RNA损伤修复

传统的观念认为RNA损伤修复远不如DNA损伤修复重要,然而,随着RNA甲基化损伤修复机制及RNA修复酶的发现,这一观点受到了巨大的挑战。RNA损伤可以诱导细胞周期阻滞和凋亡,RNA修复可能是一种细胞防御机制,在细胞损伤应激反应中发挥重要作用,还可能与肿瘤发生有关。     

长链非编码RNA调节缺血性脑卒中损伤和修复的研究进展

长链非编码RNA(long noncoding RNA,lnc RNA)是一组在转录、转录后和表观遗传水平发挥作用的调控序列,其在中枢神经系统中特异性高表达,对中枢神经系统发育和疾病发展具有重要调控作用。缺血性脑卒中诱导脑内大量lnc RNA表达改变,提示lnc RNA与缺血性脑卒中复杂的病理过程有关,这将有利于全面认识缺血性脑卒中的病理机制及脑缺血损伤后的分子调控网络,并提供新的治疗方向。尽管有少数研究报道lnc RNA在缺血性心脏病中的作用,但目前对于其在缺血性脑卒中病理发展中的作用知之甚少。综述目前已知的lnc RNA在脑缺血再灌注损伤、细胞凋亡与抗凋亡及损伤后神经再生与修复中的作用,并提出了未来可能的lnc RNA在缺血性脑卒中损伤与修复中的研究方向。     

RNA编辑的研究进展

RNA编辑,即通过碱基的插入、删除和替换对RNA进行的转录后加工过程,这一表观遗传现象也被认为是在RNA水平上对遗传信息进行修复的一种修正机制.本文主要综述了目前植物中基于PPR基因家族等编辑复合体以及动物中关于CRISPR/Cas系统的两种RNA编辑系统,并介绍了RNA编辑在植物生长发育过程中的重要作用,并展望了RN...     

RNA聚合酶监视的DNA修复机制

生物体在正常生命过程中面临内/外因来源的DNA损伤,DNA损伤不仅影响基因正确复制,也阻碍其正常转录.为避免DNA损伤带来的灾难性后果,生物体进化出一整套修复机制,以保证复制和转录的正确性、基因组的完整性和遗传的稳定性.本文重点综述了RNA聚合酶监视(RNA polymerase-surveilled,RNAP-S)的DNA修复机制.首先从RNA聚合酶(RNA polymerase,RNAP)的结构出发介绍了RNAP对DNA损伤的感知机制;其次讨论了滞留RNAP的回溯、与其模板DNA的解离以及后续修复机制的启动,真核细胞科凯恩综合征B蛋白(Cockayne syndrome protein B,CSB)及其泛素化和8-氧代鸟嘌呤DNA糖基化酶1 (8-oxoguanine DNA glycosylase1,OGG1)介导的RNAP-S修复;最后探讨了RNAP-S损伤修复的生物学意义并展望其前景.     

细菌中Ⅰ型毒素-抗毒素系统的研究进展

毒素-抗毒素系统是广泛存在于细菌和真菌细胞内的一对小型遗传控制元件,毒素基因编码稳定的蛋白质分子,抗毒素基因编码的则是稳定性较差的蛋白质或者是具有调控功能的RNA.人们对于毒素分子在细胞内的生物靶标、分子结构与功能、体内调节机制等进行了大量的研究,不仅揭示了毒素-抗毒素的生理功能,而且为多种生物技术中的应用提供了新的素材.目前发现共有5大类型的毒素-抗毒素系统,其中Ⅰ型毒素-抗毒素系统的抗毒素分子为调节型RNA,可以通过多种不同途径与毒素蛋白质的mRNAs结合从而中和毒素的细胞毒性.Ⅰ型毒素-抗毒素系统以其独特的调节性RNA的调控方式,成为目前毒素-抗毒素研究中的重要热点.本文将对目前Ⅰ型毒素-抗毒素系统的研究进展进行综述,并对其可能的应用前景进行展望.     

调控DNA损伤修复基因的微小RNA

随着对DNA损伤修复基因研究的深入,其信号转导路径及调控网络也进一步明了,调控DNA损伤修复基因的微小RNA(miRNA)也越来越多地被认识和发现。简要综述了DNA损伤途径中调控主要的损伤修复基因的miRNA,有助于深入阐明DNA损伤修复机制,为开发抗辐射药物和临床上DNA损伤修复异常相关肿瘤的基因治疗提供新的靶点。     

水稻基因组中的小RNA

水稻是一种很重要的模式植物, 其基因组框架图的完成将对植物生物学和遗传进化学等学科的研究做出巨大贡献. 目前, 水稻科研工作者们在绘制水稻完成图谱的同时, 也正在对水稻中基因和非编码区序列进行着深入的研究. 非编码RNA在生物系统中有着很重要的作用. 小RNA是非编码RNA的一种, 我们在水稻基因组中寻找已知小RNA序列, 并且在拟南芥、玉米、酵母、线虫、老鼠和猪这6个物种中一一进行比对, 结果在552个小RNA的数据库中找到160个小RNA, 它们存在于水稻的108个Scaffold中, 其中绝大部分(99.41%)都位于基因预测的内含子区. 19个小RNA只存在于水稻基因组中. 发现了两段U14小RNA保守片段, 一段是位于同系列的5个小RNA ZMU14SNR9(s)中, 它们只出现在3个植物物种上, 其中86%序列都是和水稻、拟南芥、玉米重复的序列; 另一段保守的小RNA是XLHS7CU14, 它出现在除猪以外的其他6个物种中. 所有这些结果显示小RNA在植物和动物之间并没有明显的界限.     

