Dynamics of heterochromatin DNA repair: novel role of nuclear architecture

描述(申请人提供)：DNA中的双链断裂(DSB)是环境挑战的结果，例如暴露在电离辐射(IR)中或在正常的细胞代谢过程中，例如DNA复制。在异染色质中，DSB是基因组稳定性的主要威胁，因为丰富的重复序列最大限度地增加了修复过程中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对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。它具有类似于酵母的遗传易感性，类似于哺乳动物的复杂的异染色质，并且由于不同染色体的所有着丝粒周围区域集中在一个不同的核区，因此有利于细胞学方法。我们以前对这个模型系统的研究表明，异染色质对DSB做出动态反应：整个结构域扩张，受损部位移动到结构域外，完成同源重组(HR)修复。哺乳动物细胞中的类似反应表明，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内，但后来的HR步骤被推迟，直到重新定位完成。异染色质组分的丢失会导致修复中心的缺陷重定位、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HR修复的空间和时间动态以及保护重复DNA序列免受基因组不稳定性方面的重要性。为了显著促进我们对这一重要而新颖的机制的理解，我们将结合多学科方法来确定成功修复异染色质DSB所需的前/反重组酶和核结构组件。这些研究将揭示正常细胞用来保护重复序列免受环境诱变剂影响的机制。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。这一知识有望有助于未来开发预防、诊断和治疗与反复DNA不稳定相关的人类疾病的工具，如癌症和出生缺陷。

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.