Identification of Ras, Pten and p70S6K homologs in the Pacific oyster Crassostrea gigas and diet control of insulin pathway

Molecular and structural analysis of Hdh-MIRP3 and its impact on reproductive regulation in female Pacific abalone, Haliotis discus hannai

Molluscan insulin-related peptides (MIRP) play a crucial role in various biological processes, including reproduction and larval development in mollusk species. To investigate the involvement of MIRP in the ovarian development of Pacific abalone (Haliotis discus hannai), the Hdh-MIRP3 was cloned from cerebral ganglion (CG). Hdh-MIRP3 cDNA was 993 bp long, encoded a 13.22 kDa peptide, comprising 118 amino acids. Fluorescence in situ hybridization confirmed the localization of Hdh-MIRP3 in the CG and ovary. Molecular docking revealed that Hdh-MIRP3 binds to the N-terminal region of Hdh-IRP-R. Tissue expression analysis showed the highest Hdh-MIRP3 expression in the CG, followed by ovarian tissue. Hdh-MIRP3 expression was significantly upregulated in the CG and ovary during the ripe stage of seasonal ovarian development and in effective accumulative temperature conditioned abalone. Furthermore, siRNA silencing of Hdh-MIRP3 significantly downregulated the expression of four reproduction-related genes, including Hdh-GnRH, Hdh-GnRH-R, Hdh-IRP-R, and Hdh-VTG in both the CG and ovary, and Hdh-MIRP3 as well. These results indicate that Hdh-MIRP3 acts as a regulator of ovarian development in Pacific abalone. Additionally, expression analysis indicated that Hdh-MIRP3 plays a role in embryonic and larval development. Overall, the present findings elucidate the role of Hdh-MIRP3 in reproductive development in female Pacific abalone.

Examination of the potential roles of insulin-like peptide receptor in regulating the growth of Manila clam Ruditapes philippinarum

The role of insulin/insulin-like growth factor (IGF) signaling pathway in the growth regulation of marine invertebrates has not been fully studied. In this study, the economically important species Ruditapes philippinarum was sacrificed to clarify the role of IGF system in the growth regulation of R. philippinarum by real-time quantitative PCR. Systematic bioinformatics analysis can identify the major genes of IGF signaling pathway and insulin-like peptide receptor (ILPR) - mediated signaling pathway in R. philippinarum. The expression levels of IGF and its downstream signaling pathway genes in larger clams were significantly higher than those in small clams, indicating that they were involved in the growth regulation of R. philippinarum. These results suggest that IGF signaling pathway and ILPR mediated signaling pathway to regulate the growth of R. philippinarum.

Relationship between Condition Index Values and Expression Levels of Gene and Protein in the Adductor Muscle of Diploid and Triploid Oysters Crassostrea gigas

Three proteins [myosin heavy chain (MHC), filamin-C fragment (FIL-C), and actin 2 (ACT2)] were identified in adductor muscle from diploid and triploid Pacific oysters (Crassostrea gigas) and the relationship between the condition index (CI) and mRNA expression of these genes was investigated, together with the mRNA expression of molluscan insulin-related peptide (MIP), C. gigas insulin receptor-related receptor (CIR), and insulin-like growth factor binding protein complex acid labile subunit (IGFBP-ALS). Monthly changes in the CI were similar to the changes in the tissue weight rate in both groups. ACT2 and MHC mRNA expression was statistically higher in the triploid than the diploid, while FIL-C mRNA expression was significantly higher in the diploid (p<0.05). The MIP, CIR, and IGFBP-ALS mRNA expression of the diploid oysters were all significantly higher in July than in other months (p<0.05). The MIP, CIR, and IGFBP-ALS mRNA expression in the triploid oysters was high in July, but there were no significant differences (p>0.05). Changes in the expression levels of the genes investigated in this study could be used as intrinsic indicators of the annual growth, maturity, and spawning period of cultured diploid and triploid C. gigas in Tongyeong, Korea.

