Defining the Connectivity and Dynamics of Peripheral Sour Taste Circuits

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Abstract The sense of taste is a complex and integrative chemosensory system that guides consummatory behavior. Taste receptor cells (TRCs) in the taste bud are continuously renewed and must reconnect with peripheral gustatory neurons (GNs) to relay taste signals to the brain. The turnover and re-establishment of peripheral taste synapses is vital to maintain this complex sensory system. Studies have demonstrated the molecular mechanisms governing the differentiation, maturation and turnover of TRCs as well as the identification of molecularly and functionally separate populations of geniculate ganglion neurons. However, the synaptic connectivity and dynamics between TRCs and GNs remains unknown due to the lack of technologies to examine them. To overcome this, I have developed GFP Reconstitution Across Synaptic Partners (GRASP) to visualize synaptic contacts in the taste bud. GRASP consists of pre- and post-GRASP split GFP molecules expressed, directed, and anchored into the synaptic membranes of pre- and post-synaptic cells, respectively. Because expression of the GRASP components can be controlled genetically, we can use it to assess the connectivity of specific populations. Moreover, GRASP produces bright fluorescent signals in native tissues which grants the unique ability to study synapse dynamics in time-lapse studies. In preliminary work, I have created transgenic mice that express the cyan variant of the pre-GRASP protein under the PKD2L1 promoter, a marker for sour TRCs. Additionally, I have engineered Flex-switch post-GRASP AAVs which enables us to express the post-synaptic GRASP in GNs. With this novel technique at hand, my goal is to genetically identify potential GN-TRC synaptic partners and to characterize synaptic dynamics during taste cell turnover, using sour TRCs as a model. To achieve these goals, this proposal will investigate two aims, 1) Identify synaptic partners for sour TRCs in the fungiform, circumvallate, and laryngeal taste buds, and 2) Determine the longevity and dynamics of sour TRC synapses over time. This proposal is designed to use GRASP, a novel and innovative technique, to elucidate synaptic connectivity and dynamics in the peripheral taste system, which will have far-reaching impact in the fields of taste development, connectivity, and taste disorders.