Molecular mechanisms of heterochromatin spreading at the leading edge

前沿异染色质扩散的分子机制该项目将揭示基因如何稳定关闭以产生不同类型细胞的分子细节。稳定的基因沉默可以区分单细胞生物，它也有助于人体使用相同的基因组来创造形成器官的非常不同的细胞类型。基因沉默稳定的一个主要决定因素是沉默波沿染色体传播的距离。了解传播是如何发生的以及如何阻止它是这个项目的主要焦点。实现这个项目的目标将有助于我们理解基因相同的细胞之间的变异，这种变异是发育和环境对基因调控的影响的基础。该项目将由PI领导的一个科学家团队承担，包括博士后、研究生和本科生。为少数民族人口较多的当地学校的高中生和他们的老师提供暑期研究经验，将增强项目的培训影响。团队将共同为研究做出贡献，结合他们的资源和技能，同时在各个层面上相互指导。该项目的成果将与研究界和公众广泛分享，所产生的资源将提供给科学领域。异染色质是一种基因组结构，它以一种通过细胞分裂维持表观遗传的方式抑制转录，有助于所有真核生物稳定的细胞分化。异染色质结构域的建立涉及位点特异性起始和随后在基因组大区域的扩散，结合与染色质稳定相关的抑制蛋白。扩展与组蛋白修饰在“前沿”的转换和最终过渡到稳定的异染色质状态相耦合。这种机制需要异染色质机制的两种主要作用模式：动态扩散和与染色质的稳定抑制结合。虽然我们对异染色质在多个系统中的组成成分了解甚多，但在分子分辨率上，我们还不了解这种机制是如何通过机制的各个步骤协调过渡的。该项目利用纯化的出芽酵母异染色质系统，充分概括了组蛋白修饰的动态转换和稳定抑制异染色质状态的形成。研究小组先前使用该系统的工作已经为机制中的许多步骤生成了模型，现在将在一个新的分子分辨率水平上进行测试。将使用先进的交联质谱法，结合“设计”染色质来捕获驱动表观遗传抑制基因组结构形成的多种作用模式中的异染色质机制。丰富的遗传和生物化学工具将允许鉴定异染色质组装中最重要的分子相互作用，产生对这一基本基因组调控系统的机制理解的新水平。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Molecular mechanisms of heterochromatin spreading at the leading edgeThis project will uncover molecular details of how genes are stably turned off to produce different types of cells. Stable gene silencing can distinguish single-celled organisms and it also helps the human body use the same genome to create very different cell types that form organs. One major determinant of stable gene silencing is how far along a chromosome the wave of silencing spreads. Understanding how spreading occurs and how it is stopped are the primary focuses of this project. Achieving the goals of this project will help us understand variation across genetically identical cells that underlies development and environmental effects on gene regulation. The project will be undertaken by a team of scientists lead by the PI and including postdoctoral fellows, graduate students, and undergraduates. Summer research experiences for high school students and their teachers from a local school with a high minority population will enhance the training impact of the project. Together, the team will contribute to the research, combining their resources and skill sets while mentoring each other across levels. The results from this project will be broadly shared with the research community and the public and the resources generated will be made available to the scientific field.Heterochromatin is a genomic structure that represses transcription in a manner that is epigenetically maintained through cell division, contributing to stable cell differentiation in all eukaryotes. Establishment of a heterochromatin domain involves site-specific initiation and subsequent spreading across large regions of the genome, incorporating repressor proteins that stably associate with chromatin. Spreading is coupled to the conversion of histone modifications at the “leading edge” and eventual transition to the stable heterochromatin state. This mechanism requires two main modes of action for the heterochromatin machinery: dynamic spreading and stable repressive association with chromatin. While much is known of the components of heterochromatin in multiple systems, we do not understand at molecular resolution how the machinery coordinates the transitions through the steps of the mechanism. This project harnesses a purified budding yeast heterochromatin system that fully recapitulates the dynamic conversion of histone modifications and the formation of a stable repressive heterochromatin state. Previous work from the research group using this system has generated models for many steps in the mechanism that will now be tested at a new level of molecular resolution. Advanced cross-linking mass spectrometry will be used, combined with “designer” chromatin to capture the heterochromatin machinery in the multiple modes of action that drive formation of an epigenetic repressive genomic structure. The wealth of genetic and biochemical tools available will allow for identification of the most important molecular interactions for heterochromatin assembly, generating a new level of mechanistic understanding of this fundamental genomic regulatory system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.