Molecular characterization and analysis of a truncated serotonin receptor gene expressed in neural and reproductive tissues of abalone

Abstract

In molluscs, the neurotransmitter serotonin (5-HT) has been linked to a variety of biological roles including gamete maturation and spawning. The possible involvement of 5-HT in abalone gamete release was demonstrated by a dose-dependent increase in Haliotis rubra gonad contractile bioactivity following 5-HT stimulation. Physiological functions associated with 5-HT, are mediated through binding to 5-HT receptors. A cDNA encoding a putative 5-HT receptor consisting of 359 amino acids was isolated from the tropical abalone H. asinina, termed 5-HT(1 ha). The 5-HT(1 ha) shares G-protein-coupled receptor motifs with metazoan 5-HT receptors, including predicted transmembrane domains, active sites for protein kinase action, and N-linked glycosylation sites. However, the third intracellular loop of 5-HT(1 ha) is relatively short, and only six transmembrane domains are predicted, implying a truncated receptor. Phylogenetic analysis with known 5-HT receptor genes suggests that 5-HT(1 ha) belongs to the type 1 5-HT receptor family. Expression analysis by RT-PCR showed that 5-HT(1 ha) mRNA was present in all tissues examined, including the neural ganglia and gonad tissues. Immunocytochemistry revealed the presence of 5-HT(1 ha) specifically within the soma of neuronal cells located in the outer cortex of both cerebral and pleuropedal ganglia. In ovarian and testicular tissues, 5-HT(1 ha) immunoreactivity was observed in epithelial cells of the outer capsule and connective tissue of the trabeculae to which the gamete follicles adhere. Whether this receptor transcript is translated to a functional protein needs to be verified, but if so, it could play a role in reproduction.

Invertebrate serotonin receptors: a molecular perspective on classification and pharmacology

“…Barbas et al (2002) described a receptor in A. californica that differed from the 5HT 1 receptor previously described by Angers et al (1998), and that more closely resembled the sequence from the 5-HT 1 receptor (5-HT 1Lym ) from Lymnaea stagnalis (Sugamori et al, 1993). Phylogenetic analyses (Mapara et al, 2008;Panasophonkul et al, 2009;Tanabe et al, 2010) indicate that additional molluscan 5-HT 1 receptors listed in Table 1 are also more closely related to 5-HT 1Lym than to the first receptor cloned from Aplysia (Angers et al, 1998), and the latter may derive from a recent gene duplication (Nagakura et al, 2010). It would be premature to delineate receptor subtypes in molluscs, and hence Greek letters were not applied and the two Aplysia receptors are distinguished by lowercase letters.…”

Transcriptomic Analysis of Differentially Expressed Genes During Larval Development ofRapana venosaby Digital Gene Expression Profiling

“…The expression level of 5-hydroxytryptamine receptor, neuronal acetylcholine receptor, and nitric oxide synthase were found declined after metamorphosis. Serotonin and its receptors are involved in neuronal functions in mollusks, including the circadian rhythm of Aplysia californica ( Levenson et al 1999 ), locomotion of Lymnaea stagnalis ( Filla et al 2004 ), feeding of L. stagnalis ( Kawai et al 2011 ), and development of Haliotis rubra ( Panasophonkul et al 2009 ). Pharmacological and ecological experiments suggested that the 5-hydroxytryptamine receptor mediates settlement and metamorphosis of many mollusks, such as Ilyanassa obsolete ( Leise et al 2001 ) and Helisoma trivolvis ( Glebov et al 2014 ).…”

Identification of a female spawn‐associated Kazal‐type inhibitor from the tropical abalone Haliotis asinina

“…Gonads were embedded in paraffin and 5‐µm sections cut. Staining was performed using hematoxylin and eosin (H&E; Sigma) for histological observations, as described previously .…”