Organization and Function of the Heterochromatin Holodomain and Subdomains

项目总结/摘要 这个项目的长期目标是阐明的组成，建筑，和生物物理特性的 异染色质，并了解它们如何有助于核功能。异染色质富含 重复的DNA，集中在着丝粒周围和端粒区域，并形成一个独特的和动态的三维 核内的结构域。异染色质是正常姐妹染色体配对和分离所必需的， 核结构、重组抑制、转座子沉默和基因沉默。异染色 募集受表观遗传成分和机制的调节，特别是 组蛋白H3赖氨酸9（H3 K9 me 2/3）通过特异性甲基转移酶。异染色质蛋白1（HP 1）结合这一点， “标记”并将许多蛋白质和复合物募集到异染色质。我们目前缺乏一个明确的 了解异染色质结构域的精细结构和组织，以及生物物理学 负责其功能和行为的属性。我们对果蝇的初步研究表明 异染色质的意想不到的结构复杂性和生物物理特性，提出了我们的问题， 目前对该结构域的结构和功能的理解，并表明异染色质可能形成 并通过与染色质结构无关的生物物理机制发挥作用， 功能特别是，我们的研究结果导致了一个新的假设，即异染色质结构域的形成是通过 相分离机制，最近已被证明可以划分功能分子 网络的结构，缺乏约束膜，但直到现在还没有被应用到染色质 域. 我们将利用这些新的发现，并应用先进的成像，表观基因组学，生物化学和 生物物理方法来阐明：1）结构，生物化学和生物物理特性的 异染色质结构域，2）负责异染色质形成的组分和机制，以及 3)异染色质亚结构和生物物理特性对细胞核和生物体的影响 功能协调发展的测试相分离假说将阐明有关组织的重要信息 以及异染色质在细胞和动物中的功能，提供了一个范式转换的潜力， 为了解其他染色质结构域如何形成和发挥功能奠定了基础。此外，缺陷 异染色质产生基因组不稳定性和改变的基因表达，导致癌症，出生 缺陷和老化。了解人类疾病和状况如何改变生物物理特性， 异染色质的形成和功能将最终影响其诊断方法， 治疗

PROJECT SUMMARY/ABSTRACT The long term goal of this project is to elucidate the composition, architecture, and biophysical properties of heterochromatin, and to understand how they contribute to nuclear functions. Heterochromatin is enriched in repeated DNAs, is concentrated in pericentromeric and telomeric regions, and forms a distinct and dynamic 3D domain inside nuclei. Heterochromatin is required for normal sister chromosome pairing and segregation, nuclear architecture, recombination suppression, transposon silencing, and gene silencing. Heterochromatin recruitment is regulated by epigenetic components and mechanisms, specifically di- and tri- methylation of histone H3 lysine 9 (H3K9me2/3) by specific methyltransferases. Heterochromatin Protein 1 (HP1) binds this `mark' and recruits many proteins and complexes to the heterochromatin. We currently lack a clear understanding of the fine structure and organization of the heterochromatin domain, and the biophysical properties responsible for its functions and behaviors. Our preliminary studies in Drosophila have revealed unexpected structural complexity and biophysical properties of heterochromatin that raise questions about our current understanding of the structure and function of this domain, and suggest that heterochromatin may form and function through biophysical mechanisms that have not been associated with chromatin structure and function. In particular, our findings led to the novel hypothesis that the heterochromatin domain forms through a phase separation mechanism, which has recently been shown to compartmentalize functional molecular networks into structures that lack constraining membranes, but has not until now been applied to chromatin domains. We will capitalize on these novel findings and apply advanced imaging, epigenomics, biochemical and biophysical approaches to elucidate: 1) the structural, biochemical and biophysical properties of the heterochromatin domain, 2) the components and mechanisms responsible for heterochromatin formation, and 3) the ways that heterochromatin substructure and biophysical properties contribute to nuclear and organismal functions. Testing the phase separation hypothesis will elucidate important information about the organization and function of heterochromatin in cells and animals, offering the potential of providing a paradigm-shifting foundation for understanding how other chromatin domains form and function. In addition, defective heterochromatin produces genome instability and altered gene expression, contributing to cancer, birth defects, and aging. Understanding how human diseases and conditions alter the biophysical properties that underlie heterochromatin formation and function will ultimately impact the approaches to their diagnosis and treatment.