PHYSIOLOGICAL GENOMICS OF SPINAL CORD AND LIMB REGENERATION IN A SALAMANDER, THE MEXICAN AXOLOTL

Salamanders have a remarkable ability to regenerate complex body parts including the limb, tail, and central nervous system. Although salamander regeneration has been studied for several hundred years, molecular-level studies have been limited to a relatively few important transcription factors and signaling molecules that are highly conserved among animals. Physiological genomic approaches were used here to investigate spinal cord and limb regeneration. Chapter 2 reports that hundreds of gene expression changes were identified during spinal cord regeneration, showing that a diverse injury response is activated in concert with extracellular matrix remodeling mechanisms during the early acute phase of natural spinal cord regeneration. Chapter 3 presents results that identify the salamander ortholog of mammalian Nogo-A, a gene known to inhibit mammalian nerve axon regeneration. Nogo-A gene expression was characterized during salamander development and adulthood in order to address the roles of Nogo-A in the nervous system. Chapters 4 and 5 use physiological genomic approaches to examine limb regeneration and why this process is dependent upon an intact nerve supply. Results presented in Chapter 4 showed that many processes regulated during early limb regeneration do not depend upon nerve-derived factors, but striking differences arise between innervated and denervated limbs by 14 days after amputation. Chapter 5 identified genes associated with peripheral nerve axon regeneration and identified gene candidates that may be secreted by nerves to support limb regeneration. Lastly, chapter 6 characterizes the expression of a developmentally important family of genes, matrix metalloproteinases, during tail regeneration. These results suggest that matrix metalloproteinases play multiple roles throughout the regeneration process. Primarily, this dissertation presents data from the first genomic studies of salamander regeneration. The results suggest genes such as matrix metalloproteinases, and molecular pathways such as the Wnt and FGF signaling pathways that can be exploited to enhance regenerative ability in humans