Comparison of pectoralis major muscle satellite cell assay methods: an opinion paper

摘要

The identification of satellite cells by electron microscopy juxtaposed to myofibers was originally reported by Mauro in 1961 (Mauro, 1961). Since the initial discovery in 1961, numerous studies have been conducted determining the essential role of satellite cells in posthatch skeletal muscle growth, and the repair and regeneration of myofibers following injury.As first shown by Smith (1963), muscle fiber number is determined embryonically, and all posthatch muscle fiber growth is through increased nuclear content in the myofibers through the fusion of satellite cells with existing muscle fibers. To repair and regenerate damaged myofibers, satellite cells are activated to proliferate and differentiate to reestablish a myofiber like the originating fiber. To study the complexity of satellite cell biological function, in vitro cell culture methods have been developed. The implementation of satellite cell culture studies has increased our understanding of the mechanistic role of satellite cells in regulating posthatch muscle growth (McFarland et al., 1991;Velleman et al., 2000), the regeneration of myofibers (Velleman et al., 2018), and the involvement of satellite cells in myopathies like Wooden Breast (Velleman, 2023). Satellite cells are not a homogeneous population of cells. Frequently in the literature, it is implied that satellite cells are a uniform population of cells while the existence of multiple populations and the biological significance of their heterogeneity is often overlooked. The heterogeneity of satellite cells is reviewed in Velleman (2022). The first report of satellite cell heterogeneity was based on satellite cell proliferation being age-dependent (Schultz and Lipton, 1982). Subsequent to this initial finding of satellite cell age related changes in biological function, other studies have shown heterogeneity in satellite cells from different muscle fiber types expressing the genes of the originating fiber type (Feldman and Stockdale, 1991), satellite cells isolated from the same myofiber having varying rates of proliferation and differentiation (McFarland et al., 1995;Schultz, 1996), and satellite cell populations in the pectoralis major muscle being affected by growth selection (Xu et al., 2021;2023). The McFarland (1995) study showed heterogeneity within a single fiber type muscle with isolating both fast and slow growing satellite cells from a single pectoralis major muscle from a 6 wk old tom turkey. The fastest growing satellite cells reached 65% confluency during proliferation in 17 days compared to 30 days for the slower growing cells.For the commercial poultry industry, these differences in satellite cell growth and regeneration potential becomes important in determining meat quality especially for the breast muscle where costly downgrades have been occurring due to myopathies like Wooden Breast and Spaghetti Meat. Changes in satellite cell functional activity will affect their biological activity, including but not limited to, cell migration, growth factor responsiveness, and proliferation and differentiation. Interestingly, selection for rapid breast muscle growth in broilers and turkeys has differentially altered the satellite cells. In broilers, satellite cell proliferation and differentiation has been diminished in growth selected birds (Xu and Velleman, 2023). In contrast to the broilers, selection for rapid growth and muscling in meat-type turkeys has increased satellite cell proliferation and differentiation (Xu et al., 2021). The decrease in broiler satellite cell proliferation and differentiation may be associated with myopathies like Wooden Breast requiring the repair and regeneration of myofibers which is compromised with the condition (Velleman et al., 2018).The purpose of this section is not to provide detailed satellite cell isolation methods as they have been published (McFarland et al., 1988;McFarland, 2000), but to provide the author's opinion as to when specific methodological app