Department of Biochemistry and Molecular Biology, Peking University Health Science Center, Beijing 100191, People's Republic of China.
Mol Cells. 2012 Aug;34(2):133-42. doi: 10.1007/s10059-012-2286-1. Epub 2012 Jul 18.
MyoD and myogenin (Myog) recognize sets of distinct but overlapping target genes and play different roles in skeletal muscle differentiation. MyoD is sufficient for near-full expression of early targets, while Myog can only partially enhance expression of MyoD-initiated late muscle genes. However, the way in which Myog enhances the expression of MyoD-initiated late muscle genes remains unclear. Here, we examine the effects of Myog on chromatin remodeling at late muscle gene promoters and their activation within chromatin environment. Chromatin immunoprecipitation (ChIP) assay showed that Myog selectively bound to the regulatory sequences of late muscle genes. Overexpression of Myog was found to overcome sodium butyrateinhibited chromatin at late muscle genes in differentiating C2C12 myoblasts, shifting the transcriptional activation of these genes to an earlier time period. Furthermore, overexpression of Myog led to increased hyperacetylation of core histone H4 in differentiating C2C12 myoblasts but not NIH3T3 fibroblasts, and hyperacetylated H4 was associated directly with the late muscle genes in differentiating C2C12, indicating that Myog can induce chromatin remodeling in the presence of MyoD. In addition, co-immunoprecipitation (CoIP) revealed that Myog was associated with the nuclear protein Brd4 in differentiating C2C12 myoblasts. Together, these results suggest that Myog enhances the expression of MyoD-initiated late muscle genes through MyoD-dependent ability of Myog to induce chromatin remodeling, in which Myog-Brd4 interaction may be involved.
MyoD 和 myogenin（Myog）识别出一系列不同但重叠的靶基因，并在骨骼肌分化中发挥不同的作用。MyoD 足以近乎完全表达早期靶基因，而 Myog 只能部分增强 MyoD 启动的晚期肌肉基因的表达。然而，Myog 增强 MyoD 启动的晚期肌肉基因表达的方式仍不清楚。在这里，我们研究了 Myog 对晚期肌肉基因启动子染色质重塑及其在染色质环境中激活的影响。染色质免疫沉淀（ChIP）实验表明，Myog 选择性地结合到晚期肌肉基因的调控序列上。在分化的 C2C12 成肌细胞中，过表达 Myog 被发现可以克服丁酸钠抑制的晚期肌肉基因的染色质，将这些基因的转录激活提前到更早的时期。此外，过表达 Myog 导致分化的 C2C12 成肌细胞中核心组蛋白 H4 的超乙酰化增加，但在 NIH3T3 成纤维细胞中没有，并且超乙酰化的 H4 与分化的 C2C12 中的晚期肌肉基因直接相关，表明 Myog 可以在有 MyoD 的情况下诱导染色质重塑。此外，共免疫沉淀（CoIP）显示 Myog 与分化的 C2C12 成肌细胞中的核蛋白 Brd4 相关。总之，这些结果表明，Myog 通过 Myog 依赖于 MyoD 的能力增强 MyoD 启动的晚期肌肉基因的表达，其中 Myog-Brd4 相互作用可能参与其中。
