Epigenetic Regulation of Polymerase II Transcription Initiation in Trypanosoma cruzi: Modulation of Nucleosome Abundance, Histone Modification, and Polymerase Occupancy by O-Linked Thymine DNA Glucosylation
Epigenetic Regulation of Polymerase II Transcription Initiation in Trypanosoma cruzi: Modulation of Nucleosome Abundance, Histone Modification, and Polymerase Occupancy by O-Linked Thymine DNA Glucosylation
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DOI：
10.1128/ec.05185-11
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发表时间：
2011-11-01
期刊：
影响因子：
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通讯作者：
Sabatini, Robert
中科院分区：
文献类型：
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作者：
Ekanayake, Dilrukshi;Sabatini, Robert
关于早期分化的真核生物克氏锥虫中转录是如何启动/调节的，人们知之甚少。与真核生物不同的是，T. cruzi 中由 RNA 聚合酶 (Pol) II 转录的基因排列在多顺反子转录单位 (PTU) 中。基于这种基因组织，以前认为锥虫仅依靠转录后过程来调节基因表达。我们最近将一种新的糖基化胸腺嘧啶 DNA 碱基（称为碱基 J）定位到整个锥虫基因组中 PTU 的潜在启动子区域。 JBP1（一种参与合成的胸苷羟化酶）缺失后，碱基 J 的丢失导致 Pol II 转录率和基因表达的全面增加。为了确定碱基 J 调节转录的机制，我们表征了碱基 J 丢失后染色质结构的变化和 Pol II 募集到启动子区域的情况。碱基 J 的丢失与核小体丰度的减少、组蛋白 H3/H4 乙酰化增加以及启动子区域（包括已充分表征的剪接前导 RNA 基因启动子）的 Pol II 占用率增加相一致。这些研究首次提供了通过动质体中的 DNA 修饰和染色质结构对 Pol II 转录起始进行表观遗传调控的直接证据，并提供了通过新型超修饰碱基 J 来调控锥虫基因表达的机制。
Very little is understood regarding how transcription is initiated/regulated in the early-diverging eukaryote Trypanosoma cruzi. Unusually for a eukaryote, genes transcribed by RNA polymerase (Pol) II in T. cruzi are arranged in polycistronic transcription units (PTUs). On the basis of this gene organization, it was previously thought that trypanosomes rely solely on posttranscriptional processes to regulate gene expression. We recently localized a novel glucosylated thymine DNA base, called base J, to potential promoter regions of PTUs throughout the trypanosome genome. Loss of base J, following the deletion of JBP1, a thymidine hydroxylase involved with synthesis, led to a global increase in the Pol II transcription rate and gene expression. In order to determine the mechanism by which base J regulates transcription, we have characterized changes in chromatin structure and Pol II recruitment to promoter regions following the loss of base J. The loss of base J coincides with a decrease in nucleosome abundance, increased histone H3/H4 acetylation, and increased Pol II occupancy at promoter regions, including the well-characterized spliced leader RNA gene promoter. These studies present the first direct evidence for epigenetic regulation of Pol II transcription initiation via DNA modification and chromatin structure in kinetoplastids as well as provide a mechanism for regulation of trypanosome gene expression via the novel hypermodified base J.