Expression of taste sentinels, T1R, T2R, and PLCβ2, on the passageway for olfactory signals in zebrafish.

The senses of taste and smell detect overlapping sets of chemical compounds in fish, e.g. amino acids are detected by both senses. However, so far taste and smell organs appeared morphologically to be very distinct, with a specialized olfactory epithelium for detection of odors and taste buds located in the oral cavity and lip for detection of tastants. Here, we report dense clusters of cells expressing T1R and T2R receptors as well as their signal transduction molecule PLCβ2 in nostrils of zebrafish, i.e. on the entrance funnel through which odor molecules must pass to be detected by olfactory sensory neurons. Quantitative evaluation shows the density of these chemosensory cells in the nostrils to be as high or higher than that in the established taste organs oral cavity and lower lip. Hydrodynamic flow is maximal at the nostril rim enabling high throughput chemosensation in this organ. Taken together, our results suggest a sentinel function for these chemosensory cells in the nostril.