MicroRNA研究进展

在多细胞生物的基因组中都存在一类非编码RNA基因,能够产生长度约为22个核苷酸的小分子RNA,称为microRNA(miRNA),具有调节其他基因表达活性的功能。miRNA的发现,为我们理解复杂的基因调节网络开辟了新的空间。本文概述了miRNA的产生过程、转录抑制机理、研究并预测miRNA的方法等。     

RNA干扰技术的基础研究与应用

RNA干扰技术(RNAi)是一项高效率、强特异性的基因沉默技术.自1998年发现RNA干扰现象以来,RNAi吸引很多国内外科学家的研究兴趣.经过10多年的潜心研究,现在对该技术的参与成分、作用机理都有了较深入地了解.同时,随着生物学知识的完善和生物技术与基因工程的发展,研究人员时RNAi在基因功能研究、疾病(如肿瘤)相关的基因治疗、新药的研究与开发等方面的应用进行了广泛的探索,并且已经显示该技术的潜在应用价值,但是RNAi的自身缺陷制约了其在临床治疗等方面的实际应用.综述前人的研究结果,系统阐述了RNAi的发生、作用机理、缺陷以及其应用,为相关科学研究提供参考.     

植物miRNA的功能及其作用机制

miRNAs是真核生物中的一类5’端带磷酸基团、3’端带羟基、长度在22nt左右的内源性非编码调控RNAs。miRNAs在控制植物的发育、开花时序、新陈代谢、应激反应等方面起着重要的作用。已知植物miRNAs在转录后水平上抑制基因表达,主要是通过导致mRNA的裂解,对抑制目标转录物的翻译起作用。另外其也能在转录水平上通过决定目标染色体位点的甲基化而起作用。对植物miRNAs的功能及作用机制的研究现状做一综述。     

植物小分子RNA研究进展

植物体内存在多种不同类型的小分子RNA(small RNA,sRNA),在调节植物生长发育、抑制转座子活性和抵御逆境等过程中发挥着重要的作用。近年来,人们在sRNA的产生机制、效应复合物的形成和对靶基因的调控方式及其生物学功能等方面的研究取得了很大进展。该文对这些进展作简要介绍。     

干扰小RNA与微RNA

干扰小RNA（small interfering RNA;siRNA）和微RNA（microRNA;miRNA）是两种序列特异性地转录后基因表达的调节因子,它们的相关性密切,既具有相似性,又具有差异性。该文主要介绍这两种小RNA分子的产生、作用机制,以及两者之间的联系与区别。     

植物 miRNA

植物RNA家族中最近发现和研究的一个新种类miRNA,它与动物体内的miRNA有相似点,但也有不同。它参与指导mRNA的剪切,影响转座子,目前在拟南芥中发现了19种miRNA,由Dicer酶和Argonaute蛋白作用下产生的,通过与目标序列的互补影响mRNA剪切和DNA甲基化,引起相关生理过程的发生。     

RNA干涉在提高植物营养价值上的应用

RNA干涉(RNAi)是由具同源性的外源dsRNA引起的序列特异性转录后基因沉默现象,广泛存在于各种动、植物中。人类大多数疾病,像心脏病和癌症,都能够通过食用添加具有特殊营养成分养的饮食来预防。应用RNAi技术可为人和动物提高植物的营养价值。     

植物MicroRNA功能的研究进展

MicroRNA(miRNA)是真核生物基因表达的一类负调控因子,植物miRNA主要在转录水平上通过介导靶基因的甲基化、在转录后水平介导靶mRNA的切割或降低靶mRNA的翻译来调节基因的表达,从而调控植物器官的形态建成、生长发育、激素分泌与信号转导以及植物对逆境胁迫因素的应答能力。该文主要综述了近年来植物miRNA在植物生长发育、激素调节与信号转导以及逆境胁迫应答中的重要作用,并针对miRNA的网络调控特征提出了今后miRNA功能研究的方向。     

microRNA研究进展

小分子RNA家族中的一员——microRNA,是一段非常短的非编码RNA序列,对多种生物学过程起调控作用。本文试从microRNA的结构特点、合成及作用机制和功能等方面对microRNA的研究进展作一个简单回顾。     

