Loss of limb regenerative capacity during postmetamorphic growth in the tree frog, Hyla arborea japonica.

Anuran limb regenerative capacity was investigated in froglets of various sizes (snout-vent length) and adults of the Japanese tree frog, Hyla arborea japonica by amputating forelimbs through the zeugopodium and stylopodium. Almost all limbs amputated through the zeugopodium showed heteromorphic regeneration in postmetamorphic froglets 14 to 18 mm in length. However, the larger the froglet, the lower the capacity of limb regeneration. Regenerative capacity was completely lost in adults of more than about 30 mm in length. When froglet and adult limbs were amputated through the stylopodium, no signs of limb regeneration were observed. Complete denervation of limb stumps resulted in no regeneration in all cases examined. When partial denervation was performed on limbs amputated through the zeugopodium, there were signs of regeneration in the presence of the remaining nerves, but this was limited to very young froglets. Nevertheless, the regenerates obtained were limited in gross structure compared with normal limb regenerates. However, when the nerve supply to the distal forelimb was augmented by surgically diverting ipsilateral sciatic nerve bundles, the limbs of normally nonregenerating adults regenerated after amputation through the zeugopodium. Furthermore, normally nonregenerating limbs amputated through the stylopodium also regained a limited regenerative capacity, if supported by an ipsilaterally augmented nerve. These results show that the loss of limb regenerative capacity in Hyla arborea japonica during postmetamorphic growth is caused by a deficiency in the quantity of innervation.