Molecular mechanisms in urodele amphibian regeneration

Adult salamanders such as the newt are able to regenerate their limbs with complete recovery of function. How does a salamander regenerate its limb and why can we not do this? Our research is studying some of the critical components that underly limb regeneration, and in particular the ones that are found in salamanders and not in us. The salamander and human genome projects provide important resources for identifying such components. If we understood how they worked this would provide a new impetus for trying to enhance our own abilities to regenerate.

Limb regeneration in salamanders proceeds by formation of the limb blastema, a mound of mesenchymal stem cells at the end of the stump. In earlier work we identified the GPI-anchored cell surface protein Prod 1, a member of the three-finger protein (TFP) superfamily, as a potential determinant of blastemal cell identity. Prod 1 can signal to the interior of cells in part by activating the Epidermal Growth Factor receptor. The secreted newt Anterior Gradient Protein (nAG) interacts with Prod 1 as a ligand-receptor combination. nAG expression is regulated by the nerve supply, not only during limb regeneration but also during limb development. nAG is able to rescue the regeneration of a blastema in the absence of the nerve. The mechanism of action of nAG will be studied at the molecular level in relation to its thioredoxin fold, essential cysteine residue, and possible formation of a disulphide bonded heterodimer with Prod 1. We will also study its activity in relation to confrontations of proximal and distal blastemal cells, since we propose there is a connection between the implementation of positional identity by Prod 1 and growth control by the nerve (nAG). The studies on Prod 1 signalling have led to identification of a point mutant that acts as a dominant negative (residue 59), and we propose to utilise this in transgenic axolotls in order to obtain information about Prod 1 function in regeneration. Prod 1 is the first example of a taxon-specific protein implicated in regeneration. This has important implications for our understanding of both the evolution of regeneration and how to extend regenerative ability in mammals. An expansion group of newt and axolotl TFPs derived from a single salamander-specific sequence has been identified and named the Stef genes. These GPI-anchored proteins provide a focus for efforts to define the taxon-specific aspects of the mechanism of regeneration, and the identification of their putative binding partners will be an important goal in understanding their activity. Our analysis should provide new information about the mechanism of limb regeneration, and about certain critical steps that are required to establish a regenerative outcome to limb amputation

Professorship Renewal