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NeuN is a highly conserved protein that has been considered a reliable marker of post-mitotic neurons for decades. However, recent studies have shown that injury, including disease and axotomy, can decrease NeuN expression. The absence of NeuN expression leads to the misidentification of neuronal death, although cells are alive or have regenerated. This is especially problematic for studies attempting to assess neuronal damage following injury and the success of subsequent therapies in the case of, for example, stroke victims. In my study, Ambystoma mexicanum (axolotl), which are fully capable of regenerating the spinal cord and all related tissues, were used to model neuronal injury and recovery. Here, the tip of the tail was amputated, allowed to regrow, and amputated a second time. Secondary amputation captured the effects of injury on NeuN expression. In addition, four age groups were used to assess differences in NeuN expression, ranging from juvenile to adult axolotls. Unlike humans and many other vertebrates, axolotls are neotenous and retain juvenile characteristics into adulthood, although some regenerative capabilities may be more robust earlier in life. This study aims to better understand the expression of the NeuN protein, specifically how it reacts to neuronal injury and may change as axolotls mature. Immunohistochemical labeling revealed variability in NeuN expression based on location, neuron type, regeneration period, but not necessarily age. Proximal and distal regions showed disparate patterns of expression, where NeuN labeling was localized in individual neurons in proximal sections. However, in distal sections expression was less intense and restricted to the perinuclear space of neurons. Inconsistent expression of individual neurons within the same section suggests neuron-type specific expression of NeuN. These observations were supported by patterns in number of neurons expressing and their differences in expression patterns. Therefore, my study characterized NeuN expression as highly inconsistent and dependent on a multitude of different variables, including location, neuron-type, and regeneration period.
Ulsh, Jordan, "Characterizing Expression of a Neuron Specific Protein in the Regenerating Tails of Axolotls" (2023). Biology Honors Papers. 95.