Initiation of Epigenetic Transcriptional Regulation

描述（由申请人提供） 翻译后摘要：细胞通过继承和维持他们的前辈的基因表达谱保留自己的身份。通过细胞分裂传播的基因表达模式被认为部分通过DNA和DNA相关蛋白的可逆共价修饰（即，组蛋白）。这些可遗传的基因表达模式不涉及DNA序列的变化，被称为“表观遗传”。新出现的证据表明，表观遗传在无数的发展过程中，以及作为一个重要的贡献者，人类疾病。虽然许多表观遗传修饰与特定的基因表达状态相关，但支持启动表观遗传控制基因表达的特定因素的证据仍然很少。发现表观遗传触发的分子基础将阐明在发育和疾病过程中如何建立基因表达的有丝分裂遗传模式。此外，由于表观遗传修饰的潜在可逆性，表观遗传起始物的鉴定可以为出于治疗目的操纵细胞的转录谱提供关键候选物。我们建议全面确定启动以及防止表观遗传转录失活的因素和机制，通过开创性的方法在X染色体失活的研究。X染色体失活为研究表观遗传提供了一个易于实验的系统。X染色体失活导致雌性哺乳动物中一条X染色体的有丝分裂遗传性转录失活，从而使雄性和雌性之间的X连锁基因剂量相等。已知执行X-失活的表观遗传因子和机制与调节胚胎发育和疾病进展的表观遗传因子和机制重叠（即，癌症）。因此，了解表征非活性X和活性X的表观遗传事件的级联提供了一个窗口，可以识别在发育和疾病过程中启动和阻止表观遗传转录失活的共同因素。与X-失活起始的流行模型相反，我们已经建立了令人信服的证据，即被认为触发X-失活的因子Xist RNA和Polycomb组蛋白都是在小鼠印迹X-失活期间启动染色体范围的X-连锁基因沉默的关键。我们还收集了数据，表明Xist反义转录本Tsix，提出来阻止活性X的失活，在印迹X失活的起始阶段期间阻止活性X染色体的失活。此外，阻止active-X的表观遗传转录失活的蛋白质仍然未知。总之，这些发现意味着，未被发现的表观遗传因素必须存在，以启动以及防止X-失活，是这个建议的重点。 公共卫生相关性：该提案旨在发现和描述触发表观遗传转录调控的新因素和机制。表观遗传细胞机制的失调越来越被认为是人类疾病如癌症的原因或重要贡献者。重要的是，与DNA中的不可逆突变相反，表观遗传修饰是可逆的。这种可逆性使得表观遗传变化，包括我们提出要识别的那些变化，可能易于操纵和治疗干预。

DESCRIPTION (Provided by the applicant) Abstract: Cells retain their identity by inheriting and maintaining gene expression profiles of their predecessors. Patterns of gene expression that propagate through cell division are thought to be established and maintained in part through reversible covalent modifications of DNA and DNA-associated proteins (i.e., histones). These heritable patterns of gene expression do not involve changes in the DNA sequence and are termed 'epigenetic'. Emerging evidence implicates epigenetic inheritance in a myriad of developmental processes as well as being a significant contributor to human diseases. While many epigenetic modifications correlate with specific gene expression states, evidence supporting specific factors in initiating epigenetic control of gene expression remains scant. Finding the molecular basis of epigenetic triggers will elucidate how mitotically- heritable patterns of gene expression are established during development and disease. Moreover, due to the potential reversibility of epigenetic modifications, the identification of epigenetic initiators may provide key candidates for manipulating the transcriptional profile of cells for therapeutic purposes. We propose to comprehensively identify factors and mechanisms that initiate as well as prevent epigenetic transcriptional inactivation, through a groundbreaking approach in the study of X-chromosome inactivation. X-inactivation provides an experimentally tractable system for the dissection of epigenetic inheritance. X-inactivation results in the mitotically-heritable transcriptional inactivation of one X-chromosome in female mammals, thereby equalizing X-linked gene dosage between males and females. The epigenetic factors and mechanisms that execute X-inactivation are known to overlap with those that regulate embryonic development and disease progression (i.e., cancers). Thus, understanding the cascade of epigenetic events that characterizes the inactive- as well as the active-X offers a window into identifying the common factors that initiate and prevent epigenetic transcriptional inactivation during development and disease. Contrary to the prevailing models of X- inactivation initiation, we have established compelling evidence that the factors thought to trigger X- inactivation, Xist RNA and Polycomb group proteins, are both dispensable for the initiation of chromosome- wide X-linked gene silencing during mouse imprinted X-inactivation. We have also gathered data that indicates that the Xist anti-sense transcript Tsix, proposed to forestall inactivation of the active-X, is dispensable in preventing inactivation of the active X-chromosome during the initiation phase of imprinted X- inactivation. Moreover, proteins that prevent the epigenetic transcriptional inactivation of the active-X remain unknown. In sum, these findings imply that undiscovered epigenetic factors must exist to initiate as well as prevent X-inactivation, and is the focus of this proposal. Public Health Relevance: This proposal aims to discover and delineate novel factors and mechanisms that trigger epigenetic transcriptional regulation. Dysregulation of the epigenetic cellular machinery is increasingly being recognized as a cause of, or significant contributor to, human diseases such as cancers. Importantly, as opposed to irreversible mutations in DNA, epigenetic modifications are reversible. This reversibility makes epigenetic changes, including those we propose to identify, potentially amenable to manipulation and therapeutic intervention.