COMPARATIVE GENOMIC AND FUNCTIONAL ANALYSIS OF INACTIVE X EXPRESSION

描述（由申请人提供）：X染色体失活是远程基因调控的一个特殊例子，在雌性中将一个X上的基因延伸至~150兆碱基并沉默，作为在XX雌性和XY雄性之间均衡基因剂量的一种手段。然而，并非X染色体上的所有基因都被沉默。从机制上讲，失活是如何沿着X线传播的，以及为什么有些区域“逃脱”了X线失活，这些都是很重要的问题。事实上，很少有基因调控的例子与染色体组织、进化和疾病有如此密切的联系。目前的数据支持的作用，潜在的基因组序列和绝缘的边界元素。人类的逃避基因并不罕见，但很大程度上聚集在一起，这表明它们是在协调控制的结构域中组织起来的。我们将使用比较基因组学和分子遗传学工具来解决以下假设： (1)潜在的基因组序列和边界元件调节X失活，并且在进化上是保守的。这将通过确定10种哺乳动物的X失活模式并开发计算和统计平台来鉴定候选调控序列来进行测试， (2)绝缘子是一种保守的机制来调节逃逸基因。这将通过表征人类绝缘体的表观遗传特征进行测试，该绝缘体位于逃逸过渡中，并确定 绝缘子功能是否与其他哺乳动物中的逃逸结构域相关， (3)基因组景观在功能上影响逃逸基因的表达， (4)逃逸基因机制在功能上是保守的。为了解决后两个假设，我们将在小鼠X染色体上的不同位置引入小鼠和人的逃逸基因，并确定这是否会影响它们在非活性X染色体上的表达。 所提出的实验与医学遗传学直接相关。一个不正常人的遗传 X染色体数目是很常见的，占1 650活产。一个具体的例子，特纳综合征，是女性最常见的遗传性出生缺陷。这些个体中的许多问题是由于本申请中将研究的特定基因子集。我们需要更好地了解这些基因，以解释临床特征并改进遗传咨询建议。此外，这些研究还将深入了解为什么基因被置于新的染色体环境中时会沉默，例如癌症中常见的染色体重排和基因治疗中的基因插入。

DESCRIPTION (provided by applicant): X chromosome inactivation is an extraordinary example of long-range gene regulation, extending ~150 megabases and silencing genes on one X in females as a means of equalizing gene dosage between XX females and XY males. Nonetheless, not all genes on the X are silenced. Mechanistically, how inactivation spreads along the X and why some regions "escape" X inactivation are not well understood but are important questions. Indeed, few examples of gene regulation are so intimately tied to chromosome organization, evolution and disease. Current data support a role for underlying genomic sequence and insulation by boundary elements. Human escape genes are not rare but largely cluster, suggesting that they are organized in coordinately controlled domains. We will use comparative genomics and molecular genetics tools to address the following hypotheses: (1) Underlying genomic sequences and boundary elements regulate X inactivation and are evolutionarily conserved. This will be tested by determining X inactivation patterns in ten mammals and developing a computational and statistical platform to identify candidate regulatory sequences, (2) Insulators are a conserved mechanism to regulate escape genes. This will be tested by characterizing epigenetic features of a human insulator that lies in an escape transition and determining whether insulator function correlates with escape domains in other mammals, (3) Genomic landscape functionally influences escape gene expression, and (4) Escape gene mechanisms are functionally conserved. To address these last two hypotheses, we will introduce mouse and human escape genes to different locations on the mouse X and and determine whether this affects their expression on the inactive X. The proposed experiments have direct relevance for medical genetics. The inheritance of an abnormal number of X chromosomes is quite common, accounting for 1 in 650 live births. One specific case, Turner syndrome, is the most common genetic birth defect in females. Many problems in these individuals are due to the specific subset of genes that will be studied in this application. We need to better understand these genes to explain clinical features and to improve genetic counseling recommendations. Further, these studies will also give insight into why genes are silenced when they are placed into new chromosomal environments, such as chromosome rearrangements that commonly occur in cancers and gene insertions for gene therapy.