Ying Shao-Yao, Lin Shi-Lung
Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
Methods Mol Biol. 2009;487:387-413. doi: 10.1007/978-1-60327-547-7_19.
Nearly 97% of the human genome is non-coding DNA, and introns occupy most of it around the gene-coding regions. Numerous intronic sequences have been recently found to encode microRNAs, which are responsible for RNA-mediated gene silencing through RNA interference (RNAi)-like pathways. microRNAs (miRNAs), small single-stranded regulatory RNAs capable of interfering with intracellular messenger RNAs (mRNAs) that contain either complete or partial complementarity, are useful for the design of new therapies against cancer polymorphism and viral mutation. This flexible characteristic is different from double-stranded siRNAs (small interfering RNAs) because a much more rigid complementarity is required for siRNA-induced RNAi gene silencing. miRNAs were firstly discovered in Caenorhabditis elegans as native RNA fragments that modulate a wide range of genetic regulatory pathways during embryonic development. Currently, varieties of miRNAs are widely reported in plants, animals and even microbes. Intronic microRNA is a new class of miRNAs derived from the processing of gene introns. The intronic miRNAs differ uniquely from previously described intergenic miRNAs in the requirement of type II RNA polymerases (Pol-II) and spliceosomal components for their biogenesis. Several kinds of intronic miRNAs have been identified in C. elegans, mouse and human cells; however, neither function nor application has been reported. Here, we show for the first time that intron-derived miRNAs are able to induce RNA interference in not only human and mouse cells but also zebrafishes, chicken embryos and adult mice, demonstrating the evolutionary preservation of the intron-mediated gene silencing through miRNA functionality in cell and in vivo. These findings suggest an intracellular miRNA-mediated gene regulatory system, fine-tuning the degradation of protein-coding messenger RNAs.
近97%的人类基因组是非编码DNA，内含子占据了基因编码区域周围的大部分。最近发现许多内含子序列可编码微小RNA（microRNA），这些微小RNA通过类似RNA干扰（RNAi）的途径负责RNA介导的基因沉默。微小RNA（miRNA）是一类小的单链调节RNA，能够干扰含有完全或部分互补序列的细胞内信使RNA（mRNA），有助于设计针对癌症多态性和病毒突变的新疗法。这种灵活的特性不同于双链小干扰RNA（siRNA），因为siRNA诱导的RNAi基因沉默需要更严格的互补性。miRNA最初是在秀丽隐杆线虫中作为天然RNA片段被发现的，它们在胚胎发育过程中调节广泛的基因调控途径。目前，在植物、动物甚至微生物中都广泛报道了多种miRNA。内含子微小RNA是一类新的miRNA，来源于基因内含子的加工。内含子miRNA在生物合成对II型RNA聚合酶（Pol-II）和剪接体成分的需求方面，与先前描述的基因间miRNA有独特的差异。在秀丽隐杆线虫、小鼠和人类细胞中已经鉴定出几种内含子miRNA；然而，尚未报道其功能和应用。在此，我们首次表明，内含子来源的miRNA不仅能够在人类和小鼠细胞中，还能在斑马鱼、鸡胚胎和成年小鼠中诱导RNA干扰，证明了通过细胞和体内miRNA功能实现的内含子介导的基因沉默具有进化保守性。这些发现提示了一种细胞内miRNA介导的基因调控系统，可微调蛋白质编码信使RNA的降解。
