Shared and unique G alpha proteins in the zebrafish versus mammalian senses of taste and smell.

Chemosensory systems in vertebrates employ G protein-coupled receptors as sensors. In mammals, several families of olfactory and gustatory receptors as well as specific G alpha proteins coupling to them have been identified, for example, gustducin for taste. Orthologous receptor families have been characterized in fish, but the corresponding G alpha genes have not been well investigated so far. We have performed a comprehensive search of several lower vertebrate genomes to establish the G alpha protein family in these taxa and to identify those genes that may be involved in chemosensory signal transduction in fish. We report that gustducin is absent from the genomes of all teleost and amphibian species analyzed, presumably due to independent gene losses in these lineages. However, 2 other G alpha genes, Gi1b and G14a, are expressed in zebrafish taste buds and 4 G proteins, Go1, Go2, Gi1b, and Golf2, were detected in the olfactory epithelium. Golf2, Gi1b, and G14a are expressed already shortly after hatching, consistent with the physiological and behavioral responses of larvae to odorants and tastants. Our results show general similarity to the mammalian situation but also clear-cut differences and as such are essential for using the zebrafish model system to study chemosensory perception.