正确修复DNA双链断裂可防止细胞内重要遗传信息丢失，进而避免细胞癌化或者老化。尽管负责修复此种损伤的两条通路-非同源末端连接和同源重组的机制已经被广泛研究，但是由于缺少合适的研究方法，这两种修复通路在染色质环境下如何被调控尚未被深入探索。申请者课题组发展了在同一基因组位点同时检测非同源末端连接和同源重组的报告系统，并构建了15株在不同基因组位置整合了单拷贝载体的报告细胞系。基于该独特的研究系统，申请人计划研究：（1）核小体密度以及特定组蛋白修饰与双链断裂修复效率以及精确性是否存在相关性；（2）DNA双链断裂损伤发生时相关蛋白调控核小体密度从而影响DNA双链断裂修复的分子机制；（3）DNA双链断裂发生时相关表观遗传因子及其它蛋白调控组蛋白修饰从而影响DNA双链断裂修复分子机制。

Properly fixing DNA double strand break (DSB) is essential for cells to maintain their genome integrity, hence avoiding potential tumorigenesis and stress induced premature cellular senescence. Although intensive studies have been performed to understand the molecular mechanisms of two pathways- nonhomologous end joining (NHEJ) and homologous recombination (HR)- responsible for repairing DNA DSBs, much less attention has been paid to the regulatory mechanisms of the two pathways under the chromatin context due to a lack of appropriate tools. Here, our lab developed a novel reporter cassette, which simultaneously measures repair efficiencies of two pathways at the same genome loci. Furthermore, we created 15 cell lines with the reporter integrated into various chromosomal positions. Using the cell lines, we propose the following specific aims in this study. Aim 1: to systematically analyze the correlation between nucleosome density or histone modifications and DNA repair efficiency and accuracy. Aim 2: to identify factors regulating the change of nucleosome density in response to DNA DSBs, and further elucidate the molecular mechanism. Aim 3: to study the regulatory mechanisms of DNA DSB repair by factors targeting or recognizing specific types of histone modifications.