Research progress in innate immunity of freshwater crustaceans

Effects of microplastics separate exposure and co-exposure to 17β-estradiol on the productive performance of juvenile female Chinese mitten crab (Eriocheir sinensis)

Microplastics (MPs) and endocrine-disrupting chemicals are persistent and ubiquitous pollutants in aquatic environments. The coexistence of MPs and 17β-estradiol (E2) in aquaculture water is concerning, yet their combined impact on aquaculture products remains unclear. In this study, we investigated the individual and combined effects of MPs and E2 on juvenile female Chinese mitten crabs (Eriocheir sinensis). The results revealed that MPs and E2, alone and in combination, damage the histology and ultrastructure of the hepatopancreas, reduce lipid storage, and inhibit the expression of genes related to innate immunity, energy metabolism, and reproductive development in the hepatopancreas. These effects result in decreased innate immunity and impact growth and development. MPs and E2 also damage pereiopod muscles and ovarian tissues, impairing locomotor function and reproductive development. The coexposure group exhibited the combined damage effects of MPs and E2. Fluctuations in gene expression at different time points suggest that E. sinensis is self-regulated in response to external stimuli from MPs and E2. These findings emphasize the effects of MPs and E2, indicating that their coexistence in aquaculture environments threatens the productive performance of E. sinensis.

Comparative transcriptome analysis reveals the different responding mechanisms of ovary and hepatopancreas following polyI:C challenge in Macrobrachium nipponense

The ovary in mammals has developed specialized mechanisms for protection against pathogen infections; however, the understanding of the innate immune system in the ovary of crustaceans is still limited. To elucidate the ovary's defense mechanisms in response to viral challenges, we subjected oriental river prawns (Macrobrachium nipponense) to poly I:C, a double-stranded RNA analog that emulates viral dsRNA, and analyzed the ovary's transcriptome profiles. Concurrently, RNA-seq analysis was performed on the hepatopancreas, a well-recognized immune-related tissue, following poly I:C challenge to investigate the distinct response mechanisms of the ovary and hepatopancreas and to gain a comprehensive understanding of the immune responses in both tissues. The results indicate that 1368 genes are differentially expressed in the ovary, with 903 genes upregulated and 465 genes downregulated. Subsequent analysis reveals that these differentially expressed genes (DEGs) include numerous genes associated with innate immunity, such as members of the C-type lectin, fibrinogen-related protein (Frep), Toll-like receptor, and NOD-like receptor (NLR) gene families, as well as acid phosphatase, scavenger receptor, crustin, Down syndrome cell adhesion molecule (Dscam), hemocyanin, and lipopolysaccharide and beta-1,3-glucan binding protein (LGBP). Furthermore, the DEGs include several genes related to ovary development, such as sox8, vitellogenin, progranulin, cyclin-dependent kinase, ecdysone receptor, frizzled, and members of the Fox gene family. In the hepatopancreas, a total of 729 DEGs were identified. Comparison of the DEGs in both tissues indicates that only 91 genes are common to both groups, highlighting significant tissue-specific responses to poly I:C stimulation. This study aims to enhance our understanding of the immune protective mechanisms employed by the ovary in response to pathogen exposure and establishes a foundation for investigating ovarian reproductive immunity in crustaceans.

Yorkie negatively regulates the Crustin expression during molting in Chinese mitten crab, Eriocheir sinensis

Molting is a key biological process of crustaceans, which is mainly regulated by 20-hydroxyecdyone (20E). The molting cycle could be divided into three main stages including pre-molt, post-molt and inter-molt stages. The mechanism of immune regulation during molting process still requires further exploration. Yorkie (Yki) is a pivotal transcription factor in the Hippo signaling pathway, and it plays an essential role in regulating cell growth and immune response. In the present study, a Yki gene was identified from Eriocheir sinensis (designed as EsYki), and the regulatory role of EsYki in controlling the expression of antimicrobial peptide genes throughout the molting process was investigated. The mRNA expression level of EsYki was higher at the pre-molt stage compared to the post-molt stage and inter-molt stage. Following the injection of 20E, there was a notable and consistent rise in the EsYki mRNA expression in haemocytes. The increase was observed from 3 h to 48 h with the maximum level at 12 h. And the phosphorylation of Yki in the haemocytes was also significantly up-regulated at 3 h post 20E injection. Moreover, the levels of EsYki mRNA expression at three molting stages were significantly increased post Aeromonas hydrophila stimulation. The maximum level was detected at post-molt stage following A. hydrophila stimulation, while the lowest level was observed at inter-molt stage. The expression pattern of EsCrus was in contrast to EsCrus. After EsYki mRNA transcripts were inhibited by Yki inhibitor (CA3), the mRNA expression levels of EsCrus1 and EsCrus2 following A. hydrophila stimulation were significantly elevated. Furthermore, the phosphorylation level of NF-κB was also increased following the inhibition of Yki. Collectively, our findings indicated that EsYki could be induced by 20E and has a suppressive effect on the expression of EsCrus via inhibiting NF-κB during molting process. This research contributes to the understanding of the immunological regulation mechanism during molting process in crustaceans.

