Is retinoic acid an endogenous ligand during urodele limb regeneration?

The effects of retinoids on a regenerating urodele limb make them interesting candidates for endogenous ligands during regeneration. We review the evidence for considering this possibility. This includes analysis of retinoids and retinoic acid receptors in the regenerate, and studies on activation of retinoid reporter genes. Recent work has provided evidence that the wound epidermis is a source of 9-cis retinoic acid, and may be a favorable model for studying the synthesis and release of this modulator.