Insulin-like Peptide Receptor (ILPR) in the Cuttlefish Sepiella japonica: Characterization, Expression, and Regulation of Reproduction

Insulin-like peptide receptor (ILPR) can effectively regulate ovarian development in invertebrates, but its effect in cuttlefish has not been reported. We isolated and characterized a ILPR gene from Sepiella japonica, referred to as SjILPR. This gene displayed significant homologies to Octopus bimaculoides ILPR, and contained all typical features of insulin receptors and tyrosine kinase domain structure. SjILPR is expressed in all detected tissues, with the highest expression in the ovary. During ovarian development stages, its expression levels in the ovary, pancreas, and liver were correlated to the female reproductive cycle. After the silencing of SjILPR in vivo, comparative transcriptome analysis identified 4314 differentially expressed genes (DEGs) in the injected group, including 2586 down-regulated genes and 1728 up-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that 832 DEGs were assigned to 222 pathways, many pathways of which were related to gonadal development. Four down-regulated genes relevant to ovarian development (Vitellogenin 1, Vitellogenin 2, Cathepsin L1-like, and Follistatin) were selected to confirm the accuracy of RNA-seq data by qRT-PCR. These results showed that SjILPR might regulate ovarian development to control reproduction by affecting the expression of the relevant genes in female S. japonica.

Amphioxus muscle transcriptomes reveal vertebrate-like myoblast fusion genes and a highly conserved role of insulin signalling in the metabolism of muscle

BACKGROUND

The formation and functioning of muscles are fundamental aspects of animal biology, and the evolution of 'muscle genes' is central to our understanding of this tissue. Feeding-fasting-refeeding experiments have been widely used to assess muscle cellular and metabolic responses to nutrition. Though these studies have focused on vertebrate models and only a few invertebrate systems, they have found similar processes are involved in muscle degradation and maintenance. Motivation for these studies stems from interest in diseases whose pathologies involve muscle atrophy, a symptom also triggered by fasting, as well as commercial interest in the muscle mass of animals kept for consumption. Experimentally modelling atrophy by manipulating nutritional state causes muscle mass to be depleted during starvation and replenished with refeeding so that the genetic mechanisms controlling muscle growth and degradation can be understood.

RESULTS

Using amphioxus, the earliest branching chordate lineage, we address the gap in previous work stemming from comparisons between distantly related vertebrate and invertebrate models. Our amphioxus feeding-fasting-refeeding muscle transcriptomes reveal a highly conserved myogenic program and that the pro-orthologues of many vertebrate myoblast fusion genes were present in the ancestral chordate, despite these invertebrate chordates having unfused mononucleate myocytes. We found that genes differentially expressed between fed and fasted amphioxus were orthologous to the genes that respond to nutritional state in vertebrates. This response is driven in a large part by the highly conserved IGF/Akt/FOXO pathway, where depleted nutrient levels result in activation of FOXO, a transcription factor with many autophagy-related gene targets.

CONCLUSION

Reconstruction of these gene networks and pathways in amphioxus muscle provides a key point of comparison between the distantly related groups assessed thus far, significantly refining the reconstruction of the ancestral state for chordate myoblast fusion genes and identifying the extensive role of duplicated genes in the IGF/Akt/FOXO pathway across animals. Our study elucidates the evolutionary trajectory of muscle genes as they relate to the increased complexity of vertebrate muscles and muscle development.

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.

Formation of autotriploid Carassius auratus and its fertility-related genes analysis

Background

Formation of triploid organism is useful in genetics and breeding. In this study, autotriploid Carassius auratus (3nRR, 3n = 150) was generated from Carassius auratus red var. (RCC, 2n = 100) (♀) and autotetraploid Carassius auratus (4nRR, 4n = 200) (♂). The female 3nRR produced haploid, diploid and triploid eggs, whereas the male 3nRR was infertile. The aim of the present study was to explore fertility of potential candidate genes of 3nRR.

