Maintenance of Xist Imprinting Depends on Chromatin Condensation State and Rnf12 Dosage in Mice.
Maintenance of Xist Imprinting Depends on Chromatin Condensation State and Rnf12 Dosage in Mice.
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DOI：
10.1371/journal.pgen.1006375
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发表时间：
2016-10
期刊：
影响因子：
4.5
通讯作者：
Akutsu H
中科院分区：
文献类型：
--
作者：
Fukuda A;Mitani A;Miyashita T;Sado T;Umezawa A;Akutsu H
在雌性哺乳动物中，Xist（X 失活特异性转录物）的激活对于 X 染色体失活的建立至关重要。在小鼠早期胚胎发育过程中，父系 Xist 优先表达，而母系 Xist (Xm-Xist) 被沉默。与常染色体印记基因不同，Xm-Xist 沉默的 Xist 印记在克隆或单性生殖胚胎中被消除，但在受精胚胎中未被消除。然而，人们对 Xm-Xist 印记可变性质背后的分子机制知之甚少。在这里，我们揭示了 Xm-Xist 沉默取决于 Xist/Tsix 基因组区域的染色质浓缩状态和 Rnf12 表达水平。在植入前早期，无论胚胎类型如何，通过 H3K9me3 丢失和组蛋白乙酰化增加导致的染色质去浓缩都会导致 Xm-Xist 去抑制。尽管原核形成过程中父本基因组的存在阻碍了 Xm-Xist 去抑制，但当母体基因组在受精前去浓缩时，Xm-Xist 被强烈去抑制。一旦 Xm-Xist 通过染色质改变去抑制，这种去抑制就会稳定维持并挽救 XmXpΔ 致死率，表明 Xm-Xist 印记的丧失是不可逆的。在植入前后期，Oct4 充当染色质开启子，在 Xm-Xist/Tsix 基因组位点创建转录许可状态。在孤雌胚胎中，Rnf12 过量通过 Xm-Tsix 抑制导致 Xm-Xist 去抑制；生理 Rnf12 水平对于受精胚胎中 Xm-Xist 沉默的维持至关重要。因此，染色质浓缩和 Rnf12 剂量的微调对于通过沉默 Xm-Xist 来维持 Xist 印记至关重要。 X失活特异性转录本（Xist）是雌性哺乳动物中建立X染色体失活所必需的大型非编码RNA。异常的 X 染色体失活严重影响细胞活力。因此，Xist 表达的时空调节是正常发育所必需的。在小鼠中，Xist 表达在早期胚胎发育中留下印记，而母体 Xist 在植入前阶段从不表达，无论 Xist 激活剂母体 Rnf12 是否存在。一般来说，常染色体印记基因的亲本起源特异性表达模式在各种类型的胚胎中得以维持。然而，用于母体 Xist 转录沉默的 Xist 印记在克隆或孤雌生殖胚胎中被消除，但在受精胚胎中却未被消除。在这里，我们剖析了 Xist 印记可变性质背后的分子机制。我们发现，在受精胚胎中，染色质浓缩状态是着床前早期母体 Xist 抑制所必需的，而在着床前后期，多能因子 Oct4 充当染色质开启剂，Xist 沉默的维持取决于 Rnf12 表达剂量。尽管 Oct4 介导的染色质解浓缩也发生在孤雌生殖胚胎中，但 Rnf12 过量会导致母体 Xist 在植入前后期的去抑制。因此，这些发现表明，多能因子和 Xist 激活剂剂量对染色质的调节决定了 Xist 印记状态。
In female mammals, activation of Xist (X-inactive specific transcript) is essential for establishment of X chromosome inactivation. During early embryonic development in mice, paternal Xist is preferentially expressed whereas maternal Xist (Xm-Xist) is silenced. Unlike autosomal imprinted genes, Xist imprinting for Xm-Xist silencing was erased in cloned or parthenogenetic but not fertilized embryos. However, the molecular mechanism underlying the variable nature of Xm-Xist imprinting is poorly understood. Here, we revealed that Xm-Xist silencing depends on chromatin condensation states at the Xist/Tsix genomic region and on Rnf12 expression levels. In early preimplantation, chromatin decondensation via H3K9me3 loss and histone acetylation gain caused Xm-Xist derepression irrespective of embryo type. Although the presence of the paternal genome during pronuclear formation impeded Xm-Xist derepression, Xm-Xist was robustly derepressed when the maternal genome was decondensed before fertilization. Once Xm-Xist was derepressed by chromatin alterations, the derepression was stably maintained and rescued XmXpΔ lethality, indicating that loss of Xm-Xist imprinting was irreversible. In late preimplantation, Oct4 served as a chromatin opener to create transcriptional permissive states at Xm-Xist/Tsix genomic loci. In parthenogenetic embryos, Rnf12 overdose caused Xm-Xist derepression via Xm-Tsix repression; physiological Rnf12 levels were essential for Xm-Xist silencing maintenance in fertilized embryos. Thus, chromatin condensation and fine-tuning of Rnf12 dosage were crucial for Xist imprint maintenance by silencing Xm-Xist. X-inactive specific transcript (Xist) is essential a large non-coding RNA for establishment of X chromosome inactivation in female mammals. The aberrant X chromosome inactivation critically affects cellular viability. Therefore, spatiotemporal regulation of Xist expression is required for proper development. In mice, Xist expression is imprinted in early embryonic development and maternal Xist is never expressed during preimplantation phases irrespective of the presence of Xist activator, maternal Rnf12. Generally, parental origin-specific expression pattern of autosomal imprinted genes is maintained in various types of embryos. However, Xist imprinting for transcriptional silencing of maternal Xist was erased in cloned or parthenogenetic but not fertilized embryos. Here, we dissect the molecular mechanism underlying the variable nature of Xist imprinting. We show that in fertilized embryos, chromatin condensation states are essential maternal Xist repression in early preimplantation phases, whereas at late preimplantation stages, pluripotency factor Oct4 serves as a chromatin opener and the maintenance of Xist silencing depends on Rnf12 expression dosage. Although the Oct4 mediated chromatin decondensation also occurs in parthenogetic embryos, Rnf12 overdose causes maternal Xist derepression at late preimplantation phases. Thus these findings reveal that the chromatin regulation by pluripotency factor and Xist activator dose define Xist imprinting state.
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影响因子：
4.5
作者：
Kobayashi H;Sakurai T;Imai M;Takahashi N;Fukuda A;Yayoi O;Sato S;Nakabayashi K;Hata K;Sotomaru Y;Suzuki Y;Kono T
通讯作者：
Kono T
DOI：
10.1073/pnas.1118403109
发表时间：
2012-02-21
影响因子：
11.1
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通讯作者：
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作者：
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影响因子：
16
作者：
Barakat, Tahsin Stefan;Loos, Friedemann;Gribnau, Joost
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影响因子：
64.5
作者：
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通讯作者：
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