Epigenetic Regulation of the Mutator System of Transposons

转座元件，或转座子，是DNA的一小段，可以在基因组内从一个地方移动到另一个地方。通常，它们会进入其他基因，从而突变其他基因。由于这种倾向，转座子已经成为非常有用的诱变剂，因为它们既突变又“标记”基因，使它们能够迅速恢复，特别是在玉米等大型、未测序的基因组中。在玉米中，突变转座子系统已成为基因诱变和克隆的主要手段。该体系由许多不同类别的元素组成，所有这些元素都受MuDR类别的监管。突变子(Mu)非常活跃；元素复制的频率可以超过每一代元素一个新的插入，导致突变频率的大幅增加。为了开发系统效用，有必要了解它的规则。Mu调控最少被理解的方面涉及到对原本活性的MuDR元件的表观遗传修饰。表观遗传修饰是指在不改变DNA序列的情况下改变基因活性。在变种人的情况下，这些变化可能导致可遗传的活性丧失。这个项目试图了解突变子系统中表观遗传转变的本质。该项目将利用一种最小突变体系的可用性，与用于诱变的那些品系不同，这种突变体系在已知的染色体位置携带单一的MuDR元件。沉默或重新激活这一单一MuDR元件的突变和化学试剂将被用来剖析与这些突变体活性变化相对应的分子事件。使用最小突变体系统，也可以将沉默的启动过程与维持沉默的过程分开，这对于各种表观遗传调控现象来说是一个悬而未决的问题。此外，该系统还将用于检查玉米染色质重塑基因的大量突变的影响，这些基因是亚利桑那大学之前资助的一个项目的一部分。预计这项研究将使突变体系统对玉米群落更加有用，并将阐明玉米和其他生物中关于表观遗传沉默的各种问题。对玉米界特别和立即使用的将是我们已经确定的一个被指定为Mu杀手(Mu)的基因座，它可以使原本高度活跃和诱变的玉米Mu系沉默。将提供带有Muk轨迹的线路，以及它们的使用说明。此外，影响染色质结构的突变和沉默的Mudr元件之间相互作用的初步结果将在亚利桑那大学染色质数据库(ChromDB：http://www.chromdb.org/))上公布。

Transposable elements, or transposons, are short stretches of DNA that can move from place to place within genomes. Often they move into, and thus mutagenize, other genes. Because of this propensity, transposons have become remarkably useful mutagens, as they both mutate and "tag" genes, allowing for their rapid recovery, particularly in large, unsequenced genomes such as maize. In maize, the Mutator transposon system has become the primary means by which genes are mutagenized and cloned. The system is composed of a number of different classes of elements, all of which are regulated by the MuDR class. Mutator (Mu) is remarkably active; elements can duplicate themselves at frequencies exceeding one new insertion per element per generation, resulting in massive increases in mutation frequencies. In order to exploit the systems utility, it is necessary to understand its regulation. The aspect of Mu regulation that is least understood involves epigenetic modification of otherwise active MuDR elements. Epigenetic modification involves changes in gene activity without changes in DNA sequence. In the case of Mutator these changes can result in a heritable loss of activity. This project seeks to understand the nature of epigenetic shifts in Mutator system. The project will exploit the availability of a minimal Mutator line, which, unlike those lines used for mutagenesis, carries a single MuDR element at a known chromosomal position. Mutations and chemical agents that either silence or reactivate this single MuDR element will be used to dissect the molecular events that correspond to these changes in Mutator activity. Using the minimal Mutator system it will also be possible to separate the processes involved in the initiation of silencing from those involved in its maintenance, an open question for a variety of epigenetically regulated phenomena. In addition, the system will be used to examine the effects of a large number of mutations in chromatin remodeling genes in maize that are being developed at the University of Arizona as part of a previously funded project. It is expected that this research will make the Mutator system significantly more useful to the maize community, and that it will illuminate a variety of questions concerning epigenetic silencing, both in maize and in other organisms. Of particular and immediate use to the maize community will be a locus we have identified designated Mu killer (Muk), which can silence otherwise highly active and mutagenic maize Mu lines. Lines carrying the Muk locus will be made available, along with instructions as to their use. In addition, initial results of interactions between mutations affecting chromatin structure and silenced MuDR elements will be made public on the University of Arizona chromatin database(ChromDB: http://www.chromdb.org/) as they become available.