Molecular & Biochemical Parasitology 168 (2009) 24–33 Contents lists available at ScienceDirect Molecular & Biochemical Parasitology Investigation of a dopamine receptor in Schistosoma mansoni: Functional studies and immunolocalization Amira Taman, Paula Ribeiro ∗ Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Sainte Anne de Bellevue, Quebec, Canada H9X 3V9 article info Article history: Received 7 May 2009 Received in revised form 5 June 2009 Accepted 11 June 2009 Available online 21 June 2009 Keywords: Schistosoma mansoni Dopamine G-protein coupled receptor (GPCR) Neurotransmitter Biogenic amine Saccharomyces cerevisiae abstract A dopamine receptor (SmD2) was cloned from adult Schistosoma mansoni. The receptor has the clas- sical heptahelical topology of class A (rhodopsin-like) G protein-coupled receptors (GPCR) and shares sequence homology with D2-like receptors from other species. The full length SmD2 cDNA was expressed in the yeast Saccharomyces cerevisiae and mammalian HEK293 cells. Functional assays in both expression systems revealed that SmD2 was responsive to dopamine in a dose-dependent manner, whereas other structurally related amines had no effect. Activation of SmD2 in mammalian cells caused an elevation in intracellular cAMP but not calcium, suggesting that the receptor coupled to Gs and the stimulation of adenylate cyclase. Pharmacological studies showed that the S. mansoni dopamine receptor was inhibited by apomorphine, a classical dopamine agonist, as well as known dopaminergic antagonists, including chlorpromazine, spiperone and haloperidol. SmD2 immunoreactivity was detected in membrane protein fractions of S. mansoni cercaria, in vitro transformed schistosomula and adult parasites, using a specific peptide antibody. When tested by confocal immunofluorescence, SmD2 was detected in the subtegumen- tal somatic musculature and acetabulum of all larval stages tested. In the adults, SmD2 was enriched in the somatic muscles and, to a lesser extent, the muscular lining of the caecum. The results suggest that SmD2 is an important component of the neuromuscular system in schistosomes. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Schistosoma mansoni is a human pathogen responsible for schistosomiasis, a disease that afflicts nearly 200 million people worldwide. Schistosomiasis is acquired when free-living freshwater cercaria penetrate the skin and are transformed into schistosomula. The newly transformed larvae enter the circulation and undergo a complex migration through the heart and lungs towards the hepatoportal circulation, where they continue to develop to adult male and female worms. The ability to swim in the bloodstream and to navigate towards their final destination is fundamental to schistosome survival and is coordinated by the parasite’s neuro- muscular system. S. mansoni has a complex muscle organization within the body wall, consisting of sequential layers of circu- lar, longitudinal and diagonal muscle fibers [1], which enable the worms to lengthen, shorten and bend, as needed. A vast net- work of subtegumental neuronal plexuses innervates the body wall musculature and coordinates the activity of the different types of fibers to produce controlled movement. Some of the neurotrans- mitters involved in this regulation have been identified. Serotonin (5-hydroxytryptamine: 5HT) and FMRFamide – like neuropeptides ∗ Corresponding author. Tel.: +1 514 398 7607; fax: +1 514 398 7857. E-mail address: paula.ribeiro@mcgill.ca (P. Ribeiro). (FLPs) function as excitatory neuromuscular transmitters or mod- ulators, increasing both the frequency and amplitude of muscle contraction, whereas acetylcholine (ACh) is inhibitory and causes the muscle to relax [2,3]. Dopamine (DA), a catecholamine derived from tyrosine, also has neuromuscular effects in schistosomes but its mode of action is less clear. Exogenous application of DA onto intact animals was shown to cause a lengthening of the worm [4,5]. When added directly onto preparations of body wall muscle the amine caused pronounced relaxation of both circular and longi- tudinal muscle, nearly with the same potency as that caused by cholinergic agents [6]. Moreover, the effect was reversed by co- application of a DA antagonist (spiroperidol), suggesting this was receptor-mediated and probably an important inhibitory pathway. The mechanism responsible for this inhibition has not been inves- tigated. DA is an important neurotransmitter/modulator of vertebrates and invertebrates alike. In mammals DA is responsible for many physiological functions related to movement, cognition, learning, memory and mood [7]. Disruption of dopaminergic signaling has been linked to various neurological and psychiatric disorders [7]. Among invertebrates, DA is active both within the central nervous system (CNS) and periphery of every major phylum. Many of the effects of DA in invertebrates are associated with muscle function and movement. Planarians, in particular, have an extensive network of dopaminergic neurons that control muscle-mediated movement 0166-6851/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molbiopara.2009.06.003