Potential muscles everywhere

Gerhart et al. report that stably committed muscle stem cells may wait in a quiescent state in mature nonmuscle tissues like brain and liver, retaining the ability to differentiate into skeletal muscle if the opportunity arises (page 381). This discovery may provide both an important tool for developing regenerative therapies, and a challenge to the characterization of some stem cells as multipotential, an idea based on reported conversions of one cell type to another. Some of the conversion experiments were performed with nonclonal cell populations. The current work suggests that the varied phenotypes observed in the earlier experiments may have arisen from a heterogeneous population of mature stem cells committed to different lineages.

The authors found scattered cells expressing MyoD, a marker for skeletal muscle precursors, in a wide variety of fully differentiated organs in chicken...