Mutskov Vesco, Felsenfeld Gary
Laboratory of Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD, USA.
EMBO J. 2004 Jan 14;23(1):138-49. doi: 10.1038/sj.emboj.7600013. Epub 2003 Dec 11.
Transgenes stably integrated into cells or animals in many cases are silenced rapidly, probably under the influence of surrounding endogenous condensed chromatin. This gene silencing correlates with repressed chromatin structure marked by histone hypoacetylation, loss of methylation at H3 lysine 4, increase of histone H3 lysine 9 methylation as well as CpG DNA methylation at the promoter. However, the order and the timing of these modifications and their impact on transcription inactivation are less well understood. To determine the temporal order of these events, we examined a model system consisting of a transgenic cassette stably integrated in chicken erythroid cells. We found that histone H3 and H4 hypoacetylation and loss of methylation at H3 lysine 4 all occurred during the same window of time as transgene inactivation in both multicopy and low-copy-number lines. These results indicate that these histone modifications were the primary events in gene silencing. We show that the kinetics of silencing exclude histone H3 K9 and promoter DNA methylation as the primary causative events in our transgene system.
在许多情况下，稳定整合到细胞或动物中的转基因会迅速沉默，这可能是受周围内源性浓缩染色质的影响。这种基因沉默与以组蛋白低乙酰化、H3赖氨酸4甲基化缺失、组蛋白H3赖氨酸9甲基化增加以及启动子处的CpG DNA甲基化为特征的抑制性染色质结构相关。然而，这些修饰的顺序和时间及其对转录失活的影响尚不太清楚。为了确定这些事件的时间顺序，我们研究了一个由稳定整合在鸡红细胞中的转基因盒组成的模型系统。我们发现，在多拷贝和低拷贝数品系中，组蛋白H3和H4低乙酰化以及H3赖氨酸4甲基化缺失都与转基因失活发生在同一时间段内。这些结果表明，这些组蛋白修饰是基因沉默的主要事件。我们表明，沉默动力学排除了组蛋白H3 K9和启动子DNA甲基化作为我们转基因系统中的主要致病事件。
