Characterizing long-range propagation of injury information during regeneration

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Project Summary/Abstract Some animals can regenerate complex organs or appendages after damage. Significant progress has been made on the molecular biology of stem cell differentiation, which helps explain the origin of the cellular building blocks of new tissue. However, major knowledge gaps remain about how new growth is coordinated with the rest of the body with respect to size, shape, and location, and how the whole system knows what's missing and when it is complete (so that it can stop proliferation and remodeling). This project takes advantage of the highly regenerative and tractable model system – the planarian Dugesia japonica – which serves as a proof of principle that repair of complex brains, peripheral nervous systems, muscle, and gut is possible. Most of the recent advances in planarian regeneration have focused on the wound, new growth, and stem cell pool. However, work in the Levin lab on frog leg regeneration and brain repair, and other groups working in mice, have suggested the presence of long-range signals that let healthy tissue know that damage has occurred and what it was. For example, when a frog leg is amputated, cells in the opposite side (untouched) leg exhibit a dramatic bioelectric depolarization at the same location as the amputation plane that occurred in the other leg. Similarly, when a frog limb is amputated and treated, the brain changes gene expression profiles that are different depending on the treatment applied. These kinds of data suggest that important information about anatomical defects may propagate to other organs and help coordinate system-level integrated responses. They also raise the possibility of translating this knowledge to biomedicine as techniques for surrogate site diagnostics and treatments of cells at some distance from a difficult location in the patient (as has been shown in the frog model for brain repair and cancer normalization by the host lab). However, such long-range signals during regeneration are very poorly characterized. Here, I propose to use the planarian model to 1) discover a reliable molecular marker of long-range damage information, and 2) construct and test a quantitative, biophysical model of how the information propagates. Specifically, I will use a candidate approach and an unbiased transcriptomic approach to ask which genes are up/down-regulated in the head of the flatworm when the tail is amputated, and vice-versa. Using subtractive analysis, we will look for transcripts that specifically reveal that one end of the worm has detected what is missing at the other. I will incorporate this knowledge into the existing body of work on neural and non-neural bioelectric signaling, and molecular-genetic cascades, in a constructivist biophysical model of planarian long-range signaling. This model will be analyzed for specific predictions, and I will then validate those predictions and improve the model. This work will allow me to augment my background of molecular biology with novel computational and biophysical approaches and set me up for an independent career in pursuing long-range diagnostics and functional repair signals in biomedical contexts.