[Regenerative capability in the hindlimb of Xenopus laevis during ontogenetic development]

The regenerative capacity of hindlimb of Xenopus laevis was investigated by amputating the limbs at four levels in various developmental stages including younger postmetamorphosed froglets. Amputations of limbs were performed at the base of limb in stages 50, 51, 52, 53, 54, 55, 58, and 60 (Nieuwkoop and Faber's table), at the middle of limb bud in stages 50, 51, 52 and 54, and at mid-thigh and mid-shank in stages 58 and 60, and the froglets in 2 and 3 cm in snout-vent length. In the present experiments the regenerative capacity of limbs was expressed by the rate of regeneration and morphogenesis. Tadpoles in the stages after 55 failed to regenerate when the limbs were amputated at base level, but individuals in all the other experimental series exhibited regeneration in various rates irrespective of the level of amputation and the stage. The regenerative capacity increased distally along the proximo-distal axis of the limb when amputated at the same stage, while regeneration was better in younger stages than that in older stages when amputations were made at the same levels. The regenerates obtained by amputation of limbs in stages between 50 and 54, were mainly digitated in that they had 5 toes with 3 claws which is the same pattern with the normal limb, 4 toes with 2 claws, 3 toes with 2 claws or one, and 2 toes with one claw etc. Tadpoles at stage 50 could regenerate toes and claws without defect, but in the later the regenerative capacity gradually declined by reducing the number of toes and claws and accompanied by malformation of skeleton as the stage proceeded. The tadpoles in stages after 58, and the froglets of 2 and 3 cm, produced various types of heteromorphic regenerates of shapes such as cone, spike or rod of which the centra were occupied with cartilage rods. However these regenerates showed no morphological differences according to the developmental stages. These heteromorphic regenerates continued their growth even after one year without any sign of development of digitated feet.