Department of Epigenetics, Max Planck Institute of Immunobiology and Epigenetics, Stübeweg 51, 79108 Freiburg, Germany.
Cell. 2012 Aug 31;150(5):948-60. doi: 10.1016/j.cell.2012.06.048.
Heterochromatin serves important functions, protecting genome integrity and stabilizing gene expression programs. Although the Suv39h methyltransferases (KMTs) are known to ensure pericentric H3K9me3 methylation, the mechanisms that initiate and maintain mammalian heterochromatin organization remain elusive. We developed a biochemical assay and used in vivo analyses in mouse embryonic fibroblasts to identify Prdm3 and Prdm16 as redundant H3K9me1-specific KMTs that direct cytoplasmic H3K9me1 methylation. The H3K9me1 is converted in the nucleus to H3K9me3 by the Suv39h enzymes to reinforce heterochromatin. Simultaneous depletion of Prdm3 and Prdm16 abrogates H3K9me1 methylation, prevents Suv39h-dependent H3K9me3 trimethylation, and derepresses major satellite transcription. Most strikingly, DNA-FISH and electron microscopy reveal that combined impairment of Prdm3 and Prdm16 results in disintegration of heterochromatic foci and disruption of the nuclear lamina. Our data identify Prdm3 and Prdm16 as H3K9me1 methyltransferases and expose a functional framework in which anchoring to the nuclear periphery helps maintain the integrity of mammalian heterochromatin.
异染色质具有重要的功能，它可以保护基因组的完整性并稳定基因表达程序。虽然 Suv39h 甲基转移酶（KMTs）被认为可以确保着丝粒 H3K9me3 甲基化，但启动和维持哺乳动物异染色质组织的机制仍不清楚。我们开发了一种生化测定法，并在小鼠胚胎成纤维细胞中进行体内分析，以鉴定 Prdm3 和 Prdm16 为冗余的 H3K9me1 特异性 KMTs，它们可以指导细胞质 H3K9me1 甲基化。H3K9me1 在内质网中被 Suv39h 酶转化为 H3K9me3，以加强异染色质。Prdm3 和 Prdm16 的同时耗竭会消除 H3K9me1 甲基化，阻止 Suv39h 依赖性 H3K9me3 三甲基化，并使主要卫星转录去抑制。最引人注目的是，DNA-FISH 和电子显微镜显示，Prdm3 和 Prdm16 的联合缺陷会导致异染色质焦点的解体和核纤层的破坏。我们的数据将 Prdm3 和 Prdm16 鉴定为 H3K9me1 甲基转移酶，并揭示了一个功能框架，其中锚定在核周有助于维持哺乳动物异染色质的完整性。