Results

Gonadal transcriptome profiling of four groups (3 females RCC (FRCC), 3 males 4nRR (M4nRR), 3 males 3nRR (M3nRR) and 3 females 3nRR (F3nRR)) was performed using RNA-SEq. A total of 78.90 Gb of clean short reads and 24,262 differentially expressed transcripts (DETs), including 20,155 in F3nRR vs. FRCC and 4,107 in M3nRR vs. M4nRR were identified. A total of 106 enriched pathways were identified through KEGG enrichment analysis. Out of the enriched pathways, 44 and 62 signalling pathways were identified in F3nRR vs. FRCC and M3nRR vs. M4nRR, respectively. A total of 80 and 25 potential candidate genes for fertility-related in F3nRR and M3nRR were identified, respectively, through GO, KEGG analyses and the published literature. Moreover, protein-protein interaction (PPI) network construction of these fertility-associated genes were performed. Analysis of the PPI networks showed that 6 hub genes (MYC, SOX2, BMP4, GATA4, PTEN and BMP2) were involved in female fertility of F3nRR, and 2 hub genes (TP53 and FGF2) were involved in male sterility of M3nRR.

Conclusions

Establishment of autotriploid fish offers an ideal model to study reproductive traits of triploid fish. RNA-Seq data revealed 6 genes, namely, MYC, SOX2, BMP4, GATA4, PTEN and BMP2, involved in the female fertility of the F3nRR. Moreover, 2 genes, namely, TP53 and FGF2, were related to the male sterility of the M3nRR. These findings provide information on reproduction and breeding in triploid fish.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07753-5.

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.

Insulin-Like Peptide Receptor-Mediated Signaling Pathways Orchestrate Regulation of Growth in the Pacific Oyster (Crassostrea gigas), as Revealed by Gene Expression Profiles

The involvement of insulin/insulin-like growth factor signaling (IIS) pathways in the growth regulation of marine invertebrates remains largely unexplored. In this study, we used a fast-growing Pacific oyster (Crassostrea gigas) variety “Haida No.1” as the material with which to unravel the role of IIS systems in growth regulation in oysters. Systematic bioinformatics analyses allowed us to identify major components of the IIS signaling pathway and insulin-like peptide receptor (ILPR)-mediated signaling pathways, including PI3K-AKT, RAS-MAPK, and TOR, in C. gigas. The expression levels of the major genes in IIS and its downstream signaling pathways were significantly higher in “Haida No.1” than in wild oysters, suggesting their involvement in the growth regulation of C. gigas. The expression profiles of IIS and its downstream signaling pathway genes were significantly altered by nutrient abundance and culture temperature. These results suggest that the IIS signaling pathway coupled with the ILPR-mediated signaling pathways orchestrate the regulation of energy metabolism to control growth in Pacific oysters.

The role of a new insulin-like peptide in the pearl oyster Pinctada fucata martensii

Pinctada fucata martensii, is an economically important marine bivalve species cultured for seawater pearls. At present, we know little about the molecular mechanisms of the insulin signalling pathway in this oyster. Herein, we cloned and analysed an insulin-like peptide (PfILP) and its signalling pathway-related genes. We detected their expression levels in different tissues and developmental stages. Recombinant PfILP protein was produced and found to significantly increase primary mantle cell activity and induce the expression of the proliferating cell nuclear antigen (PCNA) gene. PfILP could also regulate the 293T cell cycle by stimulating the S phase and inhibiting the G1 and G2 phases. Recombinant PfILP protein induced the expression of its signalling pathway-related genes in mantle cells. In vitro co-immunoprecipitation analysis showed that PfILP interacts with PfIRR. PfILP activated expression of the pfIRR protein, and also activated the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways by stimulating phosphorylation of MAPK and AKT. Further analysis showed that PfILP up-regulated glycogen synthesis-related genes glycogen synthase kinase-3 beta (GSK-3β), protein phosphatase 1 (PP1) and glucokinase (GK) at the mRNA level, as well as the expression of the PP1 protein, and phosphorylation of GSK-3β. These results confirmed the presence of a conserved insulin-like signalling pathway in pearl oyster that is involved in cell activity, glycogen metabolism, and other physiological processes.

