Development

Staying in Touch with Satellites

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Science  15 Jun 2007:
Vol. 316, Issue 5831, pp. 1543
DOI: 10.1126/science.316.5831.1543a

Adult skeletal muscle is remarkably proficient at repairing itself after bouts of intense exercise or injury, thanks to a population of satellite cells that are located in between the outer sheath (the basal lamina) and the inner muscle fiber. Satellite cells are normally quiescent, but in response to stress they begin dividing to generate new muscle tissue and to restore the pool of satellite cells. An unresolved question is whether satellite cells are already-committed muscle progenitors, true stem cells, or a mixture of the two. Using genetically manipulated mice and in vivo tracking of satellite cells, Kuang et al. found that this population is in fact heterogeneous. Satellite cells that coexpress the molecular markers Pax7 and Myf5 preferentially differentiate into muscle cells, whereas those that express only Pax7 (about 1 in 10) undergo self-renewal, thereby replenishing the satellite cell reservoir. Notably, Myf5-deficient satellite cells produced Myf5-expressing daughter cells when cell division was asymmetric; that is, when the mitotic spindle was oriented perpendicularly to the axis of the muscle fiber. In these instances, the daughter cell that remained attached to the basal lamina became a new satellite stem cell, but the daughter cell that lost contact with the basal lamina became committed to the muscle cell lineage. The authors speculate that a perturbation of the balance between stem cell renewal and commitment to differentiation within the satellite cell population may be a contributing factor in human diseases such as Duchenne muscular dystrophy. — PAK

Cell 129, 999 (2007).

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