RNAi and Epigenetic Control of Higher-Order Chromatin Assembly

我们实验室的研究主要集中在高阶遗传控制上。 染色质装配高阶染色体结构的动态调节控制着 从基因表达模式的稳定遗传到 对保持基因组完整性至关重要的全局染色体结构的其他方面。我们 早期的研究揭示了分子事件的顺序，导致组装 裂殖酵母裂殖酵母中的异染色质结构。我们发现 通过脱乙酰酶和甲基转移酶活性对组蛋白尾部进行共价修饰， 音乐会，以建立必要的组蛋白代码的组装 异染色质结构此外，我们发现，不同的位点特异性组蛋白H3 甲基化模式决定了染色体的组织成离散的结构， 功能域组蛋白H3在赖氨酸9处甲基化，严格定位于沉默区。 异染色质区域，而H3在赖氨酸4处甲基化，仅几个氨基酸远， 特异于周围的活性常染色质区域。我们继续专注于 组蛋白修饰和识别特定组蛋白修饰的因子 模式（如特异性结合组蛋白H3的染色体结构域蛋白Swi6， 赖氨酸9）在组装更高级的染色质结构，并取得了显着 在理解高阶染色质组装的机制方面取得了进展。更重要的是， 我们提供的证据表明，RNA干扰（RNAi），即双链RNA 沉默同源基因，在异染色质复合物靶向 基因组中的特定位置。我们最近的研究发现了一种自我强化的 环机制，通过该环机制，RNAi机器作为稳定的组件运行。 异染色质结构域（通过RNAi复合物与异染色质标记的拴系）来破坏 避免异染色质介导的转录沉默的重复转录物。在这 环机制，通过RNAi机制加工转录物产生小干扰， RNA（siRNA）用于异染色质复合物的进一步靶向，因此， 机制继续。在一项全面的研究中，我们还绘制了一幅高分辨率的地图， 异染色质和常染色质在整个裂殖酵母基因组中的分布。这些 分析与RNAi组分作图和siRNA的大规模测序 与参与异染色质沉默的RNAi效应复合物相关的研究已经产生了 新的见解，这种模式的真核基因组的表观遗传概况。之间的联系 RNAi和异染色质组装在包括哺乳动物在内的高等真核生物中是保守的， 对人类生物学和包括癌症在内的疾病的广泛影响。

Research in our laboratory is focused on the epigenetic control of higher-order chromatin assembly. The dynamic regulation of higher-order chromosome structure governs diverse cellular processes ranging from stable inheritance of gene expression patterns to other aspects of global chromosome structure essential for preserving genomic integrity. Our earlier studies revealed sequence of molecular events leading to the assembly of heterochromatic structures in the fission yeast Schizosaccharomyces pombe. We found that covalent modifications of histone tails by deacetylase and methyltransferase activities act in concert to establish the histone code essential for assembly of heterochromatic structures. Moreover, we showed that distinct site-specific histone H3 methylation patterns dictate the organization of chromosomes into discrete structural and functional domains. Histone H3 methylated at lysine 9 is strictly localized to silent heterochromatic regions whereas H3 methylated at lysine 4, only a few amino acids away, is specific to the surrounding active euchromatic regions. We have continued to focus on the role of histone modifications and the factors that recognize specific histone modifications patterns (such as a chromodomain protein Swi6 that specifically binds histone H3 methylated at lysine 9) in the assembly of higher-order chromatin structures and have made significant progress in understanding the mechanism of higher-order chromatin assembly. More importantly, we provided evidence showing that RNA interference (RNAi), whereby double-stranded RNAs silence cognate genes, plays a critical role in targeting of heterochromatin complexes to specific locations in the genome. Our recent work has led to discovery of a self-enforcing loop mechanism though which RNAi machinery operates as a stable component of the heterochromatic domains (via tethering of RNAi complexes to heterochromatin marks) to destroy repeat transcripts that escape heterochromatin-mediated transcriptional silencing. In this loop mechanism, the processing of transcripts by RNAi machinery generate small interfering RNAs (siRNAs) that are utilized for further targeting of heterochromatin complexes, so the mechanism continues. In a comprehensive study, we have also developed a high-resolution map of the heterochromatin and euchromatin distribution across the entire fission yeast genome. These analyses together with mapping of RNAi components and large scale sequencing of siRNAs assocaited with an RNAi effector complex involved in heterochromatic silencing have yielded novel insights into the epigenetic profile of this model eukaryotic genome. The link between RNAi and heterochromatin assembly is conserved in higher eukaryotes including mammals and has broad implications for human biology and disease including cancer.