Limb regeneration.

Limb regeneration is observed in certain members of the animal phyla. Some animals keep this ability during their entire life while others lose it at some time during development. How do animals regenerate limbs? Is it possible to find unifying, conserved mechanisms of limb regeneration or have different species evolved distinct means of replacing a lost limb? How is limb regeneration similar or different to limb development? Studies on many organisms, including echinoderms, arthropods, and chordates have provided significant knowledge about limb regeneration. In this focus article, we concentrate on tetrapod limb regeneration as studied in three model amphibians: newts, axolotls, and frogs. We review recent progress on tissue interactions during limb regeneration, and place those findings into an evolutionary context.