Identification, Characterization, and Expression Analysis of a FMRFamide-Like Peptide Gene in the Common Chinese Cuttlefish (Sepiella japonica)

FMRFamide G protein-coupled receptors (GPCR) in the cuttlefish Sepiella japonica: Identification, characterization and expression profile

FMRFamide is a ubiquitous neuromodulator in the animal kingdom. Once FMRFamide or similar neuropeptides bind to their G protein-coupled receptors (GPCR), a series of signal transduction events are triggered, thereby mediating various physiological effects. FMRFamide had been reported to be involved in the regulation of sexual maturation in Sepiella japonica. In this research, the full-length cDNA of FMRFamide G protein-coupled receptor of S. japonica (SjFaGPCR) was cloned. The sequence is 1396 bp long and encodes a protein consisting of 418 amino acid residues, lacking a signal peptide at the N-terminal region. The 3D structure of SjFaGPCR was predicted using Todarodes pacificus rhodopsin as a template, and the result indicated the presence of seven transmembrane regions. Multiple sequence alignments and phylogenetic trees indicated that SjFaGPCR is conserved among invertebrates, and shares highly similar sequence characteristics with other cephalopods. In situ hybridization (ISH) results revealed that significant signals of SjFaGPCR were detected in the central medulla and the granular layer cells of the optic lobe, and were also observed in the supraesophageal and subesophageal masses of the brain. Meanwhile, quantitative real-time PCR (qRT-PCR) results showed that a higher expression level of SjFaGPCR mRNA was detected in the brain and optic lobe of female cuttlefish at stage III and stage VI, and also in the brain (stage V) and optic lobe (stages IV and V) of male cuttlefish than that in other tissues. The co-localization results demonstrated that fluorescence signals of SjFMRFamide and SjFaGPCR were overlapped in HEK293 cells, suggesting a possible interaction between the SjFMRFamide and SjFaGPCR. These findings provide molecular support for further exploring the roles of FMRFamide and FaGPCR in the reproductive regulation of S. japonica.

The genome of the simultaneously hermaphroditic snail Lymnaea stagnalis reveals an evolutionary expansion of FMRFamide-like receptors

The great pond snail Lymnaea stagnalis has served as a model organism for over a century in diverse disciplines such as neurophysiology, evolution, ecotoxicology and developmental biology. To support both established uses and newly emerging research interests we have performed whole genome sequencing (avg.176 × depth), assembly and annotation of a single individual derived from an inbred line. These efforts resulted in a final assembly of 943 Mb (L50 = 257; N50 = 957,215) with a total of 22,499 predicted gene models. The mitogenome was found to be 13,834 bp long and similarly organized as in other lymnaeid species, with minor differences in location of tRNA genes. As a first step towards understanding the hermaphroditic reproductive biology of L. stagnalis, we identified molecular receptors, specifically nuclear receptors (including newly discovered 2xDNA binding domain-NRs), G protein-coupled receptors, and receptor tyrosine kinases, that may be involved in the cellular specification and maintenance of simultaneously active male and female reproductive systems. A phylogenetic analysis of one particular family of GPCRs (Rhodopsin neuropeptide FMRFamide-receptor-like genes) shows a remarkable expansion that coincides with the occurrence of simultaneous hermaphroditism in the Euthyneura gastropods. As some GPCRs and NRs also showed qualitative differences in expression in female (albumen gland) and male (prostate gland) organs, it is possible that separate regulation of male and female reproductive processes may in part have been enabled by an increased abundance of receptors in the transition from a separate-sexed state to a hermaphroditic condition. These findings will support efforts to pair receptors with their activating ligands, and more generally stimulate deeper insight into the mechanisms that underlie the modes of action of compounds involved in neuroendocrine regulation of reproduction, induced toxicity, and development in L. stagnalis, and molluscs in general.

The brain structure and the neural network features of the diurnal cuttlefish Sepia plangon

Cuttlefish are known for their rapid changes of appearance enabling camouflage and con-specific communication for mating or agonistic display. However, interpretation of their sophisticated behaviors and responsible brain areas is based on the better-studied squid brain atlas. Here we present the first detailed description of the neuroanatomical features of a tropical and diurnal cuttlefish, Sepia plangon, coupled with observations on ontogenetic changes in its visual and learning centers using a suite of MRI-based techniques and histology. We then make comparisons to a loliginid squid, treating it as a 'baseline', and also to other cuttlefish species to help construct a connectivity map of the cuttlefish brain. Differences in brain anatomy and the previously unknown neural connections associated with camouflage, motor control and chemosensory function are described. These findings link brain heterogeneity to ecological niches and lifestyle, feeding hypotheses and evolutionary history, and provide a timely, new technology update to older literature.

Identification and Characterization of Hdh-FMRF2 Gene in Pacific Abalone and Its Possible Role in Reproduction and Larva Development

FMRFamide-related peptides are neuropeptides involved in a wide range of biological processes, including reproduction and larval development. To characterize the involvement of FMRFamide in the reproduction and larval development of Pacific abalone Haliotis discus hannai, an FMRFamide cDNA (Hdh-FMRF2) was cloned from the cerebral ganglion (CG). Fluorescence in situ hybridization and qRT-PCR were performed for functional characterization. The Hdh-FMRF2 cDNA encoded 204 deduced amino acids that contained a putative signal peptide and four FaRP domains. The major population of Hdh-FMRF2 neuronal cell bodies was localized in the cortex of CG. Hdh-FMRF2 mRNA expression was significantly upregulated in CG during the mature stage of gonadal development and effective accumulative temperature (EAT) exposed abalone in both sexes. In the induced spawning event, Hdh-FMRF2 expression was significantly upregulated during spawning in males. However, no upregulation was observed in females, suggesting Hdh-FMRF2 might inhibit gamete release in female abalone. These results revealed Hdh-FMRF2 as a reproduction related peptide. Furthermore, mRNA expression in larval development suggested that this peptide was also involved in larval development during development of Pacific abalone. Collectively, this study provides evidence of possible involvement of an FMRFamide neuropeptide in the reproduction and larval development of Pacific abalone.