真核基因启动子非依赖的功能转录延伸复合物的体外组装

真核生物RNA聚合酶Ⅱ的持续合成能力对基因转录过程中每一个阶段,包括启动子脱离、转录暂停、转录终止以及转录偶联DNA损伤修复过程的调节至关重要.在RNA聚合酶Ⅱ介导的转录延伸过程中,其和模板DNA及转录产物RNA紧密结合,形成一个非常稳定的延伸三维复合物(elongationcomplex,EC).此特征性“泡”状结构的形成是RNA聚合酶Ⅱ持续合成能力所必需的.在不依赖启动子及众多转录起始因子的条件下,利用人工合成的RNA与DNA寡核苷酸,在体外组装形成具有功能转录活性的延伸复合物.结果表明,长度为9个核苷酸的RNA与模板DNA形成的杂合分子对转录延伸复合物的形成是必需的,而非转录模板DNA链的加入导致最终活性转录“泡”状复合物的形成,并可转录形成与模板相关的转录产物,进一步通过在模板DNA的特定位置引入一个乙酰氧乙酰氨基芴修饰基团,可特异性地阻断转录延伸过程,从而显示该系统在研究真核基因转录及转录偶联DNA损伤修复机制中的潜在应用价值.     

基于CRISPR-Cas13家族的RNA编辑系统及其最新进展

存在于细菌和古菌中的获得性免疫系统CRISPR-Cas目前已被广泛应用到生物技术领域,尤其是靶向DNA的CRISPR-Cas9技术。然而CRISPR-Cas系统靶向RNA的技术还处于初步应用阶段。Ⅵ型CRISPR-Cas系统(CRISPR-Cas13)的发现,揭示了RNA引导的RNA靶向性。CRISPR-Cas13是目前CRISPR-Cas家族中唯一只靶向ssRNA的系统,为RNA靶向和RNA编辑奠定了基础。根据Cas13系统发育已证明将Ⅵ型CRISPR-Cas系统分为4种亚型(A-D)。主要对目前最新的靶向RNA技术的CRISPR-Cas13家族的分类以及防御机制进行了综述,介绍了CRISPR-Cas13技术的应用以及基于CRISPR-Cas13家族的RNA编辑系统的最新研究进展。最后,对目前CRISPR-Cas13 RNA编辑技术体系存在的问题进行了分析和对未来的发展进行展望。     

非编码RNA与相分离

相分离是细胞内无膜细胞器动态组装的主要驱动力,参与多种生物学过程,成为近年来生命科学领域的研究热点。已有研究发现两类非编码RNA(non-coding RNA, ncRNA)与相分离密切相关,其中微小RNA(microRNA, miRNA)的加工受相分离的调节,并通过相分离诱导基因沉默。另一类长链非编码RNA(long non-coding RNA, lncRNA)可作为相分离行为的支架参与无膜细胞器形成、DNA损伤修复、胚层分化等生物学过程。本文综述了miRNA和lncRNA与相分离的关系,为重新审视细胞内ncRNA和相分离的组织模式和功能调控提供新的观点和研究思路。     

RNA-directed repair of DNA double-strand breaks

DNA double-strand breaks (DSBs) are among the most deleterious DNA lesions, which if unrepaired or repaired incorrectly can cause cell death or genome instability that may lead to cancer. To counteract these adverse consequences, eukaryotes have evolved a highly orchestrated mechanism to repair DSBs, namely DNA-damage-response (DDR). DDR, as defined specifically in relation to DSBs, consists of multi-layered regulatory modes including DNA damage sensors, transducers and effectors, through which DSBs are sensed and then repaired via DNAprotein interactions. Unexpectedly, recent studies have revealed a direct role of RNA in the repair of DSBs, including DSB-induced small RNA (diRNA)-directed and RNA-templated DNA repair. Here, we summarize the recent discoveries of RNA-mediated regulation of DSB repair and discuss the potential impact of these novel RNA components of the DSB repair pathway on genomic stability and plasticity.     

