Garry D J, Bassel-Duby R S, Richardson J A, Grayson J, Neufer P D, Williams R S
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, USA.
Dev Genet. 1996;19(2):146-56. doi: 10.1002/(SICI)1520-6408(1996)19:2<146::AID-DVG6>3.0.CO;2-9.
Recent progress in defining molecular components of pathways controlling early stages of myogenesis has been substantial, but regulatory factors that govern the striking functional specialization of adult skeletal muscle fibers in vertebrate organisms have not yet been identified. A more detailed understanding of the temporal and spatial patterns by which specialized fiber characteristics arise may provide clues to the identity of the relevant regulatory factors. In this study, we used immunohistochemical, in situ hybridization, and Northern blot analyses to examine the time course and spatial characteristics of expression of myoglobin protein and mRNA during development of the distal hindlimb in the mouse. In adult animals, myoglobin is expressed selectively in oxidative, mitochondria-rich, fatigue-resistant myofibers, and it provides a convenient marker for this particular subset of specialized fibers. We observed only minimal expression of myoglobin in the hindlimb prior to the second day after birth, but a rapid and large (50-fold) induction of this gene in the ensuing neonatal period. Myoglobin expression was limited, however, to fibers located centrally within the limb which coexpress myosin isoforms characteristic of type I, IIA, and IIX fibers. This induction of myoglobin expression within the early postnatal period was accompanied by increased expression of nuclear genes encoding mitochondrial proteins, and exhibited a time course similar to the upregulation of myoglobin and mitochondrial proteins, and exhibited a time course similar to the upregulation of myoglobin and mitochondrial protein expression that can be induced in adult muscle fibers by continuous motor nerve stimulation. This comparison suggests that progressive locomotor activity of neonatal animals may provide signals which trigger the development of the specialized features of oxidative, fatigue-resistant skeletal muscle fibers.
在确定控制肌生成早期阶段通路的分子成分方面，近期已取得了重大进展，但尚未鉴定出在脊椎动物机体中调控成年骨骼肌纤维显著功能特化的调节因子。更详细地了解特殊纤维特征产生的时空模式，可能为相关调节因子的身份提供线索。在本研究中，我们利用免疫组织化学、原位杂交和Northern印迹分析，来检测小鼠后肢远端发育过程中肌红蛋白蛋白和mRNA表达的时间进程及空间特征。在成年动物中，肌红蛋白在富含线粒体的抗疲劳氧化型肌纤维中选择性表达，它为这一特殊类型的特化纤维提供了一个便利的标记物。我们观察到，出生后第二天之前后肢中肌红蛋白的表达极少，但在随后的新生期该基因迅速大幅（50倍）诱导表达。然而，肌红蛋白的表达仅限于肢体中央的纤维，这些纤维共同表达I型、IIA型和IIX型纤维特有的肌球蛋白异构体。出生后早期肌红蛋白表达的这种诱导伴随着编码线粒体蛋白的核基因表达增加，并且呈现出与肌红蛋白和线粒体蛋白上调相似的时间进程，这种时间进程类似于成年肌纤维通过持续运动神经刺激可诱导的肌红蛋白和线粒体蛋白表达上调。这种比较表明，新生动物逐渐增加的运动活动可能提供信号，触发抗疲劳氧化型骨骼肌纤维特化特征的发育。
