Molecular mechanisms for germline genome activation in C. elegans

项目总结/摘要 我们正在研究一种广泛的、高度保守的、但知之甚少的转录控制形式 由此在称为基因组活化的过程中，整体水平上的基因表达突然上调。我们 系统是线虫C.因此，我们使用遗传学，基因组学， 细胞学研究基因组激活是如何控制的。我们之前公布的初步数据 研究小组已经概述了生殖系基因组激活的遗传途径，其中拓扑异构酶II（TOP-2） 酶以信号介导的方式被激活，以产生程序化的DNA断裂。施行本 断裂是将TIP 60/RUVB调节剂募集到染色质，从而发生基因组解压缩， 促进基因组活化。 在这个提议中，我们研究了我们发现的基因组激活途径的三个不同组成部分。 首先，我们研究基因组结构是如何建立在原始生殖细胞（PGCs）激活之前。我们 初步数据表明，全基因组异染色质化是这种结构被 建立和mRNA转录的手段是全面抑制静息PGCs。我们 不知道在真核生物学中有任何其他的例子，其中异染色质的形成是在这样的细胞上进行的。 因此，这些实验很可能为基因表达如何被 在静息细胞中被全面抑制。 我们还将研究TOP-2是如何被信号激活并诱导生殖细胞中的DNA断裂的 基因组一段时间以来，人们已经认识到，程序性DNA断裂发生在基因组中， 减数分裂，然而，我们发现的程序性断裂发生在种系发育的早期， 这是前所未有的，值得详细研究。我们计划研究如何监管TOP-2，我们还将 确定基因组中断裂的位置。这些实验的成功完成将提供 程序性断裂形成的新机制可能与细胞类型相关， 有机体 最后一组实验将研究基因组解压缩是如何发生的。我们的数据显示， TOP-2诱导断裂的目的是将TIP 60/RUVB染色质调节因子募集到DNA中， 可能发生解压缩。为什么PGCs采取如此极端的措施-故意诱导危险的形式 DNA损伤进入他们的基因组--为了染色质解压缩是一个迷人的问题。到 为了达到这个目的，我们将研究断裂的DNA如何招募TIP 60/RUVB，以及复合物如何分解 染色质我们将确定定位工程DNA断裂和靶基因的距离阈值 activation.最后，我们将研究令人兴奋的可能性，即细胞核内的基因移动性与 解压缩，并且移动性对于转录激活是重要的。

Project Summary/Abstract We are investigating a widespread and highly conserved, yet poorly understood, form of transcriptional control whereby gene expression on a global level is abruptly upregulated in a process termed genome activation. Our system is the developing germline of the nematode C. elegans, and thus we use genetics, genomics, and cytology to study how genome activation is controlled. Previously published and preliminary data from our group have outlined a genetic pathway for germline genome activation, whereby the topoisomerase II (TOP-2) enzyme is activated, in a signal-mediated manner, to produce programmed DNA breaks. The purpose of these breaks is to recruit the TIP60/RUVB regulator to chromatin, so that genome decompaction occurs, thereby facilitating genome activation. In this proposal we study three distinct components of the genome activation pathway that we have discovered. First, we study how genome architecture is established in primordial germ cells (PGCs) prior to activation. Our preliminary data suggest that whole-genome heterochromatization is the means by which this architecture is established and the means by which mRNA transcription is globally repressed in resting PGCs. We are unaware of any other examples in eukaryotic biology where heterochromatin formation is employed on such a grand scale, and thus these experiments are likely to supply a novel paradigm for how gene expression can be globally repressed in resting cells. We will also examine how TOP-2 is activated by signaling to go on and induce DNA breaks in the germline genome. It has been appreciated for some time that programmed DNA breaks occur in the genome during meiosis, however our discovery of programmed breaks occurring much earlier in germline development is unprecedented and worthy of detailed investigation. We plan to study how TOP-2 is regulated and we will also determine where in the genome the breaks are made. Successful completion of these experiments will provide a novel mechanism for programmed break formation that is likely to be relevant across cell types and organisms. A final set of experiments will examine how genome decompaction occurs. Our data show that the sole purpose of TOP-2 induced breaks is to recruit the TIP60/RUVB chromatin regulator to DNA so that decompaction can occur. Why PGCs take such extreme measures -- intentionally inducing a dangerous form of DNA damage into their genomes -- for the purpose of chromatin decompaction is a fascinating question. To get at this we will study how broken DNA recruits TIP60/RUVB and how the complex then decompacts chromatin. We will determine distance thresholds for positioning of engineered DNA breaks and target gene activation. Lastly, we will examine the exciting possibility that gene mobility within the nucleus is coupled to decompaction, and that mobility is important for transcriptional activation.