NSF-BSF: Circular RNAs as a primate-specific mechanism to create proteome diversity

虽然构成人体的蛋白质在老鼠和人类之间几乎是相同的，但人类有一个更优越的上级大脑。这个难题提出了一个问题：是什么分子基础使人类的大脑比其他物种的大脑优越上级？人类和其他物种之间的主要基因组差异在包含制造蛋白质指令的DNA序列之外。人类的DNA已经被短片段“入侵”，这些短片段被称为“基因元件”，现在占我们基因组的10%左右。生物素不包含制造蛋白质的指令。Alu元素的入侵始于原始猴子，在人类、黑猩猩和大猩猩中最为明显。Alu元件的数量与脑功能通过一个不清楚的分子机制相关。为了制造蛋白质，DNA被制成RNA，RNA被制成蛋白质。Alu元件促进一类新的RNA的形成，称为环状RNA，其中RNA不是具有开始和结束的线性，而是像记录一样的环状。出乎意料的是，环状RNA可以被制成蛋白质。因此，通过促进环状RNA，Alu元件可以产生新的人类特异性蛋白质。这些蛋白质将被鉴定，并测试它们对人类神经细胞的影响。该项目是与一个以色列团体合作的。为了培养下一代分子生物学家，本科生将在耶路撒冷的希伯来大学接受为期两周的RNA生物学课程，包括理论课和动手实验。这些理论课程将以免费的网络视频和书籍的形式出版。环状RNA是一类新的RNA，它是由在大脑中强烈表达的前mRNA通过反向剪接产生的。尽管它们缺乏帽或核糖体进入位点，但circRNA可以在细胞培养中在腺苷编辑后翻译为肌苷。反向剪接是由在灵长类谱系中扩展的Alu元件促进的。Alu元件和认知能力之间的相关性可能是由于形成了依赖于Alu元件的灵长类特异性环状RNA。该项目将测试总体假设，即依赖于RNA的环状RNA在源自阿达尔酶的AI编辑后被翻译，并且circRNA编码新的未发现的蛋白质。该项目将（a）研究腺苷编辑为肌苷后circRNA翻译的分子机制，假设肌苷促进核糖体进入。（B）通过确定影响内源剪接体中线性和环状RNA剪接之间竞争的因素，并通过表征相关蛋白质，对circRNA的形成进行机械表征。所选circRNA的功能将（c）在生物化学和基于细胞的测定中进行测试，假设由环状RNA制成的蛋白质干扰其线性对应物的多聚化。为了产生更广泛的影响，美国-以色列团队将在耶路撒冷的希伯来大学组织年度RNA暑期学校，包括理论讲座和实践课程。研究生水平的英语RNA讲座将被记录，西班牙语，希伯来语和阿拉伯语的字幕，并张贴在YouTube上。这项美国/以色列合作项目由美国国家科学基金会和以色列两国科学基金会支持，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Although proteins that make up the body are almost identical between mice and humans, humans have a superior brain. This conundrum raises the question: What is the molecular basis that makes human brains superior to the brains of other species? The major genomic differences between humans and other species are outside the DNA sequences containing the instructions to make proteins. Human DNA has been ‘invaded’ by short fragments, called Alu-elements that now comprise about 10% of our genome. Alu-elements do not contain instructions to make proteins. The Alu element invasion started in primitive monkeys and is most pronounced in humans, chimpanzees and gorillas. The number of Alu elements correlates with brain function via an unclear molecular mechanism. To make proteins, DNA is made into RNA, which is made into proteins. Alu elements promote the formation of a new class of RNAs, called circular RNAs, where the RNA is not linear with a beginning and an end, but circular like a record. Unexpectedly, circular RNAs can be made into proteins. Thus, by promoting circular RNAs, Alu elements could generate new human-specific proteins. These proteins will be identified and their effect on human nerve cells will be tested. The project is a collaboration with an Israeli group. To train the next generation of molecular biologists, undergraduate students will be taught in a two-week RNA biology course that involves theoretical lessons and hands-on experiments at Hebrew University in Jerusalem. The theoretical lessons will be published as free internet videos and as a book.Circular RNAs are a novel class of RNA generated through backsplicing from pre-mRNAs that are strongly expressed in brain. Despite their lack of a cap or ribosomal entry sites, circRNAs can be translated after adenosine to inosine editing in cell culture. Backsplicing is promoted by Alu elements that expanded in the primate lineage. It is possible that the observed correlation between Alu elements and cognitive abilities is due to the formation of Alu-element dependent, primate-specific circular RNAs. The project will test the overall hypothesis that Alu-dependent circular RNAs are translated after AI editing emanating from ADAR enzymes and that the circRNAs encode novel, undiscovered proteins. The project will (a) investigate the molecular mechanism of circRNA translation after adenosine to inosine editing, hypothesizing that inosines promote ribosomal entry. The formation of circRNAs will be (b) mechanistically characterized by determining the factors that influence the competition between linear and circular RNA splicing in the endogenous spliceosome, and by characterizing associated proteins. The functionality of selected circRNAs will be (c) tested in biochemical and cell-based assays, postulating that proteins made from circular RNAs interfere with the multimerization of their linear counterparts. For broader impacts, the USA-Israeli team will organize annual RNA summer schools with theoretical lectures and practical courses at Hebrew University in Jerusalem. The graduate level English RNA lectures will be recorded, subtitled with Spanish, Hebrew and Arabic and posted on YouTube. They will be accompanied by a book: ‘RNA biology: A practical approach’ to train the next generation of RNA biologists.This collaborative US/Israel project is supported by the US National Science Foundation and the Israeli Binational Science Foundation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.