Molecular and functional analysis of the insulin-like peptides gene in the oriental river prawn Macrobrachium nipponense

The physiological response of oriental river prawn Macrobrachium nipponense to starvation-induced stress

Environmental stresses play critical roles in the physiology of crustaceans. Food deprivation is an important environmental factor and a regular occurrence in both natural aquatic habitats and artificial ponds. However, the underlying physiological response mechanisms to starvation-caused stress in crustaceans are yet to be established. In the present study, the hepatopancreas tissue of Macrobrachium nipponense was transcriptome analyzed and examined for starvation effects on oxidative stress, DNA damage, autophagy, and apoptosis across four fasting stages (0 (control group), 7, 14, and 21 days). These results indicated that a ROS-mediated regulatory mechanism is critical to the entire fasting process. At the initial stage of starvation (fasting 0 d ~ 7 d), ROS concentration increased gradually, activating antioxidant enzymes to protect the cellular machinery from the detrimental effects of oxidative stress triggered by starvation-induced stress. ROS content production (hydrogen peroxide and superoxide anion) then rose continuously with prolonged starvation (fasting 7 d ~ 14 d), reaching peak levels and resulting in autophagy in hepatopancreas cells. During the final stages of starvation (fasting 14 d ~ 21 d), excessive ROS induced DNA damage and cell apoptosis. Furthermore, autophagolysosomes and apoptosis body were further identified with transmission electron microscopy. These findings lay a foundation for further scrutiny of the molecular mechanisms combating starvation-generated stress in M. nipponense and provide fishermen with the theoretical guidance for adopting fasting strategies in M. nipponense aquaculture.

Cathepsin D Plays a Vital Role in Macrobrachium nipponense of Ovary Maturation: Identification, Characterization, and Function Analysis

The oriental river prawn Macrobrachium nipponense is an economically important aquacultural species. However, its aquaculture is negatively impacted by the rapid sexual maturation of female M. nipponense. The fast sexual maturation produces a large number of offspring which leads to a reduction in resilience, a low survival rate, and an increased risk of hypoxia, this in turn, seriously affects the economic benefits of prawn farming. Cathepsin D is a lysosomal protease involved in the ovarian maturation of M. nipponense. In the current study, the cDNA of the gene encoding cathepsin D (Mn-CTSD) was cloned from M. nipponense. The total length was 2391 bp and consisted of an open reading frame (ORF) of 1158 bp encoding 385 amino acids. Sequence analysis confirmed the presence of conserved N-glycosylation sites and characteristic sequences of nondigestive cathepsin D. The qPCR analysis indicated that Mn-CTSD was highly expressed in all tissues tested, most significantly in the ovaries, whereas in situ hybridization showed that expression occurred mainly in oocyte nuclei. Analysis of its expression during development showed that Mn-CTSD peaked during the O-IV stage of ovarian maturation. For the RNAi interference experiment, female M. nipponense specimens in the ovary stage I were selected. Injection of Mn-CTSD double-stranded (ds)RNA into female M. nipponense decreased the expression of Mn-CTSD in the ovaries, such that the Gonad Somatic Index (GSI) of the experimental group was significantly lower than that of the control group (1.79% versus 4.57%; p < 0.05). Ovary development reached the O-III stage in 80% of the control group, compared with 0% in the experimental group. These results suggest that Mn-CTSD dsRNA inhibits ovarian maturation in M. nipponense, highlighting its important role in ovarian maturation in this species and suggesting an approach to controlling ovarian maturation during M. nipponense aquaculture.

Comparison of lipid metabolism between broodstock and hybrid offspring in the hepatopancreas of juvenile shrimp (Macrobrachium nipponense): Response to chronic ammonia stress

