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Distal transformation from double-half forearms in the axolotl, Ambystoma mexicanum

  • Author(s): Krasner, GN
  • Bryant, SV
  • et al.
Abstract

The capacity for distal transformation of surgically produced symmetrical forearms of the axolotl, Ambystoma mexicanum, was tested. The polar coordinate model for pattern regulation in epimorphic fields states that positional information is a property of cells which reflects their position in the field, specifically, by their location on a radius and a circumference of the field. The model proposes that for complete distal transformation to occur, a complete circumference of positional values must be present at the plane of amputation. Previous experiments have shown that surgically constructed, symmetrical upper arms of axolotls and newts are not capable of regenerating a distally complete pattern. In the present experiment, double-posterior and double-anterior symmetrical forearms were produced by exchanging the anterior half of the right forearm with the posterior portion of the left forearm. The grafts were allowed to heal for 5-35 days, at which time the limb was amputated through the center of the grafted region. Ninety-five percent of the double-anterior (left) forearms and 77% of the double-posterior (right) forearms either did not regenerate or regenerated symmetrical patterns. The regenerated patterns always converged, i.e., lost structures along the line of symmetry. The length of the healing time did not affect the number of elements regenerated. The remaining limbs regenerated asymmetrical structures, either normal, or parts of normal, hands. These results are compared with those of similar experiments previously performed on the upper arms of axolots and newts and the hindlimbs of salamanders and are discussed in light of a model for distal transformation. © 1980.

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