The Role of Wrb in Vertebrate Ribbon Synapse Formation

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Project Summary/Abstract The synapses of vertebrate photoreceptors and sensory hair cells release neurotransmitter through specialized structures known as synaptic ribbons. While ribbon synapses and conventional synapses utilize similar mechanisms for synaptic vesicle release, the protein composition at each type of synapse can vary. In a screen for insertional mutations affecting visual function in zebrafish, we identified the zebrafish pinball wizard mutant, which exhibited photoreceptor degeneration and hearing loss. The mutation disrupts the wrb gene, which encodes a novel 170 amino acid protein with no known function. In preliminary studies, we found that wrb mutants exhibited mislocalization of ribbon synapse components, reduction in the number of docked ribbons at photoreceptor synapses, and significantly reduced ERG responses. These data strongly suggest that Wrb could be integrally involved in ribbon synapse assembly and/or function. To validate this hypothesis, we will study the role of Wrb in zebrafish retina function through a combination of histological, physiological, and molecular approaches. In Aim 1, we will identify where Wrb blocks synaptic transmission by examining immunohistochemical markers for various synaptic proteins and through transgenic and electrophysiological recordings. In Aim 2, we will identify binding partners of Wrb using a transgenic approach to purify tagged Wrb complexes and subsequent analysis by mass spectroscopy. These studies will provide insights into the role of Wrb, a novel protein that may be a critical component to ribbon synapse structure and function. The identity of Wrb binding partners and the subsequent characterization of Wrb in an in vivo system will open new avenues of research on ribbon synapses and possibly provide insight into candidate genes for blindness/deafness disorders.