tRNA biology in healthy ageing: Functional differentiation and expression of tRNAiMet loci in Drosophila.

老年人在我们社会中的比例正在迅速增加。对许多人来说，老年伴随着虚弱、功能受损和疾病易感性的增加。我们的人口老龄化正在招致巨大的个人和社会经济成本，这些成本亟待解决。老龄化本身是可以调节的。了解这种可塑性为我们提供了一个机会来设计干预措施，以改善进入老年的人类健康。重要的是，直接针对衰老具有广泛改善健康的潜力，而不仅仅限于单一的疾病。这项研究项目将回答与衰老密切相关的转移RNA(TRNAs)生物学中的一个基本问题。TRNAs是普遍用于将遗传密码翻译成蛋白质的适配分子。我们对tRNA生物学的兴趣来自于我们了解细胞蛋白质合成的关键调节因子雷帕霉素激酶复合体1(TORC1)的活性促进动物衰老的分子机制。我们发现TORC1通过RNA聚合酶III发挥作用，RNA聚合酶III本身负责产生tRNA。因此，了解tRNA生物学将促进我们对衰老过程的了解。动物基因组中存在数百个tRNA基因，通常是相同序列的副本，这使得对它们的生物学分析变得复杂。在历史上，这种完全相同的拷贝被认为是简单的冗余，提供了多个模板来促进蛋白质合成所需的高表达水平。然而，人们越来越认识到，将tRNA拷贝放在不同的基因组环境中，使动物能够微调tRNA表达模式，从而使相同或相似tRNA的组织功能多样化。尽管这一假说很重要，但由于缺乏合适的动物模型和遗传试剂，这一假说在实验上仍未得到解决。果蝇是一种小动物，但它是一个强大的实验模型，事实证明，它在理解包括人类在内的动物的基本生物学以及它们如何衰老方面是有用的。为了开始探索tRNAs的生物作用，我们专注于一种专门用于启动蛋白质合成的tRNA，即启动子tRNAMet(TRNAiMet)。我们产生了一组果蝇突变体，从四个不同的基因组位置删除了tRNAiMet的拷贝。我们的初步表型显示，至少有一个tRNAiMet基因座与衰老有关，并表明这四个基因座独特而多余的器官功能相互作用。我们将使用这组突变体，以及我们已经产生的一组报告线，来回答tRNA生物学中的一个基本问题，这将帮助我们理解衰老：为什么动物的基因组中存在tRNA基因的多个相同副本？首先，我们将对单个突变体及其组合进行广泛的表型鉴定，以确定某些基因座独有的器官功能以及那些多余的功能，重点是衰老。其次，我们将使用报告线来评估每个基因座在发育过程中以及在不同的成人组织和器官中的表达。我们将把这两组发现联系起来，并通过正式测试独特的表达模式是否驱动独特的器官功能来整合它们。第三，我们将研究tRNAiMet基因座在衰老可塑性中的作用。具体地说，我们将确定营养摄入量减少或TORC1抑制导致的寿命在一定程度上是由tRNAiMet水平的变化引起的。该项目将回答tRNA生物学中的一个基本问题，为我们在动物生理学的背景下对tRNAs的理解提供一个步骤的改变。它将为我们提供一个开拓性的洞察，让我们了解它们在动物衰老中的作用，以及破译它们在TORC1下游的器官功能所需的知识。反过来，这些知识将为旨在确保人类整个生命过程健康的干预措施提供信息。

The proportion of older people in our societies is rapidly increasing. For many, older age comes with increased frailty, impaired function and increased susceptibility to disease. The ageing of our populations is incurring massive personal and socioeconomic costs that need to be urgently addressed.Ageing itself can be modulated. Understanding this plasticity presents us with an opportunity to devise interventions to improve human health into old age. Importantly, directly targeting ageing has the potential for broad health improvements not limited to a single disease.This research project will answer a fundamental question in the biology of transfer RNAs (tRNAs) with strong relevance to ageing. tRNAs are the adaptor molecules universally used to translate the genetic code into proteins. Our interest in tRNA biology comes from our work on understanding the molecular mechanisms whereby the activity of a key regulator of cellular protein synthesis, the Target of Rapamycin Kinase Complex 1 (TORC1), promotes animal ageing. We found that TORC1 acts though RNA polymerase III, which itself is responsible for generating tRNAs. Hence, understanding tRNA biology will advance our knowledge of the ageing process.100s of tRNA genes are present in animal genomes, often as copies of identical sequence, complicating the analysis of their biology. Historically, such identical copies were thought to be simply redundant, providing multiple templates to facilitate high expression levels required for protein synthesis. However, there is growing appreciation that placing tRNA copies in different genomic contexts has allowed animals to finetune tRNA expression patterns thus diversifying organismal functions of identical or similar tRNAs. This hypothesis remains experimentally unaddressed due to lack of suitable animal models and genetic reagents, despite its fundamental importance. The fruit fly is a small animal but a powerful experimental model that has proven utility in understanding the basic biology of animals, including humans, and how they age. To start probing into the organismal roles of tRNAs, we focused on a tRNA specialised for initiation of protein synthesis, the initiator tRNAMet (tRNAiMet). We generated a set of fly mutants deleting copies of tRNAiMet from four different genomic locations. Our preliminary phenotyping revealed at least one tRNAiMet locus that contributes to ageing and indicated an interplay of unique and redundant organismal functions for the four loci. We will use this set of mutants, together with a set of reporter lines we have generated, to answer a fundamental question in tRNA biology, which will help us understand ageing: Why are multiple, identical copies of tRNA genes present throughout an animal's genome?Firstly, we will perform extensive phenotyping of single mutants and their combinations to identify organismal functions that are unique to certain loci as well as those that are redundant, with focus on ageing. Secondly, we will use reporter lines to assess the expression from each locus during development and in different adult tissues and organs. We will correlate the two sets of findings as well as integrate them by formally testing if unique expression patterns drive unique organismal functions. Thirdly, we will examine the role of tRNAiMet loci in the plasticity of ageing. Specifically, we will determine if longevity resulting from a reduction in nutrient intake or TORC1 inhibition is in part caused by changes in tRNAiMet levels.The project will answer a fundamental question in tRNA biology to provide us with a step change in understanding of tRNAs in the context of animal physiology. It will provide us with a pioneering insight into their role in animal ageing, as well as the knowledge required to decipher their organismal functions downstream of TORC1. In turn, this knowledge will inform interventions aimed at ensuring human health throughout the life course.