Distinct roles for Sir2 and RNAi in centromeric heterochromatin nucleation, spreading and maintenance
Distinct roles for Sir2 and RNAi in centromeric heterochromatin nucleation, spreading and maintenance
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DOI：
10.1038/emboj.2013.72
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发表时间：
2013-05-02
期刊：
影响因子：
11.4
通讯作者：
Allshire, Robin C.
中科院分区：
文献类型：
--
作者：
Buscaino, Alessia;Lejeune, Erwan;Allshire, Robin C.
表观遗传学调节的异染色质结构域支配着基本的细胞活动。异染色质结构域的一个关键特征是低乙酰化核小体的存在，其在组蛋白H3的赖氨酸9（H3K9me）上甲基化。在这里，我们调查的要求，建立，传播和维护异染色质使用裂殖酵母着丝粒作为范例。我们发现，在着丝粒重复序列上异染色质的建立是通过RNA干扰（RNAi）在模块化的“成核位点”启动的，从而确保了带有着丝粒的微型染色体的有丝分裂稳定性。我们证明，组蛋白脱乙酰酶Sir2和Clr3和chromodomain蛋白Swi6（HP1）是所需的H3K9me从成核位点扩散，从而允许形成扩展的异染色质结构域。我们发现RNAi和Sir2沿着与Swi（6HP 1）在两个独立的途径中操作以维持异染色质。最后，我们证明了在没有RNAi的情况下，Sir2的拴系对于异染色质在异位位点的维持是关键的。这些分析表明，Sir2与RNAi一起足以确保异染色质的完整性，并为着丝粒异染色质组装中的顺序建立、扩散和维持步骤提供证据。
Epigenetically regulated heterochromatin domains govern essential cellular activities. A key feature of heterochromatin domains is the presence of hypoacetylated nucleosomes, which are methylated on lysine 9 of histone H3 (H3K9me). Here, we investigate the requirements for establishment, spreading and maintenance of heterochromatin using fission yeast centromeres as a paradigm. We show that establishment of heterochromatin on centromeric repeats is initiated at modular 'nucleation sites' by RNA interference (RNAi), ensuring the mitotic stability of centromere-bearing minichromosomes. We demonstrate that the histone deacetylases Sir2 and Clr3 and the chromodomain protein Swi6(HP1) are required for H3K9me spreading from nucleation sites, thus allowing formation of extended heterochromatin domains. We discovered that RNAi and Sir2 along with Swi(6HP1) operate in two independent pathways to maintain heterochromatin. Finally, we demonstrate that tethering of Sir2 is pivotal to the maintenance of heterochromatin at an ectopic locus in the absence of RNAi. These analyses reveal that Sir2, together with RNAi, are sufficient to ensure heterochromatin integrity and provide evidence for sequential establishment, spreading and maintenance steps in the assembly of centromeric heterochromatin.