Regeneration Potency of Xenopus Limbs

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Although amputated limbs of newts or salamanders regenerate completely, the regeneration of higher vertebrates such as mammals or birds occurs only distal margin of limbs. In frogs, the regeneration potency changes during metamorphosis. The limb bud of tadpoles at early stages regenerates completely after amputation at any proximal-distal levels, but the regeneration potency rapidly decreases and no limb regeneration is observed in the metamorphosed froglets. In Xenopus, a cartilage rod, spike, is formed instead. Thus, frog limb is a suitable material for the analysis of regeneration potency. We analyzed molecular mechanisms of limb regeneration in the frog at various stages of metamorphosis and tried to induce regeneration in the limbs with no or weak regeneration potency.The decrease in the limb regeneration potency was found to be caused by the changes of mesenchymal tissues, especially in the expression of fgf-10. Application of bead containing FGF-10 protein to the amputated site of the hindlimbs at advanced stages of metamorphosis induced the limbs with segmented and bifurcated cartilage.Dorsal-ventral signalling also affected limb regeneration potency. Signalling factor from dorsal epidermis induced Lmx-1 expression in the dorsal mesenchyme of regenrating limbs, but the factor was weak in the epidermis of the limbs at later stages of metamorphosis.In the froglet, a cartilage rod, spike, is formed after amputation, but some spikes were bifurcated or segmented. Furthermore, Hoxa-13 expression was found in the distal region of the spike as in the case of developing limbs. Application of beads containing SHH protein or PDGF increased the frequency of bifurcated or segmented spikes.