Pin C L, Merrifield P A
Department of Anatomy, University of Western Ontario, London, Canada.
Dev Genet. 1993;14(5):356-68. doi: 10.1002/dvg.1020140505.
Myosin heavy chain (MHC) is encoded by a multigene family containing members which are expressed in developmental and fiber type-specific patterns. In developing rats, primary (1 degree) and secondary (2 degrees) myotubes can be distinguished by difference in MHC expression: 1 degree myotubes coexpress embryonic and slow MHC, while 2 degrees myotubes initially express only embryonic MHC. We have used monoclonal antibodies which recognize the embryonic, slow, neonatal, and adult fast IIB/IIX MHCs to examine MHC accumulation in myoblasts obtained from hindlimbs of embryonic day (ED) 14 and ED 20 Sprague-Dawley rats during differentiation in vitro. Embryonic myoblasts (ED 14), which develop into 1 degree myotubes in vivo, differentiate as myocytes or small myotubes (i.e., 1-4 nuclei) which express both embryonic and slow MHC. They do not accumulate detectable levels of neonatal or adult fast IIB/IIX MHC. Fetal myoblasts, which develop into secondary myotubes in vivo, fuse to form large myotubes (i.e., 10-50 nuclei) and express predominantly embryonic MHC at 3 days in culture. These myotubes accumulate neonatal and adult fast IIB/IIX isoforms of MHC and eventually contract spontaneously. In contrast to embryonic myotubes, they do not accumulate slow MHC. Our results demonstrate that embryonic and fetal rat myoblasts express different phenotypes in vitro and suggest that they represent distinct myoblast lineages similar to those previously described in chickens and mice. These two lineages may be responsible for the generation of distinct populations of 1 degree and 2 degrees myotubes in vivo.
肌球蛋白重链（MHC）由一个多基因家族编码，该家族成员以发育和纤维类型特异性模式表达。在发育中的大鼠中，初级（1°）和次级（2°）肌管可通过MHC表达的差异来区分：1°肌管共表达胚胎型和慢型MHC，而2°肌管最初仅表达胚胎型MHC。我们使用了识别胚胎型、慢型、新生型和成年快肌IIB/IIX MHC的单克隆抗体，来检测从胚胎第14天（ED14）和ED20的Sprague-Dawley大鼠后肢获取的成肌细胞在体外分化过程中MHC的积累情况。在体内发育为1°肌管的胚胎成肌细胞（ED14），分化为表达胚胎型和慢型MHC的肌细胞或小肌管（即1 - 4个核）。它们不会积累可检测水平的新生型或成年快肌IIB/IIX MHC。在体内发育为次级肌管的胎儿成肌细胞，融合形成大肌管（即10 - 50个核），并在培养3天时主要表达胚胎型MHC。这些肌管积累MHC的新生型和成年快肌IIB/IIX同工型，并最终自发收缩。与胚胎肌管不同，它们不会积累慢型MHC。我们的结果表明，胚胎和胎儿大鼠成肌细胞在体外表达不同的表型，并表明它们代表了与先前在鸡和小鼠中描述的类似的不同成肌细胞谱系。这两个谱系可能负责在体内产生不同群体的1°和2°肌管。
