Browsing by Author "Matyas, John R., Cobb, John A."

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    Metamorphosis and the Coronoid Dentition in the Axolotl Salamander, Ambystoma mexicanum
    (2022-01-19) Pardo, Jason D.; Anderson, Jason S.; Matyas, John R., Cobb, John A.; Hanken, James; Jamniczky, Heather; Rose, Christopher S.
    Amphibian metamorphosis consists of rapid and substantial changes across the entire body, largely associated with shifts in respiratory function and water balance. This coincides with a decrease in regenerative potential, including continuous tooth replacement in the coronoid bone of the lower jaw. In continuous tooth replacement, new teeth are initiated in a specialized epithelial lamina medial to the functional tooth row, which is supplied by stem cell populations residing in its distal tip. However, the current state of research makes it difficult to adapt this model organism to address these questions and limits our understanding of metamorphosis. In Chapter 2, I characterize anatomical and histological changes across experimentally induced metamorphosis in the axolotl. I use this to develop the temporal, anatomical, and histological framework in which to approach subsequent studies in this thesis. In Chapter 3, I investigate the signaling basis for changes in the dentition across metamorphosis. Using RNAseq, I characterize differential expression of tooth replacement related transcripts across metamorphosis, identifying candidate genes which are distinct from candidate pathways identified in other tooth replacement systems. In Chapter 4, I show that some of these candidate genes are differentially expressed across metamorphosis in multiple tissues, notably in the lung and gill, suggesting that metamorphosis itself may be a hormone-mediated pleiotropy. I then use phylogenetic comparative methods to show that this coincides with elevated rate of coronoid tooth loss in a part of the tetrapod tree where it is thought tetrapods shifted from gill-dominated to lung-dominated respiration. In Chapter 5, I explore the impact of a histone deacetylase inhibitor, which accelerates thyroid-induced metamorphosis of the tail but slows metamorphosis in the skull, suggesting that different pathways may be active in the tailfin compared to the head. In Chapter 6, I integrate these data into a survey of the literature on salamander metamorphosis.The research presented in this thesis provides a framework for future work on salamander metamorphosis using the axolotl as a model organism. I also present several novel hypotheses which I believe have the potential to drive future work on both amphibian metamorphosis and the origin of tetrapod terrestrialization.