CBS/CSE mediated H2S production induced AMPs expression through Toll pathway in crabs with black gill syndrome

The occurrence of black gill syndrome (BGS) is a serious threat to the healthy culture of Eriocheir sinensis. Studying the innate immune ability of E. sinensis with BGS can help develop new strategies for disease prevention and treatment. Antimicrobial peptides (AMPs) have crucial roles in crustacean humoral immunity. In this study, we found that the expression levels of two antilipopolysaccharide factor (EsALF7 and EsALF-L), one Toll receptor 3 (EsToll3), and one Pelle kinase (EsPelle) were upregulated in E. sinensis with BGS. Moreover, ALFs expressions in E. sinensis with BGS were positively regulated by EsToll3 and EsPelle. The content of hydrogen sulfide (H2S) in the gills of E. sinensis with BGS was increased. Further studies showed that the expressions of cystathionine β-synthase (EsCBS) and cystathionine γ-lyase (EsCSE) in the gills of E. sinensis with BGS were upregulated, which positively regulate the production of H2S. Whether there was a correlation between the upregulation of ALFs expression and changes in H2S content? Further studies showed that 1) the expressions of EsToll3, EsPelle, EsALF7, and EsALF-L in the gills of E. sinensis were upregulated under H2S exposure and 2) the knockdown of EsCBS and EsCSE in E. sinensis reduced the transcriptions of EsToll3, EsPelle, EsALF7, and EsALF-L. To sum up, these findings suggest that upregulation of H2S content induced by CBS/CSE promotes the expression of ALFs through the Toll pathway in E. sinensis suffering from BGS.

A positive loop between relish and cuticle proteins and their roles in regulating AMPs expression during bacterial infection in Eriocheir sinensis

Cuticle proteins (CPs) are the vital components of the cuticle and chitin lining covering the digestive tract of crustaceans. In this study, four new CP genes (designated as EsCP3, EsCP4, EsCP5, and EsCP8) were initially cloned and identified from the Chinese mitten crab Eriocheir sinensis. EsCP3/4/5/8 included 375, 411, 381, and 570 bp open reading frame encoding 124, 136, 126, and 189 amino acid proteins, respectively. Except for EsCP8, EsCP3/4/5 all contained a Chitin_bind_4 domain. EsCP3/4/5/8 were clustered into different groups in the phylogenetic tree. Quantitative real-time PCR results indicated that four EsCP genes have different patterns of tissue distribution. Changes in the expression levels of these four EsCP genes were observed in the intestine of crabs under Vibrio parahaemolyticus challenge. RNA interference assay showed that the knockdown of EsCPs in the intestine could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. In addition, the knockdown of EsRelish in the intestine decreased the expression levels of these four EsCP genes. These results indicated that EsCPs were involved in regulating the expression of AMPs, and EsCPs were regulated by EsRelish.

Vitamin C as a functional enhancer in the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab, Scylla paramamosain

