The synapses of vertebrate photoreceptors and sensory hair cells release neurotransmitter through specialized structures known as synaptic ribbons. In a screen for insertional mutations affecting visual function in zebrafish, we identifie the zebrafish wrb 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, reduced numbers 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 synaptic function through a combination of histological and molecular approaches.
In Aim 1, we will identify the subcellular localization of Wrb using transgenic approaches, we will determine if Wrb affects ribbon assembly during development, how loss of Wrb affects dendritic morphology of postsynaptic cells, and whether Wrb blocks synaptic vesicle release or membrane endocytosis.
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 synaptic architecture and possibly provide insight into candidate genes for blindness/deafness disorders.
Both photoreceptors and hair cells of the inner ear transmit information to downstream neurons through specialized structures termed ribbon synapses. The precise composition and functional dynamics of ribbon synapses are poorly understood. The zebrafish wrb mutant shows defects in ribbon synapse structure and this mutant affects a novel gene with no known function. Investigations into the cellular consequences of mutating the wrb gene and identifying protein binding partners of the Wrb protein will provide insight into the mechanisms that lead to blindness and deafness.