The Role of Shelterin-Mediated Telomere Remodeling in Chromosome End Protection

本项目的目标是阐明人类染色体末端端粒的保护和维持机制。真核生物染色体的末端需要被保护以防止不适当的DNA损伤修复反应（DDR）、DNA降解和不完全的DNA复制，以维持基因组的稳定性和正常功能。这些挑战的解决方案是形成保护性端粒帽结构，其由专门的重复DNA序列和共同形成shelterin复合物的相关因子组成。分裂细胞中端粒的逐渐缩短触发DDR和细胞周期停滞。因此，端粒被称为决定生物体增殖寿命的内部生物钟，并作为主要的抗癌屏障发挥作用。为了更好地理解衰老和癌症，需要详细了解端粒如何在染色体末端形成保护帽，以及进行性端粒缩短如何导致复制性衰老。该项目还将帮助建立教育推广计划，高中学生从奥克兰，加利福尼亚州的贫困地区。为了吸引高中生和本科生进行科学研究，将在当地公立学校组织夏季研究机会、研讨会和科学展览会。这项研究的结果将被整合到一个新的课程中，该课程将为希望在生命科学领域从事研究生职业的物理学本科生开发。shelterin如何阻止DDR机器进入染色体末端，特别是单链端粒突出端，目前尚不清楚。最近，有人建议，shelterin重塑端粒染色质成一个高度紧凑的结构，减少了接近的DDR蛋白端粒末端。利用体内超分辨率成像，该项目旨在揭示shelterin在保护端粒染色质内端粒突出端中的作用。随着端粒在分裂细胞中缩短，端粒染色质组织的变化将被确定，以了解衰老前触发染色体末端DDR积累的机制。此外，为了确定是否需要致密的端粒束和足以拮抗DDR蛋白质的端粒突出端的结合，shelterin结合的端粒DNA的结构将解决使用冷冻电子断层扫描和其结构-功能特性将在体外通过单分子实验进行研究。

The goal of this project is to elucidate the mechanism of protection and maintenance of telomeres at the ends of human chromosomes. The ends of eukaryotic chromosomes need to be protected against inappropriate DNA damage repair reactions (DDR), DNA degradation and incomplete DNA replication in order to maintain genomic stability and proper functioning. The solution to these challenges is to form a protective telomere cap structure that consists of specialized repeat DNA sequences and associated factors that together form the shelterin complex. Gradual shortening of telomeres in dividing cells triggers DDR and cell cycle arrest. Thus telomeres are referred to as internal biological clocks that determine the proliferative lifespan of an organism and function as major anticancer barriers. Detailed knowledge of how telomeres form a protective cap at the chromosome end and how progressive telomere shortening leads to replicative senescence is needed to better understand aging and cancer. This project will also help to establish educational outreach programs for high school students from underprivileged areas of Oakland, CA. To attract high school and undergraduate students to scientific research, summer research opportunities, seminars and science fairs will be organized in local public schools. The results of the research will be integrated into a new curriculum that will be developed for Physics undergraduates wishing to pursue a graduate career in the life sciences.How shelterin prevents the DDR machinery from gaining access to chromosome ends, particularly the single-stranded telomeric overhang, remains unclear. Recently, it has been suggested that shelterin remodels telomeric chromatin into a highly compact structure that reduces the accessibility of DDR proteins to telomere ends. Using super-resolution imaging in vivo, the project aims to reveal the role of shelterin in safeguarding the telomeric overhang within telomeric chromatin. The changes in organization of telomeric chromatin will be determined as telomeres shorten in dividing cells to understand the mechanism that triggers DDR accumulation at chromosome ends before senescence. Additionally, to determine whether compaction of telomeric tracts is required and sufficient to antagonize binding of DDR proteins to telomeric overhangs, the structure of shelterin-bound telomeric DNA will be solved using cryoelectron tomography and its structure-function properties will be investigated by single molecule experiments in vitro.