Crustacean cardioactive peptides: Expression, localization, structure, and a possible involvement in regulation of egg-laying in the cuttlefish Sepia officinalis

Crustacean cardioactive peptide signaling system in the gastropod mollusk Pacific abalone

Crustacean cardioactive peptide (CCAP) signaling systems have been characterized in a diverse range of protostomes, representatively in arthropods. The cyclic CX5C-type CCAP regulates various biological activities through CCAP receptors (CCAPRs), which are orthologous to neuropeptide S receptors (NPSRs) in deuterostomes. However, the CCAPRs of the lophotrochozoa remain poorly characterized; therefore, the relationship between the CCAP, NPS, and CX4C-type oxytocin/vasopressin (OT/VP) signaling systems is unclear. In this study, we identified a CCAP precursor and two CCAPR isoforms in the Pacific abalone (Haliotis discus hannai; Hdh). The Hdh-CCAP precursor was found to harbor three CX5C-type and one CX4C-type CCAPs. The Hdh-CCAPRs displayed homology with protostome CCAPRs and deuterostome NPSRs, having characteristics of the rhodopsin-type G protein-coupled receptors. Phylogenetic analysis showed that lophotrochozoan CCAPRs, including Hdh-CCAPRs, form a monophyletic group distinct from arthropod CCAPRs. Reporter assays demonstrated that all examined Hdh-CCAPs and insect CCAP-induced intracellular Ca2+ mobilization and cAMP accumulation in Hdh-CCAPR-expressing HEK293 cells, whereas none of the CCAP peptides inhibited the forskolin-stimulated cAMP signaling pathway even at micromolar concentrations. In silico ligand-receptor docking models showed that the N-terminal FCN motifs of Hdh-CCAPs are deeply inserted inside the binding pocket of Hdh-CCAPR, forming extensive hydrophobic interactions. In mature Pacific abalone, the transcripts for Hdh-CCAP precursor and Hdh-CCAPR were highly expressed in the neural ganglia compared to the peripheral tissues. Collectively, this study characterized the first CCAP signaling system linked to both Ca2+/PKC and cAMP/PKA signal transduction pathways in gastropod mollusks and gives insights into the evolutional origins of deuterostomian NPS and OT/VP signaling systems.

PepTraq: a toolbox for in silico data mining and fast sequence filtering

The development of de novo sequencing tools has led to the massive production of genomes and transcriptomes from many unconventional animal models. To tackle this huge flow of data, PepTraq brings together many functionalities generally scattered in multiple tools, so that sequences can be filtered on the basis of multiple criteria. It is particularly suitable for the identification of non-annotated transcripts, re-annotation, extraction of secretomes, neuropeptidomes, targeted search for peptides and proteins, preparing specific proteomics/peptidomics fasta files for mass spectrometry (MS) applications, MS data processing, etc. PepTraq is developed in Java, and is available as a desktop application that can be downloaded from https://peptraq.greyc.fr . It is also available as a web application at the same URL for processing small files (10-20 MB). The source code is open under a CeCILL-B licence.

Structural and Functional Characterization of Orcokinin B-like Neuropeptides in the Cuttlefish (Sepia officinalis)

The cuttlefish (Sepia officinalis) is a Cephalopod mollusk that lives in the English Channel and breeds in coastal spawning grounds in spring. A previous work showed that the control of egg-laying is monitored by different types of regulators, among which neuropeptides play a major role. They are involved in the integration of environmental cues, and participate in the transport of oocytes in the genital tract and in the secretion of capsular products. This study addresses a family of neuropeptides recently identified and suspected to be involved in the control of the reproduction processes. Detected by mass spectrometry and immunocytochemistry in the nerve endings of the accessory sex glands of the females and ovary, these neuropeptides are also identified in the hemolymph of egg-laying females demonstrating that they also have a hormone-like role. Released in the hemolymph by the sub-esophageal mass, a region that innervates the genital tract and the neurohemal area of the vena cava, in in vitro conditions these neuropeptides modulated oocyte transport and capsular secretion. Finally, in silico analyses indicated that these neuropeptides, initially called FLGamide, had extensive structural homology with orcokinin B, which motivated their name change.

Transcriptome Profiling of the Pacific Oyster Crassostrea gigas Visceral Ganglia over a Reproduction Cycle Identifies Novel Regulatory Peptides

The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.

