A muscular path to quiescence

Muscle stem cells called satellite cells can pull back from the brink, according to Zammit et al. (page 347). When activated by muscle damage, the cells divide and start uniformly down a differentiation path. Only at the last minute do some of the cells split off to revert to a quiescent, stem cell phenotype.

Satellite cells sit quietly underneath the basal lamina of myofibers until a muscle is damaged. Either mitogens leaking into a damaged muscle or signals from a deinnervated muscle may wake up the satellite cells, which then divide and supply new cells that fuse to repair or replace damaged myofibers.

Zammit et al. isolated intact myofibers and placed them in mitogen-laden cultures to activate the satellite cells. The activated cells, which...