Ammonia nitrogen is a major pollutant that causes great physiological harm to crustaceans in culture. In this study, we conducted a 28 day chronic ammonia nitrogen stress experiment with broodstock populations (Dianshan, DS) and hybrid offspring populations (DS ♀ × CD (Changjiang ♂ × Dongting ♀), SCD) exposed to 0, 1 and 10 mg/L of ammonia concentrations. A 28 day feeding trial and chronic ammonia nitrogen stress were used to investigate the effects on the growth performance, histological structure and lipid metabolism of juvenile shrimp, Macrobrachium nipponense. Our results indicated that survival rates in the SCD groups were significantly higher than those in the DS groups, whereas weight and length gain rates were not significantly different between the groups (p > 0.05). Histological structure results showed that the number of vacuoles in the DS group was significantly higher than that in the SCD group and hepatopancreas cell structures were disrupted in the ammonia treatment groups. The results of oil red staining showed that the number of lipid droplets increased significantly with the increase in ammonia concentration. As the ammonia concentration increased, fatty acid contents, lipid enzyme activities and lipid metabolism-related gene expression all tended to rise. In conclusion, ammonia nitrogen exposure caused damage to the hepatopancreas structure of juvenile shrimp and disturbed the lipid metabolism of the hepatopancreas. In addition, the SCD population had stronger stress resistance than the DS population when subjected to the same concentration of ammonia nitrogen stress.

Insulin-like signaling promotes limb regeneration in the Chinese mitten crab (Eriocheir sinensis)

In the pond culture of Chinese mitten crabs, limb autotomy seriously affects the feeding efficiency, immunity and survival. Therefore, it is crucial to understand the mechanism of limb regeneration of mitten crabs, so that culture strategies could be developed to reduce the limb impairment rate. The insulin-like signaling (ILS) pathway is evolutionarily conserved, and plays key roles in the growth and immunity of various species. In this study, a full-length cDNA of insulin-like receptor (EsInR) was identified from Eriocheir sinensis, and its mRNA expression patterns during limb regeneration was evaluated. The cDNA of EsInR includes a 4326 bp ORF encoding a protein of 1441 amino acids, with conserved α-and β-subunits. The EsInR and genes related to ILS were found to be upregulated during limb regeneration, which indicated that ILS plays a key role in limb regeneration of E. sinensis. Our experiment revealed that inhibition of ILS through injection of the InR inhibitor GSK1838705A at the blastema formation stage significantly reduced the limb regeneration rate compared to control group. In addition, injection of GSK1838705A also reduced the size of newly formed limbs after the molting cycle. Furthermore, we found that genes related to myogenesis were downregulated following injection of InR inhibitor both before and after molting. The results also indicated that cyclins and CDK1 were downregulated, while CKIs were upregulated following treatment with the InR inhibitor. These results suggest that ILS regulates limb regeneration in E. sinensis by promoting muscle growth and regeneration in response to autotomy stress. Thus, we identified a conserved insulin-like receptor in E. sinensis, and provide new evidence for the involvement of ILS in the regulation of limb autotomy and regeneration in crustaceans.

Dietary chromium modulates glucose homeostasis and induces oxidative stress in Pacific white shrimp (Litopenaeus vannamei)

While chromium (Cr) has been recognized as an essential nutrient for all animals, and dietary supplementation can be beneficial, it can also be toxic. The present study aimed to investigate the contrasting effects of dietary chromium in Pacific white shrimp Litopenaeus vannamei. Five experimental diets were formulated to contain Cr at levels of 0.82 (Cr0.82, unsupplemented diet), 1.01 (Cr1.01), 1.22 (Cu1.22), 1.43 (Cr1.43) and 1.63 (Cr1.63) mg/kg and were fed to shrimp for 8 weeks. Highest weight gain was recorded in shrimp fed the diet containing 1.22 mg/kg Cr. Shrimp fed the diet containing the highest level of Cr (1.63 mg/kg) showed the lowest weight gain and clear signs of oxidative stress and apoptosis as evidenced by higher levels of H₂O₂, malondialdehyde and 8-hydroxydeoxyguanosine, and expression of caspase 2, 3, 5, and lower contents of total and oxidized glutathione, and expression of Cu/Zn sod, cat, gpx, mt, bcl2. Chromium supplementation promoted glycolysis and inhibited gluconeogenesis as shown by increased activities of hexokinase, phosphofructokinase and pyruvate kinase, and reduced activity of phosphoenolpyruvate carboxykinase in shrimp fed the diet containing 1.43 mg/kg Cr. Shrimp fed the diet with 1.63 mg/kg Cr had lowest contents of crustacean hyperglycemic hormone and insulin like peptide in hemolymph. Expression of genes involved in insulin signaling pathway and glycose metabolism including insr, irs1, pik3ca, pdpk1, akt, acc1, gys, glut1, pk, hk were up-regulated, and foxO1, gsk-3β, g6pc, pepck were down-regulated in shrimp fed the diets supplemented with Cr. This study demonstrated that optimum dietary supplementation of Cr had beneficial effects on glucose homeostasis and growth, whereas excess caused oxidative damage and impaired growth. The results contribute to our understanding of the biological functions of chromium in shrimp.

