Condensin II subunit dCAP-D3 restricts retrotransposon mobilization in Drosophila somatic cells.
Condensin II subunit dCAP-D3 restricts retrotransposon mobilization in Drosophila somatic cells.
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Condensin II亚基DCAP-D3限制了果蝇体细胞中的逆转录子动员。
DOI：
10.1371/journal.pgen.1003879
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发表时间：
2013-10
期刊：
影响因子：
4.5
通讯作者：
Longworth MS
中科院分区：
文献类型：
--
作者：
Schuster AT;Sarvepalli K;Murphy EA;Longworth MS
逆转录转座子序列位于几乎所有已测序的真核生物的基因组中。由于这些元件的动员可能对生物体基因组的转录调节和稳定性产生不利影响，因此大多数生物体已经进化出抑制其运动的机制。在这里，我们发现了果蝇凝缩蛋白 II 亚基 dCAP-D3 在阻止位于体细胞常染色质中的逆转录转座子的动员中的新作用。 dCAP-D3 调节含有或接近反转录转座子序列的常染色质基因簇的转录。 ChIP 实验表明 dCAP-D3 与这些位点结合，对于维持逆转录转座子边界内受抑制的染色质结构和抑制逆转录转座子转录非常重要。我们发现，dCAP-D3 可以防止逆转录转座子序列内双链 DNA 断裂的积累，并且 dCAP-D3 水平的降低会导致某些 dCAP-D3 调节的基因簇中逆转录转座子序列的精确丢失，以及基因组其他位置的序列获得。同源染色体在果蝇体细胞中表现出高水平的配对，并且我们的 FISH 分析表明，含有逆转录转座子的常染色质位点实际上比不含逆转录转座子序列的常染色质区域配对更少。 dCAP-D3 表达减少会增加组织培养细胞中含有同源逆转录转座子的基因座的配对。我们认为，dCAP-D3 缺陷对双链断裂水平、染色质结构、转录和含反转录转座子基因座配对的综合影响可能导致 1) dCAP-D3 缺陷细胞中反转录转座子侧翼重复序列之间的同源重组水平更高，2) 反转录转座增加。这些发现确定了 dCAP-D3/Condensin II 的抗配对活性的新作用，并揭示了 dCAP-D3/Condensin II 影响局部染色质结构以帮助维持基因组稳定性的新方式。凝缩蛋白是保守的复合物，以其在早期有丝分裂过程中促进染色体有效凝结的作用而闻名。此前，我们已经证明果蝇凝缩蛋白 II 亚基 dCAP-D3 在发育后期也具有调节体细胞转录的功能。发现大量 dCAP-D3 调节基因在簇中彼此非常接近。在这项研究中，我们报告了一些受最强烈调控的 dCAP-D3 基因簇位于逆转录转座子附近。出乎意料的是，我们发现 dCAP-D3 表达减少导致这些位点逆转录转座子序列的精确丢失。此外，dCAP-D3 敲低会导致逆转录转座子序列内双链断裂水平增加、该区域染色质开放、逆转录转座子转录增加以及该位点同源配对的显着增加。综上所述，这些结果表明 dCAP-D3/Condensin II 的功能是防止同源染色体之间的逆转录转座子重组以及可能的逆转录转座。该报告确定了 Condensin II 的一个新功能，该功能可能有助于其在基因组组织中的作用。
Retrotransposon sequences are positioned throughout the genome of almost every eukaryote that has been sequenced. As mobilization of these elements can have detrimental effects on the transcriptional regulation and stability of an organism's genome, most organisms have evolved mechanisms to repress their movement. Here, we identify a novel role for the Drosophila melanogaster Condensin II subunit, dCAP-D3 in preventing the mobilization of retrotransposons located in somatic cell euchromatin. dCAP-D3 regulates transcription of euchromatic gene clusters which contain or are proximal to retrotransposon sequence. ChIP experiments demonstrate that dCAP-D3 binds to these loci and is important for maintaining a repressed chromatin structure within the boundaries of the retrotransposon and for repressing retrotransposon transcription. We show that dCAP-D3 prevents accumulation of double stranded DNA breaks within retrotransposon sequence, and decreased dCAP-D3 levels leads to a precise loss of retrotransposon sequence at some dCAP-D3 regulated gene clusters and a gain of sequence elsewhere in the genome. Homologous chromosomes exhibit high levels of pairing in Drosophila somatic cells, and our FISH analyses demonstrate that retrotransposon-containing euchromatic loci are regions which are actually less paired than euchromatic regions devoid of retrotransposon sequences. Decreased dCAP-D3 expression increases pairing of homologous retrotransposon-containing loci in tissue culture cells. We propose that the combined effects of dCAP-D3 deficiency on double strand break levels, chromatin structure, transcription and pairing at retrotransposon-containing loci may lead to 1) higher levels of homologous recombination between repeats flanking retrotransposons in dCAP-D3 deficient cells and 2) increased retrotransposition. These findings identify a novel role for the anti-pairing activities of dCAP-D3/Condensin II and uncover a new way in which dCAP-D3/Condensin II influences local chromatin structure to help maintain genome stability. Condensins are conserved complexes that are well known for their roles in promoting the efficient condensation of chromosomes during early mitosis. Previously, we have shown that the Drosophila Condensin II subunit, dCAP-D3, also functions to regulate transcription in somatic cells during the later stages of development. A significant number of dCAP-D3 regulated genes were found to be positioned very close to one another in clusters. In this study, we report that some of the most strongly regulated dCAP-D3 gene clusters are positioned near retrotransposons. Unexpectedly, we find that decreased dCAP-D3 expression results in a precise loss of retrotransposon sequence at these loci. Additionally, dCAP-D3 knockdown causes increased levels of double strand breaks within retrotransposon sequence, an opening of the chromatin in the region, increased retrotransposon transcription and a very significant increase in homologous pairing at the locus. Taken together, these results suggest that dCAP-D3/Condensin II functions to prevent recombination of retrotransposons between homologous chromosomes and possibly retrotransposition as well. This report identifies a novel function for Condensin II that may contribute to its role in genome organization.
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