Epigenetic Control and the Checkpoint-Exempt Status of Telomeres

表观遗传控制和端粒的检查点豁免状态

• 批准号: 1516220
• 负责人: Kurt Runge
• 金额: $ 66万
• 依托单位: Cleveland Clinic Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1516220&HistoricalAwards=false
• 关键词: Epigenetic; Control; Checkpoint; Exempt; Status

This project will address a key feature of an organism's response to DNA damage that permits it to survive and divide. Cells as diverse as yeast and humans package their DNA with proteins called histones. One particular chemical modification of histone allows cells to recognize, respond to and repair damage to DNA. However, this histone modification is present in some parts of the DNA but absent in others, and the regions lacking this special modification have a reduced response to damaged DNA. This project will determine how this particular modification is excluded from some histones, and what role this exclusion has in normal cell growth. The outcomes of this work will greatly improve our understanding of how humans and other organisms respond to environmental insults that damage DNA, and provide a vehicle for training graduate students in the thinking and practice of science. This project will also provide undergraduate students with their first experience in scientific research beyond the classroom, and with real-world applications of their science, technology and math skills before entering the work force. Telomeres are the regions at the ends of chromosomes, and the manner in which the stable telomere ends are distinguished from the unstable ends generated by double-strand breaks elsewhere in chromatin is a fundamental question in the fields of genome integrity and chromosome biology. While double-strand breaks cause growth arrest and promote genomic instability by DNA recombination, telomeres have functions that allow continuous cell growth and the complete replication of the chromosome end. Telomeres are composed of DNA repeat tracts bound by specific proteins, and previous studies have focused on the role of telomere proteins in suppressing recombination and cell cycle arrest. However, recent work in the fission yeast Schizosaccharomyces pombe has implicated an epigenetic modification in this process. Specifically, a key feature that prevents damaged telomeres with bound DNA damage response proteins from causing cell cycle arrest is the lack of dimethylation of histone H4 lysine 20 (H4K20me2) in nucleosomes near the telomere DNA. The H4K20me2 modification is conserved from S. pombe to mammals, and its absence near telomeres is thought to allow them to incur damage and still allow cell growth, making telomeres a DNA damage checkpoint-exempt region of the genome. How telomeres exclude H4K20me2 is unknown. This project will advance our understanding of H4K20me2 exclusion using a rapidly inducible telomere formation system in S. pombe. This system will be used to determine how the H4K20me2-free state is established. Defining how much of the chromosomal end excludes H4K20me2 has important implications for the portions of the genome exempt from DNA damage-induced arrest, and also for our understanding of how cells regulate genome stability. Using a combination of chromatin immunoprecipitation and genetic approaches, this project will determine if the H4K20me2-free state is restricted to telomeres, or also spreads into the adjacent chromatin.

该项目将介绍生物体对DNA损伤的反应的关键特征，从而使其生存和分裂。 像酵母一样多样化的细胞和人类将其DNA与称为组蛋白的蛋白质包装。组蛋白的一种特殊化学修饰使细胞可以识别，响应和修复对DNA的损害。 但是，这种组蛋白的修饰存在于DNA的某些部分，但在其他部分中不存在，缺乏这种特殊修饰的区域对受损DNA的反应减少了。 该项目将确定如何将这种特定的修饰排除在某些组蛋白之外，以及该排除在正常细胞生长中的作用。 这项工作的结果将大大提高我们对人类和其他生物如何应对损害DNA的环境侮辱的理解，并为培训科学思维和实践的培训研究生提供工具。 该项目还将为本科生提供他们在课堂以外的科学研究方面的第一个经验，并在进入劳动力之前的科学，技术和数学技能的现实应用。端粒是染色体末端的区域，稳定的端粒末端与染色体其他地方的双链破裂产生的不稳定末端的区别是基因组完整性和染色体生物学领域的一个基本问题。 尽管双链断裂会导致生长停滞并通过DNA重组促进基因组不稳定，但端粒具有允许连续细胞生长和染色体末端的完全复制的功能。 端粒由由特定蛋白结合的DNA重复区组成，以前的研究集中在端粒蛋白在抑制重组和细胞周期停滞中的作用。 然而，裂变酵母裂菌酵母中的最新工作暗示了这一过程中的表观遗传修饰。 具体而言，阻止端粒受损的端粒受损的关键特征是导致细胞周期停滞的导致细胞周期停滞的是缺乏在端粒DNA附近的核小体中组蛋白H4赖氨酸20（H4K20ME2）的二甲基化。 H4K20ME2的修饰是从S. pombe到哺乳动物的保守的，其在端粒附近的缺席被认为使它们造成损害并仍然允许细胞生长，从而使端粒成为基因组的DNA损伤检查点 - 避免了基因组的豁免区域。 端粒如何排除H4K20me2是未知的。 该项目将使用S. Pombe中快速诱导的端粒形成系统来促进我们对H4K20ME2排除的理解。 该系统将用于确定如何建立H4K20ME2的状态。 定义多少染色体端排除了H4K20me2，对免于DNA损伤引起的抑制的基因组的部分具有重要意义，也是我们对细胞如何调节基因组稳定性的理解。使用染色质免疫沉淀和遗传方法的组合，该项目将确定H4K20ME2无态是否仅限于端粒，或者也扩散到相邻的染色质中。