Epigenetic and small RNA regulation of senescence

Leaf senescence is regulated through a complex regulatory network triggered by internal and external signals for the reprogramming of gene expression. In plants, the major developmental phase transitions and stress responses are under epigenetic control. In this review, the underlying molecular mechanisms are briefly discussed and evidence is shown that epigenetic processes are also involved in the regulation of leaf senescence. Changes in the chromatin structure during senescence, differential histone modifications determining active and inactive sites at senescence-associated genes and DNA methylation are addressed. In addition, the role of small RNAs in senescence regulation is discussed.     

非编码RNA与基因表达调控

近年来,随着对基因组的深入研究,发现真核生物中存在许多形态和功能各异的非编码RNA分子,这类RNA分子并不表达蛋白质,但它们在基因转录水平、转录后水平及翻译水平起了重要的调控作用。具有调控作用的RNA分子种类非常丰富,如长链非编码RNA(long non-coding RNA,lncRNA)、miRNA、PIWI相互作用RNA(PIWI-interacting RNA,piRNA)、内源性小干扰RNA(endogenous small interfering RNA,endo-siRNA)、竞争性内源RNA(competitive endogenous RNA,ceRNA)等,它们使基因表达过程更为丰富、严谨和有序。本文综述几类典型的非编码RNA对基因表达的调节作用,以助于理解细胞中RNA分子调节网络的功能和机制。     

Spectroscopic observation of RNA chaperone activities of Hfq in post-transcriptional regulation by a small non-coding RNA

Hfq protein is vital for the function of many non-coding small (s)RNAs in bacteria but the mechanism by which Hfq facilitates the function of sRNA is still debated. We developed a fluorescence resonance energy transfer assay to probe how Hfq modulates the interaction between a sRNA, DsrA, and its regulatory target mRNA, rpoS. The relevant RNA fragments were labelled so that changes in intra- and intermolecular RNA structures can be monitored in real time. Our data show that Hfq promotes the strand exchange reaction in which the internal structure of rpoS is replaced by pairing with DsrA such that the Shine-Dalgarno sequence of the mRNA becomes exposed. Hfq appears to carry out strand exchange by inducing rapid association of DsrA and a premelted rpoS and by aiding in the slow disruption of the rpoS secondary structure. Unexpectedly, Hfq also disrupts a preformed complex between rpoS and DsrA. While it may not be a frequent event in vivo, this melting activity may have implications in the reversal of sRNA-based regulation. Overall, our data suggests that Hfq not only promotes strand exchange by binding rapidly to both DsrA and rpoS but also possesses RNA chaperoning properties that facilitates dynamic RNA-RNA interactions.     

Inhibiting gene expression in vivo by virus-mediated small interfering RNA

Inhibiting gene expression in specific tissues and organs through intravenous injection would be the ultimately preferred method of disease therapy. Here, we report the successful delivery of lentivirus-mediated small interfering RNA (siRNA) to suppress GFP gene expression in living mice. First, a lentiviral vector with siRNA (len-siRNA) driven by H1 promoter was constructed to effectively suppress GFP expression in Mel cells. When the len-siRNA virus was injected into transgenic mice, the GFP expression was significantly suppressed (over 15% reduction) in the recipient mice compared to the control mice and the suppressing effect lasted more than 1 week after injection. Our results demonstrate a new effective approach to inhibit gene expression by siRNA and lentiviral vectors. Further development of this drug for suppression of gene expression siRNA should result in applications not only for cancers but also for infectious and immune diseases. Published in Russian in Molekulyarnaya Biologiya, 2008, Vol. 42, No. 6, pp. 990–996. The text was submitted by the authors in English.     

大肠杆菌Small RNA EsrE的转录调控

【背景】大肠杆菌中Small RNA EsrE调控琥珀酸脱氢酶的表达并影响细胞生长,对其调控机制的探究有利于加深EsrE对细胞生长影响的认识。【目的】探究大肠杆菌Small RNA EsrE的转录调控机制。【方法】通过双质粒报告系统筛选转录调控因子,并通过凝胶迁移实验(electrophoretic mobilityshiftassay,EMSA)和qRT-PCR研究方法验证转录调控因子。【结果】双质粒报告系统证明RNA聚合酶亚基σ~(32) (RpoH)上调P_(esrE),β-羟酰-ACP脱水酶(FabZ)下调PesrE。EMSA结果和体内实验显示RpoH结合P_(esrE)片段,FabZ不结合P_(esrE)片段。【结论】RpoH直接结合启动子序列参与调控,FabZ以其他方式间接参与Small RNA EsrE的转录调控。     

Bacterial gene regulation: metal ion sensing by proteins or RNA

Until recently, metal sensing in bacteria seemed to be accomplished exclusively by metalloregulatory proteins; however, a surprising new finding is that a metal ion itself can act as a riboswitch ligand to shut down gene expression. Interestingly, this ion is Mg(2+), known to be required for a wide variety of cellular functions and for correct folding of RNAs. It remains to be discovered whether other ion-dependent riboswitches exist, which would open up a new dimension for regulatory RNAs.     

Diverse roles for RNA in gene regulation

A report of the Keystone Symposium 'Diverse roles for RNA in gene regulation', Breckenridge, USA, 8-15 January 2005.