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RESEARCH PRODUCT

Piecing together the taste signaling puzzle

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International audience; The identification of the genes coding for bitter, umami, sweet and sour taste receptors has provided us with unique tools to investigate the gustatory system. As a consequence, tremendous progress towards our understanding of the functional organization of the peripheral taste system has been achieved over the past decade. In particular, key components of the taste receptors signaling cascades have been identified as well as populations of chemosensory cells in the olfactory, respiratory and digestive systems expressing taste receptors. Besides sharing receptors and signaling molecules (gustducin, phospholipase-C b2…) with taste bud cells, these cells display a similar spatial and functional organization likely to drive the assembly of specialized protein complexes at their basal or apical poles. We have used a yeast two-hybrid approach to dissect the networks involved in bringing together taste receptors and signaling complexes. Recently we reported the expression of two GDP exchange factors (Ric-8A and Ric-8B) in a large proportion of taste bud cells mostly co-expressing IP3R-3 a marker for sweet, bitter and umami receptor containing cells. Ric-8A interacts with Ga-gustducin and Gai2 through which it amplifies the signal transduction of hT2R16, a receptor for bitter compounds. We also uncovered a candidate scaffolding protein linking the sweet receptor to actin for which we mapped the interaction domains these types of receptors. When T1R3 is knocked out, mice still demonstrate physiological and behavioral responses to umami. In mGluR4-knockout mice, umami taste preference was dramatically altered. Our functional imaging data also suggest that different groups of cells in taste buds respond to different umami stimuli. On the basis of molecular, cellular, physiological and behavioral data, we propose that umami taste detection is complex and involves multiple receptors in different subsets of taste cells. This receptor diversity may underlie the complex experience of umami.