Poised transcription factories prime silent uPA gene prior to activation.
Poised transcription factories prime silent uPA gene prior to activation.
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DOI：
10.1371/journal.pbio.1000270
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发表时间：
2010-01
期刊：
影响因子：
9.8
通讯作者：
Crippa MP
中科院分区：
文献类型：
--
作者：
Ferrai C;Xie SQ;Luraghi P;Munari D;Ramirez F;Branco MR;Pombo A;Crippa MP
当基因位于其染色体区域内部时，平衡基因与转录工厂的关联可能有助于响应刺激而快速转录激活和沉默。基因在间期核中的位置及其与功能标志的关联与表达的活跃和/或沉默状态相关。基因激活可以诱导染色体区域 (CT) 的染色质环化，并且被认为需要与转录工厂从头关联。我们确定了两种类型的工厂：“平衡转录工厂”，包含在 Ser5 残基上磷酸化的 RNA 聚合酶 II，但在 Ser2 残基上不磷酸化，这与与两个残基磷酸化相关的“活性工厂”不同。使用尿激酶型纤溶酶原激活剂（uPA）基因作为模型系统，我们发现该诱导基因主要与激活前的平衡（S5p+S2p−）工厂相关，并定位于 CT 内部。诱导后不久，发现 uPA 基因座与活性 (S5p+S2p+) 工厂相关，并从其 CT 中循环出来。然而，在激活之前和之后，与平衡或活跃的转录工厂相关的基因水平与相对于其 CT 的基因座定位无关。 RNA-FISH分析表明，激活后，uPA基因在每个CT位置以相同的频率转录。出乎意料的是，在激活之前，CT 内部的 uPA 位点很少具有转录活性，而 CT 外部发现的少量 uPA 位点的转录频率与诱导后一样频繁。诱导基因在激活前与平衡的转录工厂的关联可能有助于响应外部刺激而快速而有力地诱导基因表达，而基因定位在 CT 内部可能对于强化诱导前的沉默机制很重要。细胞核内基因组的空间组织对于调节基因表达和对外部刺激的反应非常重要。改变空间组织的例子是在基因表达诱导过程中染色体区域外的基因重新定位，以及在转录工厂（富含活性 RNA 聚合酶的离散焦点）处聚集活性基因。最近，RNA 聚合酶 II 的全基因组图谱已确定其存在于许多准备激活的基因中，这提高了这些基因可能与准备激活的转录工厂相关的可能性。使用诱导型哺乳动物基因、尿激酶型纤溶酶原激活剂（uPA）以及该基因准备表达的系统，我们表明uPA在激活之前与准备好的转录工厂相关联。基因激活诱导两个独立的事件：向其染色体区域外部重新定位以及与活性转录工厂关联。令人惊讶的是，在激活之前位于染色体区域内部的基因不太可能被主动转录，这表明位于区域内部的基因在基因沉默中发挥着作用。
The association of poised genes with transcription factories may contribute to rapid transcriptional activation in response to stimuli and to silencing when genes are located at the interior of their chromosome territories. The position of genes in the interphase nucleus and their association with functional landmarks correlate with active and/or silent states of expression. Gene activation can induce chromatin looping from chromosome territories (CTs) and is thought to require de novo association with transcription factories. We identify two types of factory: “poised transcription factories,” containing RNA polymerase II phosphorylated on Ser5, but not Ser2, residues, which differ from “active factories” associated with phosphorylation on both residues. Using the urokinase-type plasminogen activator (uPA) gene as a model system, we find that this inducible gene is predominantly associated with poised (S5p+S2p−) factories prior to activation and localized at the CT interior. Shortly after induction, the uPA locus is found associated with active (S5p+S2p+) factories and loops out from its CT. However, the levels of gene association with poised or active transcription factories, before and after activation, are independent of locus positioning relative to its CT. RNA-FISH analyses show that, after activation, the uPA gene is transcribed with the same frequency at each CT position. Unexpectedly, prior to activation, the uPA loci internal to the CT are seldom transcriptionally active, while the smaller number of uPA loci found outside their CT are transcribed as frequently as after induction. The association of inducible genes with poised transcription factories prior to activation is likely to contribute to the rapid and robust induction of gene expression in response to external stimuli, whereas gene positioning at the CT interior may be important to reinforce silencing mechanisms prior to induction. The spatial organization of the genome inside the cell nucleus is important in regulating gene expression and in the response to external stimuli. Examples of changing spatial organization are the repositioning of genes outside chromosome territories during the induction of gene expression, and the gathering of active genes at transcription factories (discrete foci enriched in active RNA polymerase). Recent genome-wide mapping of RNA polymerase II has identified its presence at many genes poised for activation, raising the possibility that such genes might associate with poised transcription factories. Using an inducible mammalian gene, urokinase-type plasminogen activator (uPA), and a system in which this gene is poised for expression, we show that uPA associates with poised transcription factories prior to activation. Gene activation induces two independent events: repositioning towards the exterior of its chromosome territory and association with active transcription factories. Surprisingly, genes inside the interior of the chromosome territory prior to activation are less likely to be actively transcribed, suggesting that positioning at the territory interior has a role in gene silencing.
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影响因子：
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