This experiment was conducted to explore the effects of dietary vitamin C supplementation on non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab (Scylla paramamosain). Mud crabs with an initial weight of 14.67 ± 0.13 g were randomly divided into 6 treatments and fed diets with 0.86 (control), 44.79, 98.45, 133.94, 186.36 and 364.28 mg/kg vitamin C, respectively. The experiment consisted of 6 treatments, each treatment was designed with 4 replicates and each replicate was stocked with 8 crabs. After 42 days of feeding experiment, 2 crabs were randomly selected from each replicate, and a total of 8 crabs in each treatment were carried out 72 h low-temperature challenge experiment. The results showed that crabs fed diets with 186.36 and 364.28 mg/kg vitamin C significantly improved the activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in hemolymph and hepatopancreas (P < 0.05). Crabs fed diet with 133.94 mg/kg vitamin C significantly decreased the concentration of nitric oxide (NO) and the activity of nitric oxide synthase (NOS) in hemolymph (P < 0.05). Diet with 133.94 mg/kg vitamin C was improved the activity of polyphenol oxidase (PPO) and the concentration of albumin (ALB) in hemolymph. Crabs fed diet with 133.94 mg/kg vitamin C showed lower concentration of malondialdehyde (MDA) in hemolymph and hepatopancreas than those fed the other diets. Meanwhile, crabs fed diet with 98.45 mg/kg vitamin C showed higher activity of total superoxide dismutase (T-SOD) in hemolymph, and crabs fed diet with 133.94 mg/kg vitamin C showed higher activity of T-SOD in hepatopancreas. Crabs fed diet with 186.36 mg/kg vitamin C significantly decreased the concentration of reduced glutathione (GSH) and the activity of glutathione peroxidase (GSH-PX) in hepatopancreas (P < 0.05). In normal temperature, crabs fed diets with 133.94 mg/kg vitamin C significantly up-regulated the expression levels of gpx (glutathione peroxidase) and trx (thioredoxin) in hepatopancreas compared with the control treatment (P < 0.05). The highest expression levels of relish, il16 (interleukin 16), caspase 2 (caspase 2), p38 mapk (p38 mitogen-activated protein kinases) and bax (bcl-2 associated x protein) in hepatopancreas were found at crabs fed control diet (P < 0.05). Moreover, crabs fed diet with 133.94 mg/kg vitamin C showed higher expression levels of alf-3 (anti-lipopolysaccharide factor 3) and bcl-2 (B-cell lymphoma 2) in hepatopancreas than those fed the other diets (P < 0.05). Under low-temperature stress, crabs fed diet with 133.94 mg/kg vitamin C significantly improved the expression levels of hsp90 (heat shock protein 90), cat (catalase), gpx, prx (thioredoxin peroxidase) and trx in hepatopancreas (P < 0.05). In addition, dietary with 133.94 vitamin C significantly up-regulated the expression levels of alf-3 and bcl-2 (P < 0.05). Based on two slope broken-line regression analysis of activity of PPO against the dietary vitamin C level, the optimal dietary vitamin C requirement was estimated to be 144.81 mg/kg for juvenile mud crab. In conclusion, dietary 133.94-144.81 mg/kg vitamin C significantly improved the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab.

Differential expression of microRNAs in giant freshwater prawn (Macrobrachium rosenbergii) during the infection of Vibrio parahaemolyticus

MicroRNAs (miRNAs) are a category of small non-coding RNAs regarded as vital regulatory factors in various biological processes, especially immune regulation. The differently expressed miRNAs in Macrobrachium rosenbergii after the challenge of Vibrio parahaemolyticus were identified using high-throughput sequencing. A total of 18 known as well as 12 novel miRNAs were markedly differently expressed during the bacterial infection. The results of the target gene prediction and enrichment analysis indicated that a total of 230 target genes involved in a large variety of signaling pathways and biological processes were mediated by the miRNAs identified in the current research. Additionally, the effects of novel-miR-56, a representative differentially expressed miRNA identified in the previous infection experiment, on the immune-related gene expression in M. rosenbergii were explored. The expression of the immune-related genes including Spätzle1(Spz1), Spz4, Toll-like receptor 1 (TLR1), TLR2, TLR3, immune deficiency (IMD), myeloid differentiation factor 88 (MyD88), anti-lipopolysaccharide factor 1 (ALF1), crustin1, as well as prophenoloxidase (proPO) was significantly repressed in the novel-miR-56-overexpressed prawns. The expression of these genes tested in the novel-miR-56-overexpressed M. rosenbergii was still signally lower than the control in the subsequent V. parahaemolyticus challenge, despite the gene expression in each treatment increased significantly after the infection. Additionally, the cumulative mortality of the agomiR-56-treated prawns was significantly higher than the other treatments post the bacterial challenge. These results suggested that novel-miR-56 might function as a negative regulator of the immune-related gene expression of M. rosenbergii in the innate immune defense against V. parahaemolyticus.

Dietary β-1,3-Glucan Promotes Growth Performance and Enhances Non-Specific Immunity by Modulating Pattern Recognition Receptors in Juvenile Oriental River Prawn (Macrobrachium nipponense)

As a typical pathogen-associated molecular pattern (PAMP), β-1,3-glucan can engage with pattern recognition receptors (PRRs) to initiate an immune response. In this study, we investigated the effects of dietary β-1,3-glucan on growth performance, antioxidant capacity, immune response, intestinal health, and bacterial resistance in juvenile Macrobrachium nipponense. Prawns were fed with five experimental diets containing 0%, 0.05%, 0.1%, 0.2%, and 0.4% β-1,3-glucan for eight weeks. The findings demonstrated that the inclusion of β-1,3-glucan improved weight gain and survival rate in prawns. Prawns fed with β-1,3-glucan exhibited elevated activities of hepatopancreatic ACP (acid phosphatase), AKP (alkaline phosphatase), and SOD (superoxide dismutase), while MDA (malondialdehyde) content was reduced. Expression levels of PRRs related genes including LGBP (lipopolysaccharide and β-1,3-glucan binding protein), lectin, and LBP (lipopolysaccharide-binding protein) were significantly increased in prawns fed with β-1,3-glucan. Intestinal flora analysis revealed suppression of Cyanobacteria abundance at the Phylum level and enhancement in Rhodobacter abundance at the genus level in prawns fed with a 0.2% β-1,3-glucan diet. Furthermore, prawns fed with 0.1%, 0.2%, and 0.4% β-1,3-glucan demonstrated significantly higher survival rates following Aeromonas hydrophila infection. In conclusion, β-1,3-glucan can activate PRRs to improve immune responses in M. nipponese. Within the range of β-1,3-glucan concentrations set in this experiment, it is recommended to add 0.18% of β-1,3-glucan to the diet, taking into account the positive effect of β-1,3-glucan on the survival rate of M. nipponensecu.