Inhibition of growth in juvenile manila clam Ruditapes philippinarum: Potential adverse outcome pathway of TBBPA

Tetrabromobisphenol A (TBBPA) is ubiquitous and its contents showing an increasing trend in the coastal environment. In order to investigate the effects of TBBPA on marine bivalves, juvenile manila clams Ruditapes phillipinarum were exposed to TBBPA for 28 days. The results showed that shell growth rate of juvenile clams after exposure to 62.5-1000 μg L^-1 TBBPA for 28 d were significantly inhibited (p < 0.05). Then in order to link the changes in filtration rate, mRNA expression of insulin-like growth factor homologue (IGF) and tissue thyroid hormone (TH) contents to growth, juvenile clams were exposed to 62.5 and 500 μg L^-1 TBBPA for 14 days. The transcriptional levels of neuroendocrine signals (NPF and insulin homologue) associated with filter feeding regulation, and genes of TH synthesis-related enzymes were also examined. The results showed that filtration rates was significantly reduced to 44.1% and 14% of controls after 14 d of exposure. In parallel, exposure to TBBPA significantly increased the expression levels of insulin which may elicit the filter feeding inhibition. TBBPA exposure caused alterations in tissue content of THs and mRNA expression of TH synthesis-related enzymes. However, the data showed increased T₃ content, T₃/T₄ ratio and mRNA expression of IGF. These data demonstrated that the most important key event of TBBPA could be linked to growth impairment in juveniles was the reduction of filtration rate. These results provide a robust framework towards revealing the underlying mechanism of the growth inhibition caused by TBBPA on bivalves and understanding the adverse outcome pathway across taxonomic phyla.

Molecular evolution and functional characterisation of insulin related peptides in molluscs: Contributions of Crassostrea gigas genomic and transcriptomic-wide screening

Insulin Related Peptides (IRPs) belong to the insulin superfamily and possess a typical structure with two chains, B and A, linked by disulphide bonds. As the sequence conservation is usually low between members, IRPs are classified according to the number and position of their disulphide bonds. In molluscan species, the first IRPs identified, named Molluscan Insulin-related Peptides (MIPs), exhibit four disulphide bonds. The genomic and transcriptomic data screening in the Pacific oyster Crassostrea gigas (Mollusc, Bivalvia) allowed us to identify six IRP sequences belonging to three structural groups. Cg-MIP1 to 4 have the typical structure of MIPs with four disulphide bonds. Cg-ILP has three disulphide bonds like vertebrate Insulin-Like Peptides (ILPs). The last one, Cg-MILP7 has a significant homology with Drosophila ILP7 (DILP7) associated with two additional cysteines allowing the formation of a fourth disulphide bond. The phylogenetic analysis points out that ILPs may be the most ancestral form. Moreover, it appears that ILP7 orthologs are probably anterior to lophotrochozoa and ecdysozoa segregation. In order to investigate the diversity of physiological functions of the oyster IRPs, we combine in silico expression data, qPCR measurements and in situ hybridization. The Cg-ilp transcript, mainly detected in the digestive gland and in the gonadal area, is potentially involved in the control of digestion and gametogenesis. The expression of Cg-mip4 is mainly associated with the larval development. The Cg-mip transcript shared by the Cg-MIP1, 2 and 3, is mainly expressed in visceral ganglia but its expression was also observed in the gonads of mature males. This pattern suggested the key roles of IRPs in the control of sexual reproduction in molluscan species.

