Pattern regulation during regeneration of embryonically produced symmetrical forelimbs in the axolotl, ambystoma mexicanum.

Embryonic axolotls (Stages 32-34) underwent surgery during which a graft of flank tissue was transferred from a donor animal to the anterior margin of the forelimb field in a host animal. Double-posterior forelimbs containing from one to eight digits developed. These limbs were amputated at a level proximal to the elbow to assess their regenerative ability. The majority (62%) of these limbs failed to regenerate externally visible structures. Symmetrical limbs bearing five digits or more than five digits regenerated with greatest frequency (54%). Symmetrical forelimbs bearing four digits or fewer that four digits regenerated less frequently (31%). All regenerates displayed double-posterior symmetry and usually contained fewer digits than were present in the original limb. The significance of these findings is discussed in the context of the current model for pattern regulation in epimorphic fields.