Inhibitory Effect of FMRFamide on NO Production During Immune Defense in Sepiella japonica

Neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide), specifically existing in invertebrates, plays pivotal roles in various physiological processes. The involvement in neuroendocrine-immune regulation was explored in recent years, and it could modulate nitric oxide (NO) production under immune stress. However, detailed knowledge is still little known. In this study, we identified FMRFamide as an inhibitory factor on NO production in the immune reaction of Sepiella japonica. Firstly, Vibrio harveyi incubation caused significantly upregulated expression of FMRFamide precursor and NO synthase (NOS) in just hatched cuttlefish with quantitative Real-time PCR (qRT-PCR), which indicated that both were likely to be involved in the immune defense. The whole-mount in situ hybridization (ISH) detected FMRFamide precursor and NOS-positive signals appeared colocalization, suggesting that at histological and anatomical levels FMRFamide might interact with NOS. Next, NOS mRNA was highly significantly upregulated at 72 h when FMRFamide precursor mRNA was knocked down effectively with the RNA interference (RNAi) method; the results hinted that FMRFamide was likely to regulate NO production. Continuously, the inflammatory model was constructed in RAW 264.7 cells induced by lipopolysaccharide (LPS), FMRFamide administration resulted in a highly significant reduction of the NO level in dose- and time-response manners. Although the addition of the selected inducible NOS (iNOS) inhibitor had inhibited the NO production induced by LPS, the additional FMRFamide could still furtherly sharpen the process. Collectively, it was concluded that neuropeptide FMRFamide could indeed inhibit NO production to serve as feedback regulation at the late stage of immune response to protect hosts from excessive immune cytotoxicity. The inhibitory effect on NO production could not only be mediated by the NOS pathway but also be implemented through other pathways that needed to be furtherly explored. The results will provide data for comparing the structure and immune function of neuroendocrine-immune system (NEIS) between "advanced" cephalopods and other invertebrates and will provide new information for understanding the NEIS of cephalopods.

An FMRFamide Neuropeptide in Cuttlefish Sepia pharaonis: Identification, Characterization, and Potential Function

Neuropeptides are released by neurons that are involved in a wide range of brain functions, such as food intake, metabolism, reproduction, and learning and memory. A full-length cDNA sequence of an FMRFamide gene isolated from the cuttlefish Sepia pharaonis (designated as SpFMRFamide) was cloned. The predicted precursor protein contains one putative signal peptide and four FMRFamide-related peptides. Multiple amino acid and nucleotide sequence alignments showed that it shares 97% similarity with the precursor FMRFamides of Sepiella japonica and Sepia officinalis and shares 93% and 92% similarity with the SpFMRFamide gene of the two cuttlefish species, respectively. Moreover, the phylogenetic analysis also suggested that SpFMRFamide and FMRFamides from S. japonica and S. officinalis belong to the same sub-branch. Tissue expression analysis confirmed that SpFMRFamide was widely distributed among tissues and predominantly expressed in the brain at the three development stages. The combined effects of SpFMRFamide+SpGnRH and SpFLRFamide+SpGnRH showed a marked decrease in the level of the total proteins released in the CHO-K1 cells. This is the first report of SpFMRFamide in S. pharaonis and the results may contribute to future studies of neuropeptide evolution or may prove useful for the development of aquaculture methods for this cuttlefish species.

Identification and functional characterization of interferon-γ-inducible lysosomal thiol reductase (GILT) gene in common Chinese cuttlefish Sepiella japonica

Interferon-γ-inducible lysosomal thiol reductase (GILT) is a pivotal enzyme involved in the histocompatibility complex (MHC) class II-restricted antigen processing whereby it catalyzes the disulfide bond reduction in the endocytic pathway. Here, a novel GILT homologue termed as SjGILT firstly identified from common Chinese cuttlefish Sepiella japonica. SjGILT shared domain topology containing a signal peptide, a signature sequence CQHGX₂ECX₂NX₄C, an activate-site CXXC motif, two potential N-glycosylation sites and six conserved cysteins with its counterparts in other animals. SjGILT transcripts were constitutively expressed in all examined tissues in S. japonica, with the higher expression levels in immune-related tissues such as pancreas, intestines, liver and gills. Upon lipopolysaccharide (LPS) challenge, SjGILT transcripts were significantly induced in liver and gill tissues, and SjGILT protein transferred to late endosomes and lysosomes in HeLa cells. Further study showed that recombinant SjGILT had obvious thiol reductase activity demonstrated by reducing the interchain disulfide bonds of IgG under acidic conditions. Taken together, these results suggested that SjGILT may be involved in the immune response to bacteria challenge, and then might play an important role in the processing of MHC class II-restricted antigens in S. japonica.