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

Molecular Cloning, Characterization, and Function of Insulin-Related Peptide 1 (IRP1) in the Haliotis discus hanna

Abalone is a popular mollusk in the marine aquaculture industry of China. However, existing challenges, like slow growth, individual miniaturization, and the absence of abundant abalone, have emerged as significant obstacles impeding its long-term progress in aquaculture. Studies have demonstrated that insulin-related peptide (IRP) is a crucial factor in the growth of marine organisms. However, limited studies have been conducted on IRP in abalone. This study indicated that the hdh-MIRP1 open reading frame (ORF) was composed of 456 base pairs, which encoded 151 amino acids. Based on the gene expression and immunofluorescence analyses, the cerebral ganglion of Haliotis discus hannai (H. discus hannai) was the primary site of hdh-MIRP1 mRNA expression. Moreover, hdh-MIRP1 expression was observed to be higher in the larger group than in the smaller group abalones. Only single nucleotide polymorphism (SNP) was related to their growth characteristics. However, approximately 82 proteins that may interact with hdh-MIRP1 were identified. The functional enrichment analysis of the 82 genes indicated that hdh-MIRP1 may be involved in the regulation of glucose metabolism and the process of growth. This study established a benchwork for further investigating the role of IRP in the growth of abalone.

Characterization of Insulin-like Peptide (ILP) and Its Potential Role in Ovarian Development of the Cuttlefish Sepiella japonica

The insulin-like peptide (ILP) family is well known for regulating reproduction in invertebrates, while its role in mollusks remains largely unknown. In this study, we first isolated and characterized the ILP gene in the cuttlefish Sepiella japonica. The full-length SjILP cDNA obtained was 926 bp and encoded a precursor protein of 161 amino acids. The precursor protein consisted of a signal peptide, a B chain, a C-peptide, and an A chain. It possessed the typical features of ILP proteins, including two cleavage sites (KR) and eight conserved cysteines. To define the function of SjILP, the expression of SjILP in different tissues and ovarian development stages were analyzed using qRT-PCR. SjILP was mainly expressed in the ovary, and its gene expression correlated with ovarian development. Furthermore, silencing SjILP using RNA interference (RNAi) dramatically decreased the expression levels of four ovarian-development-related genes (vitellogenin1, vitellogenin2, cathepsin L1-like, and follistatin). These data suggest the critical role of SjILP in the regulation of ovarian development in S. japonica.

Gamma-aminobutyric acid regulates glucose homeostasis and enhances the hepatopancreas health of juvenile Chinese mitten crab (Eriocheir sinensis) under fasting stress

The ability of immune defense and resistance to physiological stress is crucial to animal health and survival. This study investigated the regulation of γ-aminobutyric acid (GABA) on metabolic homeostasis and its enhancement of hepatopancreas health in juvenile Chinese mitten crab (Eriocheir sinensis) under food deprivation. Juvenile crabs of 400 individuals were divided into four treatment groups: a control group without injection, and injections with a phosphate-buffered saline solution, 100 μmol GABA/mL and 1000 μmol GABA/mL, respectively. Hypoglycemia was induced by fasting, whereas the GABA treatment regulated hemolymph glucose homeostasis. The quantitative real-time PCR (qRT-PCR) results showed that the GABA treatment significantly up-regulated the mRNA expression levels of crustacean hyperglycemic hormone (CHH) and pyruvate kinase (PK). In contrast, the expression of E. sinensis insulin-like peptide (EsILP) was significantly down-regulated in the cranial ganglia, thoracic ganglia and hepatopancreas. Moreover, acid phosphatase (ACP), alkaline phosphatase (AKP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were significantly increased in the hepatopancreas by the GABA treatment. Furthermore, the hemocyanin content in serum was significantly increased with the GABA injection, and the glutathione (GSH) content, total superoxide dismutase (T-SOD) activity and catalase (CAT) activity in the hepatopancreas showed a similar increasing trend with the dose elevation of GABA. Therefore, these results indicate that GABA can effectively maintain the hemolymph glucose homeostasis by regulating the levels of glucose metabolism-related hormones and key enzymes to promote the degradation and utilization of hepatopancreas glycogen. Meanwhile, GABA can improve the hepatopancreas function and immune status of juvenile E. sinensis under fasting stress. The treatment with GABA may provide a clue to guide health management in crab farming.