Multiplex PCR for the rapid detection of insulin-like growth factor in the Pacific oyster, Crassostrea gigas: a useful indicator for growth assessment

Insulin-like growth factor (IGF) expression plays a critical role in the endocrine regulation of proliferation, differentiation, and growth in shellfish as well as in fish. The Pacific oyster, Crassostrea gigas, is a significant aquaculture species that comprises a large percentage of the Korean shellfish industry; moreover, its growth is economically important in aquaculture. However, when measuring the growth rate in shellfish, the soft tissue weight is difficult to determine because of the shell weight. In the present study, we describe an indirect method of measuring the growth rate using multiplex polymerase chain reaction (PCR) and analyzing levels of molluscan insulin-related peptide (MIP), the acid labile subunit of the IGF-binding protein complex (IGFBP ALS), and insulin-related peptide receptor (CIR) in Pacific oysters. The predicted sizes of amplicons were 776, 537, 380, and 198 bp, and the detection limit of the annealing temperatures was confirmed to be 65 °C. The annual expression of MIP and IGFBP ALS in tissues reached high levels in the winter following the condition index (CI). MIP and IGFBP ALS in male gonads and CIR in female gonads were related to the CI. This newly improved multiplex PCR provides an indirect measure of the growth rate; thus, it can be used to rapidly assess the growth rate. In addition, this method can supplement traditional growth data from oyster farms.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Genome-Wide Analysis of Alternative Splicing Provides Insights into Stress Adaptation of the Pacific Oyster

Alternative splicing (AS) is thought to enhance transcriptome diversity dramatically and play an important role in stress adaptation. While well studied in vertebrates, AS remains poorly understood in invertebrates. Here, we used high-throughput RNA-sequencing data to perform a genome-wide survey of AS in the Pacific oyster (Crassostrea gigas), an economically important mollusk that is cultivated worldwide. This analysis identified 8223 AS events corresponding to 4480 genes in the Pacific oyster, suggesting that about 16 % of oyster multiexonic genes undergo AS. We observed that a majority of the identified AS events were related to skipped exons (37.8 %). Then Gene Ontology analysis was conducted to analyze the function of the genes that undergo AS and the genes that produce more than five AS isoforms. After that, the expression of AS isoforms facing temperature, salinity, and air exposure challenge were examined. To validate our bioinformatic-predicted results and examine whether AS affects stress adaptation, we selected heat-shock protein 60 (HSP60) and HSP90 genes, both of which experience AS, for reverse transcription PCR (RT-PCR). We also performed quantitative real-time PCR (qRT-PCR) to determine the relative expression of each AS isoform among different stress adapted populations. Our study indicates that AS events are likely complex in the Pacific oyster and may be related to stress adaptation. These results will complement the predicted gene database of C. gigas and provide an invaluable resource for future functional genomic studies on molluscs.

The Kinome of Pacific Oyster Crassostrea gigas, Its Expression during Development and in Response to Environmental Factors

Oysters play an important role in estuarine and coastal marine habitats, where the majority of humans live. In these ecosystems, environmental degradation is substantial, and oysters must cope with highly dynamic and stressful environmental constraints during their lives in the intertidal zone. The availability of the genome sequence of the Pacific oyster Crassostrea gigas represents a unique opportunity for a comprehensive assessment of the signal transduction pathways that the species has developed to deal with this unique habitat. We performed an in silico analysis to identify, annotate and classify protein kinases in C. gigas, according to their kinase domain taxonomy classification, and compared with kinome already described in other animal species. The C. gigas kinome consists of 371 protein kinases, making it closely related to the sea urchin kinome, which has 353 protein kinases. The absence of gene redundancy in some groups of the C. gigas kinome may simplify functional studies of protein kinases. Through data mining of transcriptomes in C. gigas, we identified part of the kinome which may be central during development and may play a role in response to various environmental factors. Overall, this work contributes to a better understanding of key sensing pathways that may be central for adaptation to a highly dynamic marine environment.