Cloning, functional and regulation analysis of a novel male reproduction-related protein gene from the oriental river prawn Macrobrachium nipponense

Gonadogenesis processes in crustaceans are complex. There, however, has been a large amount of research focused on regulation of female gonad (ovary) development in crustaceans, however, there has been little focus on the male gonad (testis). In the current study, a novel male reproduction-related protein gene (Mn-MRP) was identified from Macrobrachium nipponense. The relative abundance of Mn-MRP mRNA transcript in tissues and at different developmental stages were investigated. The relative abundance of Mn-MRP mRNA transcript was larger in the testis than other tissues, and during the testis maturation stage than at other developmental stages, suggesting Mn-MRP may have important functions in reproduction processes. The RNA interference (RNAi) was used to further investigate the Mn-MRP biological function. Silencing of the Mn-MRP gene effectively decreased the abundance of the sperm gelatinase (Mn-SG) mRNA transcript, implying the protein encoded by this gene may have functions in sperm activity during the fertilization process. Further studies with RNAi and eyestalk ablation confirmed that gonad inhibiting hormone gene (Mn-GIH) is a negative regulator of Mn-MRP, and that the insulin-like androgenic gland hormone gene (Mn-IAG) is a positive regulator. There, therefore, was cloning of the Mn-MRP gene, and investigation of its potential biological function, as well as elucidation of the positive/negative regulators in current study. The results from this study provide for a greater understanding of regulatory mechanisms of male reproduction in crustaceans.

MicroRNA transcriptome analysis of oriental river prawn Macrobrachium nipponense in responding to starvation stress

Food deprivation or fasting is an important environmental factor, and a regular occurrence in both natural aquatic habitats and artificial ponds. However, the potential immunoregulatory mechanisms underlying starvation stress in crustaceans remain unclear. MicroRNAs (miRNAs) are a new class of non-coding RNAs that can regulate various biological processes, such as stress and immune responses. In the present work, miRNAs related to starvation stress responses and immune properties were identified and characterised in oriental river prawn Macrobrachium nipponense using high-throughput sequencing and bioinformatics analyses. Twelve small RNA libraries from hepatopancreas tissue were sequenced across four fasting stages lasting 0, 7, 14 or 21 days. In total, 550 miRNAs were identified including 198 putative novel miRNAs and 352 conserved miRNAs belonging to 57 families. Moreover, compared with expression levels at 0 days, 27, 27 and 43 miRNAs were differentially expressed (DE-miRNAs) at 7, 14 and 21 days, respectively. Among these, four DE-miRNAs (ame-miR-190-5p, dme-miR-307a-3p, hme-miR-2788-3p and novel_68) were co-expressed at all three timepoints. Furthermore, 661 target genes regulated by these DE-miRNAs were identified, and associated functional annotations were derived by GO enrichment and KEGG pathway analyses, which showed that most DE-miRNAs were mainly participated in metabolic processes and immune responses. Furthermore, 26 host DE-miRNAs potentially participated in interactions with white spot syndrome virus (WSSV) were identified by predicting and analysing target genes from WSSV. The further WSSV challenge under starvation stress showed that dme-miR-307a-3p played a part in the antiviral responses against WSSV. Our results demonstrate that dme-miR-307a-3p may play vital regulatory roles in responding to starvation stress and WSSV infection. The findings contribute new insight into the molecular mechanisms associated with immune responses to environmental stress in crustaceans.

