Figure 6.

Simplified scheme of muscle cell differentiation. Muscle-derived stem cells are quiescent cells but already pre-programmed towards myogenic differentiation. Upon activation of transcription factor Pax7, muscle stem cells become satellite cells. Satellite cells reside in skeletal muscles. Activation by hypoxia, stress (muscle injury), or by certain cytokines activates satellite cells to then express myogenic differentiation factors such as MyoD. After continued stimulation by cytokines and tissue regenerative signals, proliferation of myogenic precursor cells is elevated, and such cells form myoblasts that fuse to multinuclear myofibers.