ABSTRACT
Previous investigations have shown that axolotl double anterior thighs regenerate only a tapered extension of the femur after simple amputation, but undergo intercalary regeneration of the femur and a symmetrical tibia when a normal wrist blastema is grafted to the thigh. There are two possibilities to account for these results: (1) distal transformation in both terminal and intercalary regeneration depends upon special properties of posterior cells (such as polarizing ability) that are lacking in the anterior half of the limb, but which would be provided by the posterior half of a normal wrist blastema graft, or (2) the pattern of cellular interactions required for distal transformation during terminal regeneration is different from that required for distal transformation during intercalary regeneration.
These alternatives were tested by grafting axolotl double anterior wrist blastemas to double anterior thighs. The host thighs regenerated a femur and symmetrical tibia that structurally were the same as the bones intercalated after grafting a normal wrist blastema to a double anterior thigh. In all cases, the graft developed as a symmetrical hand comprising one to three carpals and one to two digits. These results rule out the necessity of any special properties of posterior cells for distal transformation or polarization of the anterior-posterior axis and suggest instead that distal transformation during intercalary regeneration involves a different pattern of cellular interactions than in terminal regeneration.
