Identification of regenerative roadblocks via repeat deployment of limb regeneration in axolotls

Axolotl salamanders are powerful models for understanding how regeneration of complex body parts can be achieved, whereas mammals are severely limited in this ability. Factors that promote normal axolotl regeneration can be examined in mammals to determine if they exhibit altered activity in this context. Furthermore, factors prohibiting axolotl regeneration can offer key insight into the mechanisms present in regeneration-incompetent species. We sought to determine if we could experimentally compromise the axolotl’s ability to regenerate limbs and, if so, discover the molecular changes that might underlie their inability to regenerate. We found that repeated limb amputation severely compromised axolotls’ ability to initiate limb regeneration. Using RNA-seq, we observed that a majority of differentially expressed transcripts were hyperactivated in limbs compromised by repeated amputation, suggesting that mis-regulation of these genes antagonizes regeneration. To confirm our findings, we additionally assayed the role of amphiregulin , an EGF-like ligand, which is aberrantly upregulated in compromised animals. During normal limb regeneration, amphiregulin is expressed by the early wound epidermis, and mis-expressing this factor lead to thickened wound epithelium, delayed initiation of regeneration, and severe regenerative defects. Collectively, our results suggest that repeatedly amputated limbs may undergo a persistent wound healing response, which interferes with their ability to initiate the regenerative program. These findings have important implications for human regenerative medicine. Persistent healing blocks salamander limb regeneration Understanding a roadblock to limb regeneration in salamanders could help develop suitable regenerative therapies for humans. Jessica Whited of the Harvard Stem Cell Institute and colleagues in the US found that repeatedly amputating a limb in Mexican salamanders compromised their normal ability to regenerate it. The team found high levels of a gene encoding a damage-protecting protein, called amphiregulin, at the wound site. Artificially inducing the expression of this gene in salamanders whose limbs were amputated just once also led to slow and poor regeneration. The findings suggest that high levels of amphiregulin induce a persistent wound-healing response that interferes with the salamanders’ ability to initiate regeneration. Pushing organisms with strong regenerative abilities into a non-regenerative state can he