myoblast

A myoblast is a mononucleated precursor cell that differentiates into skeletal muscle fibers during embryonic development and postnatal growth. In vertebrates, myoblasts arise from the mesoderm, particularly the paraxial mesoderm and somites. They proliferate and migrate, and upon receiving myogenic cues they exit the cell cycle and fuse with one another to form multinucleated myotubes, which mature into muscle fibers. A related population, called satellite cells, resides between the basal lamina and sarcolemma of mature fibers and serves as a reservoir of muscle stem cells that can be activated in response to injury or stress to support growth and regeneration.

Muscle formation involves two waves of myogenesis in development: primary myogenesis, which forms primary myotubes, and secondary myogenesis, which generates additional myotubes and increases fiber number. Growth and maintenance of skeletal muscle later rely on the fusion of satellite cells with existing fibers. The differentiation process is regulated by myogenic regulatory factors, including MyoD, Myf5, myogenin, and MRF4, along with other transcription factors such as Pax7 that mark progenitor and satellite cell states.

Functionally, myoblasts are essential for the formation, growth, and repair of skeletal muscle. Although skeletal muscle development is driven by myoblasts, cardiac and smooth muscle develop via distinct programs and do not primarily rely on skeletal myoblast fusion. In medicine and research, myoblasts have been studied for regenerative approaches and basic muscle biology; cell lines like C2C12 are commonly used to study differentiation and muscular gene expression.