Regulation of Injury and Stress Responses in Planarians
Date of Award
Doctor of Philosophy
Dr. Wendy S. Beane
Dr. John A. Jellies
Dr. Pamela E. Hoppe
Dr. John T. Wertz
Planaria, reactive oxygen species, quantum, regeneration, wound healing, toxicology
All multicellular organisms possess some type of ability to respond to injury and repair tissue. However, even though most animals can respond to a wound, whether missing tissue regenerates or fibrotic scarring occurs differs from species to species. Reactive oxygen species (ROS) production has been identified as a conserved injury and stress response occurring in both plants and animals, and further research shows ROS is required for regeneration to proceed in multiple animal models. Planarians are an established historical model used to study regeneration due to their robust ability to regenerate any organ from just a tiny fragment, including a bi-lobed (true) brain. ROS in planarians has been shown to be required for brain patterning during regrowth and to initiate signals required for proper regeneration. However, little is known about ROS during planarian wound healing and how ROS signaling may regulate regenerative mechanisms. Studying the role of ROS in stress and injury responses that promote healing and growth in a model exhibiting robust regeneration may identify conserved but latent mechanisms in humans required for regeneration.
Our data reveals that environmental hurdles, such as the common biocide methylisothiazolinone (MIT), can interrupt wound healing and subsequent regeneration. Concentrations well below approved manufacturing levels induce a variety of toxicological readouts, including epithelial defects and neuromuscular effects. Similar concentrations leave planarian wounds open for up to 7 days, when regeneration should be occurring. Those animals that are able to regenerate show morphological defects such as the absence of eyes.
Our data also shows that a second environmental factor, weak magnetic fields (WMFs; <1 mT), can modulate planarian regenerative outgrowth depending on field strength. Previously thought to be too weak to be biologically relevant, our data shows that WMFs—which are a byproduct of electrical current—can alter regenerative outgrowth after amputation in planarians. Different strengths of WMFs are able to produce opposite effects on the blastema (new tissue), consistent with our theoretical model of spin dynamics; certain WMF strengths inhibit growth, while others result in significantly increased growth. WMF-modulated growth is mediated by ROS and downstream heat shock protein 70 (Hsp70) expression, leading to stem cell proliferation and differentiation.
After establishing that ROS is required for new tissue growth, we also investigate the role of ROS in wound healing and early injury signaling. We find that ROS signaling is also required for planarian wound healing by promoting actin-mediated epithelial stretching and wound closure. ROS signaling during wound closure is mediated by jun-1, a transcription factor that has been linked to successful epithelial cell migration after wounding. Lastly, we show that jun-1 is upregulated early after injury and in all wound types, while Hsp70 is found both early and late, but only in wounds inducing regeneration. These data suggest that ROS-mediated jun-1 is important to the wound healing process, while ROS-mediated Hsp70 is indicative of and required for regeneration.
Restricted to Campus until
Van Huizen, Alanna V., "Regulation of Injury and Stress Responses in Planarians" (2021). Dissertations. 3744.