Xu Eugenia Y, Zawadzki Karl A, Broach James R
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.
Mol Cell. 2006 Jul 21;23(2):219-29. doi: 10.1016/j.molcel.2006.05.035.
Analysis of transcriptional silencing in Saccharomyces has provided valuable insights into heterochromatin formation and function. However, most of these studies revealed only the average behaviors of populations of cells. Here, we examined transcriptional silencing by monitoring individual yeast cells carrying distinguishable fluorescent reporter genes inserted at two different silent loci. These studies showed that two silent loci in a single cell behave independently, demonstrating that heterochromatin formation is locus autonomous. Furthermore, some silencing mutants with an intermediate phenotype, such as sir1, consist of two distinct populations, one repressed and one derepressed, while other mutants, such as those inactivating the SAS-I histone H4 K16 acetylase, consist of cells all with an intermediate level of expression. Finally, both establishment and decay of silencing can be influenced by specific gene activators, with establishment occurring stochastically over several generations. Thus, quantifying silencing in individual cells reveals aspects of silencing not evident from population-wide measurements.
对酿酒酵母中转录沉默的分析为异染色质的形成和功能提供了宝贵的见解。然而，这些研究大多只揭示了细胞群体的平均行为。在这里，我们通过监测携带插入两个不同沉默位点的可区分荧光报告基因的单个酵母细胞来研究转录沉默。这些研究表明，单个细胞中的两个沉默位点独立发挥作用，这表明异染色质的形成是位点自主的。此外，一些具有中间表型的沉默突变体，如sir1，由两个不同的群体组成，一个是受抑制的，一个是去抑制的，而其他突变体，如使SAS-I组蛋白H4 K16乙酰转移酶失活的突变体，则由所有表达水平处于中间水平的细胞组成。最后，沉默的建立和衰退都可能受到特定基因激活剂的影响，建立过程在几代细胞中随机发生。因此，对单个细胞中的沉默进行量化揭示了群体水平测量中不明显的沉默方面。
