼中的直系同源物相同，这与超过 400 Myr 的独立进化的功能保守一致。脱孤的第二个腔棘鱼受体 T2R02 被类固醇激素和胆汁酸激活，这些进化老分子可能是口外 T2R 的内源性合成激动剂。对于斑马鱼，我们报告了特化和混杂的 T2R 受体的存在。而且，