Tavner F, Frampton J, Watson R J
Department of Virology, Faculty of Medicine, Imperial College London, London, UK.
Oncogene. 2007 Apr 26;26(19):2727-35. doi: 10.1038/sj.onc.1210087. Epub 2006 Oct 30.
Previous studies have shown that the cell cycle-regulated B-myb promoter contains a conserved E2F binding site that is critical for repressing transcription in quiescent cells. To investigate its significance for permanent promoter silencing, we have inactivated this binding site in the mouse genome. Mice homozygous for the mutant B-mybmE2F allele were fully viable, however, B-myb transcription was derepressed during quiescence in mouse embryo fibroblasts (MEFs) derived from mutant animals. Moreover, it was found that mutation of the E2F site resulted in abnormal maintenance of B-myb expression in senescent MEFs and in differentiated brain tissue. These findings therefore reveal a direct and primary role for repressive E2F complexes in silencing gene expression in post-mitotic cells. Analysis of histone modifications at the promoter showed that histone H3 lysine 9 was constitutively acetylated throughout the cell cycle in homozygous mutant MEFs. This mouse system is the first description of an E2F site mutation in situ and will facilitate the study of E2F function in vivo.
先前的研究表明，细胞周期调控的B-myb启动子含有一个保守的E2F结合位点，该位点对于静止细胞中转录的抑制至关重要。为了研究其对启动子永久沉默的意义，我们在小鼠基因组中使该结合位点失活。纯合突变B-mybmE2F等位基因的小鼠完全存活，然而，在源自突变动物的小鼠胚胎成纤维细胞（MEF）静止期，B-myb转录被解除抑制。此外，发现E2F位点的突变导致衰老MEF和分化脑组织中B-myb表达的异常维持。因此，这些发现揭示了抑制性E2F复合物在有丝分裂后细胞中基因表达沉默中的直接和主要作用。对启动子处组蛋白修饰的分析表明，在纯合突变MEF的整个细胞周期中，组蛋白H3赖氨酸9持续乙酰化。该小鼠系统是对E2F位点原位突变的首次描述，将有助于体内E2F功能的研究。