Molecular and physiological characterization of a crustacean cardioactive signaling system in a lophotrochozoan - the Pacific oyster (Crassostrea gigas): a role in reproduction and salinity acclimation

The crustacean cardioactive peptide (CCAP) is an important neuropeptide involved in the regulation of a variety of physiological processes in arthropods. Although this family of peptides has an ancestral origin, its function remains poorly understood among protostome species - apart from arthropods. We functionally characterized three G protein-coupled receptors (GPCRs) in the oyster Crassostrea gigas, phylogenetically related to ecdysozoan CCAP receptors (CCAPRs) and to chordate neuropeptide S receptors (NPSRs). Cragi-CCAPR1 and Cragi-CCAPR2 were specifically activated by the Cragi-CCAP1 and Cragi-CCAP2 peptides, respectively, both derived from the same CCAP precursor. In contrast, Cragi-CCAPR3 was only partially activated by CCAP1 and CCAP2 at high concentrations. The Cragi-CCAPR1 and Cragi-CCAPR2 genes were expressed in various adult tissues. They are both most expressed in the gills, while Cragi-CCAPR3 is mainly expressed in the visceral ganglia (VG). Cragi-CCAP precursor transcripts are higher in the VG, the labial palps and the gills. Receptor and ligand-encoding transcripts are more abundantly expressed in the gonads in the first stages of gametogenesis, while the Cragi-CCAP precursor is upregulated in the VG in the last stages of gametogenesis. This suggests a role of the CCAP signaling system in the regulation of reproductive processes. A role in water and ionic regulation is also supported considering the differential expression of the CCAP signaling components in oysters exposed to brackish water.

Ancient origins of arthropod moulting pathway components

Ecdysis (moulting) is the defining character of Ecdysoza (arthropods, nematodes and related phyla). Despite superficial similarities, the signalling cascade underlying moulting differs between Panarthropoda and the remaining ecdysozoans. Here, we reconstruct the evolution of major components of the ecdysis pathway. Its key elements evolved much earlier than previously thought and are present in non-moulting lophotrochozoans and deuterostomes. Eclosion hormone (EH) and bursicon originated prior to the cnidarian-bilaterian split, whereas ecdysis-triggering hormone (ETH) and crustacean cardioactive peptide (CCAP) evolved in the bilaterian last common ancestor (LCA). Identification of EH, CCAP and bursicon in Onychophora and EH, ETH and CCAP in Tardigrada suggests that the pathway was present in the panarthropod LCA. Trunk, an ancient extracellular signalling molecule and a well-established paralog of the insect peptide prothoracicotropic hormone (PTTH), is present in the non-bilaterian ctenophore Mnemiopsis leidyi. This constitutes the first case of a ctenophore signalling peptide with homology to a neuropeptide.

Animals such as insects, crabs and spiders belong to one of the most species-rich animal groups, called the arthropods. These animals have exoskeletons, which are hard, external coverings that support their bodies. Arthropods shed their exoskeletons as they grow, a process called ecdysis or moulting, and this behaviour is controlled by a set of hormones and small protein-like molecules called neuropeptides that allow communication between neurons.

Other animals, such as roundworms, also moult; and together with arthropods they are classified into a group called the Ecdysozoa. Since moulting is a common behaviour in ecdysozoans, it was previously assumed that its signalling components had evolved in the common ancestor of roundworms and arthropods, although differences in the moulting machinery between both groups exist.

Here, De Oliveira et al. investigate the evolutionary origins of the arthropod moulting machinery and find that some of the hormones and neuropeptides involved appeared long before the arthropods themselves.

Database searches showed that important hormones and neuropeptides involved in arthropod moulting can be found in diverse animal groups, such as jellyfish, molluscs and starfish, confirming that these molecules evolved before the last common ancestor of roundworms and arthropods. These animals must therefore use the hormones and neuropeptides in many processes unrelated to moulting. De Oliveira et al. also found that roundworms have lost most of these molecules, and that moulting in these animals must be driven by a different complement of hormones and neuropeptides.

These results invite research into the role of moulting hormones and neuropeptides in animals outside the Ecdysozoa. They also show that signalling pathways and the processes they regulate are highly adaptable: two animals can use the same hormone in entirely different processes, but conversely, the same behaviour may be regulated by different molecules depending on the animal. This means that the evolution of a process and the evolution of its regulation can be decoupled, a finding that has important implications for the study of signalling pathways and their evolution.

