Fujisawa-Sehara A, Nabeshima Y, Komiya T, Uetsuki T, Asakura A, Nabeshima Y
Division of Molecular Genetics, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan.
J Biol Chem. 1992 May 15;267(14):10031-8.
We have isolated cDNAs encoding a chicken homologue of MRF4 (cMRF4) in addition to chicken MyoD (CMD1) and myogenin (c-myogenin) described previously. In an attempt to understand the roles that cMRF4, CMD1, and c-myogenin play in chicken myogenesis, the effects of these factors on muscle-specific cis-elements identified in regulatory regions of myosin alkali light chain (MLC) genes were examined. The promoter analysis of some of MLC genes has revealed two sorts of muscle-specific positive regulatory elements to date, an enhancer located upstream of the adult type LC1 gene and a cis-element, termed an MLC box, conserved among promoters of various MLC genes. The LC1 enhancer was exclusively trans-activated by CMD1. Although c-myogenin also activated transcription driven by the LC1 promoter, it was suggested that c-myogenin requires a cis-element(s) other than the CMD1-responsive enhancer. Chicken MRF4 could not trans-activate any of the constructs containing the LC1 promoter. In contrast, the promoter of the embryonic L23 gene was trans-activated by all of the three factors. From deletion and mutation analysis, the MLC box was shown to be involved in their positive regulation. These results extend previous observations that individual myogenic regulatory factors exhibit different capabilities in transcriptional activation of muscle-specific genes by acting distinctively upon their regulatory elements.
除了先前描述的鸡源MyoD（CMD1）和肌细胞生成素（c-肌细胞生成素）之外，我们还分离出了编码MRF4鸡同源物（cMRF4）的cDNA。为了了解cMRF4、CMD1和c-肌细胞生成素在鸡肌肉生成过程中所起的作用，我们研究了这些因子对在肌球蛋白碱性轻链（MLC）基因调控区域中鉴定出的肌肉特异性顺式元件的影响。到目前为止，对一些MLC基因的启动子分析已经揭示了两种肌肉特异性正调控元件，一种是位于成年型LC1基因上游的增强子，另一种是在各种MLC基因启动子中保守的顺式元件，称为MLC框。LC1增强子仅由CMD1反式激活。虽然c-肌细胞生成素也能激活由LC1启动子驱动的转录，但有人认为c-肌细胞生成素需要除CMD1反应性增强子之外的顺式元件。鸡MRF4不能反式激活任何含有LC1启动子的构建体。相反，胚胎L23基因的启动子被所有这三种因子反式激活。通过缺失和突变分析表明，MLC框参与了它们的正调控。这些结果扩展了先前的观察结果，即单个生肌调节因子通过对其调节元件的独特作用，在肌肉特异性基因的转录激活中表现出不同的能力。
