11loxP and Cre-driver lines that can be bred together and supplemented with tamoxifen
to induce Cre-mediated recombination [ 51 ]. Such technologies have already allowed
fate mapping studies in the axolotl to be performed and have provided the tools nec-
essary to design complex experiments, which have yielded evidence for species spe-
cifi c mechanisms of tissue regeneration [ 131 ]. It should be noted that considerable
time is required for germline transgenesis to occur. Thus targeting specifi c cell types
can be achieved in mosaic backgrounds by delivering vectors such as vaccinia virus,
adenovirus, pseudotyped virus, and foamy virus to allow more rapid analysis of phe-
notypes [ 133 , 171 , 173 , 174 ].
Traditionally tools to perform loss of function genetics during regeneration in thesalamander were limited to the use of morpholinos, which have potential to cause off-
target effects [ 53 , 96 , 180 ]. Alternative protocols to perturb gene function have
focused on inducing double-strand breaks , which often leave insertions or deletions
following non-homologous end joining repair. Two of these methods; transactivator-
like effector nucleases (TALENs) and clustered regularly interspaced short palindromic
repeat (CRISPR) have already completed proof of concept studies in the axolotl, red-
spotted and Iberian ribbed newt ( Pleurodeles waltl ) [ 28 , 54 , 111 , 177 , 178 ].
1.5 Conclusions
1.5.1 The Infl uence of Regeneration Research in Salamanders
Many underlying concepts concerning the determinants for successful regeneration
have arisen from research in salamanders. Understanding how regenerating cells can
dynamically navigate across a three-dimensional axis and recapture its original form
is critical in developing complex tissue transplantation models. Innervation and the
supply of neurotrophic signals to the tissues of the regenerate has been explored and
implicated in both teleost and mammalians models of regeneration including the heart,
digit tip, earlobe, bone marrow, and hair follicles [ 181 – 186 ]. The resolution of wound
healing and the subsequent transition to cell cycle re-entry requires precise co-ordina-
tion between infi ltrating immune cells and the local tissue environment harboring resi-
dent progenitor-stem populations. Evidence for this emerging theme is springing from
the salamander, anuran amphibian, and teleost systems, which has infl uenced transi-
tional studies in most mammalian models of regeneration [ 187 – 191 ].
1.5.2 Future Perspectives
Considerable advances have been made in recent years to improve genomic and
molecular resources in all salamander species that are regularly used in the labora-
tory. These technologies have enabled scientists to revisit classic experiments with
1 Research into the Cellular and Molecular Mechanisms of Regeneration...