Roles of small RNAs in guarding germ cell genomes

描述(由申请人提供)： 至关重要的是，基因组要从父母忠实地传给他们的后代。对忠实的基因组传输的威胁来自于对复制保真度的限制，染色体分离的错误，以及寄生遗传元件转座子的有害活动，转座子通过增加其在生殖细胞基因组中的拷贝数来传播。控制转座子的挑战是巨大的。在果蝇中，200多种不同的元素分布在高度不同的家族中。这些元件使用不同的动员策略，并且不共享通用的蛋白质或辅助因子。因此，宿主必须以某种方式将这种多样性的元素与蛋白质编码基因区分开来，并选择性地使前者沉默。在过去的6年里，我们逐渐认识到，piRNA途径在生殖组织中发挥着关键作用，体现了对可移动遗传元件的基本防御机制。主要是在果蝇和小鼠身上的研究，已经建立了一个关于piRNA途径如何运作的分子框架，并涉及到越来越多的蛋白质辅助因子在其不同阶段。虽然我们已经为piRNA的产生和该途径沉默转座子的机制建立了一个粗略的模型，但我们才刚刚开始了解形成这种先天性免疫系统的机制基础的许多分子事件。我们在这个提案中的目标是解决三个关键的悬而未决的问题。首先，我们希望了解转座子的定义是如何以piRNA谱系的形式建立的。这需要破译piRNA发生位点的调节，标记RNA被加工成piRNA的机制，以及piRNA生物发生的机制。其次，我们将在转录和转录后水平上揭示Piwi蛋白/piRNA复合体抑制靶标的生物化学。第三，将探讨母系遗传的piRNAs的功能及其在生殖细胞和体细胞中的作用。通过实现这些目标，我们将有助于理解最根深蒂固的生物学要求之一，即保护生殖系完整性的必要性。

DESCRIPTION (provided by applicant): It is essential that the genome be passed faithfully from parents to their offspring. Threats to faithful genome transmission come from limitations on the fidelity of replication, errors in chromosome segregation, and from the deleterious activity of parasitic genetic elements, transposons, which propagate by increasing their copy numbers in germ cell genomes. The challenge of transposon control is formidable. In Drosophila, more than 200 different elements are distributed among highly divergent families. These elements use different mobilization strategies and share no universal proteins or cofactors. Thus, the host must somehow discriminate this diversity of elements from protein coding genes and selectively silence the former. Over the past 6 years, we have come to understand that the piRNA pathway plays a critical role in reproductive tissues, embodying an essential defense mechanism against mobile genetic elements. Studies, mainly in Drosophila and mice, have established a molecular framework for how the piRNA pathway operates and have implicated a growing list of protein cofactors in its various stages. While we have produced a coarse model for piRNA production and for the mechanisms by which the pathway silences transposons, we are only just beginning to understand many of the molecular events that form the mechanistic basis of this innate immune system Our goal in this proposal is to address three key, outstanding issues. First, we wish to understand how the definition of a transposon is established in the form of a piRNA repertoire. This entails deciphering the regulation of piRNA generative loci, the mechanisms which mark RNAs to be processed into piRNAs, and the mechanics of piRNA biogenesis. Second, we will uncover the biochemistry of target repression by Piwi protein/piRNA complexes at both the transcriptional and post-transcriptional levels. Third, will probe the functions of maternally inherited piRNAs and their roles in germ cells and in the soma. By accomplishing these aims, we will contribute to the understanding of one of the most deeply rooted biological imperatives, the need to conserve the integrity of the germ line