Interdisciplinary Center for Aquaculture Research (INCAR), Víctor Lamas 1290, PO Box 160-C, Concepción, Chile.
Epigenetics Chromatin. 2013 Jul 17;6(1):22. doi: 10.1186/1756-8935-6-22.
The specific deposition of histone variants into chromatin is an important epigenetic mechanism that contributes to gene regulation through chromatin architectural changes. The histone variant H2A.Z is essential in higher eukaryotes, and its incorporation within chromatin is a relevant process for gene expression and genome stability. However, the dual positive and negative roles of H2A.Z in gene regulation still remain unclear. We previously reported that acclimatization in common carp fish (Cyprinus carpio) involves cyclical seasonal gene reprogramming as an adaptation response to its natural environment, when rRNA synthesis and processing are profoundly affected. Epigenetic mechanisms primarily contribute to the transcriptional modulation of ribosomal genes concomitant with the acclimatization process, thus significantly regulating this process. The aim of this study was to describe the presence of several H2A.Z subtypes in carp, and assess the role of H2A.Z on the ribosomal cistron in summer- and winter-acclimatized carp.
This paper reports for the first time about the transcriptional expression of four different H2A.Z subtypes belonging to the same organism. Remarkably, a novel H2A.Z.7 was found, which corresponds to a tissue-specific histone subtype that contains seven amino acid residues longer than the canonical H2A.Z. Moreover, H2A.Z enrichment through the ribosomal cistron was significantly higher during summer, when rRNA transcription and processing are highly active, than it was in winter. Similar patterns of H2A.Z enrichment are found in two seasonally active promoters for genes transcribed by RNA polymerase II, the L41 and Δ9-desaturase genes. Interestingly, ubiquitylated-H2A.Z (H2A.Zub) was strongly enriched on regulatory regions of the ribosomal cistron in summer-acclimatized carp. Additionally, H2A.Z was present in both heterochromatin and euchromatin states on ribosomal cistron and RNA polymerase II promoters.
Our study revealed seasonally-dependent H2A.Z enrichment for active ribosomal cistron and RNA polymerase II promoters during the carp environmental adaptation. Moreover, seasonal H2A.Zub enrichment appears as a specific mechanism contributing to the regulation of chromatin architecture under natural conditions. The existence of several H2A.Z subtypes in carp suggests that the epigenetic regulation in this species constitutes a complex and finely tuned mechanism developed to cope with seasonal environmental changes that occur in its habitat.
组蛋白变体特异性沉积到染色质中是一种重要的表观遗传机制，通过染色质结构的改变来促进基因调控。组蛋白变体 H2A.Z 在高等真核生物中是必不可少的，其在染色质中的掺入是基因表达和基因组稳定性的相关过程。然而，H2A.Z 在基因调控中的双重正、负作用仍然不清楚。我们之前的研究报告表明，鲤鱼的驯化涉及周期性的季节性基因重编程，作为对其自然环境的适应反应，当 rRNA 合成和加工受到深刻影响时。表观遗传机制主要有助于核糖体基因的转录调节，伴随着驯化过程，从而显著调节这个过程。本研究的目的是描述鲤鱼中存在几种 H2A.Z 亚型，并评估 H2A.Z 在夏季和冬季驯化鲤鱼的核糖体基因上的作用。
本文首次报道了同一生物体中四种不同 H2A.Z 亚型的转录表达。值得注意的是，发现了一种新的 H2A.Z.7，它对应于一种组织特异性组蛋白亚型，比典型的 H2A.Z 长七个氨基酸残基。此外，在夏季，当 rRNA 转录和加工高度活跃时，核糖体基因上 H2A.Z 的富集程度明显高于冬季。在两个由 RNA 聚合酶 II 转录的季节性活跃启动子（L41 和 Δ9-去饱和酶基因）上也发现了类似的 H2A.Z 富集模式。有趣的是，在夏季驯化的鲤鱼中，泛素化的 H2A.Z（H2A.Zub）在核糖体基因的调控区域强烈富集。此外，H2A.Z 存在于核糖体基因和 RNA 聚合酶 II 启动子的异染色质和常染色质状态。
我们的研究表明，在鲤鱼的环境适应过程中，核糖体基因和 RNA 聚合酶 II 启动子的 H2A.Z 富集具有季节性依赖性。此外，季节性 H2A.Zub 富集似乎是一种特定的机制，有助于在自然条件下调节染色质结构。鲤鱼中存在几种 H2A.Z 亚型表明，该物种的表观遗传调控构成了一种复杂而精细的机制，以应对其栖息地中发生的季节性环境变化。
