拟南芥ILP1、NTR1复合物调控miRNA生成的分子机制研究

MicroRNAs (miRNAs) are negative regulators of gene expression and play critical roles in normal development and responses to environmental stimuli in both plants and animals. A biochemical pathway of miRNA metabolism has been well established. However, how the pathway is precisely regulated is largely unknown. Moreover, it has been widely appreciated that splicing occurs co-transcriptionally and defects in splicing may in turn affect transcription. Unlike canonical introns for protein coding genes, sites for splicing in MIR genes are usually under weak or no selection during evolution due to their non-coding nature, and are considered as suboptimal. We hypothesized that it is generally more difficult for the spliceosome to accurately identify splicing sites and determine whether or not to splice for suboptimal sites (i.e. alternatively spliced introns) than optimal ones (i.e. fully spliced introns). As a result, splicing process for such suboptimal substrates can be more frequently stalled and/or terminated. By using a reverse genetic approach, we have identified ILP1 and NTR1, two major components of the spliceosome disassembly complex, as new players of miRNA biogenesis. In this project, we propose to utilize a combination of genetic, biochemical and molecular biological approaches to study the how ILP1 and NTR1 regulate pri-miRNA splicing fidelity and how this process in turn affect MIR gene transcription and/or miRNA processing. This research will expand our knowledge on how the quality control mechanism for co-transcriptional splicing regulates non-coding RNA splicing, transcription and/or processing.

MicroRNA (miRNA)是基因表达的负调节因子，在动植物生长发育和响应外界环境等方面起重要作用。miRNA合成的生化途径已经明晰，但对该途径调控的研究方兴未艾。前期研究发现多个剪切相关蛋白在MIR基因转录或加工过程中发挥作用，但其工作机制并不清楚。Pre-mRNA的剪切通常伴随转录发生，剪切过程的异常可影响转录。与编码基因的内含子不同，MIR基因由于不编码蛋白质，其剪切位点在进化过程中受到的选择压较低，因此推测剪切复合体扫描到pri-miRNA后较难进行准确识别及判断是否剪切，剪切过程中断或出错的几率更高。我们前期分离鉴定了两个可能与剪切复合体解离有关的蛋白ILP1和NTR1参与miRNA生成。本项目拟在前期研究的基础上进一步探讨ILP1、NTR1复合物对MIR基因转录、剪切以及miRNA加工中的交互作用机制。该研究将拓展我们对剪切复合体调控非编码RNA剪切并影响转录或加工的认识。

MiRNA在动植物生长发育以及响应外界环境等方面发挥重要作用。MIRNA基因由于不编码蛋白质，因而其内含子位点在进化过程中受到的选择压较低。前期研究表明多个剪接复合物相关蛋白参与调控miRNA生成，但具体功能及工作机制不清。在本项目的资助下，我们通过基于候选基因的反向遗传筛选，分离鉴定了两个在动植物中保守的剪接复合物解离因子ILP1、NTR1参与miRNA生物合成。生化分析表明ILP1、NTR1、PRP43等剪接因子共同组成植物内含子-套索RNA剪接（ILS）复合物，调控数百个编码和非编码基因的可变剪接。机制研究揭示ILP1、NTR1通过与miRNA加工复合物成员DCL1、SE相互作用，广谱性调控MIRNA基因的转录延伸，且该过程独立于两者对RNA可变剪接的调控。上述研究丰富了剪接因子参与非编码RNA共转录调控的分子机理。已在Nucleic Acids Res，PNAS等高水平期刊发表论文5篇，应邀撰写方法学图书章节1章。

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