Megeney L A, Rudnicki M A
Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, ON, Canada.
Biochem Cell Biol. 1995 Sep-Oct;73(9-10):723-32. doi: 10.1139/o95-080.
The myogenic regulatory factors (MRFs) form a family of basic helix-loop-helix transcription factors consisting of Myf-5, MyoD, myogenin, and MRF4. The MRFs play key regulatory roles in the development of skeletal muscle during embryogenesis. Sequence homology, expression patterns, and gene-targeting experiments have revealed a two-tiered subclassification within the MRF family. Myf-5 and MyoD are more homologous to one another than to the others, are expressed in myoblasts before differentiation, and are required for the determination or survival of muscle progenitor cells. By contrast, myogenin and MRF4 are more homologous to one another than to the others and are expressed upon differentiation, and myogenin is required in vivo as a differentiation factor while the role of MRF4 remains unclear. On this basis, MyoD and Myf-5 are classified as primary MRFs, as they are required for the determination of myoblasts, and myogenin and MRF4 are classified as secondary MRFs, as they likely function during terminal differentiation.
生肌调节因子（MRFs）构成了一个由Myf-5、MyoD、肌细胞生成素和MRF4组成的碱性螺旋-环-螺旋转录因子家族。MRFs在胚胎发育过程中对骨骼肌的发育起着关键的调节作用。序列同源性、表达模式和基因靶向实验揭示了MRF家族内的两级亚分类。Myf-5和MyoD彼此之间的同源性高于与其他成员的同源性，在分化前的成肌细胞中表达，是肌肉祖细胞的确定或存活所必需的。相比之下，肌细胞生成素和MRF4彼此之间的同源性高于与其他成员的同源性，在分化时表达，肌细胞生成素在体内作为分化因子是必需的，而MRF4的作用仍不清楚。在此基础上，MyoD和Myf-5被归类为初级MRFs，因为它们是成肌细胞确定所必需的，而肌细胞生成素和MRF4被归类为次级MRFs，因为它们可能在终末分化过程中发挥作用。
