Small RNAs and their role in trypanosome biology

描述（由申请人提供）：所有真核生物都具有基因沉默途径，一方面作为防御核酸入侵者（如病毒、移动元件和异常转录物）的防御机制，另一方面参与基因表达的调控。RNA干扰或RNAi就是这样一种途径，是一种转录后基因沉默机制，基因特异性双链RNA （dsRNA）通过该机制触发同源细胞转录物的降解。发现小的非编码rna（小干扰rna或sirna）是这一过程的标志，很快就认识到小的非编码rna在核和细胞质区室的几个不同水平上参与调节真核基因表达。人们之所以将布鲁氏锥虫作为研究RNAi及其相关RNA沉默机制的模式系统，主要是因为它的进化地位和生物学特性。锥虫原虫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RNA沉默的机制可能为我们了解这一机制的进化及其生物学意义提供线索。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起核心作用。事实上，我们已经提供的证据表明，RNAi在锥虫中的生物学功能之一是沉默逆转录子转录本，以最有可能预防或减少逆转录及其对基因组完整性的有害影响。本课题的长期目标是了解布氏体小rna的生物学功能，具体目的如下：1.研究布氏体小rna的生物学功能。克隆和鉴定布氏体的非编码小rna，并研究其他着丝体科是否存在类似的rna。2. 分析布鲁氏体RNAi消融的生物学后果。3. 探讨消融性RNAi对布鲁氏体基因表达的影响。

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.