Dynamics of heterochromatin DNA repair: novel role of nuclear architecture

描述（由申请人提供）：DNA中的双链断裂（DSBs）是环境挑战的结果，例如暴露于电离辐射（IR）或正常细胞代谢（例如DNA复制）。在异染色质中，dsb是对基因组稳定性的主要威胁，因为大量重复序列在修复过程中最大限度地增加了异常重组和基因组不稳定的可能性。然而，在这个大的染色质结构域中操作的修复过程的调节大多是未知的。果蝇模型系统是研究异染色质DSB反应的理想模型。它具有与酵母相似的遗传易感性，与哺乳动物相似的复杂异染色质，并且有利于细胞学方法，因为不同染色体的所有近着丝粒区域都集中在一个不同的核结构域。我们之前对该模型系统的研究表明，异染色质对DSBs的反应是动态的：整个结构域扩展，受损位点移动到结构域外完成同源重组（HR）修复。哺乳动物细胞中类似的反应表明这一途径是高度保守的。虽然dsb的早期HR处理发生在异染色质结构域中，但后期的HR步骤被推迟到重新定位完成。异染色质成分的缺失导致修复中心的重新定位缺陷、异常重组和染色体重排。这些结果揭示了异染色质蛋白在协调异染色质中HR修复的时空动态以及保护重复DNA序列免受基因组不稳定的重要性。为了进一步了解这一重要的新机制，我们将结合多学科方法来鉴定异色dsb成功HR修复所需的亲/抗重组酶和核结构成分。这些研究将揭示正常细胞用来保护重复序列免受环境突变的机制。此外，这项研究将有助于我们理解当突变或环境挑战使保护机制失活时产生染色体重排的机制。这一知识预计将有助于未来开发预防、诊断和治疗与重复DNA不稳定相关的人类疾病（如癌症和出生缺陷）的工具。

DESCRIPTION (provided by applicant): Double-strand breaks (DSBs) in DNA occur as a result of environmental challenges, such as exposure to ionizing radiation (IR) or during normal cell metabolism, such as DNA replication. In heterochromatin, DSBs are a major threat to genome stability, since the abundance of repetitive sequences maximizes the potential for aberrant recombination and genome instability during repair. However, the regulation of repair processes operating in this large chromatin domain is mostly unknown. The Drosophila model system is ideal for studying heterochromatin DSB response. It features genetic tractability comparable to yeast, complex heterochromatin similar to mammals, and is advantageous for cytological approaches because all pericentromeric regions of different chromosomes are concentrated in one distinct nuclear domain. Our previous studies with this model system revealed that heterochromatin responds dynamically to DSBs: the entire domain expands and the damaged sites move to outside the domain to complete homologous recombination (HR) repair. Similar responses in mammalian cells suggest that this pathway is highly conserved. While early HR processing of DSBs occurs within the heterochromatin domain, later HR steps are postponed until relocalization is complete. Loss of heterochromatin components results in defective relocalization of repair centers, aberrant recombination and chromosome rearrangements. These results reveal the importance of heterochromatin proteins in coordinating the spatial and temporal dynamics of HR repair in heterochromatin and in protecting repeated DNA sequences from genome instability. To significantly advance our understanding of this important and novel mechanism, we will combine multi-disciplinary approaches to identify pro-/anti-recombinases and nuclear architecture components required for successful HR repair of heterochromatic DSBs. These studies will uncover the mechanisms that normal cells use to protect repeats from environmental mutagens. In addition, this research will contribute to our understanding of the mechanisms that generate chromosome rearrangements when mutations or environmental challenges inactivate the safeguarding mechanisms. This knowledge is expected to contribute to the future development of tools for prevention, diagnosis, and treatment of human diseases associated with repeated DNA instability, such as cancer and birth defects.