Myogenesis

Myogenesis is the developmental process by which skeletal muscle tissue forms. It encompasses the specification of muscle progenitor cells, their differentiation into myoblasts, and the fusion of these cells to form multinucleated myotubes and mature muscle fibers. In mammals, myogenesis occurs during embryonic development and is followed by postnatal growth and repair that rely on resident stem cells. The term also applies to muscle formation in other vertebrates and to muscle regeneration after injury in adults.

In vertebrate development, skeletal muscle arises from the paraxial mesoderm, organized into somites. The dermomyotome portion of each somite provides muscle progenitors that express Pax3 and Pax7. The myogenic regulatory factors—Myf5 and MyoD—commit cells to the myogenic lineage, with Myf5 initiating specification and MyoD reinforcing the program. As differentiation proceeds, myoblasts express later factors such as myogenin and MRF4, driving myoblast fusion and myotube formation. Fusion yields mature muscle fibers, and transcriptional activity is coordinated with MEF2 co-factors. Growth factors such as IGF-1 and signaling pathways including Wnt modulate progression and maturation, while myostatin acts as a negative regulator of muscle growth.

Postnatally, skeletal muscle contains satellite cells, a population of Pax7-positive stem cells beneath the basal lamina. Upon injury or increased demand, satellite cells activate, proliferate, and differentiate into myoblasts to repair or replace damaged fibers. Notch, Wnt, FGF, and IGF-1 signaling influence activation and differentiation, with the myogenic regulatory factors reappearing during regeneration. Proper regulation of myogenesis is essential for normal muscle development and maintenance, while dysregulation can contribute to muscle diseases and wasting.