Understanding how RIF1 and KAP1 enable the choice of the future active and inactive X chromosomes: the establishment of functional asymmetry.

了解 RIF1 和 KAP1 如何选择未来的活性和非活性 X 染色体：功能不对称的建立。

• 批准号: BB/W015544/1
• 负责人: Sara Buonomo
• 金额: $ 85.29万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FW015544%2F1
• 关键词: Understanding; how; RIF1; KAP1; enable

In humans, every chromosome is present in two copies, except in men, where there is one copy of each of the sex chromosomes, the X and the Y. Women have two copies of the X chromosome. One of the two X chromosomes in women is inactivated (silenced), so that male and female cells have the same amounts of the gene products coming from the X chromosomes. This process of silencing is called X-inactivation. Either of the two X chromosomes can be inactivated randomly. This means that, in every tissue, half of the cells would have one X chromosome inactive (A) and half would have the other one inactive (B). How is the random choice of one of the two X chromosome initially made? What are the mechanisms that inform one chromosome that other has been chosen? How is a different choice stably maintained in the progeny of each cell, throughout the life of an individual? These are all still unanswered or only partially-answered questions. In addition, in reality, the two copies of the X chromosome are never completely identical and the small differences in their DNA sequences can result in one of the two copies being silenced more easily. As a consequence, for example, if it is easier to silence X chromosome A, then most of the cells in a human organ will have an active B X chromosome, rather than a mixture of cells with an active A and cells with an active B. This is very important when one of the two X chromosomes contains a completely or partially defective gene which can cause a disease. If the X chromosome that is preferentially silenced carries the disease version of the gene, the organ will be functional and the woman will be healthy. But if, instead, the X chromosome, which is preferentially silenced, is the one carrying the normal version of the gene, the organ will not be able to function properly and the woman will suffer from the disease. Identifying the features of the DNA sequences that drive this skew and understanding how X-inactivation works are therefore very important, as they will allow the early identification of the patients at risk of developing severe symptoms, among the women carriers of X-linked diseases. An example of such a disease, where skewed X-inactivation plays a role in the severity of the symptoms, is Duchenne muscular dystrophy, where some female patients are completely asymptomatic and others are severely ill.In our project, we use mouse embryonic stem cells to investigate three molecules, an RNA and two proteins, that we have shown to be essential for the initial choice of which X chromosome will be inactivated. By studying how these three molecules interact with each other and with the X chromosome DNA, we will identify the molecular mechanism that establishes the choice of the identity of the future active and inactive X chromosomes. In addition, we will explore the role of DNA sequences that can determine skewed X chromosome silencing and investigate how these sequences relate to the unbalanced X chromosome inactivation observed in patients.

在人类中，每条染色体都有两个拷贝，除了男性，男性的性染色体X和Y各有一个拷贝。女性有两个X染色体副本。女性两条X染色体中的一条被灭活（沉默），因此男性和女性细胞具有相同数量的来自X染色体的基因产物。这种沉默过程被称为X失活。两条X染色体中的任何一条都可以随机失活。这意味着，在每个组织中，一半的细胞将有一个X染色体失活（A），另一半将有另一个失活（B）。最初是如何随机选择两个X染色体中的一个的？是什么机制让一条染色体知道另一条染色体已被选中？在个体的一生中，不同的选择是如何稳定地保持在每个细胞的后代中的？这些都是尚未得到解答或只有部分解答的问题。此外，在现实中，X染色体的两个副本永远不会完全相同，它们的DNA序列中的微小差异可能导致两个副本中的一个更容易沉默。因此，例如，如果更容易使X染色体A沉默，那么人体器官中的大多数细胞将具有活性B X染色体，而不是具有活性A的细胞和具有活性B的细胞的混合物。当两条X染色体中的一条含有可能导致疾病的完全或部分缺陷基因时，这一点非常重要。如果优先沉默的X染色体携带该基因的疾病版本，则该器官将具有功能，并且该女性将是健康的。但是，如果优先沉默的X染色体携带正常版本的基因，那么器官将无法正常运作，女性将患有这种疾病。因此，确定驱动这种偏斜的DNA序列的特征并了解X失活如何起作用是非常重要的，因为它们将允许在X连锁疾病的女性携带者中早期识别有发展严重症状风险的患者。这种疾病的一个例子，其中偏斜X失活在症状的严重程度中起作用，是杜氏肌营养不良症，其中一些女性患者完全没有症状，而其他人则病情严重。在我们的项目中，我们使用小鼠胚胎干细胞来研究三种分子，一种RNA和两种蛋白质，我们已经证明这三种分子对于最初选择哪一个X染色体将被失活是必不可少的。通过研究这三种分子如何相互作用以及如何与X染色体DNA相互作用，我们将确定确定未来活动和非活动X染色体身份选择的分子机制。此外，我们将探讨DNA序列的作用，可以确定偏斜的X染色体沉默，并研究这些序列如何与患者中观察到的不平衡的X染色体失活。