COMPARATIVE GENOMIC AND FUNCTIONAL ANALYSIS OF INACTIVE X EXPRESSION

描述（由申请人提供）：X 染色体失活是长程基因调控的一个非凡例子，它在女性的一个 X 上延伸约 150 兆碱基并沉默基因，作为均衡 XX 女性和 XY 男性之间基因剂量的一种手段。尽管如此，并非 X 上的所有基因都被沉默了。从机制上讲，失活如何沿着 X 传播以及为什么某些区域“逃避”X 失活尚不清楚，但却是重要的问题。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。目前的数据支持基础基因组序列和边界元素隔离的作用。人类逃逸基因并不罕见，但大部分是簇集的，这表明它们是在协调控制的域中组织的。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) 基础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。这将通过确定十种哺乳动物的 X 失活模式并开发计算和统计平台来识别候选调控序列来进行测试， (2)绝缘子是调控逃逸基因的保守机制。这将通过表征处于逃逸转变的人类绝缘体的表观遗传特征并确定 绝缘子功能是否与其他哺乳动物的逃逸域相关， (3) 基因组景观在功能上影响逃逸基因表达，以及 (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，我们将在小鼠 X 上的不同位置引入小鼠和人类逃逸基因，并确定这是否会影响它们在不活跃 X 上的表达。 所提出的实验与医学遗传学有直接关系。异常的遗传 X染色体数量相当普遍，占活产儿的六百五十分之一。特纳综合征是女性最常见的遗传性出生缺陷之一。这些个体的许多问题都是由于本申请中将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被沉默，例如癌症中常见的染色体重排和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.