Epigenetic Regulation of Drosophila Telomere Function

描述（由申请人提供）：真核生物染色体生物学的一个中心问题是如何区分线性染色体的正常末端（端粒）和双链断裂。一种公认的机制是通过序列特异性DNA结合蛋白如人TRF2识别端粒特异性序列。然而，一些观察结果表明，其他机制在端粒保护中起着重要的作用，但知之甚少。其中最引人注目的例子是对果蝇的研究，在这些研究中，分离和维持染色体的末端没有端粒特异性序列是可能的。这些研究表明，一个独立的序列，即表观遗传，机制调节果蝇端粒保护。果蝇端粒保护涉及两种细胞途径。染色质相关蛋白HP1和端粒特异性结合伴侣HOAP定位于端粒，并且是保护端粒所必需的。我们还发现DNA损伤反应激酶ATM和ATR的突变导致端粒HP1-HOAP的丢失和端粒保护的丢失。ATM/ATR激酶对染色体末端的识别可以提供一种不依赖于序列的方法来将蛋白质募集到端粒上，但该模型没有解决这些蛋白质如何区分染色体断裂和端粒。我们假设DNA损伤反应途径通过稳态机制来保护端粒，通过招募HP1-HOAP复合物来保护不完全保护的端粒。为了测试这个模型，我们将探测ATM/ATR激酶在正常端粒和有缺陷的HP1扩散的端粒的活性。此外，我们的初步结果表明，mutator-2基因可能是DNA损伤反应途径和HP1之间的联系，但它也有第二个功能，当端粒变得完全不受保护时，它会融合端粒。通过了解端粒中mutator-2的作用，我们可以了解端粒和染色体断裂处的损伤反应是如何调节的。端粒似乎在人类癌症和衰老中起着核心作用。这些研究将有助于阐明一类新的表观遗传，端粒功能的非序列依赖性调节。鉴于HP1和DNA损伤反应途径在人类端粒中发挥作用，了解果蝇端粒的功能可能会导致缩短或延长人类端粒的新方法。端粒，染色体的正常末端，似乎在人类衰老和癌症中起着重要作用。我们正在使用模式生物果蝇来研究识别受损染色体的蛋白质如何帮助调节端粒功能。对端粒调控的进一步理解可能为调节人类衰老和癌症提供新的策略。

DESCRIPTION (provided by applicant): A central question in eukaryotic chromosome biology is how the normal ends of linear chromosomes, telomeres, are distinguished from double strand breaks. One well-established mechanism is the recognition of telomeric-specific sequences by sequence specific DNA binding proteins such as human TRF2. However, several observations demonstrate that other mechanisms play an essential, but poorly understood role in telomere protection. Among the most striking examples are studies in Drosophila in which it is possible to isolate and maintain chromosomes with no telomere-specific sequences at their ends. These studies indicate that a sequence-independent, i.e. epigenetic, mechanism regulates telomere protection in Drosophila. Two cellular pathways have been implicated in Drosophila telomere protection. The chromatin-associated protein HP1 and a telomere-specific binding partner, HOAP, are localized to telomeres and are required for their protection. We have also found that mutations in the DNA damage response kinases ATM and ATR lead to loss of telomeric HP1-HOAP and loss of telomere protection. Recognition of chromosome ends by ATM/ATR kinases could provide a sequence-independent means to recruit proteins to telomeres, but this model does not address how these proteins distinguish between chromosome breaks and telomeres. We hypothesize that DNA damage response pathways act by a homeostatic mechanism to protect telomeres by recruiting HP1-HOAP complexes to incompletely protected telomeres. To test this model, we will probe the activity of ATM/ATR kinases at normal telomeres and at telomeres with defective HP1 spreading. In addition, our preliminary results suggest that the mutator-2 gene may act as a link between the DNA damage response pathway and HP1, but that it also has a second function fusing telomeres when they become completely unprotected. By understanding the role of mutator-2 at telomeres, we may learn how the damage response is modulated at telomeres and at chromosome breaks. Telomeres appear to play a central role in human cancer and aging. These studies will help elucidate a new category of epigenetic inheritance, sequence-independent regulation of telomere function. Given that both HP1 and DNA damage response pathways play roles at human telomeres, understanding telomere function in Drosophila may lead to new ways to shorten or extend telomeres in humans. PUBLIC HEALTH RELEVANCE: Telomeres, the normal ends of chromosomes, appear to play important roles in human aging and cancer. We are using the model organism Drosophila melanogaster to study how proteins that recognize damaged chromosomes also help regulate telomere function. Improved understanding of telomere regulation may provide new strategies to modulate human aging and cancer.