The Histone Variant H3.3 Is Enriched at Drosophila Amplicon Origins but Does Not Mark Them for Activation.
The Histone Variant H3.3 Is Enriched at Drosophila Amplicon Origins but Does Not Mark Them for Activation.
复制标题
组蛋白变体H3.3富含果蝇扩增子的起源，但没有标记它们以进行激活。
DOI：
10.1534/g3.116.028068
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发表时间：
2016-06-01
期刊：
影响因子：
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通讯作者：
Calvi BR
中科院分区：
文献类型：
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作者：
Paranjape NP;Calvi BR
真核DNA复制从多个起源开始。起始识别复合物（ORC）结合起始DNA并支撑复制前复合物（pre-RC）的组装，其随后被激活以启动DNA复制。在多细胞真核生物中，起源不共享严格的DNA共有序列，并且它们的活性在发育期间与染色质状态一致地变化，但机制不明确。先前在果蝇和其他生物体中的全基因组分析揭示了ORC结合位点与组蛋白变体H3.3之间的相关性。这种相关性表明，H3.3可能指定起源地点，但这一想法尚未得到验证。为了解决这个问题，我们研究了H3.3的富集和功能的起源负责发育基因扩增的体细胞卵泡细胞的果蝇卵巢。我们发现H3.3在这些扩增子起点处是丰富的。当复制起始被阻断时，H3.3水平保持高水平，表明在前RC活化之前，H3.3在起始处是丰富的。H3.3也在卵子发生早期的起源处富集，这提高了H3.3标记位点用于以后扩增的可能性。然而，果蝇中两个H3.3基因的果蝇无效突变体在发育基因扩增或基因组复制方面没有明显缺陷，这表明H3.3对于起源时前RC的组装或激活并不是必需的。相反，我们的结果意味着H3.3和ORC位点之间的相关性反映了对起源功能重要的其他染色质属性。
Eukaryotic DNA replication begins from multiple origins. The origin recognition complex (ORC) binds origin DNA and scaffolds assembly of a prereplicative complex (pre-RC), which is subsequently activated to initiate DNA replication. In multicellular eukaryotes, origins do not share a strict DNA consensus sequence, and their activity changes in concert with chromatin status during development, but mechanisms are ill-defined. Previous genome-wide analyses in Drosophila and other organisms have revealed a correlation between ORC binding sites and the histone variant H3.3. This correlation suggests that H3.3 may designate origin sites, but this idea has remained untested. To address this question, we examined the enrichment and function of H3.3 at the origins responsible for developmental gene amplification in the somatic follicle cells of the Drosophila ovary. We found that H3.3 is abundant at these amplicon origins. H3.3 levels remained high when replication initiation was blocked, indicating that H3.3 is abundant at the origins before activation of the pre-RC. H3.3 was also enriched at the origins during early oogenesis, raising the possibility that H3.3 bookmarks sites for later amplification. However, flies null mutant for both of the H3.3 genes in Drosophila did not have overt defects in developmental gene amplification or genomic replication, suggesting that H3.3 is not essential for the assembly or activation of the pre-RC at origins. Instead, our results imply that the correlation between H3.3 and ORC sites reflects other chromatin attributes that are important for origin function.