Post‐translational modifications of histone tails play a crucial role in gene regulation. Here, we performed chromatin profiling by quantitative targeted mass spectrometry to assess all possible modifications of the core histones. We identified a bivalent combination, a dually marked H3K9me3/H3K14ac modification in the liver, that is significantly decreased in old hepatocytes. Subsequent sequential ChIP‐Seq identified dually marked single nucleosome regions, with reduced number of sites and decreased signal in old livers, confirming mass spectrometry results. We detected H3K9me3 and H3K14ac bulk ChIP‐Seq signal in reChIP nucleosome regions, suggesting a correlation between H3K9me3/H3K14ac bulk bivalent genomic regions and dually marked single nucleosomes. Histone H3K9 deacetylase Hdac3, as well as H3K9 methyltransferase Setdb1, found in complex Kap1, occupied both bulk and single nucleosome bivalent regions in both young and old livers, correlating to presence of H3K9me3. Expression of genes associated with bivalent regions in young liver, including those regulating cholesterol secretion and triglyceride synthesis, is upregulated in old liver once the bivalency is lost. Hence, H3K9me3/H3K14ac dually marked regions define a poised inactive state that is resolved with loss of one or both of the chromatin marks, which subsequently leads to change in gene expression.

中文翻译：

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Hdac3、Setdb1 和 Kap1 标记年轻和老年肝脏中的 H3K9me3/H3K14ac 二价区域。

组蛋白尾部的翻译后修饰在基因调控中起着至关重要的作用。在这里，我们通过定量靶向质谱法进行染色质分析，以评估核心组蛋白的所有可能修饰。我们确定了一种二价组合，即肝脏中双重标记的 H3K9me3/H3K14ac 修饰，在旧肝细胞中显着减少。随后的连续 ChIP-Seq 鉴定了双重标记的单个核小体区域，旧肝脏中的位点数量减少，信号降低，证实了质谱结果。我们在 reChIP 核小体区域检测到 H3K9me3 和 H3K14ac 块状 ChIP-Seq 信号，表明 H3K9me3/H3K14ac 块状二价基因组区域与双重标记的单个核小体之间存在相关性。组蛋白 H3K9 去乙酰化酶 Hdac3，以及 H3K9 甲基转移酶 Setdb1，在复合体 Kap1 中发现，在年轻和年老肝脏中占据大量和单个核小体二价区域，与 H3K9me3 的存在相关。一旦双价丧失，与年轻肝脏中二价区域相关的基因的表达，包括那些调节胆固醇分泌和甘油三酯合成的基因，在老年肝脏中就会上调。因此，H3K9me3/H3K14ac 双重标记区域定义了一种稳定的不活动状态，该状态随着染色质标记中的一个或两个丢失而解决，这随后导致基因表达的变化。一旦失去二价性，在旧肝脏中就会上调。因此，H3K9me3/H3K14ac 双重标记区域定义了一种稳定的不活动状态，该状态随着染色质标记中的一个或两个丢失而解决，这随后导致基因表达的变化。一旦失去二价性，在旧肝脏中就会上调。因此，H3K9me3/H3K14ac 双重标记区域定义了一种稳定的不活动状态，该状态随着染色质标记中的一个或两个丢失而解决，这随后导致基因表达的变化。