Roles of small RNAs in guarding germ cell genomes

描述（由申请人提供）： 基因组必须忠实地从父母传给后代。对基因组忠实传递的威胁来自复制保真度的限制、染色体分离的错误以及寄生遗传元件转座子的有害活性，转座子通过增加生殖细胞基因组中的拷贝数来繁殖。转座子控制的挑战是巨大的。在果蝇中，200多种不同的元素分布在高度分化的家族中。这些元件使用不同的动员策略，并且不共享通用蛋白质或辅因子。因此，宿主必须以某种方式区分这种多样性的元件和蛋白质编码基因，并选择性地沉默前者。在过去的6年中，我们已经了解到皮尔纳通路在生殖组织中起着关键作用，体现了针对移动的遗传元件的重要防御机制。主要在果蝇和小鼠中进行的研究已经建立了皮尔纳通路如何运作的分子框架，并涉及越来越多的蛋白质辅因子在其各个阶段。虽然我们已经为皮尔纳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免疫系统的机制基础的许多分子事件。首先，我们希望了解转座子的定义是如何以皮尔纳库的形式建立的。这需要破译皮尔纳生成基因座的调控、标记RNA以加工成piRNA的机制以及皮尔纳生物发生的机制。其次，我们将揭示Piwi蛋白/皮尔纳复合物在转录和转录后水平上的靶抑制的生物化学。第三，将探索母系遗传的piRNA的功能及其在生殖细胞和索马中的作用。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必要性之一，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