The effects of rotation and positional change of stump tissues upon morphogenesis of the regenerating axolotl limb.

Rotation of a skin cuff 180° around the proximodistal axis of the upper arm in the axolotl results in the formation of multiple regenerates in about 80° of cases after amputation of the limb through the rotated skin. Rotation of the dermis or the flexor and extensor muscles folowed by amputation produced similar percentages of multiple regenerates. Rotated bone produced no abnormalities, and rotated stump epidermis was minimally effective in stimulating multiple regeneration. A thin strip of normally oriented skin interposed between a rotated skin cuff and the amputation surface blocks the morphogenetic effect of the rotated stump skin whereas removal of the normal skin between a rotated proximal skin cuff and the amputation surface allows the formation of a low percentage of multiple regenerates. Gross rotation of stump tissue components can be broken down into axial rotation per se and positional dislocation. Experiments conducted upon skin and muscle have shown that positional dislocation along the anteroposterior axis rather than axial rotation is the manipulation that leads to the formation of multiple regenerates. The first morphological indication of multiple regeneration is the appearance of a triaxial apical ridge on the blastema. Subsequently, digits form along the apical ridges.