New tricks for old drugs: the anticarcinogenic potential of DNA repair inhibitors

Defective or abortive repair of DNA lesions has been associated with carcinogenesis. Therefore it is imperative for a cell to accurately repair its DNA after damage if it is to return to a normal cellular phenotype. In certain circumstances, if DNA damage cannot be repaired completely and with high fidelity, it is more advantageous for an organism to have some of its more severely damaged cells die rather than survive as neoplastic transformants. A number of DNA repair inhibitors have the potential to act as anticarcinogenic compounds. These drugs are capable of modulating DNA repair, thus promoting cell death rather than repair of potentially carcinogenic DNA damage mediated by error-prone DNA repair processes. In theory, exposure to a DNA repair inhibitor during, or immediately after, carcinogenic exposure should decrease or prevent tumorigenesis. However, the ability of DNA repair inhibitors to prevent cancer development is difficult to interpret depending upon the system used and the type of genotoxic stress. Inhibitors may act on multiple aspects of DNA repair as well as the cellular signaling pathways activated in response to the initial damage. In this review, we summarize basic DNA repair mechanisms and explore the effects of a number of DNA repair inhibitors that not only potentiate DNA-damaging agents but also decrease carcinogenicity. In particular, we focus on a novel anti-tumor agent, β-lapachone, and its potential to block transformation by modulating poly(ADP-ribose) polymerase-1.     

Age-dependent usage of double-strand-break repair pathways

A DNA double-strand break (DSB) can be repaired by any of several alternative and competing mechanisms. The repaired sequences often differ from the original depending on which mechanism was used so that the cell's "choice" of repair mechanism can have profound genetic consequences. DSBs can accumulate with age , and human diseases that mimic some of the effects of aging, such as increased susceptibility to cancer, are associated with certain defects in DSB repair . The premeiotic germ cells of Drosophila provide a useful model for exploration of the connection between aging and DNA repair because these cells are subject to mortality and other age-related changes , and their DNA repair process is easily quantified. We used Rr3, a repair reporter system in Drosophila, to show that the relative usage of DSB repair mechanisms can change substantially as an organism ages. Homologous repair increased linearly in the male germline from 14% in young individuals to more than 60% in old ones, whereas two other pathways showed a corresponding decrease. Furthermore, the proportion of longer conversion tracts (>156 bp) also increased nearly 2-fold as the flies aged. These findings are relevant to the more general question of how DNA damage and repair are related to aging.     

Emerging models for DNA repair: Dictyostelium discoideum as a model for nonhomologous end-joining

DNA double strand breaks (DSBs) are a particularly cytotoxic variety of DNA lesion that can be repaired by homologous recombination (HR) or nonhomologous end-joining (NHEJ). HR utilises sequences homologous to the damage DNA template to facilitate repair. In contrast, NHEJ does not require homologous sequences for repair but instead functions by directly re-joining DNA ends. These pathways are critical to resolve DSBs generated intentionally during processes such as meiotic and site-specific recombination. However, they are also utilised to resolve potentially pathological DSBs generated by mutagens and errors during DNA replication. The importance of DSB repair is underscored by the findings that defects in these pathways results in chromosome instability that contributes to a variety of disease states including malignancy. The general principles of NHEJ are conserved in eukaryotes. As such, relatively simple model organisms have been instrumental in identifying components of these pathways and providing a mechanistic understanding of repair that has subsequently been applied to vertebrates. However, certain components of the NHEJ pathway are absent or show limited conservation in the most commonly used invertebrate models exploited to study DNA repair. Recently, however, it has become apparent that vertebrate DNA repair pathway components, including those involved in NHEJ, are unusually conserved in the amoeba Dictyostelium discoideum. Traditionally, this genetically tractable organism has been exploited to study the molecular basis of cell type specification, cell motility and chemotaxis. Here we discuss the use of this organism as an additional model to study DNA repair, with specific reference to NHEJ.     

Proliferating cell nuclear antigen-dependent abasic site repair in Xenopus laevis oocytes: an alternative pathway of base excision DNA repair.

DNA damage frequently leads to the production of apurinic/apyrimidinic (AP) sites, which are presumed to be repaired through the base excision pathway. For detailed analyses of this repair mechanism, a synthetic analog of an AP site, 3-hydroxy-2-hydroxymethyltetrahydrofuran (tetrahydrofuran), has been employed in a model system. Tetrahydrofuran residues are efficiently repaired in a Xenopus laevis oocyte extract in which most repair events involve ATP-dependent incorporation of no more than four nucleotides (Y. Matsumoto and D. F. Bogenhagen, Mol. Cell. Biol. 9:3750-3757, 1989; Y. Matsumoto and D. F. Bogenhagen, Mol. Cell. Biol. 11:4441-4447, 1991). Using a series of column chromatography procedures to fractionate X. laevis ovarian extracts, we developed a reconstituted system of tetrahydrofuran repair with five fractions, three of which were purified to near homogeneity: proliferating cell nuclear antigen (PCNA), AP endonuclease, and DNA polymerase delta. This PCNA-dependent system repaired natural AP sites as well as tetrahydrofuran residues. DNA polymerase beta was able to replace DNA polymerase delta only for repair of natural AP sites in a reaction that did not require PCNA. DNA polymerase alpha did not support repair of either type of AP site. This result indicates that AP sites can be repaired by two distinct pathways, the PCNA-dependent pathway and the DNA polymerase beta-dependent pathway.