Cell-Cell Interactions and Distal Outgrowth in Amphibian Limbs

SYNOPSIS. A current model concerning the process of limb regeneration in vertebrates is examined. According to this model (Bryant et al, 1981), new positional values in the proximal-distal limb axis are laid down as a result of local interactions between cells in the limb circumference. Cells with disparate circumferential positional values come together at the site of future outgrowth and intercalation between them generates more distal levels of the pattern. The results of a number of experiments on surgically created symmetrical limb stumps are discussed in relation to this model. In addition, an extension of this model to account for digit formation is presented, and the implications of this formulation for limb evolution are discussed.