小分子RNA

小分子RNA(miRNA)是继siRNA之后发现的调节mRNA稳定和mRNA翻译并普遍存在于动植物体内的一类内源非编码RNA。这类非编码RNAs长约22 nt,在动植物的基因调控中起着重要的作用。它是近几年生命科学研究的热点之一。在2002年,miRNA被Science杂志评为十大科技突破之一。     

Potent RNAi by short RNA triggers

RNA interference (RNAi) is a gene-silencing mechanism by which a ribonucleoprotein complex, the RNA-induced silencing complex (RISC) and a double-stranded (ds) short-interfering RNA (siRNA), targets a complementary mRNA for site-specific cleavage and subsequent degradation. While longer dsRNA are endogenously processed into 21- to 24-nucleotide (nt) siRNAs or miRNAs to induce gene silencing, RNAi studies in human cells typically use synthetic 19- to 20-nt siRNA duplexes with 2-nt overhangs at the 3′-end of both strands. Here, we report that systematic synthesis and analysis of siRNAs with deletions at the passenger and/or guide strand revealed a short RNAi trigger, 16-nt siRNA, which induces potent RNAi in human cells. Our results indicate that the minimal requirement for dsRNA to trigger RNAi is an ~42 Å A-form helix with ~1.5 helical turns. The 16-nt siRNA more effectively knocked down mRNA and protein levels than 19-nt siRNA when targeting the endogenous CDK9 gene, suggesting that 16-nt siRNA is a more potent RNAi trigger. In vitro kinetic analysis of RNA-induced silencing complex (RISC) programmed in HeLa cells indicates that 16-nt siRNA has a higher RISC-loading capacity than 19-nt siRNA. These results suggest that RISC assembly and activation during RNAi does not necessarily require a 19-nt duplex siRNA and that 16-nt duplexes can be designed as more potent triggers to induce RNAi.     

microRNA的研究进展

在多细胞生物的基因组中都存在一类非编码RNA基因,能够产生长度约为22个核苷酸的小分子RNA,称为microRNA（miRNA）,具有调节其他基因表达活性的功能。miRNA的发现,为我们理解复杂的基因调节网络开辟了新的空间。本文概述了miRNA的产生过程、转录抑制机理、研究并预测miRNA的方法等。     

Quantitative evaluation of siRNA delivery in vivo

Effective small interfering RNA (siRNA)-mediated therapeutics require the siRNA to be delivered into the cellular RNA-induced silencing complex (RISC). Quantitative information of this essential delivery step is currently inferred from the efficacy of gene silencing and siRNA uptake in the tissue. Here we report an approach to directly quantify siRNA in the RISC in rodents and monkey. This is achieved by specific immunoprecipitation of the RISC from tissue lysates and quantification of small RNAs in the immunoprecipitates by stem-loop PCR. The method, expected to be independent of delivery vehicle and target, is label-free, and the throughput is acceptable for preclinical animal studies. We characterized a lipid-formulated siRNA by integrating these approaches and obtained a quantitative perspective on siRNA tissue accumulation, RISC loading, and gene silencing. The described methodologies have utility for the study of silencing mechanism, the development of siRNA therapeutics, and clinical trial design.     

Focusing on RISC assembly in mammalian cells

RISC (RNA-induced silencing complex) is a central protein complex in RNAi, into which a siRNA strand is assembled to become effective in gene silencing. By using an in vitro RNAi reaction based on Drosophila embryo extract, an asymmetric model was recently proposed for RISC assembly of siRNA strands, suggesting that the strand that is more loosely paired at its 5′ end is selectively assembled into RISC and results in target gene silencing. However, in the present study, we were unable to establish such a correlation in cell-based RNAi assays, as well as in large-scale RNAi data analyses. This suggests that the thermodynamic stability of siRNA is not a major determinant of gene silencing in mammalian cells. Further studies on fork siRNAs showed that mismatch at the 5′ end of the siRNA sense strand decreased RISC assembly of the antisense strand, but surprisingly did not increase RISC assembly of the sense strand. More interestingly, measurements of melting temperature showed that the terminal stability of fork siRNAs correlated with the positions of the mismatches, but not gene silencing efficacy. In summary, our data demonstrate that there is no definite correlation between siRNA stability and gene silencing in mammalian cells, which suggests that instead of thermodynamic stability, other features of the siRNA duplex contribute to RISC assembly in RNAi.