Chambers A E, Logan M, Kotecha S, Towers N, Sparrow D, Mohun T J
Laboratory of Developmental Biochemistry, National Institute for MedicalResearch, London, UK.
Genes Dev. 1994 Jun 1;8(11):1324-34. doi: 10.1101/gad.8.11.1324.
We have examined the role of two RSRF/MEF2 proteins in the onset of skeletal and cardiac muscle differentiation in early Xenopus embryos. In normal development, zygotic expression of SL1 (MEF2D) precedes that of SL2 (MEF2A) by several hours, but neither gene is expressed prior to the accumulation of MyoD and Myf5 transcripts in the somitic mesoderm. Ectopic expression of the myogenic factors in explants of presumptive ectoderm induces expression of both SL1 and SL2, whereas in reciprocal experiments, neither RSRF protein activates the endogenous myoD or Myf5 genes. We conclude that SL1 and SL2 lie downstream of these myogenic factors in the skeletal myogenic pathway. SL1 is distinguished from SL2 in being expressed in the presumptive heart region of the early tailbud embryo, prior to detection of any markers for cardiac muscle differentiation. Furthermore, ectopic SL1 induces the expression of an endogenous cardiac muscle-specific myosin light-chain (XMLC2) gene in cultured blastula animal pole explants, whereas SL2 has no comparable effect. These results demonstrate that in addition to a possible role in skeletal myogenesis, SL1 also acts in vivo as a regulator of cardiac muscle-specific transcription.
我们研究了两种RSRF/MEF2蛋白在非洲爪蟾早期胚胎骨骼肌和心肌分化起始过程中的作用。在正常发育过程中，SL1（MEF2D）的合子表达比SL2（MEF2A）早几个小时，但在体节中胚层中MyoD和Myf5转录本积累之前，这两个基因均未表达。在假定外胚层的外植体中异位表达生肌因子可诱导SL1和SL2的表达，而在反向实验中，两种RSRF蛋白均未激活内源性myoD或Myf5基因。我们得出结论，在骨骼肌生肌途径中，SL1和SL2位于这些生肌因子的下游。SL1与SL2的区别在于，在检测到任何心肌分化标志物之前，它就在早期尾芽胚胎的假定心脏区域表达。此外，异位表达的SL1可在培养的囊胚动物极外植体中诱导内源性心肌特异性肌球蛋白轻链（XMLC2）基因的表达，而SL2则没有类似作用。这些结果表明，除了在骨骼肌生成中可能发挥的作用外，SL1在体内还作为心肌特异性转录的调节因子发挥作用。
