Population of muscle satellite cells in relation to age and mitotic activity

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Abstract
Summary The changes in number and proportion of muscle satellite cells during foetal, adolescent and adult periods of life in the mouse m. peroneus longus and the rat m. subclavius were studied by light and electron microscopic histometric methods. At birth, satellite cell nuclei identified by electron microscopy, were 30-35% of the total muscle fibre nuclei. The percentage fell during growth and was less than 5% in the adult animal. Electron microscopic criteria for distinguishing between single satellite cells and syncytial fibre nuclei are noted. Mitotic figures were present in satellite cells in neonatal, 10-, 15- and 21 -day-old animals, but were not seen in myonuclei. Experiments involving colchicine-induced metaphase arrest and quantitative autoradiographic 3H nuclear labelling both indicate that mitotic proliferation of nuclei during muscle fibre growth is confined to satellite cells and that a proportion of the daughter cells are incorporated into the population of fibre myonuclei.