myoblasts

Myoblasts are mononucleated precursor cells that give rise to skeletal muscle fibers. During embryonic development they originate from the mesoderm, proliferate as myoblasts, and fuse to form multinucleated myotubes, which mature into functional myofibers.

The process of myogenesis is orchestrated by a set of transcription factors known as myogenic regulatory factors (MRFs): Myf5, MyoD, MRF4, and myogenin. Activation of these genes coordinates myoblast proliferation, withdrawal from the cell cycle, differentiation, and fusion. Embryonic development features primary myogenesis that produces early fiber tracts, followed by secondary myogenesis that adds more fibers.

In adult muscle, a population of satellite cells resides beneath the basal lamina of mature fibers. These cells are quiescent but can activate and proliferate to generate new myoblasts in response to injury or resistance training. The myoblasts then differentiate and fuse to repair damaged fibers or contribute to muscle growth. Aging and disease can impair satellite cell function.

Functions: The fusion of myoblasts creates long multinucleated fibers essential for contraction. Myoblasts also supply new nuclei that support fiber growth and repair. The precise balance of proliferation and differentiation controls muscle mass, fiber type composition, and regeneration capacity.

Clinical relevance: Abnormal myogenesis is linked to congenital myopathies and muscular dystrophies. Understanding myoblast biology informs regenerative medicine approaches, including cell-based therapies and tissue engineering for muscle repair.