Functional Expression of Odorant Receptors of the Zebrafish Danio rerio and of the Nematode C. elegans in HEK293 Cells

Odorant receptors of zebrafish and C. elegans were functionallyexpressed in vertebrate kidney cells (HEK293) using the eucaryoticexpression vector pSMyc. Receptor-encoding cDNA cloned intothis vector was expressed as a fusion protein with the N-terminalmembrane import sequence of the guinea-pig serotonin receptorfollowed by a myc tag. Immunocytochemical evidence indicatesthat this strategy directs a protein with the predicted immunoreactivityand approximate molecular weight to the plasma membrane. Fishfood extract (TetraMin) evoked a transient increase in intracellular[Ca²⁺] in HEK293 cells transiently transfected with plasmidscontaining cDNA for three fish odorant receptors and convertedto stable cell lines. The effect of the extract was concentrationdependent and limited to the fraction of the extract <5 kDa.Pretreating the transfected cells with the PLC inhibitor U73122reduced the odor-evoked signal. Fish food extract also evokeda transient increase in intracellular [Ca²⁺] in HEK293 cellstransiently transfected with plasmids containing cDNA for singlefish odorant receptors. Diacetyl evoked a transient increasein intracellular [Ca²⁺] in HEK293 cells transiently transfectedwith plasmids encoding the cDNA of ODR10, an odorant receptorof C. elegans suggested in other work to be specific for diacetyl.These results strongly imply that odorant receptors can be functionallyexpressed in HEK293 cells using this novel expression protocol.Chem. Senses 22: 467–476, 1997.