Date of Award
Doctor of Philosophy (PhD)
Although much is known about how axons and dendrites are guided to a target tissue, little is understood regarding how pre- and postsynaptic partners are matched for synapse formation. The zebrafish lateral line offers the opportunity for greater insight into this process. Hair cells in the lateral-line neuromast exist as two intermingled subpopulations, anteriorly and posteriorly polarized cells. Afferent neurons form synapses with hair cells of only one subpopulation, and this polarity-specific innervation arises independently of synaptic activity. The research presented in my thesis deepens the understanding of synapse formation in the zebrafish lateral line. First, I examine the neuronal architecture of the neuromast at nanometer-scale resolution by imaging the tissue by serial block-face electron microscopy. The data demonstrate that afferent neurons show a polarity preference at the earliest stages of hair-cell innervation, and additionally that the synaptic arrangement appears to arise from interactions among neurons for access to synaptic ribbons rather than being mediated by an accessory cell. I next describe a novel phenomenon, the extension of transient, dynamic projections from the base of nascent hair cells beginning shortly after mitosis. The projections extend toward nearby mature hair-cell synapses and filopodia arising from afferent terminals extend directly along them toward unoccupied synaptic ribbons. Hair-cell projections lacking stable association of afferent neurons are larger than those that are stably innervated. The appearance of hair-cell projections is contemporaneous with the initiation of contact between afferent neurons and nascent hair cells, and the disappearance of projections coincides with the appearance of pre- and postsynaptic markers proteins. I propose a model in which hair-cell projections act as cellular scaffolds for the guidance of neurons to available synaptic sites. Finally, I describe a novel method for collecting subpopulations of cells for gene expression analysis, which I employ to compare the transcriptomes of anteriorly and posteriorly polarized hair cells. I identified a number of differentially expressed candidate genes that might mediate polarity-specific afferent innervation. This work expands the repertoire of tools available for investigations of the neuromast and enhances the understanding of synapse formation in the zebrafish lateral line.
Dow, Eliot, "Synapse Formation in the Zebrafish Lateral Line" (2015). Student Theses and Dissertations. 277.