A newt myofiber contains a satellite cell (green) that is encapsulated by the basement membrane (red).

Limb regeneration, as seen in amphibians, might not be as far from humanly possible as once thought. On page 433, Morrison et al. show that the regeneration of newt limbs hinges on the activation of muscle satellite cells—the same sort of stem cells that help to heal our own injured muscles.

Unlike the mammalian version, newt satellite cells are separated from muscle fibers by a basement membrane. As their existence had not been proved until now, scientists thought that regeneration was fueled by the breakdown and dedifferentiation of multinucleated muscle fibers into a proliferating multipotent cell mass—something mammalian muscle fibers cannot generate.

Dedifferentiated fibers might indeed contribute to regeneration. But, in the new report, all of the cells from the newt limb stump that proliferated in vitro derived from satellite cells. Labeled cultured satellite cells injected before limb amputation also contributed to various nonmuscle tissues of regenerating limbs, including the epidermis and cartilage. Whether they do so without prior in vitro expansion is the difficult final step that remains to be shown.

As mammalian satellite cells are also activated by wounding, amphibian limb regeneration now appears to be more similar to human repair systems. The trick now will be to figure out how to instruct our own satellite cells to repair and regenerate more tissues than just muscle.