Neurodegenerative diseases are a diverse group of progressive diseases that include Alzheimer’s disease (AD) and prion disease. Although these diseases differ in etiology, they share a number of similarities at the molecular level. For instance, microRNA (miRNA), small RNA molecules that post-translationally regulate gene expression, are often differentially regulated during disease. A previous study identified key miRNA that are dysregulated during prion disease in the hippocampus. Of these miRNA, miR-16-5p is of particular interest, as it has also been found to be dysregulated in AD. The objective of this thesis is to characterize the role of miR-16-5p within hippocampal neurons in order to understand its function during neurodegeneration. It is hypothesized that hippocampal miR-16-5p, given its induction in hippocampal neurons during preclinical disease, plays a role in regulating the dendritic remodeling and synaptic pruning that is the earliest pathological feature of neuronal degeneration in prion disease. To address this hypothesis, primary hippocampal neurons were dissected from embryonic day 18 mice and treated with a lentiviral vector at maturity. This vector either encoded miR-16 or miRZIP-16, causing overexpression or knockdown of miR-16, respectively. Immunoprecipitation of the miRNA-16 enriched RISC complex was then performed, and the co-immunoprecipitated target mRNA was subjected to a whole genome microarray. Analysis of microarray data in Ingenuity Pathway Analysis pinpointed 181 genes involved in neuronal morphology and neurological disease targeted by miR-16. In particular, the MAPK/ERK pathway was targeted at TrkB, MEK1 and c-Raf. This is of interest, as we know that this pathway is disrupted in other neurodegenerative diseases and is directly implicated in neuronal morphology. Subsequent morphological analysis revealed that overexpression of miR-16 in neuronal cells decreased neurite length and branching, consistent with the downregulation of components of the MAPK/ERK pathway. In conclusion, miR-16 targets many mRNA transcripts within the hippocampus that are important members of pathways involved in neuronal development and neurodegeneration, including the MAPK/ERK pathway. / February 2017