Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

Abstract

Neuropeptides play essential roles in regulation of reproduction and growth in marine molluscs. But their function in marine bivalves – a group of animals of commercial importance – is largely unexplored due to the lack of systematic identification of these molecules. In this study, we sequenced and analyzed the transcriptome of nerve ganglia of Yesso scallop Patinopecten yessoensis, from which 63 neuropeptide genes were identified based on BLAST and de novo prediction approaches, and 31 were confirmed by proteomic analysis using the liquid chromatography-tandem mass spectrometry (LC-MS/MS). Fifty genes encode known neuropeptide precursors, of which 20 commonly exist in bilaterians and 30 are protostome specific. Three neuropeptides that have not yet been reported in bivalves were identified, including calcitonin/DH31, lymnokinin and pleurin. Characterization of glycoprotein hormones, insulin-like peptides, allatostatins, RFamides, and some reproduction, cardioactivity or feeding related neuropeptides reveals scallop neuropeptides have conserved molluscan neuropeptide domains, but some (e.g., GPB5, APGWamide and ELH) are characterized with bivalve-specific features. Thirteen potentially novel neuropeptides were identified, including 10 that may also exist in other protostomes, and 3 (GNamide, LRYamide, and Vamide) that may be scallop specific. In addition, we found neuropeptides potentially related to scallop shell growth and eye functioning. This study represents the first comprehensive identification of neuropeptides in scallop, and would contribute to a complete understanding on the roles of various neuropeptides in endocrine regulation in bivalve molluscs.

In silico prediction of neuropeptides from the neural ganglia of Pacific abalone Haliotis discus hannai (Mollusca: Gastropoda)

“…The open reading frames (ORF) of allatostatin A1 and A2 cDNA sequences encoded deduced proteins of 114 and 129 amino acids with theoretical molecular mass of 12.60 and 14.06 kDa, respectively. The peptide precursor contains GxLamide at the C-terminal end, which is in agreement with a previous report on allatostatins A in D. reticulatum and P. yessoensis (Ahn et al 2017;Zhang et al 2018). Phylogenetic analysis revealed that buccalin precursors A1 and A2 of H. discus hannai were most closely related to D. reticulatum buccalin A1 and C. virginica buccalinlike neuropeptide precursors, respectively (Figure 1).…”

“…In H. discus hannai, allatostatin B was identified. It was found to encode a 25-residue signal peptide followed by four putative allatostatin B peptides that contained conserved W residues at both ends, consistent with the results of previous studies (Ahn et al 2017;Zhang et al 2018).…”

“…This neuropeptide was first isolated from Aplysia californica (Miller et al 1993). It has been also reported in L. gigantea (Veenstra 2010), C. gigas (Stewart et al 2014), D. reticulatum (Ahn et al 2017), and P. yessoensis (Zhang et al 2018). In H. discus hannai, two buccalin transcripts, allatostatin A1 and A2, were identified that encode 24 and 30-residue signal peptides and 3 and 5 copies of the mature peptide, respectively.…”

“…Sequence alignment of bioactive peptides revealed that H. discus hannai and D. reticulatum FFamide-1 shared the same residues (Figure 4). The characteristic Leu/Met and Arg/Asn substitutions were observed in FFamide of M. yessoensis (Zhang et al 2018).…”

“…Two peptides of the vasopressin-oxytocin family have been identified and characterized in marine gastropod mollusks (Cruz et al 1987). In addition, neuropeptides have been identified from Lottia gigantea (Veenstra 2010), Deroceras reticulatum (Ahn et al 2017), Charonia tritonis (Bose et al 2017), and Patinopecten yessoensis (Zhang et al 2018), all of which provide valuable information to understand the mechanisms of neuroendocrine regulation in mollusks.…”