Mechanism of Epigenetic Inheritance

摘要 在真核细胞中，基因组DNA被包装成染色质，该染色质编码表观遗传信息并维持 基因组完整性。染色质进一步被组织成不同的功能区，如异染色质和 常染色质，含有不同的翻译后组蛋白修饰(PTM)。染色质有何不同 S时期的细胞周期状态是遗传研究中最具挑战性的问题之一 染色质和表观遗传场。在这个复杂的过程中，第一步是将复制的DNA组装成 核小体在与正在进行的过程中紧密耦合的过程中使用亲代组蛋白和新合成的组蛋白 DNA合成。我们一直在研究DNA复制后核小体是如何形成的，并已经 为这一进程作出了多项重大贡献。然而，亲本组蛋白(H3-H4)2四聚体是如何 主要载体的表观遗传修饰，是转移到复制的DNA仍然知之甚少，其中 阻碍了我们对表观遗传信息向子代细胞传递的理解。少校 理解亲本组蛋白(H3-H4)2组装的挑战是缺乏追踪这一组装的方法 进程。我们已经开发了eSPAN(浓缩和测序蛋白质相关新生DNA) 一种方法，可以辨别蛋白质是结合在DNA复制叉的前导链还是滞后链上 酵母和小鼠胚胎干细胞。这种方法使我们有可能识别在 亲代组蛋白(H3-H4)2的核小体组装。此外，我们还发现亲本细胞存在缺陷 组蛋白转移损害内源性逆转录病毒(ERV)的抑制，ERV是重复的DNA元件，可 通常通过基于异染色质的机制沉默。其他研究表明，ERV在癌症中重新激活 细胞导致对免疫治疗的反应增强。在这个提案中，我们将阐明分子 酵母DNA复制后亲本(H3-H4)2重组为核小体的机制 和小鼠ES细胞，并确定这一过程中的缺陷如何影响ERV沉默。加在一起，这些 研究将解决有关染色质复制和表观遗传的基本问题，而 也为一个主要的表观遗传机制提供了新的见解，该机制增强了癌细胞对 免疫疗法。

Abstract In eukaryotic cells, genomic DNA is packaged into chromatin that encodes epigenetic information and maintain genome integrity. Chromatin is further organized into distinct functional domains, such as heterochromatin and euchromatin, that contain different post-translational histone modifications (PTM). How different chromatin states are inherited during S phase of the cell cycle is one of the most challenging questions in the chromatin and epigenetic fields. The “first” step in this complex process is the assembly of replicated DNA into nucleosomes using both parental and newly-synthesized histones in a process that is tightly coupled to ongoing DNA synthesis. We have been studying how nucleosomes are formed following DNA replication and have made multiple major contributions to this process. However, how parental histone (H3-H4)2 tetramers, the primary carrier of epigenetic modifications, are transferred to replicating DNA is still poorly understood, which hinders our understanding of the transmission of epigenetic information into daughter cells. The major challenge to understanding parental histone (H3-H4)2 assembly is a lack of methods to track this process. We have developed the eSPAN (enrichment and Sequencing Protein- Associated Nascent DNA) method that can discern whether a protein binds to leading or lagging strands of DNA replication forks in both yeast and mouse embryonic stem (ES) cells. This method makes it possible to identify factors that function in nucleosome assembly of parental histone (H3-H4)2. Moreover, we discovered that cells defective in parental histone transfer compromise the repression of endogenous retrovirus (ERVs), repetitive DNA elements that are normally silenced via a heterochromatin-based mechanism. Others show that ERV reactivation in cancer cells leads to increased response to immunotherapy. In this proposal, we will elucidate the molecular mechanisms whereby parental (H3-H4)2 are reassembled into nucleosomes following DNA replication in yeast and mouse ES cells and determine how deficiencies in this process impact ERV silencing. Together, these studies will address fundamental questions regarding chromatin replication and epigenetic inheritance, while also providing novel insights into a major epigenetic mechanism that boosts the response of cancer cells to immunotherapy.