Identification, expression, and innate immune responses of two insulin-like peptide genes in the razor clam Sinonovacula constricta

Insulin-like peptide (ILP) has emerged as a cell regulatory factor with multiple functions in vertebrates and invertebrates. In the present study, we identified and characterized two ILP genes, ILP1 and ILP2, in the razor clam Sinonovacula constricta. Both ILPs have a signal peptide and a mature domain consisting of six strictly conserved cysteines. The tertiary structure is divided into three main α-helices with a C-domain loop that separates helix 1 from helix 2. Both of ILPs were found to be regulated according to tissue type and developmental stage. After challenge with Vibrio anguillarum, Vibrio parahaemolyticus and Micrococcus lysodeikticus, the expression of two ILP genes was significantly up-regulated in the liver, hemocytes and mantle tissues, suggesting that the ILPs may play roles in the innate immunity in the razor clam Sinonovacula constricta.

PfIRR Interacts with HrIGF-I and Activates the MAP-kinase and PI3-kinase Signaling Pathways to Regulate Glycogen Metabolism in Pinctada fucata

The insulin-induced mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways are major intracellular signaling modules and conserved among eukaryotes that are known to regulate diverse cellular processes. However, they have not been investigated in the mollusk species Pinctada fucata. Here, we demonstrate that insulin-related peptide receptor of P. fucata (pfIRR) interacts with human recombinant insulin-like growth factor I (hrIGF-I), and stimulates the MAPK and PI3K signaling pathways in P. fucata oocytes. We also show that inhibition of pfIRR by the inhibitor PQ401 significantly attenuates the basal and hrIGF-I-induced phosphorylation of MAPK and PI3K/Akt at amino acid residues threonine 308 and serine 473. Furthermore, our experiments show that there is cross-talk between the MAPK and PI3K/Akt pathways, in which MAPK kinase positively regulates the PI3K pathway, and PI3K positively regulates the MAPK cascade. Intramuscular injection of hrIGF-I stimulates the PI3K and MAPK pathways to increase the expression of pfirr, protein phosphatase 1, glucokinase, and the phosphorylation of glycogen synthase, decreases the mRNA expression of glycogen synthase kinase-3 beta, decreases glucose levels in hemocytes, and increases glycogen levels in digestive glands. These results suggest that the MAPK and PI3K pathways in P. fucata transmit the hrIGF-I signal to regulate glycogen metabolism.

Additive transcriptomic variation associated with reproductive traits suggest local adaptation in a recently settled population of the Pacific oyster, Crassostrea gigas

Background

Originating from Northeast Asia, the Pacific oyster Crassostrea gigas has been introduced into a large number of countries for aquaculture purpose. Following introduction, the Pacific oyster has turned into an invasive species in an increasing number of coastal areas, notably recently in Northern Europe.

Methods

To explore potential adaptation of reproductive traits in populations with different histories, we set up a common garden experiment based on the comparison of progenies from two populations of Pacific oyster sampled in France and Denmark and their hybrids. Sex ratio, condition index and microarray gene expression in gonads, were analyzed in each progeny (n = 60).

Results

A female-biased sex-ratio and a higher condition index were observed in the Danish progeny, possibly reflecting an evolutionary reproductive strategy to increase the potential success of natural recruitment in recently settled population. Using multifarious statistical approaches and accounting for sex differences we identified several transcripts differentially expressed between the Danish and French progenies, for which additive genetic basis is suspected (showing intermediate expression levels in hybrids, and therefore additivity). Candidate transcripts included mRNA coding for sperm quality and insulin metabolism, known to be implicated in coordinated control and success of reproduction.

Conclusions

Observed differences suggest that adaptation of invasive populations might have occurred during expansion acting on reproductive traits, and in particular on a female-biased sex-ratio, gamete quality and fertility.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1972-8) contains supplementary material, which is available to authorized users.

