The taste of ribonucleosides: The molecular and cellular basis underlying chemosensory detection of previously unknown macronutrients

昆虫是仅次于脊椎动物的最丰富的一类动物。例如， 仅白蚁一种就能与最丰富的哺乳动物人类相媲美。有名字的昆虫约有100万种 物种和大约另外500万尚未分类，相比之下，约66，000种 脊椎动物虽然总体上对我们的生态系统有益，但一些昆虫对我们的生态系统有相当大的负面影响。 人体健康病媒，主要是苍蝇和蚊子，是微生物的主要传播者， 包括黄热病、登革热、疟疾和寨卡病毒在内的毁灭性人类疾病。这些带菌者杀死 每年增加到100万人，增加数亿人，每年产生数十亿美元的成本 治疗和生产力的损失。其他昆虫物种是农业害虫，消耗农作物和水果 导致了世界上许多地方的饥荒。根据这些事实，一个更好的 了解昆虫的生物学和行为，特别是化学感受行为，对于 制定具体有效的有害害虫种群控制战略。 黑腹果蝇拥有一系列的实验工具，是唯一适合于揭示 这些行为背后的原则。像哺乳动物和其他昆虫一样，果蝇依赖于 化学感觉系统来适当地导航它们的外部世界。味觉尤其是 重要的是确定食物来源和避免有害化学品。确保所有必需的食品化学品 被消耗，昆虫已经进化出三种主要常量营养素，蛋白质， 碳水化合物和脂肪。有趣的是，果蝇幼虫，与成年果蝇相反， 核糖核苷和核糖核酸。这些化学品是一种必要的资源， 在快速生长的幼虫阶段快速生长和存活。大规模雇用少数密切 相关的味觉感受器，味觉感受器（Grs）28检测这些化学物质。Gr28基因是 在最保守的昆虫味觉受体基因中，在所有昆虫基因组中都发现了其同源物， 从面粉甲虫到蜜蜂再到蚊子。这些观察结果表明，Gr28基因具有 保守的作用，即检测昆虫中的RNA和核糖核苷。值得注意的是，一些Gr28基因 与温度和光的感知有关，将它们的作用扩展到感官通路， 味道因此，深入了解RNA和核糖核苷受体的功能， 相当大的兴趣，特别是因为它们在不同的昆虫物种中广泛保守， 病媒（蚊子和苍蝇）、农业害虫（甲虫、蚱蜢）和生态 有益的传粉者（蜜蜂）。利用昆虫的能力来感知RNA和核糖核苷， 特定的味觉感受器可能为开发控制有害昆虫的策略提供新的机会。

Insects are the most abundant class of animals, next to vertebrates. For example, the biomass of termites alone equals that of humans, the most abundant mammal. There are about 1 million named insect species and approximately another 5 million yet to be classified, compared to about 66,000 species of vertebrates. While overall beneficial to our ecosystem, some insects have considerable negative impact on human health. Disease vectors, mostly flies and mosquitoes, are major transmitter of microbes that cause devasting human diseases, including yellow fever, dengue, malaria and zika. These insect vectors kill close to a million people each year, sicken hundreds of millions more and incur billions of dollars annually in costs for treatment and lost productivity. Other insect species are agricultural pests and consume crops and fruits of cultivated plants, leading to famine in many parts of the world. In light of these facts, a better understanding of insect biology and behavior, in particular chemosensory behavior, is paramount for developing specific and effective strategies for population control of harmful pests. Drosophila melanogaster, with its array of experimental tools, is uniquely suited to uncover the basic principles underlying these behaviors. Like mammals and other insects, Drosophila depend on chemosensory systems to navigate their external world appropriately. The sense of taste is particularly important to identify food sources and avoid harmful chemicals. To assure that all essential food chemicals are consumed, insects have evolved appetitive taste receptors for the three major macronutrients, proteins, carbohydrates and fats. Intriguingly, Drosophila larvae, in contrast to adult flies, can also sense ribonucleosides and RNA in their food. These chemicals represent an essential resource required to support rapid growth and survival during the fast-growing larval stages. Larvae employ a small number of closely related taste receptors, the Gustatory Receptors (Grs) 28 to detect these chemicals. The Gr28 genes are among the most conserved insect taste receptor genes, homologs of which are found in all insect genomes, from flour beetles to honeybees to mosquitoes. These observations suggest that the Gr28 genes have a conserved role, namely to detect RNA and ribonucleosides in insects. Remarkably, some of the Gr28 genes have been implicated in temperature and light sensing, expanding their role to sensory pathways beyond taste. Thus, an in-depth understanding of the function of receptors for RNA and ribonucleosides is of considerable interest, especially because they are broadly conserved in diverse insect species, from disease vectors (mosquitoes and flies), to agricultural pests (beetles, grasshoppers) and ecologically beneficial pollinators (honeybees). Exploiting the ability of insects to sense RNA and ribonucleosides via specific taste receptors may provide new opportunities to develop strategies for control of harmful insects.