Characterization of a cloned locust tyramine receptor cDNA by functional expression in permanently transformed Drosophila S2 cells.

The cDNA for Tyr-Loc, a G protein-coupled receptor that clearly shows homology to a number of mammalian and fruit fly receptors for biogenic amines, was cloned from the nervous system of Locusta migratoria. Functional expression of the cloned cDNA was obtained in cultured insect cells, i.e., in Spodoptera SF9 cells using a baculoviral expression system and in stably transformed Drosophila Schneider 2 (S2) cells. Multiple copies of the receptor expression construct are inserted into the genome of these permanently transformed cells. The expression of the receptor cDNA was driven by the upstream sequences of a Bombyx mori baculoviral immediate early gene. Tyramine shows a much higher binding affinity to this receptor than other possible endogenous ligands. It also reduces forskolin-induced cyclic AMP production in the permanently transformed S2 cells. The pharmacological profile of the Tyr-Loc receptor is distinct from that of any locust receptor-type described so far, but it is similar to that of the Drosophila tyramine/octopamine receptor. In the locust CNS, the Tyr-Loc mRNA is not present in the distal part of the optic lobes but has a widespread distribution in the brain and the ventral nerve cord.