Rachele Mariano started conducting research in Professor Gardiner’s lab in Fall 2008, where she became involved in studying the effects of the extracellular matrix in axolotl limb regeneration. Focusing on a specific aspect of skin grafts in axolotls, Rachele helped determine significant limitations on the growth of ectopic limbs, a finding that could someday help determine a method for limb regeneration in humans. Rachele hopes to continue her education, eventually earning a dental degree.

Tiffany Vu wanted a hands-on research experience to go along with what she was learning in her classes. She found Professor Gardiner’s limb regeneration research particularly interesting, working specifically on limb regeneration in axolotls. The surgeries involved in the project were an initial challenge, but Tiffany appreciated how her confidence and skill grew as the project proceeded. Tiffany hopes to pursue a career in dentistry.

As embryos, vertebrates have multipotent cells, allowing them to regenerate any body part. However, most cannot regenerate after the embryonic stage. Fully-developed salamanders, particularly the axolotl, retain the ability to regenerate any body part following an injury. Unlike most vertebrates, axolotls do not form scars; their cells have the ability to dedifferentiate and form ectopic blastemas. Axolotl cells also contain information that specifies their location in the body during development. We used nerve deviations and extracellular matrix (ECM) grafting to test for interaction between limb components of differing positional values during the axolotl wound healing process. We discovered that grafting urea-treated anterior ECM into an anterior wound site does not produce an ectopic blastema. However, urea-treated posterior ECM grafts result in asymmetric, ectopic blastema formation. Urea-treated anterior ECM grafts further treated with the enzyme heparitinase-III (HepIII) regained the ability to induce blastema development. All grafts that were treated with fibroblast growth factor-2 (FGF2) induced blastema formation in an anterior wound site. We hypothesize that heparan sulfates within the ECM play a regulatory role in growth factor activity, and that signaling from the ECM is necessary for the induction of ectopic blastemas but is not sufficient for ectopic limb development.

David M. Gardiner School of Biological Sciences

Undergraduate research projects are an important opportunity for our students to experience life in the lab with its many challenges, frustrations, and successes. Rarely do such projects lead to the important insights that Tiffany and Rachele have discovered. Their discovery of how the extracellular matrix can regulate growth and pattern formation during limb regeneration has caused us to rethink how growth factor signaling is regulated. Based on their findings, we have begun a new series of experiments that likely will lead to novel therapeutic approaches to inducing a regenerative response in humans.