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

昆虫是种类最多的动物，仅次于脊椎动物。例如，地球的生物量 仅白蚁一项就相当于人类的数量，人类是最丰富的哺乳动物。大约有100万只命名的昆虫 另有约500万个物种有待分类，相比之下，约有66,000个物种 脊椎动物。虽然总体上对我们的生态系统有利，但一些昆虫对 人类健康。病媒，主要是苍蝇和蚊子，是引起 毁灭性的人类疾病，包括黄热病、登革热、疟疾和寨卡病毒。这些昆虫媒介可以近距离杀死 每年导致100万人死亡，数亿人患病，每年造成数十亿美元的成本 用于治疗和丧失生产力。其他种类的昆虫是农业害虫，以农作物和水果为食 种植的植物，导致世界许多地区发生饥荒。鉴于这些事实，一个更好的 了解昆虫的生物学和行为，特别是化学感觉行为，对 制定具体有效的有害生物种群控制战略。 拥有一系列实验工具的黑腹果蝇，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 化学传感系统，以适当地导航其外部世界。特别是味觉 识别食物来源和避免有害化学物质的重要性。以确保所有必需的食品化学物质 昆虫被消耗后，进化出对三种主要常量营养素、蛋白质、 碳水化合物和脂肪。有趣的是，与成年果蝇相比，果蝇幼虫也能感觉到 食物中的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。幼虫利用少量紧密的 相关的味觉受体，味觉受体(GRS)28来检测这些化学物质。Gr28基因是 在最保守的昆虫味觉受体基因中，其同源基因在所有昆虫基因组中都存在， 从粉甲虫到蜜蜂再到蚊子。这些观察结果表明，Gr28基因具有 保守作用，即检测昆虫中的RNA和核糖核苷。值得注意的是，Gr28基因中的一些 与温度和光感应有关，将它们的作用扩展到感官通路之外 品尝一下。因此，深入了解RNA和核糖核苷受体的功能是 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，来自 病媒(蚊子和苍蝇)、农业害虫(甲虫、蝗虫)和生态学 有益的传粉者(蜜蜂)。利用昆虫感知RNA和核糖核苷的能力 特定的味觉受体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.