Regeneration of whole limbs from shank stumps in toad tadpoles treated with vitamin A.

Young tadpoles of the toad,Bufo melanostictus (Schneider), were immersed in 15 IU/ml vitamin-A palmitate solution for 3 days, only prior to amputation through the shank. In more than 65% of cases the resultant regenerates were whole limbs containing the skeletal elements from femur to phallanges; in several of them a new girdle had also differentiated. In others regenration had progressed only up to the blastema stage and postblastemic development was inhibited. Opposite results were obtained when treatment was extended to another 3 days after amputation. A normal control-type regenerate consisting of parts distal to amputation level was not obtained in any case treated in either manner. The removed distal part of the shank was not restored in any treated case. It appears that, if suitably administered, vitamin A can make the limb regeneration blastema of amphibians completely equivalent to the original limb bud, probably by intensifying dedifferentiation of its cells. It is suggested that this chemical can be a useful tool to investigate the biochemical and genetic changes which occur during dedifferentiation and also whether through this process differentiated cells can really revert to a pluripotent state.