Defining the Specificity and Dynamics of Peripheral Sour Taste Circuits

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 brain1. The turnover and re-establishment of these taste synapses is crucial for the preservation of taste perception over time. In an effort to identify GN-TRC relationships. recent single-cell transcriptomic studies have found genetically distinct subpopulations of geniculate ganglion GNs2. One of these populations. marked by the expression of Penk-Cre. is primarily activated by sour taste stimuli in calcium imaging assays. Given this data. three questions have been raised: 1) Do Penk-Cre expressing gustatory neurons synapse with sour TRCs. 2) If so. are they the only population of GNs to do so. 3) And how do sour taste synapses change over time during TRC turnover? 
 To visualize synaptic contacts between sour TRCs and GNs in vivo. I will use GRASP (GFP Reconstitution Across Synaptic Partners). GRASP is the only technique that can be applied in vitro to observe synapse specificity and in vivo to study the formation. maintenance. and turnover of taste synapses in time-lapse experiments. In preliminary work. I have engineered transgenic mice expressing the pre-synaptic cyan GRASP component in the sour TRCs (PKD2L1-pre-CRASP) and viral tools for Cre-dependent post-synaptic GRASP expression in the GNs. This system produces bright. cyan-fluorescent puncta on the surface of sour TRCs within the taste bud. Here. using GRASP. I propose to investigate the connectivity. specificity. and dynamics of sour taste synapses.