Regulation of dermal fibroblast dedifferentiation and redifferentiation during wound healing and limb regeneration in the Axolotl.

Adult urodeles (salamanders) are unique in their ability to regenerate complex organs perfectly. The Accessory Limb Model (ALM) in the axolotl allows for the identification of signals from the wound epidermis, nerves and dermal fibroblasts that interact to regenerate a limb. In the present study, we have used the ALM to identity the axolotl (Ambystoma mexicanum) orthologue of Twist (AmTwist), a basic helix-loop-helix transcription factor that is involved in the regeneration of the dermis during limb regeneration. AmTwist is expressed during the blastema stages in regeneration, but is inhibited by signals from the nerve during the early stages when dermal fibroblasts dedifferentiate to form blastema cells. As the dermis regenerates, AmTwist is expressed in association with the synthesis of type I collagen in the proximal region of the blastema. Exogenous bone morphogenetic protein-2 leads to an increase in AmTwist expression, and therefore may function as an endogenous regulator of AmTwist expression and dermis regeneration. The nerve appears to have a dual function in regeneration by coordinately regulating dedifferentiation and redifferentiation of dermal fibroblasts.