Cox R D, Garner I, Buckingham M E
Department of Molecular Biology, Pasteur Institute, Paris, France.
Differentiation. 1990 Jun;43(3):183-91. doi: 10.1111/j.1432-0436.1990.tb00445.x.
During terminal differentiation of skeletal muscle cells in vitro there is a transition from a predominantly nonmuscle contractile protein phenotype to a sarcomeric contractile protein phenotype. In order to investigate whether this transition and subsequent changes in expression are primarily transcriptionally regulated, we have analysed the rate of transcription and level of corresponding RNA accumulation of actin and myosin light chain genes during differentiation of a mouse muscle cell line under different culture conditions (low-serum and serum-free). We have found by 'nuclear run-on' analysis, that the alpha-cardiac actin, alpha-skeletal actin, myosin light chain 1F/3F and embryonic myosin light chain genes are transcriptionally activated as myoblasts begin to fuse to form myotubes. In contrast the nonsarcomeric beta-actin gene is transcribed at high levels in myoblasts and is transcriptionally down-regulated during differentiation. There is a sequential transition in transcription and RNA accumulation from predominantly alpha-cardiac to predominantly alpha-skeletal actin during subsequent myotube maturation, which reflects the pattern of expression found during development in vivo. A similar transition from embryonic to adult patterns of myosin light chain expression does not occur. RNA accumulation of actin and myosin light chains is regulated at both transcriptional and post-transcriptional levels. In our culture system the expression of myosin light chains 1F and 3F, which are encoded by a single gene, is uncoupled, 3F predominating. These data are discussed in the context of gene regulation mechanisms.
在体外骨骼肌细胞的终末分化过程中，存在从主要的非肌肉收缩蛋白表型向肌节收缩蛋白表型的转变。为了研究这种转变及随后的表达变化是否主要受转录调控，我们分析了在不同培养条件（低血清和无血清）下小鼠肌肉细胞系分化过程中肌动蛋白和肌球蛋白轻链基因的转录速率及相应RNA积累水平。通过“核转录分析”我们发现，随着成肌细胞开始融合形成肌管，α-心脏肌动蛋白、α-骨骼肌肌动蛋白、肌球蛋白轻链1F/3F和胚胎型肌球蛋白轻链基因被转录激活。相反，非肌节β-肌动蛋白基因在成肌细胞中高水平转录，在分化过程中转录下调。在随后的肌管成熟过程中，转录和RNA积累从主要的α-心脏肌动蛋白向主要的α-骨骼肌肌动蛋白发生顺序转变，这反映了体内发育过程中发现的表达模式。肌球蛋白轻链表达从胚胎型向成年型的类似转变并未发生。肌动蛋白和肌球蛋白轻链的RNA积累在转录和转录后水平均受到调控。在我们的培养系统中，由单一基因编码的肌球蛋白轻链1F和3F的表达解偶联，3F占主导。这些数据将在基因调控机制的背景下进行讨论。
