Heterochromatin on the human inactive X chromosome

描述(申请人提供)：非活跃X染色体(XI)的基因沉默是通过形成兼性异染色质实现的，这一特征在随后的细胞分裂过程中非常稳定并忠实地保留在XI。我们发现人类XI的异染色质被组织成占据确定的基因组间隔的非重叠类型的异染色质。根据特征染色质标志物的存在，可以定义两种不同的异染色质类型：I，大H_2A和XIST RNA；II，HP1和组蛋白H3在赖氨酸-9处甲基化。这些表观遗传特征的严格空间排列与S晚期复制模式的变化以及xi基因的表达谱直接相关。 这些数据为测试XI异染色质表观遗传特征和表观表型特征之间的相互关系提供了框架。 这里描述的实验有两个具体的目的：(I)准确地定义主要的xi-I型区域的近端和远端边界；(Ii)研究每个区域的蛋白质组分在维持和/或限制xi沿线异染色质类型方面的作用。 这些实验将在指定的时间间隔内生成详细的图谱，使我们能够确定表观遗传标记相对于彼此和xi表型的精确组织，从而作为整个xi的模型。通过选择性地去除特定的异染色质标记，我们将能够监测对XI所有特征的影响，从而使我们能够确定表观遗传成分在维持XI异染色质方面的功能意义。这些数据不仅将大大提高我们对X失活的理解，还将提供对基因表达调控和明确染色质状态遗传的有价值的见解，这是所有人类发育和细胞分化的一个至关重要的方面。

DESCRIPTION (provided by applicant): Gene silencing at the inactive X-chromosome (Xi) is achieved through the formation of facultative heterochromatin, a feature that is remarkably stable and faithfully retained at the Xi throughout subsequent cell divisions. We have found that heterochromatin of the human Xi is organized into non-overlapping types of heterochromatin that occupy defined genomic intervals. Two distinct heterochromatin types can be defined based upon the presence of characteristic chromatin markers: I,macroH2A and XIST RNA; II, HP1 and histone H3 methylated at lysine-9. The strict spatial arrangement of these epigenetic features correlates directly with variation in the pattern of replication in late S-phase and with the Xi gene expression profile. These data provide the framework for testing interrelationships between the epigenetic and epiphenotypic features of Xi heterochromatin. The experiments described here have two specific aims: (i) To precisely define the proximal and distal boundaries of the major Xi Type-I territory; and (ii) To investigate the role of the protein components of each territory in maintaining and/or constraining the heterochromatin types along the Xi. These experiments will generate a detailed map across the specified interval, allowing us to determine the precise organization of epigenetic markers relative both to one another and to the Xi epiphenotypes, thus acting as a model for the entire Xi. By selectively removing specific heterochromatin markers, we will be able to monitor the effects on all features of the Xi, allowing us to determine the functional significance of the epigenetic components in maintaining Xi heterochromatin. Not only will these data substantially advance our understanding of X-inactivation, they will also provide valuable insight generally into the regulation of gene expression and the inheritance of defined chromatin states, a critically important aspect of all human development and cellular differentiation.