Small RNAs and their role in trypanosome biology

描述(申请人提供)：所有真核生物都有基因沉默途径，一方面作为防御病毒、可移动元件和异常转录本等核酸入侵的机制，另一方面参与基因表达的调节。RNA干扰或RNAi指的是这样一种途径，是一种转录后基因沉默机制，基因特异性双链RNA(DsRNA)通过这种机制引发同源细胞转录产物的降解。人们发现小的非编码RNA(小干扰RNA或siRNAs)是这一过程的标志，随后很快就意识到小的非编码RNA参与了真核基因在几个不同水平上的调控，包括在细胞核和细胞质中。布鲁氏锥虫作为研究RNAi和相关RNA沉默机制的模式系统的兴趣主要源于它的进化地位和生物学特性。锥虫原生动物是真核生物谱系中最深的分支之一，因此被认为是“古代”真核生物的后代。因此，了解锥虫体内RNA沉默的机制可能会给我们提供关于这一机制的进化及其生物学意义的线索。此外，鉴于在锥虫中，大多数基因调控发生在转录后水平，RNA沉默可能在基因表达调控中发挥核心作用。事实上，我们已经提供了证据表明，锥体中RNAi的生物学功能之一是沉默逆转录本，以最有可能防止或减少逆转录及其对基因组完整性的有害影响。本研究的长期目标是了解布氏毛滴虫小RNA的生物学功能，具体目标如下：1.克隆和鉴定布氏毛滴虫的非编码小RNA，并研究在其他动植物体内是否存在类似的RNAs。2.分析布氏毛滴虫RNAi消融的生物学后果。3.研究去除RNAi机制对布氏毛滴虫基因表达的影响。

DESCRIPTION (provided by the applicant): All eukaryotic organisms possess gene silencing pathways that on one hand function as defense mechanisms against nucleic acid invaders such as viruses, mobile elements and aberrant transcripts, and on the other hand are involved in the regulation of gene expression. RNA interference or RNAi refers to one such pathway and is a post-transcriptional gene silencing mechanism through which gene-specific double-stranded RNA (dsRNA) triggers degradation of homologous cellular transcripts. The discovery that small non-coding RNAs (small interfering RNAs or siRNAs) are the hallmarks of this process was very soon followed by the realization that small non-coding RNAs are involved in regulating eukaryotic gene expression at several different levels, in both the nuclear and cytoplasmic compartments. The interest in Trypanosoma brucei as a model system to study RNAi and related RNA silencing mechanisms stems primarily from its evolutionary position and its biology. Trypanosomatid protozoa represent one of the deepest branches of the eukaryotic lineage and are therefore considered descendants of "ancient" eukaryotes. Thus, understanding the mechanism of RNA silencing in trypanosomes might give us clues to the evolution of this mechanism and to its biological significance. Furthermore, given that in trypanosomes most gene regulation takes place at the post-transcriptional level, there is the possibility that RNA silencing plays a central role in the regulation of gene expression. Indeed, we have provided evidence that one of the biological functions of RNAi in trypanosomes is to silence retroposon transcripts to most likely prevent or reduce retroposition and its deleterious effects on genome integrity. The long-term goal of this proposal is to understand the biological function of small RNAs in T. brucei with the following specific aims: 1. Clone and characterize small non-coding RNAs in T. brucei and investigate whether similar RNAs exist in other kinetoplastidae. 2. Analyze the biological consequences of ablation of RNAi in T. brucei. 3. Investigate the consequences of ablation of the RNAi mechanism on gene expression in T. brucei.