An insulin-like peptide serves as a regulator of glucose metabolism in the immune response of Chinese mitten crab Eriocheir sinensis

A robust immune response against invading pathogens greatly depends on the balance of metabolism, which could be vigorously modulated by insulin/IGF signaling (IIS) pathway in vertebrates. However, knowledge on the IIS pathway, especially the function of insulin-like peptides (ILPs) in invertebrates remained largely unknown. In the present study, a novel ILP was identified from Eriocheir sinensisis (designated EsILP). The coding sequence of EsILP was of 216 bp, which encoded a polypeptide of 71 amino acids containing an IlGF-like domain with four conserved cysteine residues. The mRNA transcripts of EsILP were found to be expressed dominantly in eyestalks and hepatopancreas, and EsILP protein was found to be distributed in the anterior median area of thoracic ganglion mass and the edges of hepatic tubules correspondingly. After Aeromonas hydrophila stimulation, EsILP transcripts were significantly increased at 3, 12 and 24 h post-stimulation in eyestalks and 6 and 48 h in hemocytes, respectively. In contrast, the expression level of EsILP decreased significantly in hepatopancreas from 6 h to 12 h after the stimulation. The glucose level in the hemolymph of crabs was significantly decreased from 6 to 12 h after the injection of recombinant EsILP. These results collectively demonstrated that the ancient ILP protein in E. sinensisis could negatively regulate glucose metabolism and participate in the immune response of the crabs against pathogen infection, which provided clues for the further investigation about the evolution and function of the IIS pathway in invertebrates.

Monitoring nearshore ecosystem health using Pacific razor clams (Siliqua patula) as an indicator species

An emerging approach to ecosystem monitoring involves the use of physiological biomarker analyses in combination with gene transcription assays. For the first time, we employed these tools to evaluate the Pacific razor clam (Siliqua patula), which is important both economically and ecologically, as a bioindicator species in the northeast Pacific. Our objectives were to (1) develop biomarker and gene transcription assays with which to monitor the health of the Pacific razor clam, (2) acquire baseline biomarker and gene transcription reference ranges for razor clams, (3) assess the relationship between physiological and gene transcription assays and (4) determine if site-level differences were present. Pacific razor clams were collected in July 2015 and 2016 at three sites within each of two national parks in southcentral Alaska. In addition to determining reference ranges, we found differences in biomarker assay and gene transcription results between parks and sites which indicate variation in both large-scale and local environmental conditions. Our intent is to employ these methods to evaluate Pacific razor clams as a bioindicator of nearshore ecosystem health. Links between the results of the biomarker and gene transcription assays were observed that support the applicability of both assays in ecosystem monitoring. However, we recognize the need for controlled studies to examine the range of responses in physiology and gene transcripts to different stressors.

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.

Polymorphisms of LAP3 gene and their association with the growth traits in the razor clam Sinonovacula constricta

Leucine aminopeptidase 3 (LAP3) is an important proteolytic enzyme that catalyzes the hydrolysis of leucine residues from the amino termini of protein or peptide substrates and plays a critical role in protein metabolism and growth. In the present study, we investigated the full-length cDNA sequence of the LAP3 gene in Sinonovacula constricta (ScLAP3) using expressed sequence tags and rapid amplification of cDNA ends. The full-length ScLAP3 cDNA was 2885 bp, with a 1560 bp open reading frame encoding 519 amino acids. Sequence analysis revealed that ScLAP3 shared 70.9% identity with LAP3 from the blood clam Tegillarca granosa and 62.0-68.0% with other species. ScLAP3 was expressed in all six tested tissues, with significantly higher expression levels in the foot compared with mantle, adductor muscle, liver, gills, and siphon tissues in adults (P < 0.01). In the eight developmental stages, ScLAP3 expression gradually increased, with significantly higher levels in D-shaped larvae compared with other developmental stages (P < 0.01), suggesting that it may be involved in the formation of certain organs during early development. Association analysis identified three shared single nucleotide polymorphisms (SNPs), c.1073A > G, c.1139C > T and c.1154A > G in exons of ScLAP3 gene from 177 individuals of two groups, one selective strain and one wild population, which had significant effects on growth traits of S. constricta. The results provided candidate genetic markers to assist selective breeding of razor clams toward improved growth.

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.

Hemolytic reactions in the hemolymph of bivalve Sinonovacula constricta show complement-like activity

The complement-like hemolysis method was used to determine the total complement-like activity of the plasma of Sinonovacula constricta. In this study, the effects of both physical and chemical conditions on complement hemolysis of S. constricta were measured. Physical conditions included proportion (S. constricta plasma: 2% rabbit red blood cells), temperature, time, and incubation, while the chemical factors consisted of Lipopolysaccharide (LPS), Flagellin (FLA), Zymosan, Peptidoglycan (PGN), Phenylmethanesulfonyl fluoride (PMSF), Methylamine, and Poly (I: C). The results showed that LPS, flagellin, Zymosan and PGN could activate complement-like activity of S. constricta plasma and cause hemolysis. PMSF and methylamine inhibited complement-like activity, resulting in the disappearance of hemolysis. Poly (I: C) had no effect on plasma complement-like activity. When the reaction temperature was less than 50 °C, hemolytic activity would increase following an increase in temperature. The ratio of plasma to rabbit blood cells had a great impact on the rate of hemolysis. Additionally, incubation with low speed oscillation could improve the hemolysis rate. It is indicated that the hemolytic reactions in the hemolymph of bivalve S. constricta show complement-like activity. The results contribute to further research on immune function of complement in bivalve.