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First published online February 29, 2008
Journal of Experimental Biology 211, 900-910 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013953

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Identification, molecular structure and expression of two cloned serotonin receptors from the pond snail, Helisoma trivolvis

Sabeen Mapara¹, Shawn Parries¹, Caitlin Quarrington¹, Kee-Chan Ahn¹, Warren J. Gallin¹ and Jeffrey I. Goldberg^1,2,*

¹ Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9
² Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada, T2N 1N4

^* Author for correspondence (e-mail: jigoldbe{at}ucalgary.ca)

Accepted 10 January 2008

Helisoma trivolvis has served as a model system to study the functions of serotonin (5-HT) from cellular, developmental, physiological and behavioural perspectives. To further explore the serotonin system at the molecular level, and to provide experimental knockout tools for future studies, in this study we identified serotonin receptor genes from the H. trivolvis genome, and characterized the molecular structure and expression profile of the serotonin receptor gene products. Degenerate oligonucleotide primers, based on conserved regions of the Lymnaea stagnalis 5-HT_1Lym receptor, were used to amplify G protein-coupled biogenic amine receptor sequences from H. trivolvis genomic cDNA, resulting in the cloning of two putative serotonin receptors. The deduced gene products both appear to be G protein-coupled serotonin receptors, with well-conserved structure in the functional domains and high variability in the vestibule entrance of the receptor protein. Phylogenetic analysis placed these receptors in the 5-HT₁ and 5-HT₇ families of serotonin receptors. They are thus named the 5-HT_1Hel and 5-HT_7Hel receptors, respectively. In situ hybridization and immunofluorescence studies revealed that these genes and gene products are expressed most heavily in the ciliated pedal and mantle epithelia of H. trivolvis embryos. In adults, widespread expression occurred in all ganglia and connectives of the central nervous system. Expression of both receptor proteins was localized exclusively to neurites when examined in situ. In contrast, when isolated neurons were grown in culture, 5-HT_1Hel and 5-HT_7Hel immunoreactivity were located primarily in the cell body. This is the first study to reveal a 5-HT₇ receptor in a molluscan species.

Key words: serotonin receptor, gastropod, mollusc, phylogenetic analysis, receptor expression