Comparing nerve-mediated FGF signalling in the early initiation phase of organ regeneration across mutliple amphibian species

Amphibians have a very high capacity for regeneration among tetrapods. This superior regeneration capability in amphibians can be observed in limbs, the tail, teeth, external gills, the heart, and some internal organs. The mechanisms underlying the superior organ regeneration capability have been studied for a long time. Limb regeneration has been investigated as the representative phenomenon for organ-level regeneration. In limb regeneration, a prominent difference between regenerative and nonregenerative animals after limb amputation is blastema formation. A regeneration blastema requires the presence of nerves in the stump region. Thus, nerve regulation is responsible for blastema induction, and it has received much attention. Nerve regulation in regeneration has been investigated using the limb regeneration model and newly established alternative experimental model called the accessory limb model. Previous studies have identified some candidate genes that act as neural factors in limb regeneration, and these studies also clarified related events in early limb regeneration. Consistent with the nervous regulation and related events in limb regeneration, similar regeneration mechanisms in other organs have been discovered. This review especially focuses on the role of nerve-mediated fibroblast growth factor in the initiation phase of organ regeneration. Comparison of the initiation mechanisms for regeneration in various amphibian organs allows speculation about a fundamental regenerative process.