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Satellite or myosatellite cells are multipotent, adult stem cells retained in an inactive state and located near differentiated muscle cells.

These cells are capable of self-renewal, proliferation, and differentiation when muscle regeneration is required. External stimulation or mechanical stress, including physical exercise, activates myosatellite cells.

Some of the same transcription factors used for myoblast activation during normal muscle fiber formation are also used for myosatellite activation during muscle regeneration.

Upon activation, the myosatellite cells first divide, differentiate into myoblasts, and then fuse with damaged myotubes to form mature muscle fibers.

Satellite cells repair damaged muscles in diseases such as Duchenne muscular dystrophy or DMD.  DMD is a genetic disorder where a non-functional dystrophin protein leads to a loss of muscle mass.

In DMD, the myosatellite cells fail  to adequately regenerate myoblasts for muscle repair. This results in the progressive weakening of the existing muscles, affecting daily life.