Comparison of growth performance and biochemical components between parent and hybrid offspring in the oriental river prawn, Macrobrachium nipponense

Macrobrachium nipponense, as one of the large-yield farmed shrimp, is facing germplasm degradation. Genetic improvement through hybridization is one of the effective methods to solve this problem. In this study, using a three-line hybrid strategy, two-hybrid F1 populations were obtained using three local populations of M. nipponense as parents for crossbreeding. Five populations were then cultured for 3 months. Growth rate performance was measured by the hepatosomatic index, weight gain, body length growth rate and special growth rate. Biochemical components were also assessed. The results showed that the survival rate and growth performance of the hybrid progeny were better than those of the parents. The levels of triglycerides, total cholesterol, glycogen and lactic acid of the hybrid population were higher than those of the parents. This was consistent with variation in the activity of four digestive enzymes. Compared with the results of the fatty acid and amino acid analysis, it was found that the contents of polyunsaturated fatty acids such as eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid and eight essential amino acids in the hybrid populations were significantly higher than those of their parents, and the contents of flavor amino acids were higher. The expression level of molting genes related to the growth of the parent populations was lower than that of the hybrids. These results show that crossbreeding is effective for the genetic improvement of M. nipponense germplasm. Hybrids showed advantages in growth and nutrition and multigenerational breeding will be required to form a stable germplasm.

Signaling Pathways That Regulate the Crustacean Molting Gland

A pair of Y-organs (YOs) are the molting glands of decapod crustaceans. They synthesize and secrete steroid molting hormones (ecdysteroids) and their activity is controlled by external and internal signals. The YO transitions through four physiological states over the molt cycle, which are mediated by molt-inhibiting hormone (MIH; basal state), mechanistic Target of Rapamycin Complex 1 (mTORC1; activated state), Transforming Growth Factor-β (TGFβ)/Activin (committed state), and ecdysteroid (repressed state) signaling pathways. MIH, produced in the eyestalk X-organ/sinus gland complex, inhibits the synthesis of ecdysteroids. A model for MIH signaling is organized into a cAMP/Ca²⁺-dependent triggering phase and a nitric oxide/cGMP-dependent summation phase, which maintains the YO in the basal state during intermolt. A reduction in MIH release triggers YO activation, which requires mTORC1-dependent protein synthesis, followed by mTORC1-dependent gene expression. TGFβ/Activin signaling is required for YO commitment in mid-premolt. The YO transcriptome has 878 unique contigs assigned to 23 KEGG signaling pathways, 478 of which are differentially expressed over the molt cycle. Ninety-nine contigs encode G protein-coupled receptors (GPCRs), 65 of which bind a variety of neuropeptides and biogenic amines. Among these are putative receptors for MIH/crustacean hyperglycemic hormone neuropeptides, corazonin, relaxin, serotonin, octopamine, dopamine, allatostatins, Bursicon, ecdysis-triggering hormone (ETH), CCHamide, FMRFamide, and proctolin. Contigs encoding receptor tyrosine kinase insulin-like receptor, epidermal growth factor (EGF) receptor, and fibroblast growth factor (FGF) receptor and ligands EGF and FGF suggest that the YO is positively regulated by insulin-like peptides and growth factors. Future research should focus on the interactions of signaling pathways that integrate physiological status with environmental cues for molt control.

Effects of nanoplastics on antioxidant and immune enzyme activities and related gene expression in juvenile Macrobrachium nipponense

Nanoplastics are widely distributed in aquatic environments, and nanoplastic pollution has become a global concern. However, few studies have evaluated the toxicity of nanoplastics to freshwater crustaceans. In this study, by adding different concentrations of nanoplastics to water, we explored the effects of nanoplastics on the survival, antioxidant activity, immune enzyme activity, and related gene expression levels in juvenile Macrobrachium nipponense. The results showed that the 96 -h half-lethal concentration of nanoplastics to juvenile shrimp was 396.391 mg/L. As the concentration of nanoplastics increased, the activities of antioxidant enzymes generally decreased, while the contents of hydrogen peroxide and lipid peroxidation products increased. The activities of non-specific immune enzymes first increased and then decreased with increasing nanoplastic concentration. The trends in the expressions of antioxidant-related genes were generally consistent with those in the activities of antioxidant enzymes. As the nanoplastic concentration increased, the expressions of immune-related genes generally increased at first and then decreased. These results indicate that low concentrations of nanoplastics (5 mg/L) may enhance the viability of juvenile shrimp, whereas high concentrations (10,20, 40 mg/L) have inhibitory and/or toxic effects. The findings provide basic information on the toxic effects of nanoplastics in juvenile shrimp.