Some current problems in amphibian limb regeneration.

Limb regeneration in adult urodele amphibians proceeds by formation of a blastema at the amputation plane. This paper discusses how the blastema forms, and how its positional identity on the proximodistal axis is manifest. Retinoic acid is able to reset axial specification and there is particular interest in determining how it acts. Although limb regeneration is restricted among vertebrates to the urodeles, its mechanism poses fundamental questions in development biology.