ABSTRACT

During early nervous system development, neural stem cells exit the cell cycle and commit to the neuronal phenotype, after which begins the process of neurite outgrowth that gives rise to axons and dendrites. Axons are responsible for establishing and maintaining synaptic connections with target tissues during nervous system development, and are thus essential for the continued development and functionality of the central nervous system (CNS). Folate receptor 1 (Folr1), one of several folate uptake systems, is necessary for the formation of the neural tube, a process that occurs before neurons differentiate and adopt their neuronal morphology. Deficiency of Folr1 in developing vertebrate embryos leads to neural tube defects because of the failure of the neural tube to form and close. Whether Folr1 is important for later stages of spinal cord development is not yet known. Thus, the focus of my thesis is to investigate the role of Folr1 in axon development in the embryonic spinal cord. Here I show that Folr1 is expressed throughout the axons of embryonic spinal cord explants isolated from neural tube stage X. laevis embryos. Using a loss-of-function approach I show that knockdown of Folr1 in embryonic spinal cord explants results in axon retraction, as well as reduced βIII-tubulin enrichment in axons and altered filopodia production and actin dynamics in axonal growth cones. Moreover, I find that the elongation factor eEF1A2, a GTP-binding protein that non-canonically regulates F-actin dynamics, interacts and colocalizes with Folr1 in embryonic spinal cord neuron axons. Knockdown of Folr1 results in depletion of eEF1A2 and phospho(Ser358)-eEF1A2 in axons, and altered localization of eEF1A2 in growth cones. Taken together, these results indicate that Folr1 is important for axon outgrowth during spinal cord development and suggest that interaction of Folr1 with eEF1A2 facilitates proper function of cytoskeletal proteins important for growth cone dynamics.