Molecular Characterization and Functional Analysis of a Putative Octopamine/Tyramine Receptor during the Developmental Stages of the Pacific Oyster, Crassostrea gigas.

Peng Ji,Baoyu Huang,Fei Xu,Li Li,Yingxiang Li,Guofan Zhang,Thiyagarajan Vengatesen

doi:10.1371/journal.pone.0168574

Abstract

Octopamine (OA) and its precursor, tyramine (TA), participate in invertebrate development such as growth, maturation, and reproduction by activating their corresponding G protein-coupled receptors (GPCRs). Although OA was first discovered in mollusks (octopus), subsequent studies on OA, TA and related receptors have primarily been conducted in Ecdysozoa, especially in insects. Accordingly, only limited reports on OA/TA receptors in mollusks are available and their physiological roles remain unclear. Here, a full-length cDNA encoding a putative 524 amino acid OA/TA receptor (CgGPR1) was isolated from the Pacific oyster Crassostrea gigas. CgGPR1 was most closely related to the Lymnaea stagnalis OA receptor OAR2 in sequence. Phylogenetic analysis showed that CgGPR1 belongs to a poorly studied subfamily of invertebrate OA/TA receptors. The spatio-temporal expression of CgGPR1 in C. gigas larvae was examined by quantitative real-time PCR and Western blot analysis. CgGPR1 was expressed during all developmental stages of C. gigas with higher levels at mid-developmental stages, indicating its potential role in embryogenesis and tissue differentiation. Immunoreactive fluorescence of CgGPR1 was mainly observed in the velum, foot, gill and mantle of C. gigas larvae. CgGPR1 transcripts were detected in all the tested organs of adult C. gigas, with highest level in the mantle. Pharmacological analysis showed that cAMP and Ca2+ concentrations remained unchanged in HEK293 cells expressing CgGPR1 upon addition of OA, TA or related amines, suggesting that CgGPR1 modulates other unknown molecules rather than cAMP and Ca2+. Our study sheds light on CgGPR1 function in oysters.

Highlights

Biogenic amines, including octopamine (OA), tyramine (TA), and other amines, comprise a large family of basic neuroactive factors and have significant physiological functions in most organisms ranging from microorganisms to animals
Hydrophobicity analysis revealed that CgGPR1 contains seven putative transmembrane segments (TM) connected by intra and extra-cellular loops including an extracellular N-terminus and a cytoplasmic C-terminus, and that CgGPR1 and its homologs have a relatively large loop connecting the TM5 and TM6 regions (Fig 1)
Phylogenetic analysis showed that CgGPR1 belongs to a poorly studied invertebrate OA/TA receptor subfamily that, until now, contained only three known members

Summary

Introduction

Biogenic amines, including octopamine (OA), tyramine (TA), and other amines, comprise a large family of basic neuroactive factors and have significant physiological functions in most organisms ranging from microorganisms to animals. OA, first discovered in mollusks (octopus), is synthesized from the amino acid tyrosine through TA in the animal body. OA represents one of the major biogenic amines and plays important roles in aggressive behaviors, sleep and reproductive processes. Similar functions are usually associated with both adrenaline and noradrenaline [1,2,3]. TA, as the precursor of OA, performs many functional roles in invertebrates, including olfaction in insects and reversal behavior in Caenorhabditis elegans [4, 5]. Little is known regarding OA and TA in mollusks

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