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，在雌性中延长~150兆碱基并沉默一个X上的基因，作为在XX雌性和XY雄性之间平衡基因剂量的手段。然而，并不是所有的X基因都是沉默的。从机制上讲，失活是如何沿着X区扩散的，以及为什么一些区域“逃脱”了X区失活，这些都是很重要的问题。事实上，很少有基因调控与染色体组织、进化和疾病如此密切相关的例子。目前的数据支持潜在的基因组序列和隔离的边界元素的作用。人类的逃避基因并不罕见，但很大程度上是集群的，这表明它们是在协调控制的域内组织的。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：

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.