COMPARATIVE GENOMIC AND FUNCTIONAL ANALYSIS OF INACTIVE X EXPRESSION

描述(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，在女性中，X染色体上延伸了约150兆碱基，并使X上的基因沉默，以此来平衡XX女性和XY男性之间的基因剂量。然而，并不是X上的所有基因都是沉默的。从机制上讲，失活是如何沿着X扩散的，以及为什么一些区域“逃脱”了X失活，这并不是很清楚，但都是重要的问题。事实上，很少有基因调控的例子与染色体组织、进化和疾病如此密切相关。目前的数据支持潜在的基因组序列和边界元素的隔离作用。人类逃逸基因并不罕见，但在很大程度上是聚集的，这表明它们是在协调控制的区域中组织的。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)基因组序列和边界元件调节X的失活，并且在进化上是保守的。这将通过确定十种哺乳动物的X失活模式并开发一个计算和统计平台来确定候选调控序列来进行测试， (2)绝缘体是调节逃逸基因的保守机制。这一点将通过表征处于逃逸转变的人类绝缘体的表观遗传学特征并确定 绝缘体功能是否与其他哺乳动物的逃逸结构域相关， (3)基因组图谱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。为了解决最后两个假设，我们将把小鼠和人类的逃逸基因引入小鼠X上的不同位置，并确定这是否影响它们在非活性X上的表达。 拟议中的实验与医学遗传学有直接关系。一个变态的继承 X染色体的数量相当常见，占活产婴儿的1/650。特纳综合征是女性最常见的遗传先天缺陷。这些个体中的许多问题是由于将在这一应用中研究的特定基因子集造成的。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用于基因治疗的基因插入。

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.