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

该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。真核生物的染色体末端需要受到保护，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和正常的功能。解决这些挑战的办法是形成一种保护性的端粒帽结构，它由特殊的重复DNA序列和相关因素组成，这些DNA重复序列和相关因素共同形成了保护素复合体。细胞分裂过程中端粒的逐渐缩短会触发DDR和细胞周期停滞。因此，端粒被称为内部生物钟，它决定了生物体的增殖寿命，并发挥着主要的抗癌屏障的作用。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，以及渐进性端粒缩短如何导致复制性衰老。该项目还将帮助为加利福尼亚州奥克兰贫困地区的高中生建立教育推广计划。为了吸引高中生和本科生从事科学研究，当地公立学校将组织暑期研究机会、研讨会和科学博览会。这项研究的结果将被整合到一门新的课程中，该课程将为希望在生命科学领域寻求研究生职业生涯的物理学本科生开发。目前尚不清楚庇护如何阻止DDR机制接触到染色体末端，特别是单链端粒突出部分。最近，有研究表明，Shelterin将端粒染色质重塑为高度致密的结构，从而减少了DDR蛋白对端粒末端的可及性。利用体内的超分辨率成像，该项目旨在揭示保护素在保护端粒染色质内的端粒悬垂中的作用。端粒染色质的组织变化将随着端粒在细胞分裂过程中的缩短而确定，以了解在衰老之前触发染色体末端DDR积累的机制。此外，为了确定是否需要端粒束的紧致以及是否足以拮抗DDR蛋白与端粒突出物的结合，将使用低温电子断层扫描技术解决与Shelterin结合的端粒DNA的结构，并将通过体外单分子实验来研究其结构-功能特性。

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.