CLONING AND FUNCTIONAL-CHARACTERIZATION OF A NOVEL DOPAMINE-RECEPTOR FROM DROSOPHILA-MELANOGASTER

A cDNA clone is described that encodes a novel G-protein-coupled dopam ine receptor (DopR99B) expressed in Drosophila heads. The DopR99B rece ptor maps to 99B3-5, close to the position of the octopamine/tyramine receptor gene at 99A10B1, suggesting that the two may be related throu gh a gene duplication. Agonist stimulation of DopR99B receptors expres sed in Xenopus oocytes increased intracellular Ca2+ levels monitored a s changes in an endogenous inward Ca2+-dependent chloride current. In addition to initiating this intracellular Ca2+ signal, stimulation of DopR99B increased cAMP levels. The rank order of potency of agonists i n stimulating the chloride current is: dopamine > norepinephrine > epi nephrine > tyramine, Octopamine and 5-hydroxytryptamine are not active (<100 mu M). This pharmacological profile plus the second-messenger c oupling pattern suggest that the DopR99B receptor is a D1-like dopamin e receptor. However, the hydrophobic core region of the DopR99B recept or shows almost equal amino acid sequence identity (40-48%) with verte brate serotonergic, alpha 1- and beta-adrenergic, and D1-like and D2-l ike dopaminergic receptors. Thus, this Drosophila receptor defines a n ovel structural class of dopamine receptors. Because DopR99B is the se cond dopamine receptor cloned from Drosophila, this work establishes d opamine receptor diversity in a system amenable to genetic dissection.