2013年6月6日,，北京生命科學研究所朱冰實驗室在《PLOS Genetics》雜志上在線發(fā)表題為“H3.3-H4 tetramer splitting events feature cell-type specific enhancers”的文章,。這篇文章首次報道了組蛋白H3.3-H4四聚體拆分事件的全基因組分布情況，并發(fā)現(xiàn)H3.3-H4四聚體拆分事件富集于增強子,。
組蛋白修飾是表觀遺傳信息的重要組成部分,，其承載的表觀遺傳信息在細胞有絲分裂過程中的繼承機制是表觀遺傳領域的重要問題和朱冰實驗室的主要研究方向。
組蛋白H3-H4四聚體是核小體的核心組成部分,，該四聚體在DNA復制中的分配模式是組蛋白修飾繼承性研究的基本問題,。朱冰實驗室徐墨等人結合定量質譜技術與傳統(tǒng)生物化學手段，在數(shù)年前澄清了四聚體分配方式這一長期爭論的問題（Xu et al.,， Science. 2010）,。該工作發(fā)現(xiàn)常規(guī)組蛋白四聚體通過全保留方式進行分配,，并意外地發(fā)現(xiàn)一部分含組蛋白變體H3.3的H3-H4四聚體會發(fā)生拆分事件，產(chǎn)生含一分子“新”H3.3和一分子“舊”H3.3的混合型核小體,。H3.3-H4四聚體的拆分事件是一個全新的發(fā)現(xiàn),，其機理和功能意義均未知。
在本研究中,，朱冰實驗室建立了一個可經(jīng)雙重誘導表達兩種帶不同標簽組蛋白H3.3的HeLa穩(wěn)定細胞系,，通過控制兩種外源H3.3的表達時序并利用雙輪親和純化獲得含一分子“新”H3.3和一分子“舊”H3.3的混合型單核小體，也即發(fā)生了拆分事件的H3.3核小體,。然后通過DNA高通量測序,，首次測定了組蛋白H3.3-H4四聚體拆分事件的全基因組分布譜，并發(fā)現(xiàn)H3.3-H4四聚體拆分事件顯著富集于增強子,。表明該事件可能參與增強子的功能調節(jié),。
我所與中國農業(yè)大學聯(lián)合培養(yǎng)的黃暢博士以及朱冰實驗室張珠強博士為本論文的共同第一作者，其他作者還有徐墨博士,，李穎峰,，李珍，馬妍婷和蔡濤博士,。朱冰博士為本文通訊作者,。該研究由科技部、北京市科委和HHMI國際青年科學家項目資助,，在北京生命科學研究所完成,。（生物谷Bioon.com）
doi:10.1371/journal.pgen.1003558
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H3.3-H4 Tetramer Splitting Events Feature Cell-Type Specific Enhancers
Huang C, Zhang Z, Xu M, Li Y, Li Z, et al
Previously, we reported that little canonical (H3.1–H4)2 tetramers split to form “hybrid” tetramers consisted of old and new H3.1–H4 dimers, but approximately 10% of (H3.3–H4)2 tetramers split during each cell cycle. In this report, we mapped the H3.3 nucleosome occupancy, the H3.3 nucleosome turnover rate and H3.3 nucleosome splitting events at the genome-wide level. Interestingly, H3.3 nucleosome turnover rate at the transcription starting sites (TSS) of genes with different expression levels display a bimodal distribution rather than a linear correlation towards the transcriptional activity, suggesting genes are either active with high H3.3 nucleosome turnover or inactive with low H3.3 nucleosome turnover. H3.3 nucleosome splitting events are enriched at active genes, which are in fact better markers for active transcription than H3.3 nucleosome occupancy itself. Although both H3.3 nucleosome turnover and splitting events are enriched at active genes, these events only display a moderate positive correlation, suggesting H3.3 nucleosome splitting events are not the mere consequence of H3.3 nucleosome turnover. Surprisingly, H3.3 nucleosomes with high splitting index are remarkably enriched at enhancers in a cell-type specific manner. We propose that the H3.3 nucleosomes at enhancers may be split by an active mechanism to regulate cell-type specific transcription.
