Radice G P
Department of Biology, University of Richmond, VA 23173, (USA).
Acta Anat (Basel). 1995;153(4):254-62. doi: 10.1159/000147726.
Vertebrate skeletal muscles contain a family of myosin heavy chain (MyHC) proteins whose expression varies with clonal origin, developmental age, hormonal state, and innervation patterns. The number of MyHC genes and their regulation have been intensely studied in mammals and birds. However, Comparatively little is known about MyHC expression in other vertebrates. To understand better MyHC regulation in amphibians, I have examined the fiber type expression of two tadpole stage-specific MyHC transcripts in Xenopus laevis. cDNAs for these transcripts, called MyHC E3 and MyHC E19, were used to synthesize digoxigenin labeled antisense RNA probes. In situ hybridization of these probes revealed that MyHC E3 was expressed through the myotome but was most abundant in the core fibers of the axial muscles, which are larval type II. In contrast, E19 was expressed most abundantly in the small diameter peripheral fibers of the axial muscles, which are larval type I. Transcripts of both genes were detected exclusively in skeletal muscles neither heavy chain was expressed in cardiac muscle, smooth muscle, or lymph heart muscle. E3 expression was first detected at late gastrula in both segmented and unsegmented dorsal mesoderm. It remained abundant throughout premetamorphosis in myotomal muscle, and was also found in the levator hyoideus and mandibularis muscle of the head, and in abdominal wall muscles. In contrast, E19 was first detected at tailbud in the tail tip and its expression spread anteriorly among larval type I and type II fibers of the myotome and head muscles during the next few hours of development. The patterns of expression suggest that MyHC E3 is expressed predominately in larval type II fibers, and MyHC E19 is initially expressed predominately in larval type I fibers but as development proceeds is expressed in both type I and type II.
脊椎动物的骨骼肌包含一组肌球蛋白重链（MyHC）蛋白，其表达随克隆起源、发育年龄、激素状态和神经支配模式而变化。在哺乳动物和鸟类中，对MyHC基因的数量及其调控进行了深入研究。然而，对于其他脊椎动物中MyHC的表达了解相对较少。为了更好地理解两栖动物中MyHC的调控，我研究了非洲爪蟾蝌蚪阶段特异性的两种MyHC转录本的纤维类型表达。用于这些转录本（称为MyHC E3和MyHC E19）的cDNA被用于合成地高辛标记的反义RNA探针。这些探针的原位杂交显示，MyHC E3在整个肌节中表达，但在轴肌的核心纤维中最为丰富，这些核心纤维是幼虫II型。相比之下，E19在轴肌的小直径外周纤维中表达最为丰富，这些外周纤维是幼虫I型。两个基因的转录本仅在骨骼肌中检测到，两种重链在心肌、平滑肌或淋巴心肌中均不表达。E3的表达最早在原肠胚晚期的分段和未分段背侧中胚层中检测到。在整个变态前阶段，它在肌节肌中一直丰富表达，并且在头部的舌骨提肌和下颌肌以及腹壁肌肉中也有发现。相比之下，E19最早在尾芽期的尾尖检测到，在接下来的几个小时发育过程中，其表达在肌节和头部肌肉的幼虫I型和II型纤维中向前扩散。表达模式表明，MyHC E3主要在幼虫II型纤维中表达，而MyHC E19最初主要在幼虫I型纤维中表达，但随着发育进行，在I型和II型纤维中均有表达。
