Tissue regeneration in the amputated forelimb of Xenopus laevis froglets

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Abstract
The present study directly compares the response of amputated forelimbs in Xenopus laevis froglets with epimorphic regeneration of forelimbs in adult newts (Notophthalmus viridescens). Epidermal wound healing was initiated following limb amputation in both froglets and newts. Dedifferentiation of mesodermal stump tissues was comparatively extensive in the regenerating newt limb, whereas Xenopus forelimbs underwent little if any tissue dedifferentiation. Blastema accumulation and growth are prominent features of newt forelimb regeneration. In contrast, only a small fibroblastlike cell accumulation was observed at the distal tip of the Xenopus limbs. Differentiation of blastemal cells in the urodele limb was delayed until extensive blastema growth was achieved, whereas differentiation was immediate in Xenopus. Morphogenesis of the regenerative outgrowth in Xenopus was limited to the differentiation of connective tissue elements, primarily cartilage. In contrast, complete regeneration of all limb tissues occurred in newt forelimbs. We conclude from our findings that a dominant tissue regenerative response exists following forelimb amputation in Xenopus froglets, whereas epimorphic regeneration prevails in the amputated adult newt limb.