Changes in gene expression via chromatin-mediated mechanisms are important for reprogramming and differentiation, but uncontrolled changes can potentially lead to harmful or adaptive phenotypic alteration. Thus, diversification of the genome-wide chromatin state must be strictly limited, but the underlying mechanism of this regulation is largely unknown. In this review, we focused on distribution of heterochromatin, a tight chromatin structure that negatively regulates gene expression. Heterochromatin is characterized by methylation of histone H3 at lysine 9, and its formation and spreading are controlled by H3K9-specific methyltransferases and reversal factors such as histone demethylases. We summarize recent findings and discuss how variability in the heterochromatin distribution is controlled in the unicellular eukaryote fission yeast. In this context, we recently found that the anti-silencing factor Epe1 plays a key role in the formation of the individual-specific heterochromatin distribution. In conclusion, recent studies revealed that there are many potential heterochromatin formation sites in the fission yeast genome, and several proteins contribute to suppression of spreading and genome-wide dispersal of heterochromatin; knowledge from fission yeast studies may provide insights into the mechanisms regulating epigenetic diversification in multicellular eukaryotes.

中文翻译：

---

由异位异染色质的随机形成介导的未编程表观遗传变异。

通过染色质介导的机制的基因表达变化对于重编程和分化很重要，但不受控制的变化可能会导致有害或适应性表型改变。因此，必须严格限制全基因组染色质状态的多样化，但是这种调节的基本机制尚不清楚。在这篇综述中，我们专注于异染色质的分布，异染色质是一种紧密的染色质结构，对基因表达具有负调节作用。异染色质的特征在于组氨酸H3在赖氨酸9处甲基化，其形成和扩散受H3K9特异性甲基转移酶和组蛋白脱甲基酶等逆转因子控制。我们总结了最近的发现，并讨论了如何在单细胞真核生物裂变酵母中控制异染色质分布的变异性。在这种情况下，我们最近发现，抗沉默因子Epe1在个体特异性异染色质分布的形成中起着关键作用。总之，最近的研究表明，裂变酵母基因组中有许多潜在的异染色质形成位点，并且有几种蛋白质有助于抑制异染色质的扩散和全基因组扩散。裂变酵母研究的知识可能会为调节多细胞真核生物中表观遗传多样化的机制提供见解。几种蛋白质有助于抑制异染色质的扩散和全基因组扩散。裂变酵母研究的知识可能会为调节多细胞真核生物中表观遗传多样化的机制提供见解。几种蛋白质有助于抑制异染色质的扩散和全基因组扩散。裂变酵母研究的知识可能会为调节多细胞真核生物表观遗传多样化的机制提供见解。