Department of Plant Biology, University of Geneva, Geneva, Switzerland.
PLoS Genet. 2010 Oct 28;6(10):e1001175. doi: 10.1371/journal.pgen.1001175.
Constitutive heterochromatin comprising the centromeric and telomeric parts of chromosomes includes DNA marked by high levels of methylation associated with histones modified by repressive marks. These epigenetic modifications silence transcription and ensure stable inheritance of this inert state. Although environmental cues can alter epigenetic marks and lead to modulation of the transcription of genes located in euchromatic parts of the chromosomes, there is no evidence that external stimuli can globally destabilize silencing of constitutive heterochromatin. We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner. This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms. Such induced release of silencing is mostly transient, and rapid restoration of the silent state occurs without the involvement of factors known to be required for silencing initiation. Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved.
组成型异染色质包括染色体的着丝粒和端粒部分，包含被高水平甲基化标记的 DNA，这些 DNA 与被抑制标记修饰的组蛋白有关。这些表观遗传修饰沉默转录，确保这种惰性状态的稳定遗传。尽管环境线索可以改变表观遗传标记，并导致位于染色体常染色质部分的基因转录的调节，但没有证据表明外部刺激可以全局破坏组成型异染色质沉默。我们发现，在经历特定温度条件的拟南芥植物中，与异染色质相关的沉默以全基因组的方式被释放。这种情况的发生没有改变抑制性表观遗传修饰，也不涉及常见的表观遗传机制。这种诱导的沉默释放大多是短暂的，并且沉默状态的快速恢复不涉及已知沉默起始所必需的因素。因此，我们的结果揭示了组成型异染色质中转录抑制的新调控方面，并为鉴定相关的分子机制开辟了可能性。
