Allen David L, Weber Jesse N, Sycuro Laura K, Leinwand Leslie A
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA.
J Biol Chem. 2005 Apr 29;280(17):17126-34. doi: 10.1074/jbc.M501207200. Epub 2005 Feb 22.
Adult fast muscle fibers express distinct myosin heavy chains (MyHC) in differing proportions, but the mechanisms underlying their differential expression remain undefined. We used a variety of in vitro and in vivo approaches to explore the contribution of transcriptional regulation to adult fast MyHC expression. Here we show that 800-1000 bp of a sequence upstream of the three mouse adult fast MyHC genes (Ia, IIb, and IId/x) are sufficient to drive muscle-specific and fiber-specific expression in vivo. We show that the upstream promoter region of the gene most abundantly expressed in mouse skeletal muscles, IIb MyHC, retains binding activity and transcriptional activation for three positive transcription factors, the serum response factor, Oct-1, and myocyte enhancer factor-2, whereas the other two genes (IIa and IId/x) have nucleotide substitutions in these sites that reduce binding and transcriptional activation. Finally, we demonstrate that regions upstream of 300 bp modulate the effects of these elements. Together, these data demonstrate that the quantitative differences in MyHC expression in mouse skeletal muscle have evolved at least in part through the elimination of positive-acting transcription factor binding sites.
成年快肌纤维以不同比例表达不同的肌球蛋白重链（MyHC），但其差异表达背后的机制仍不明确。我们采用了多种体外和体内方法来探究转录调控对成年快肌MyHC表达的作用。在此我们表明，三种小鼠成年快肌MyHC基因（Ia、IIb和IId/x）上游800 - 1000 bp的序列足以在体内驱动肌肉特异性和纤维特异性表达。我们发现，在小鼠骨骼肌中表达最丰富的基因IIb MyHC的上游启动子区域，对三种正向转录因子——血清反应因子、Oct - 1和肌细胞增强因子 - 2——保持结合活性和转录激活作用，而另外两个基因（IIa和IId/x）在这些位点存在核苷酸替换，从而降低了结合和转录激活。最后，我们证明300 bp上游区域调节这些元件的作用。这些数据共同表明，小鼠骨骼肌中MyHC表达的定量差异至少部分是通过消除正向作用的转录因子结合位点而演变而来的。
