Epigenetic Mechanisms of X-chromosome Inactivation

细胞保留tlieir特性的部分原因是继承了它们的前身的基因表达谱。在细胞分裂中存活的转录模式被认为部分是通过组蛋白和DNA的共价修饰来建立和维持的，并不涉及DNA序列本身的变化。新出现的证据越来越多地表明，这种表观遗传模式参与了无数的发育过程，也是人类疾病的原因或重要贡献者。本研究旨在通过对X染色体失活(XCI)的研究，加深我们对表观遗传学机制的理解。XCI是哺乳动物体内的一种剂量补偿工具，它导致早期雌性胚胎中两条X染色体中的一条上的基因跨区域沉默。一旦在单个细胞中生效，XCI就会稳定地传播，从而使所有后代细胞保持该X染色体的沉默。由于整个染色体是失活的，因此很容易被检测到，XCI是研究转录记忆机制的一个模型系统。重要的是，在XCI过程中工作的记忆机制也广泛适用于基因调控，并被发现在细胞命运决定过程中起着重要作用 胚胎发生和干细胞生物学以及疾病发展过程中的研究。 我们最近发现了一种新的富含在非活性X染色体上的蛋白质，该蛋白质被预测为一种新的推测的甲基转移酶。Xi是两个已知的MTase(Ezh2和Pr-Set7)的靶标，这两个酶作用于Xi，通过单独或与其他蛋白质形成的复合体催化组蛋白的甲基化来传播转录记忆。因此，我们将检测这种新的蛋白质是否通过组蛋白甲基化来介导细胞记忆，使用已建立的生化分析方法来检测核心组蛋白和核小体底物上的组蛋白甲基化。我们的目标也是识别与之相互作用的蛋白质。我们还将产生携带该基因条件性零突变的小鼠，以分析其在XCI中的需求。

Cells retain tlieir identity in part by inheriting gene expression profiles of their predecessors. Patterns of transcription that survive cell division are thought to be established and maintained partly through covalent modifications of histones and DNA, and do not involve changes in the DNA sequence itself. Emerging evidence increasingly implicates this epigenetic mode of inheritance in a myriad of developmental processes as well as a cause of or a significant contributor to human disease. My research strives to further our understanding of epigenetic mechanisms through the study of X-chromosome Inactivation (XCI). XCI is an instrument of dosage compensation in mammals that results in the transraiptlonal silencing of genes on one of the two X-chromosomes in eariy female embryos. Once enacted in individual cells, XCI is stably transmitted such that all descendant ceils maintain silencing of that X-chromosome. Since an entire chromosome is inactivated and tfierefore easily detected, XCI is a model system to investigate transcriptional memory mechanisms. Importantly, the memory mechanisms that operate during XCI also apply broadly to gene regulation and are being found to be important in cell fate decisions during embryogenesis and in stem cell biology as well as during disease progression. We have recently identified a novel protein enriched on the inactive X-chromosome (Xi), This protein is predicted to be a novel putative methyltransferase. The Xi is a target of two known MTases (Ezh2 and Pr- Set7), which operate on the Xi to propagate transcriptional memory by catalyzing the methylation of histones either on their own or In a complex with other proteins. We will therefore deteimine if the novel protein mediates cellular memory through histone methylation, using established biochemical assays to detect histone methylation on core histones as well as on nudeosome substrates. We also aim to Identify proteins that with which It interacts. We will also generate mice bearing a conditional-null mutation in the gene to analyze its requirement in XCI.