Myogenesis Sample Clauses

Myogenesis. During embryogenesis, cells from the myotome or from the precordal mesoderm migrate and differentiate into muscle precursor cells called myoblasts (schematized in Figure 1.2A). Precursor cells differentiate to committed post-mitotic myocytes, which fuse to form immature myofibers (Reviewed in (Buckingham 1992)). Myofibers form in two waves during embryonic development. Primary myofibers form first and tend to be slow twitch myofibers (Draeger, Weeds et al. 1987, Buckingham, Bajard et al. 2003). The second wave of myofibers form around primary myofibers and produce various kinds of fast twitch myofibers (Xxxx, Xxxxxx et al. 1987, Xxxxxx, Xxxxxx et al. 1989). This initial embryonic phase of myogenesis gives way to the fetal phase mostly defined by growth. Postnatally muscles continue to grow and reserve precursor cells are designated to become satellite cells (Reviewed in (Xxxxxxxxx 2005)). However, muscle satellite cells remain relatively active throughout juvenile development as muscle continues to grow, up until three months of age in mice (Xxxxxxxxxxx, Xxxxxxx et al. 2015). Growth and maintenance of skeletal muscle in juveniles and adults depends on satellite cells. Satellite cells activate from quiescence and divide. In an asymmetric cell division, one daughter cell returns to quiescence, maintaining the satellite cell pool; the other daughter cell differentiates and fuses into a myofiber (Xxxxx, Kuroda et al. , Shinin, Xxxxxxx-Xxxxx et al. 2006). To summarize, developmental myogenesis relies on several rounds of progenitor differentiation and incorporation to produce highly ordered skeletal muscle tissue. Skeletal muscle is a highly regenerative tissue. Following injury, a series of coordinated events result in regeneration of the injured site (schematized in Figure 1.2B). First, M1 pro-inflammatory macrophages invade the site of injury and break down the damaged tissue (Xxxxxxx and Xxxxxxxx 2010). Fibroadipogenic progenitor cells proliferate rapidly during this time and are potentially involved in stimulating the activation of satellite cells and promoting matrix deposition (Xxxxx, Babaeijandaghi et al. 2015). The macrophages then shift from pro-inflammatory M1 macrophages to anti-inflammatory M2 macrophages (Xxxxxxx and Xxxxxxxx 2010), and FAPs undergo apoptosis (Xxxxx, Babaeijandaghi et al. 2015). Satellite cells proliferate and produce a large number of muscle progenitor cells. These progenitors differentiate and either fuse into existing damaged m...