Polycomb-mediated heterochromatin formation in Tetrahymena

描述（由申请人提供）：Polycomb group （PcG）蛋白是转录抑制的重要表观遗传调控因子，长期以来一直被积极研究其在果蝇和哺乳动物系统中Hox基因调控、x失活和肿瘤发生中的作用。最近发现PcG蛋白在四膜虫中是保守的，这使得利用单细胞模型系统中可用的强大的遗传和生化工具来解决Polycomb抑制的一些基本机制成为可能。发育调控的异染色质形成发生在四膜虫的种系-体细胞分化过程中。已经确定这是一种依赖rnai的pcg介导途径。提出的研究将探索PcG蛋白被RNAi机制招募的机制，这一机制可能在高等真核生物中保守。我们还将研究H3K27甲基化和H2A泛素化之间潜在的串音，这是PcG蛋白沉积的两个保守的表观遗传标记。特别是，我们将评估它们在转录抑制中的协同功能，并探讨潜在的机制。这些研究将大大提高我们对PcG蛋白在基因组组织和转录抑制中的功能的认识。鉴于PcG蛋白在干细胞多能性、细胞分化和细胞恶性肿瘤中发挥关键作用，拟议的研究也将在公共卫生，包括疾病诊断和治疗方面具有重要意义。该项目符合国家普通医学研究所的任务，五年期预算为1 250 000美元。

DESCRIPTION (provided by applicant): Polycomb group (PcG) proteins are important epigenetic regulators of transcription repression and have long been under active investigation for their roles in Hox gene regulation, X-inactivation, and tumorigenesis in Drosophila and mammalian systems. Recent findings that PcG proteins are conserved in Tetrahymena make it possible to address some of the fundamental mechanisms of Polycomb repression with powerful genetic and biochemical tools available in the unicellular model system. Developmentally regulated heterochromatin formation occurs during the germline-somatic differentiation in Tetrahymena. It has been established that this is an RNAi-dependent PcG-mediated pathway. The proposed studies will explore the mechanism by which the PcG proteins are recruited by RNAi machinery, a mechanism likely to be conserved in higher eukaryotes. We will also examine the potential crosstalk between H3K27 methylation and H2A ubiquitylation, two conserved epigenetic marks deposited by PcG proteins. In particular, we will assess their concerted functions in transcription repression and probe the underlying mechanism. The proposed studies will significantly advance our knowledge for the function of PcG proteins in genome organization and transcription repression. Given that PcG proteins play critical roles in stem cell pluripotency, cell differentiation, and cell malignancy, the proposed studies will also have important implications in public health, including disease diagnosis and treatment. The project matches with the mission of the National Institute of General Medical Science (NIGMS) and is budgeted at $1,250,000 for a five-year period. PUBLIC HEALTH RELEVANCE: Project Narrative Polycomb group proteins are involved in stem cell pluripotency, cell differentiation, and cell malignancy. The proposed studies will significantly advance our knowledge for the underlying mechanism, particularly the function of PcG proteins in genome organization and gene repression. This will have important implications in public health, including disease diagnosis and treatment.