Ichida M, Endo H, Ikeda U, Matsuda C, Ueno E, Shimada K, Kagawa Y
Department of Biochemistry, Jichi Medical School, Minamikawachi-machi, Kawachi-gun, Tochigi 329-04, Japan.
J Biol Chem. 1998 Apr 3;273(14):8492-501. doi: 10.1074/jbc.273.14.8492.
Muscle-specific alternative RNA splicing is an essential step during myogenesis. In this paper, we report that a muscle-specific transcription factor, MyoD, plays a central role in the induction of muscle-specific alternative splicing during myogenesis. Recently, we reported that muscle and nonmuscle isoforms of the mitochondrial ATP synthase gamma-subunit (F1gamma) were generated by alternative splicing and that acidic stimulation promoted this muscle-specific alternative splicing (Endo, H., Matsuda, C., and Kagawa, Y. (1994) J. Biol. Chem. 269, 12488-12493). In this report, mouse myoblasts are shown to express the muscle-specific isoform of F1gamma after induction with low-serum medium (differentiation medium) or acidic medium, although myotube formation was not detected after acidic induction. RNA blot analysis revealed that the expression levels of both MEF2 and myogenin were increased by low-serum induction, but not by acidic induction. High expression of MyoD mRNA was observed after both types of induction. Overexpression of exogenous MyoD in fibroblasts showed that MyoD was necessary for muscle-specific alternative splicing in both types of induction. Exogenous Id, a negative regulator of MyoD, blocked muscle-specific alternative splicing of F1gamma pre-mRNA by both types of induction. In addition, MyoD induced several muscle-specific alternative splicings, including structural protein pre-mRNAs such as beta-tropomyosin and neural-cell adhesion molecule and transcriptional protein pre-mRNAs such as MEF2A and MEF2D. Our analysis of the two induction systems shows a common MyoD-dependent mechanism of muscle-specific alternative splicing in several genes, independent of MEF2 and myogenin.
肌肉特异性可变RNA剪接是肌生成过程中的一个关键步骤。在本文中，我们报道了一种肌肉特异性转录因子MyoD在肌生成过程中诱导肌肉特异性可变剪接方面发挥着核心作用。最近，我们报道线粒体ATP合酶γ亚基（F1γ）的肌肉型和非肌肉型异构体是通过可变剪接产生的，并且酸性刺激促进了这种肌肉特异性可变剪接（远藤浩、松田聪、河合洋（1994年）《生物化学杂志》第269卷，第12488 - 12493页）。在本报告中，尽管酸性诱导后未检测到肌管形成，但小鼠成肌细胞在用低血清培养基（分化培养基）或酸性培养基诱导后显示出表达F1γ的肌肉特异性异构体。RNA印迹分析表明，低血清诱导可增加MEF2和肌细胞生成素的表达水平，但酸性诱导则不然。两种诱导后均观察到MyoD mRNA的高表达。在成纤维细胞中外源MyoD的过表达表明，MyoD对于两种诱导类型中的肌肉特异性可变剪接都是必需的。MyoD的负调节因子外源Id通过两种诱导类型均阻断了F1γ前体mRNA的肌肉特异性可变剪接。此外，MyoD诱导了几种肌肉特异性可变剪接，包括结构蛋白前体mRNA，如β - 原肌球蛋白和神经细胞黏附分子，以及转录蛋白前体mRNA，如MEF2A和MEF2D。我们对这两种诱导系统的分析表明，在几个基因中存在一种共同的依赖MyoD的肌肉特异性可变剪接机制，该机制独立于MEF2和肌细胞生成素。
