GC-rich sequence elements recruit PRC2 in mammalian ES cells.
GC-rich sequence elements recruit PRC2 in mammalian ES cells.
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富含GC的序列元件在哺乳动物ES细胞中募集PRC2。
DOI：
10.1371/journal.pgen.1001244
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发表时间：
2010-12-09
期刊：
影响因子：
4.5
通讯作者：
Bernstein BE
中科院分区：
文献类型：
--
作者：
Mendenhall EM;Koche RP;Truong T;Zhou VW;Issac B;Chi AS;Ku M;Bernstein BE
多梳蛋白是表观遗传调节因子，定位于早期胚胎的发育位点，在那里它们介导谱系特异性基因抑制。在果蝇中，这些阻遏物被与Polycomb阻遏复合物2（PRC2）相关的DNA结合蛋白募集到序列元件中。然而，在哺乳动物细胞中招募PRC2的序列仍然不清楚。为了解决这个问题，我们将一系列工程细菌人工染色体整合到胚胎干细胞（ES）中，并检查了它们的染色质。我们发现对应于Zfpm2基因座的44 kb区域启动PRC2的从头募集。然后，我们在这个位点内精确定位了一个CpG岛，这对于PRC2的招募是必要的和足够的。基于这种因果关系的证明和先前的基因组分析，我们假设，大GC丰富的元素耗尽激活转录因子基序介导PRC2招聘哺乳动物。我们从两个方面验证了这个模型。首先，我们表明，一个组成型活性的CpG岛能够招募PRC2后，切除一簇激活基序。其次，我们发现，两个1 kb的序列间隔与GC含量相当的哺乳动物CpG岛的大肠杆菌基因组都能够招募PRC2时，整合到ES细胞基因组。我们的研究结果表明，GC丰富的序列在PRC2招聘的因果关系的作用，并牵连一个特定的子集的CpG岛耗尽激活基序作为工具，在哺乳动物基因组中的这个关键调节器的初始本地化。关键的发育基因在发育过程中被精确地打开或关闭，从而创造出复杂的多组织胚胎。抑制基因的机制对正常发育至关重要。在胚胎干细胞中，Polycomb抑制复合物2（PRC2）被招募到这些发育基因的启动子中，并有助于在发育过程中维持适当组织中的抑制。PRC2最初是如何在早期胚胎中被招募到这些基因中的仍然是难以捉摸的。在这里，我们实验证明，富含GC的DNA，称为CpG岛，可以启动招聘PRC2在胚胎干细胞时，他们是转录不活跃。令人惊讶的是，我们发现来自细菌基因组的富含GC的DNA也可以在胚胎干细胞中启动PRC2的募集。这支持了一个模型，其中即使在没有更复杂的DNA序列基序的情况下，无活性的富含GC的DNA本身也足以招募PRC2。
Polycomb proteins are epigenetic regulators that localize to developmental loci in the early embryo where they mediate lineage-specific gene repression. In Drosophila, these repressors are recruited to sequence elements by DNA binding proteins associated with Polycomb repressive complex 2 (PRC2). However, the sequences that recruit PRC2 in mammalian cells have remained obscure. To address this, we integrated a series of engineered bacterial artificial chromosomes into embryonic stem (ES) cells and examined their chromatin. We found that a 44 kb region corresponding to the Zfpm2 locus initiates de novo recruitment of PRC2. We then pinpointed a CpG island within this locus as both necessary and sufficient for PRC2 recruitment. Based on this causal demonstration and prior genomic analyses, we hypothesized that large GC-rich elements depleted of activating transcription factor motifs mediate PRC2 recruitment in mammals. We validated this model in two ways. First, we showed that a constitutively active CpG island is able to recruit PRC2 after excision of a cluster of activating motifs. Second, we showed that two 1 kb sequence intervals from the Escherichia coli genome with GC-contents comparable to a mammalian CpG island are both capable of recruiting PRC2 when integrated into the ES cell genome. Our findings demonstrate a causal role for GC-rich sequences in PRC2 recruitment and implicate a specific subset of CpG islands depleted of activating motifs as instrumental for the initial localization of this key regulator in mammalian genomes. Key developmental genes are precisely turned on or off during development, thus creating a complex, multi-tissue embryo. The mechanism that keeps genes off, or repressed, is crucial to proper development. In embryonic stem cells, Polycomb repressive complex 2 (PRC2) is recruited to the promoters of these developmental genes and helps to maintain repression in the appropriate tissues through development. How PRC2 is initially recruited to these genes in the early embryo remains elusive. Here we experimentally demonstrate that stretches of GC-rich DNA, termed CpG islands, can initiate recruitment of PRC2 in embryonic stem cells when they are transcriptionally-inactive. Surprisingly, we find that GC-rich DNA from bacterial genomes can also initiate recruitment of PRC2 in embryonic stem cells. This supports a model where inactive GC-rich DNA can itself suffice to recruit PRC2 even in the absence of more complex DNA sequence motifs.
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