The mRNA cap epitranscriptome: Understanding an essential novel layer of gene expression in neuronal differentiation and function

mRNA 帽表观转录组：了解神经元分化和功能中基因表达的重要新层

• 批准号: BB/X008193/1
• 负责人: Matthias Soller
• 金额: $ 78.63万
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FX008193%2F1
• 关键词: mRNA; cap; epitranscriptome; Understanding; essential

The information for life is encoded in the DNA of the genes harboured in our chromosomes. The DNA in a chromosome is a very long chain consisting of four different nucleotides: G, A, C and T. For most genes this code is then converted into a messenger RNA intermediate (mRNA) that has a cap structure and a polyA tail to protect it from degradation. This mRNA is then translated in the cytoplasm into a chain of amino acids called proteins, which fulfil a function; for example an enzymatic reaction to generate energy from the nutrients we eat to allow for the electrical communication among neurons in our brain. Although the sequence of mRNA only consist of four nucleotides, many can be modified by addition of small chemical groups to increase the regulatory portfolio and coding capacity. The most prominent modification in mRNA are methyl groups added to the nucleotides adjacent to the cap structure. Animals including humans have two cap methyltransferase enzymes (CMTrs) that add these modifications. Also many parasites have a CMTr gene in their genome that is required for their propagation. In mice, CMTrs are essential and required for neuronal development, however, the biological functions of CMTrs and the mRNA cap modifications remain largely unexplained.We recently discovered that mutant Drosophila lacking both CMTrs are viable, although they suffer from neurological and learning defects. Intriguingly, we further discovered that in these mutant flies, mRNAs were not properly transported to synapses, which are the sites where signals are transmitted to neighbouring neurons. In particular, we could show that some mRNAs are only made into protein at synapses. Hence, the cap modifications have an essential role in directing the synthesis of new proteins locally at synapses suggesting that this process is required for learning of new associations, that are then stored as memory in the brain. However, we currently do not know which genes are expressed in this way at synapses nor what the sequence code is to direct mRNAs to synapses for localized expression.We now have the ideal animal model to address the very fundamental questions about how this enigmatic modifications direct local expression of genes to synapses. Our preliminary data indicate that the cap modifications vary between different animals and conditions. Since CMTrs also localize to synapses, our data suggest a dynamic code important for local protein synthesis. In a first step to crack this code, we will identify specific mRNAs that localize to synapses allowing us to build a reporter system to test the code. To complement this analysis we will further determine the sequence preferences of CMTrs in biochemical assays and identify proteins important for CMTr specificity and decoding of the cap modification code. These studies are essential to understand the vital function of the cap modifications in the regulation of gene expression and how its aberrant regulation can lead to neurological defects in humans, or can be exploited to interfere with viral replication such as in SARS-CoV-2.

生命的信息被编码在我们染色体中的基因的DNA中。染色体中的DNA是一条很长的链，由四种不同的核苷酸组成：G，A，C和T。对于大多数基因来说，这种编码然后被转化为信使RNA中间体（mRNA），该中间体具有帽结构和polyA尾以保护其免受降解。然后，这种mRNA在细胞质中被翻译成一种称为蛋白质的氨基酸链，这种蛋白质实现了一种功能;例如，通过酶促反应从我们吃的营养物质中产生能量，以允许我们大脑中神经元之间的电通信。虽然mRNA的序列仅由四个核苷酸组成，但许多可以通过添加小的化学基团来修饰，以增加调控组合和编码能力。mRNA中最突出的修饰是添加到帽结构附近的核苷酸上的甲基。包括人类在内的动物具有两种添加这些修饰的帽甲基转移酶（CMTrs）。许多寄生虫的基因组中也有CMTr基因，这是它们繁殖所必需的。在小鼠中，CMTrs是神经元发育所必需的，然而，CMTrs的生物学功能和mRNA帽修饰仍然在很大程度上无法解释。我们最近发现，缺乏CMTrs的突变果蝇是可行的，尽管它们患有神经和学习缺陷。有趣的是，我们进一步发现，在这些突变的果蝇中，mRNA没有被正确地运输到突触，而突触是信号传递到邻近神经元的场所。特别是，我们可以证明一些mRNA只在突触处被转化为蛋白质。因此，帽修饰在指导突触局部合成新蛋白质方面具有重要作用，这表明该过程是学习新关联所必需的，然后将其作为记忆存储在大脑中。然而，我们目前还不知道哪些基因在突触上以这种方式表达，也不知道将mRNA引导到突触进行局部表达的序列密码是什么，我们现在有了理想的动物模型来解决关于这种神秘的修饰如何将基因的局部表达引导到突触的非常基本的问题。我们的初步数据表明，帽修改不同的动物和条件。由于CMTR也定位于突触，我们的数据表明，一个动态的代码重要的局部蛋白质合成。在破解这一密码的第一步中，我们将识别定位于突触的特定mRNA，从而使我们能够建立一个报告系统来测试这一密码。为了补充该分析，我们将进一步确定生物化学测定中CMTr的序列偏好，并鉴定对CMTr特异性和帽修饰代码解码重要的蛋白质。这些研究对于理解帽修饰在基因表达调控中的重要功能以及其异常调控如何导致人类神经系统缺陷，或如何被利用来干扰病毒复制（如SARS-CoV-2）至关重要。