Neural Ganglia Transcriptome and Peptidome Associated with Sexual Maturation in Female Pacific Abalone (Haliotis discus hannai)

Genetic information of reproduction and growth is essential for sustainable molluscan fisheries and aquaculture management. However, there is limited knowledge regarding the reproductive activity of the commercially important Pacific abalone Haliotisdiscushannai. We performed de novo transcriptome sequencing of the ganglia in sexually immature and mature female Pacific abalone to better understand the sexual maturation process and the underlying molecular mechanisms. Of the ~305 million high-quality clean reads, 76,684 transcripts were de novo-assembled with an average length of 741 bp, 28.54% of which were annotated and classified according to Gene Ontology terms. There were 256 differentially expressed genes between the immature and mature abalone. Tandem mass spectrometry analysis, as compared to the predicted-peptide database of abalone ganglia transcriptome unigenes, identified 42 neuropeptide precursors, including 29 validated by peptidomic analyses. Label-free quantification revealed differential occurrences of 18 neuropeptide families between immature and mature abalone, including achatin, FMRFamide, crustacean cardioactive peptide, and pedal peptide A and B that were significantly more frequent at the mature stage. These results represent the first significant contribution to both maturation-related transcriptomic and peptidomic resources of the Pacific abalone ganglia and provide insight into the roles of various neuropeptides in reproductive regulation in marine gastropods.

Emergence of a cholecystokinin/sulfakinin signalling system in Lophotrochozoa

Chordate gastrin/cholecystokinin (G/CCK) and ecdysozoan sulfakinin (SK) signalling systems represent divergent evolutionary scenarios of a common ancestral signalling system. The present article investigates for the first time the evolution of the CCK/SK signalling system in a member of the Lophotrochozoa, the second clade of protostome animals. We identified two G protein-coupled receptors (GPCR) in the oyster Crassostrea gigas (Mollusca), phylogenetically related to chordate CCK receptors (CCKR) and to ecdysozoan sulfakinin receptors (SKR). These receptors, Cragi-CCKR1 and Cragi-CCKR2, were characterised functionally using a cell-based assay. We identified di- and mono-sulphated forms of oyster Cragi-CCK1 (pEGAWDY(SO₃H)DY(SO₃H)GLGGGRF-NH₂) as the potent endogenous agonists for these receptors. The Cragi-CCK genes were expressed in the visceral ganglia of the nervous system. The Cragi-CCKR1 gene was expressed in a variety of tissues, while Cragi-CCKR2 gene expression was more restricted to nervous tissues. An in vitro bioassay revealed that different forms of Cragi-CCK1 decreased the frequency of the spontaneous contractions of oyster hindgut. Expression analyses in oysters with contrasted nutritional statuses or in the course of their reproductive cycle highlighted the plausible role of Cragi-CCK signalling in the regulation of feeding and its possible involvement in the coordination of nutrition and energy storage in the gonad. This study confirms the early origin of the CCK/SK signalling system from the common bilaterian ancestor and delivers new insights into its structural and functional evolution in the lophotrochozoan lineage.

Characterization of NGFFYamide Signaling in Starfish Reveals Roles in Regulation of Feeding Behavior and Locomotory Systems

Neuropeptides in deuterostomian invertebrates that have an Asn-Gly motif (NG peptides) have been identified as orthologs of vertebrate neuropeptide-S (NPS)-type peptides and protostomian crustacean cardioactive peptide (CCAP)-type neuropeptides. To obtain new insights into the physiological roles of NG peptides in deuterostomian invertebrates, here we have characterized the NG peptide signaling system in an echinoderm-the starfish Asterias rubens. The neuropeptide NGFFYamide was identified as the ligand for an A. rubens NPS/CCAP-type receptor, providing further confirmation that NG peptides are orthologs of NPS/CCAP-type neuropeptides. Using mRNA in situ hybridization, cells expressing the NGFFYamide precursor transcript were revealed in the radial nerve cords, circumoral nerve ring, coelomic epithelium, apical muscle, body wall, stomach, and tube feet of A. rubens, indicating that NGFFYamide may have a variety of physiological roles in starfish. One of the most remarkable aspects of starfish biology is their feeding behavior, where the stomach is everted out of the mouth over the soft tissue of prey. Previously, we reported that NGFFYamide triggers retraction of the everted stomach in A. rubens and here we show that in vivo injection of NGFFYamide causes a significant delay in the onset of feeding on prey. To investigate roles in regulating other aspects of starfish physiology, we examined the in vitro effects of NGFFYamide and found that it causes relaxation of acetylcholine-contracted apical muscle preparations and induction of tonic and phasic contraction of tube feet. Furthermore, analysis of the effects of in vivo injection of NGFFYamide on starfish locomotor activity revealed that it causes a significant reduction in mean velocity and distance traveled. Interestingly, experimental studies on mammals have revealed that NPS is an anxiolytic that suppresses appetite and induces hyperactivity in mammals. Our characterization of the actions of NGFFYamide in starfish indicates that NPS/NG peptide/CCAP-type signaling is an evolutionarily ancient regulator of feeding and locomotion.