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In Vivo Development of Zebrafish Retinal Ganglion Cell Dendritic Patterns
Date of Award
Doctor of Philosophy (PhD)
Many neurons, such as cerebellar Purkinje cells, stellate cells in the barrel cortex, mitral cells, or retinal ganglion cells (RGCs), form asymmetric dendritic arbors oriented specifically toward their afferents at maturity. However, few studies have shown how dendrites form polarized dendritic arbors during development in vivo. My thesis takes advantage of the zebrafish retina to perform live imaging experiments designed to reveal the cellular mechanisms underlying dendritic patterning in RGCs. Timelapse imaging of individual RGCs from the early stages of dendritic development showed RGCs initially have unbiased arbors, but acquire an apically biased arbor within 2-8 hours of initial dendritic outgrowth between 40-60 hours post-fertilization. Analysis of the dynamic behavior of apical and basal dendrites revealed a preferential decrease of basal dendrite addition (while they maintain their rate of apical dendrite addition), but no significant difference in neurite stability or motility rates, during the formation of a biased arbor. The Golgi apparatus relocated to the apical pole of the cell body as the dendritic arbor became apically biased, but did not necessarily relocate prior to the formation of a biased arbor.
The role of cell positioning, or cellular environment, was assessed in zebrafish heart-and-soul (has) mutants, which exhibit a non-cell autonomous defect in RGC migration. RGCs in the has retina formed polarized dendritic arbors regardless of their somal position, but projected their arbors differently according to their apicobasal location. Although RGCs did not consistently orient their arbors apically as in the wild type retina, they consistently oriented their arbors toward nearby neuropil. Like wild type RGCs, has RGCs generally projected their dendrites in the direction opposite of the viinitial axon trajectory, although dendritic arbors favored the direction of a nearby neuropil (over the direction opposite of initial axon trajectory). The neurites of their presynaptic partners, that is amacrine cells and bipolar cells, consistently formed neuropil with RGCs, even in ectopic locations. Interestingly, RGCs dendrites contacted both bipolar cell ‘axon-like’ (basal neurites) and ‘dendrite-like’ processes (apical neurites) in the has retina, although they specifically form synapses with bipolar cell axons in the wild type retina.
Taken together, RGCs likely respond to cell-extrinsic cues from the inner plexiform layer to preferentially maintain their rate of apical dendrite addition as they form a polarized dendritic arbor toward their presynaptic targets.
Chair and Committee
Rachel Wong, David Beebe, Aaron DiAntonio, Paul Gray, Kristen Kroll, Peter Lukasiewicz
Choi, Jung-Hwan, "In Vivo Development of Zebrafish Retinal Ganglion Cell Dendritic Patterns" (2009). Arts & Sciences Electronic Theses and Dissertations. 46.