Functional characterization of a short neuropeptide F-related receptor in a lophotrochozoan, the mollusk Crassostrea gigas

Members of the short neuropeptide F (sNPF) family of peptides and their cognate receptors play key roles in a variety of physiological processes in arthropods. In silico screening of GigasDatabase, a specific expressed sequence tag database from the Pacific oyster Crassostrea gigas, resulted in the identification of a receptor (Cg-sNPFR-like) phylogenetically closely related to sNPF receptors (sNPFRs) of insects. A reverse endocrinology approach was undertaken to identify the peptide ligand(s) of this orphan receptor. Though structurally distinct from insect sNPFs, three RFamide peptides derived from the same precursor, i.e. GSLFRFamide, SSLFRFamide and GALFRFamide, specifically activate the receptor in a dose-dependent manner, with respective EC50 values (half-maximal effective concentrations) of 1.1, 2.1 and 4.1 μmol l(-1). We found that both Cg-sNPFR-like receptor and LFRFamide encoding transcripts are expressed in the oyster central nervous system and in other tissues as well, albeit at lower levels. Mass spectrometry analysis confirmed the wide distribution of LFRFamide mature peptides in several central and peripheral tissues. The Cg-sNPFR-like receptor was more abundantly expressed in ganglia of females than of males, and upregulated in starved oysters. In the gonad area, highest receptor gene expression occurred at the start of gametogenesis, when storage activity is maximal. Our results suggest that signaling of LFRFamide peptides through the Cg-sNPFR-like receptor might play a role in the coordination of nutrition, energy storage and metabolism in C. gigas, possibly by promoting storage at the expense of reproduction.

Reproduction-related genes in the pearl oyster genome

Molluscan reproduction has been a target of biological research because of the various reproductive strategies that have evolved in this phylum. It has also been studied for the development of fisheries technologies, particularly aquaculture. Although fundamental processes of reproduction in other phyla, such as vertebrates and arthropods, have been well studied, information on the molecular mechanisms of molluscan reproduction remains limited. The recently released draft genome of the pearl oyster Pinctada fucata provides a novel and powerful platform for obtaining structural information on the genes and proteins involved in bivalve reproduction. In the present study, we analyzed the pearl oyster draft genome to screen reproduction-related genes. Analysis was mainly conducted for genes reported from other molluscs for encoding orthologs of reproduction-related proteins in other phyla. The gene search in the P. fucata gene models (version 1.1) and genome assembly (version 1.0) were performed using Genome Browser and BLAST software. The obtained gene models were then BLASTP searched against a public database to confirm the best-hit sequences. As a result, more than 40 gene models were identified with high accuracy to encode reproduction-related genes reported for P. fucata and other molluscs. These include vasa, nanos, doublesex- and mab-3-related transcription factor, 5-hydroxytryptamine (5-HT) receptors, vitellogenin, estrogen receptor, and others. The set of reproduction-related genes of P. fucata identified in the present study constitute a new tool for research on bivalve reproduction at the molecular level.

Regulation of a truncated isoform of AMP-activated protein kinase α (AMPKα) in response to hypoxia in the muscle of Pacific oyster Crassostrea gigas

AMP-activated protein kinase α (AMPKα) is a key regulator of energy balance in many model species during hypoxia. In a marine bivalve, the Pacific oyster Crassostrea gigas, we analyzed the protein content of adductor muscle in response to hypoxia during 6 h. In both smooth and striated muscles, the amount of full-length AMP-activated protein kinase α (AMPKα) remained unchanged during hypoxia. However, hypoxia induced a rapid and muscle-specific response concerning truncated isoforms of AMPKα. In the smooth muscle, a truncated isoform of AMPKα was increased from 1 to 6 h of hypoxia, and was linked with accumulation of AKT kinase, a key enzyme of the insulin signaling pathway which controls intracellular glucose metabolism. In this muscle, aerobic metabolism was maintained over the 6 h of hypoxia, as mitochondrial citrate synthase activity remained constant. In contrast, in striated muscle, hypoxia did not induce any significant modification of neither truncated AMPKα nor AKT protein content, and citrate synthase activity was altered after 6 h of hypoxia. Together, our results demonstrate that hypoxia response is specific to muscle type in Pacific oyster, and that truncated AMPKα and AKT proteins might be involved in maintaining aerobic metabolism in smooth muscle. Such regulation might occur in vivo during tidal intervals that cause up to 6 h of hypoxia.