Figure 1

Reparative regeneration as a function of developmental stage among vertebrate models ofregeneration. Panels depict how the regenerative ability of homologous structures varies acrossontogeny for the primary vertebrate models of regeneration. Regenerative ability is presented on a 0to 5 scale; five represents perfect regeneration and zero no regeneration. Major ontogenetic stagesare represented as embryo, larva, juvenile and adult with metamorphosis, puberty or both indicatedfor each species. (a) Zebrafish exhibit lifelong regenerative capacity of spinal cord, brain,and heart. They cannot regenerate a lens at any time in development and while pectoral fins(homologous to tetrapod limbs) regenerate in juveniles, their regenerative capacity is reducedfollowing puberty, with females retaining a higher capacity for complete regeneration. (b)Salamanders and newts are the archetypical tetrapod regenerator, retaining near perfectregeneration of most organs and appendages well into adulthood (although almost no studies havetested these abilities in old animals). They do, however, experience a decline in limb regenerationfollowing metamorphosis, which usually manifests as patterning defects and loss of limb elements.Axolotls can only regenerate lenses as early stage larvae. (c) Although most frogs exhibitsome degree of regeneration as larvae, with the exception of limited digit and very restricted limbregeneration in some species, they do not exhibit regenerative ability as adults. (d) Mammalsexhibit some regenerative capacity as embryos but lose almost all of this ability before or shortlyafter birth for the structures listed.