Ca²⁺ as a coordinator of skeletal muscle differentiation, fusion and contraction

Figures

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  Fig. 1. Schematics of the role of myoblast fusion during embryonic myogenesis and regeneration across vertebrates. The figure shows distinct stages of myogenesis along with stage‐specific marker proteins. As activated SCs enter the differentiation programme, they undergo significant morphological changes to generate myotubes that eventually mature into myofibers. Activated SCs divide asymmetrically to generate both quiescent and activated SCs. The upregulation of Wnt signalling and downregulation of notch signalling pathways contribute to the exit from senescence and the initiation of differentiation in activated SCs. Activated SCs generate MyoD‐expressing myoblasts that form terminally differentiated myocytes. Myocytes fuse with other myocytes during embryonic myogenesis and with pre‐existing myofibers during regeneration. The multinucleated myotubes then mature to contractile myofibers via myofibrillogenesis.

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  Fig. 2. Illustration summarizing the evolutionary changes in muscle formation during embryonic myogenesis across chordates. The lineage (left) and the corresponding muscle structure (right) are shown. In all vertebrates, the muscle forms after somitogenesis. In the anamniotes (fish and amphibians; blue lines), the somite undergoes a 90° rotation during embryonic myogenesis and later differentiates to form muscle progenitor cells. This feature of whole somite rotation is specific to anamniotes. Myoblasts in amniotes and lower amphibians bypass fusion during embryonic myogenesis and differentiate directly into mononucleated myotubes. Later, the SCs fuse with mononucleated myotubes and form multinucleated myotubes that later mature to form myofibers. Different lineages of fish differ in the process of muscle formation. For example, in teleost fish, myoblast fuse to form multinucleated myotubes during embryonic myogenesis, and these grow further in adulthood by adding mononucleated myocytes derived from SC differentiation. However, in Neoteleost and Euteleost fish lineages, myoblasts fuse to form multinucleated muscle lamellae that undergo longitudinal splitting to form cylindrical muscle…