The characteristics of local application of retinoic acid to the regenerating axolotl limb

Abstract

The work described here is concerned with the effects of local application of retinoic acid to the regenerating limb, administered in silastin blocks. Using 14 C RA we have shown that its rate of diffusion into medium was the same as into regenerating limbs and that the curve of percent loss shows a fast rise tailing off to a plateau. RA caused specific alterations in the proximodistal axis of the regenerate such that complete limbs could be produced from distal amputation planes. Increasing concentrations of RA caused regeneration to commence from increasingly more proximal levels. The effect of time of administration after amputation on proximodistal duplication has been investigated as well as position effects with silastin blocks placed either at the anterior, posterior or dorsal poles of the blastema. These data permitted an estimate of the absolute amount of RA needed to cause alterations in the proximodistal axis −2 to 16 μg per limb or 1 ng per cell. Supernumerary limbs were also induced by these local implants and here there was a distinct position effect with the dorsal side causing the highest frequency. This reveals a possible effect of RA on the anteroposterior axis of regenerating limbs, but some of these supernumeraries were thought to arise from the irritant action of RA rather than a specific effect on pattern formation. The relevance of these results to those obtained on other systems is discussed.