Maier A, McEwan J C, Dodds K G, Fischman D A, Fitzsimons R B, Harris A J
Department of Cell Biology, University of Alabama, Birmingham 35294.
J Muscle Res Cell Motil. 1992 Oct;13(5):551-72. doi: 10.1007/BF01737997.
The myosin heavy chain (MHC) composition of single muscle fibres in developing sheep tibialis cranialis muscles was examined immunohistochemically with monoclonal antibodies to MHC isozymes. Data were collected with conventional microscopy and computerized image analysis from embryonic day (E) 76 to postnatal day (PN) 20, and from adult animals. At E76, 23% of the young myofibres stained for slow-twitch MHC. The number of these fibres considerably exceeded the number of primary and secondary myotubes. By E100, smaller fibres, negative for slow-twitch MHC, encircled each fibre from the initial population to form rosettes. A second population of small fibres appeared in the unoccupied spaces between rosettes. Small fibres, whether belonging to rosettes or not, did not initially express slow-twitch MHC, expressing mainly neonatal myosin instead. These small fibres then diverged into three separate groups. In the first group most fibres transiently expressed adult fast myosin (maximal at E110-E120), but in the adult expressed slow myosin. This transformation to the slow MHC phenotype commenced at E110, was nearing completion by 20 postnatal days, and was responsible for approximately 60% of the adult slow twitch fibre population. In the other two groups expression of adult fast MHC was maintained, and in the adult they accounted for 14% (IIa MHC) and 17% (IIb MHC) of the total fibre numbers. We conclude that muscle fibre formation in this large muscle involves at least three generations of myotube. Secondary myotubes are generated on a framework of primary myotubes and both populations differentiate into the young myofibres which we observed at E76 to form rosettes. Tertiary myotubes, in turn, appear in the spaces between rosettes and along the borders of fascicles, using the outer fibres of rosettes as scaffolds.
利用针对肌球蛋白重链（MHC）同工酶的单克隆抗体，通过免疫组织化学方法检测了发育中的绵羊颅侧胫骨肌单根肌纤维的MHC组成。从胚胎期（E）76天到出生后（PN）20天以及成年动物，采用传统显微镜和计算机图像分析收集数据。在E76时，23%的幼肌纤维对慢肌动蛋白MHC呈阳性染色。这些纤维的数量大大超过了初级和次级肌管的数量。到E100时，对慢肌动蛋白MHC呈阴性的较小纤维围绕着最初群体中的每根纤维形成玫瑰花结。第二批小纤维出现在玫瑰花结之间的空闲空间中。小纤维，无论是否属于玫瑰花结，最初都不表达慢肌动蛋白MHC，而是主要表达新生肌球蛋白。然后这些小纤维分为三个不同的组。在第一组中，大多数纤维短暂表达成年快肌球蛋白（在E110 - E120时达到最大值），但在成年时表达慢肌球蛋白。这种向慢MHC表型的转变在E110开始，出生后20天时接近完成，约占成年慢肌纤维群体的60%。在另外两组中，成年快MHC的表达得以维持，成年时它们分别占总纤维数的14%（IIa MHC）和17%（IIb MHC）。我们得出结论，这块大肌肉中的肌纤维形成至少涉及三代肌管。次级肌管在初级肌管的框架上产生，这两个群体都分化为我们在E76时观察到的幼肌纤维以形成玫瑰花结。反过来，三级肌管出现在玫瑰花结之间的空间以及束状结构的边界处，以玫瑰花结的外层纤维为支架。
