Participation of grafted nerves in amphibian limb regeneration
Irradiated axolotl arms bearing grafts of brachial nerves can regenerate, albeit imperfectly. The origin of the regenerated tissues has been traced by means of the difference between dark and white genotypes. Although the origin of the melanophores cannot be decided in this way, their abundance identifies the genotype of the tissue they occupy. Sections of nine regenerates provide consistent evidence for the following conclusions. (1) The epidermis of the regenerate is probably an extension of the irradiated host epidermis. (2) All other tissues of the regenerate which differentiate from a mesenchymal blastema originate from the non-irradiated graft. Regeneration thus involves a true dedifferentiation and redifferentiation (i.e. a loss of determination and equivalent gain in potency for histological transformation). Irradiated cells apparently also dedifferentiate but cannot undergo the normal sequence of proliferation and redifferentiation, and so are not found in the mesodermal component of the regenerate.