[Differences in the mechanism of muscle regeneration between the larval and metamorphosed newts.]

The newt switches the cellular mechanism for limb regeneration from a stem/progenitor-based mechanism(larval mode)to a dedifferentiation-based one(adult mode)as it grows beyond metamorphosis. When it comes to muscle, larval newts regenerate muscle from muscle stem/progenitor cells such as satellite cells, but after metamorphosis the animals recruit muscle fibers for the same purpose by means of dedifferentiation in which muscle fibers(multinucleated cell)at the stump are fragmented to produce mononucleated cells, the primary cell source for new muscle. Dedifferentiation of muscle fibers may have been advantageous for the newt, during its evolution, to quickly regenerate the limbs by supplementing satellite cells whose number and potency become restricted by metamorphosis(transformation to adapt to terrestrial environments)or aging. The ability of dedifferentiation may have been invented in this animal through modifications of the molecular mechanism(or program)which runs in dying or degenerating muscle fibers.