The regeneration of tissues and organs lost to injury or disease is a key goal of biomedicine. Induction of regeneration in clinical contexts will require a molecular dissection of the relevant patterning signals operating in animals that are able to regenerate. This field has been dominated by a focus on chemical signals and is ready for fresh approaches to the problem. Our lab merges functional physiology with molecular genetics to understand novel biophysical controls of patterning and use them to control tissue growth. When amputated, the Xenopus tail forms a regeneration bud that rapidly produces a perfect duplicate of the original tail, including nerves, blood vessels, and muscle. Using this powerful vertebrate system, we discovered that endogenous ion fluxes and membrane voltage gradients play a crucial role in regeneration. Our drug screen implicated a H+ pump, a K+ channel, and a Na+ channel as required for regeneration but not for wound healing or primary tail growth; the activity of these transporters establishes a moderate zone of depolarization in the bud that is crucial for regeneration. We used mutant transporter constructs to inhibit or rescue regeneration, demonstrating that H+ flux is necessary and sufficient for inducing regeneration. These biophysical events function upstream of and control: known regeneration marker expression, up-regulation of cell proliferation in the bud, and axon patterning. We propose to begin to understand the role of ion flux in regeneration by characterizing: (1) the time-course and properties of blastema currents, (2) the expression of implicated electrogenic genes, (3) the downstream steps linking membrane voltage to molecular and morphogenetic events during regeneration. Our data provide the first induction of regeneration by molecular modulation of ion flows, and the proposed work will answer the most important open questions in this new field. This proposal incorporates a high degree of novelty because it is focused on a paradigm that has not been previously addressed using molecular genetic tools: electrical controls of regeneration. It is high-reward because it would lay bare a new set of control parameters for the regeneration of a complex vertebrate structure (including spinal cord). This will have important implications for understanding basic morphogenetic mechanisms as well as establishing a foundation for promising medical approaches to augment or induce regeneration in non-regenerating tissues. The ability to regenerate tissues and organs is crucial to the medical management of injury, aging, infection, or surgical removal of cancer. Our work will provide an entirely new modality that may, one day, allow human beings to regenerate important tissues and organs (including muscle and spinal cord). ? ? ?
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