Salamanders are unique among tetrapods in that they possess the unrestricted capacity to fully regenerate limbs upon amputation. Why is this the only tetrapod taxon harbouring such a striking regenerative potential and how did it evolve are two of the biggest outstanding questions in regenerative research. Over the past two decades, transposable elements (TEs) have emerged as one of the major drivers of regulatory evolution, and it has yet to be explored whether their spectacular numbers in salamander genomes might provide a rationale for the emergence of such an extraordinary phenotype.
The first aim of this work will be to develop an ensemble of state-of-the-art, long-read sequencing compatible approaches to profile the highly-repetitive Axolotl genome and identify the full complement of cis-regulatory-elements (CREs) driving limb regeneration. Two methyltransferase-based technologies for the profiling of chromatin accessibility and histone modifications will be developed, applied to the regenerating limb at different timepoints and later used to identify TE-derived CREs.
This approach will not only shed light on the evolution and molecular mechanisms of limb regeneration but will also set the stage for the provocative possibility of using TEs to rewire mammalian gene-regulatory-networks (GRNs) and enable regeneration. While extensively employed in a wide range of genome engineering approaches, TEs have yet to be harnessed for the regulatory rewiring of GRNs in a directed evolution context. As part of the second aim of this work, I will establish an innovative, TE-based system for the regulatory rewiring of GRNs and employ it to screen for synthetic GRNs capable of reprogramming mouse fibroblasts into a limb-bud-like state, just as it occurs during regeneration in axolotl. Ultimately, by understanding the evolutionary mechanisms behind the emergence of limb regeneration, this work aims to provide an uncharted avenue for the development of regenerating mammals.
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