Su Ruey-Chyi, Brown Karen E, Saaber Sanam, Fisher Amanda G, Merkenschlager Matthias, Smale Stephen T
Howard Hughes Medical Institute and Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, California 90095-1662, USA.
Nat Genet. 2004 May;36(5):502-6. doi: 10.1038/ng1351. Epub 2004 Apr 18.
Considerable knowledge has been gained from temporal analyses of molecular events culminating in gene activation, but technical hurdles have hindered comparable studies of gene silencing. Here we describe the temporal assembly of silent chromatin at the mouse terminal transferase gene (Dntt), which is silenced and repositioned to pericentromeric heterochromatin during thymocyte maturation. Silencing was nucleated at the Dntt promoter by the ordered deacetylation of histone H3 at Lys9 (H3-Lys9), loss of methylation at H3-Lys4 and acquisition of methylation at H3-Lys9, followed by bidirectional spreading of each event. Deacetylation at H3-Lys9 coincided with pericentromeric repositioning, and neither of these early events required de novo protein synthesis. CpG methylation increased primarily in mature T cells that had left the thymus. A transformed thymocyte line supported reversible inactivation of Dntt without repositioning. In these cells, histone modification changes were nucleated at the promoter but did not spread. These results provide a foundation for elucidating the mechanisms of silent chromatin assembly during development.
通过对最终导致基因激活的分子事件进行时间分析，我们已经获得了相当多的知识，但技术障碍阻碍了对基因沉默进行类似的研究。在此，我们描述了小鼠末端转移酶基因（Dntt）沉默染色质的时间组装过程，该基因在胸腺细胞成熟过程中被沉默并重新定位到着丝粒周围的异染色质。沉默在Dntt启动子处起始，通过组蛋白H3赖氨酸9（H3-Lys9）的有序去乙酰化、H3-Lys4甲基化的丧失以及H3-Lys9甲基化的获得，随后每个事件双向扩展。H3-Lys9的去乙酰化与着丝粒周围重新定位同时发生，而且这些早期事件均不需要从头合成蛋白质。CpG甲基化主要在离开胸腺的成熟T细胞中增加。一个转化的胸腺细胞系支持Dntt的可逆失活而无需重新定位。在这些细胞中，组蛋白修饰变化在启动子处起始但不扩展。这些结果为阐明发育过程中沉默染色质组装的机制提供了基础。
