Damage to the spinal cord causes one of the most debilitating injuries to the human body. The challenge of promoting the regeneration of this dense network of neurons and glia after spinal cord injury has been seen as insurmountable. However, new techniques emerging from the field of regenerative medicine have illustrated the possibility of encouraging the body to repair these injuries on its own. In the Wills Lab, we study the model organism Xenopus tropicalis, or the Western clawed frog, which has the ability to regenerate its spinal cord and associated tissue following amputation. My project focuses on how X. tropicalis uses the developmental morphogen Sonic Hedgehog (Shh) to re-establish the dorsal-ventral (DV) patterning of the spinal cord during regeneration. I have used cyclopamine, a Shh inhibitor, and SAG, an agonist, in order to perturb Shh signaling during regeneration. I then monitored the effect on DV patterning via immunohistochemical labeling of dorsal and ventral markers. Work so far has shown that Shh signaling is in fact necessary to the establishment of proper DV domains in the regenerate spinal cord. However, my research has also hinted that this specification is complex. Shh appears to have a more proliferative role early on, with patterning effects coming later. In addition, there appears to be an interaction between Shh and other signals that specify anterior-posterior polarity. Overall, my research so far has generated new evidence for how developmental signals are repurposed in the context of regeneration. 

North American Beavers (Castor canadensis) are a semi-aquatic species in the family Rodentia and agents of biogeomorphic change in watersheds. Research in the last 20 years has demonstrated that beaver activity can reduce downstream flooding and significantly improve water quality. Beavers have inhabited the North Creek Wetlands (NCW) at the University of Washington Bothell (UWB) since 2008. In Autumn 2023, they constructed several dams that inundated the northern third of the wetlands, creating a new opportunity for studying the impacts of the dams on surface water dynamics in the NCW. I want to estimate how much water the beaver dams are holding back in the NCW and how that impoundment affects sediment movement and water quality above and below the dams. To address these questions, I have estimated water storage in the northern third of the NCW using both aerial drone photography and previous site documentation. Sedimentation is being investigated with sediment traps placed throughout the affected area. Water temperature, turbidity, and dissolved oxygen are being measured at several sampling sites that have been used for many years for water quality testing, providing significant baseline data against which to compare final results. I anticipate that results will indicate the beaver dams have increased NCW water storage, increased sedimentation in the northern third of the NCW, and are improving water quality in the North Creek before it discharges into the Sammamish River. Understanding the impacts of beaver activity on the NCW will help the UWB and local stakeholders to better balance the risk of flooding near campus with the beaver’s benefits to water quality and reducing downstream flooding and may inform future actions by the UWB Facilities Services and Campus Operations Department.

One of the most prevalent issues in regenerative medicine is the impact of spinal cord injuries, as it can lead to an irreparable buildup of inhibitory scar tissue and, thus, paralysis. However, organisms such as Xenopus tropicalis tadpoles are able to regenerate their tails as soon as one week post-injury. By studying how they successfully regenerate, we can start to generate effective therapies for spinal cord medicine. I specifically want to know how quickly neurons populate the regenerating spinal cord and how this repopulation leads to functional motor recovery. To do this, I used the process of immunohistochemistry, where a fluorescent marker antibody binds to specific cells to create a fluorescent image for visualization purposes. First, I amputated around â…“ of their tail and created clutches of tadpoles stained for a neuron-specific protein. From my imaging, I noticed that the neurons populated the regenerating spinal cord by five days post-amputation (dpa). I became curious about how this regeneration rate impacted their ability to swim. To test this question, we set up a camera with a lightbox to set up Petri dishes of tadpoles. Then, I uploaded recordings of their swimming into a platform called ImageJ to use particle tracking to quantify the paths of each tadpole into measures such as distance, displacement, and velocity. Currently, we are trying to find other antibody markers that can provide more specific staining of neurons so the program can count them. With more specific staining, I hope to count the number of neurons over a set of zero, three, five, and seven dpa tadpoles. This project will help us answer foundational questions about how Xenopus tropicalis tadpoles regenerate functional neurons after injury.