The Role of Epigenetics in Amphibian Regeneration

Up until recently, epigenetic mechanisms for epimorphic regeneration have not been studied. Epigenetic mechanisms present a possible method for control over the regeneration process and an explanation as to why some animals possess regenerative abilities and others do not. This thesis provides evidence for a role for histone acetylation and DNA methylation in amphibian regeneration. Results from this thesis show that histone deacetylase (HDAC) enzymes and consequently histone hypoacetylation are needed for successful regeneration with X. laevis tadpoles, treated with HDAC inhibitors, failing to regenerate tails and limbs. HDACs are also shown to be necessary for A. mexicanum tail regeneration however HDAC inhibition only slows limb regeneration in A. mexicanum. HDAC inhibition is shown not to affect limb or tail development in X. laevis but to slow development in A. mexicanum. Direct measurement of HDAC activity in X. laevis is consistent with the results of HDAC inhibitor treatment, with increased HDAC activity being associated with regeneration success in X. laevis. Regeneration competent tadpoles show increased HDAC activity with amputation and regeneration incompetent refractory stage tadpoles show a decrease in HDAC activity with amputation. HDAC activity is possibly associated with the BMP and Notch signalling pathways as well as retinoic acid signalling. Global DNA methylation is also measured in X. laevis. Low levels of DNA methylation are shown to be associated with regeneration success following amputation, with regeneration competent tadpoles showing lower levels of methylation than refractory stage tadpoles. This is consistent with the illustrated variable regenerative response to methyltransferase inhibitor treatment in regeneration competent tadpoles treated after amputation. It is also consistent with the increased regenerative success seen when refractory stage tadpoles are treated with a methyltransferase inhibitor. The evidence presented in this thesis illustrates the importance of epigenetic mechanisms in vertebrate regeneration. This research may have important implications for medical research