Exploitation of multiple host-derived nutrients by the yellow catfish epidermal environment facilitates Vibrio mimicus to sustain infection potency and susceptibility

Infection with Vibrio mimicus in the Siluriformes has demonstrated a rapid and high infectivity and mortality rate, distinct from other hosts. Our earlier investigations identified necrosis, an inflammatory storm, and tissue remodeling as crucial pathological responses in yellow catfish (Pelteobagrus fulvidraco) infected with V. mimicus. The objective of this study was to further elucidate the impact linking these pathological responses within the host during V. mimicus infection. Employing metabolomics and transcriptomics, we uncovered infection-induced dense vacuolization of perimysium; Several genes related to nucleosidase and peptidase activities were significantly upregulated in the skin and muscles of infected fish. Concurrently, the translation processes of host cells were impaired. Further investigation revealed that V. mimicus completes its infection process by enhancing its metabolism, including the utilization of oligopeptides and nucleotides. The high susceptibility of yellow catfish to V. mimicus infection was associated with the composition of its body surface, which provided a microenvironment rich in various nucleotides such as dIMP, dAMP, deoxyguanosine, and ADP, in addition to several amino acids and peptides. Some of these metabolites significantly boost V. mimicus growth and motility, thus influencing its biological functions. Furthermore, we uncovered an elevated expression of gangliosides on the surface of yellow catfish, aiding V. mimicus adhesion and increasing its infection risk. Notably, we observed that the skin and muscles of yellow catfish were deficient in over 25 polyunsaturated fatty acids, such as Eicosapentaenoic acid, 12-oxo-ETE, and 13-Oxo-ODE. These substances play a role in anti-inflammatory mechanisms, possibly contributing to the immune dysregulation observed in yellow catfish. In summary, our study reveals a host immune deviation phenomenon that promotes bacterial colonization by increasing nutrient supply. It underscores the crucial factors rendering yellow catfish highly susceptible to V. mimicus, indicating that host nutritional sources not only enable the establishment and maintenance of infection within the host but also aid bacterial survival under immune pressure, ultimately completing its lifecycle.

Effects of dietary glycerol monolaurate on growth and digestive performance, lipid metabolism, immune defense and gut microbiota of shrimp (Penaeus vannamei)

The advancement of the Penaeus vannamei industry in a sustainable manner necessitates the creation of eco-friendly and exceptionally effective feed additives. To achieve this, 720 similarly-sized juvenile shrimp (0.88 ± 0.02 g) were randomly divided into four groups in this study, with each group consisting of three replicates, each tank (400 L) containing 60 shrimp. Four experimental diets were formulated by adding 0, 500, 1000, and 1500 mg kg-1 glycerol monolaurate (GML) to the basal diet, and the feeding trial lasted for 42 days. Subsequently, a 72-h White Spot Syndrome Virus (WSSV) challenge test was conducted. Polynomial orthogonal contrasts analysis revealed that with the increase in the concentration of GML, those indicators related to growth, metabolism and immunity, exhibit linear or quadratic correlations (P < 0.05). The results indicate that the GML groups exhibited a significant improvement in the shrimp weight gain rate, specific growth rate, and a reduction in the feed conversion ratio (P < 0.05). Furthermore, the GML groups promoted the lipase activity and reduced lipid content of the shrimp, augmented the expression of triglyceride and fatty acid decomposition-related genes and lowered the levels of plasma triglycerides (P < 0.05). GML can also enhanced the humoral immunity of the shrimp by activating the Toll-like receptor and Immune deficiency immune pathways, improved the phagocytic capacity and antibacterial ability of shrimp hemocytes. The challenge test revealed that GML significantly reduced the mortality of the shrimp compared to control group. The 16S rRNA sequencing indicates that the GML group can increases the abundance of beneficial bacteria. However, 1500 mg kg-1 GML adversely affected the stability of the intestinal microbiota, significantly upregulating intestinal antimicrobial peptide-related genes and tumor necrosis factor-alpha levels (P < 0.05). In summary, 1000 mg kg-1 GML was proven to enhance the growth performance, lipid absorption and metabolism, humoral immune response, and gut microbiota condition of P. vannamei, with no negative physiological effects.

Genome assembly of redclaw crayfish (Cherax quadricarinatus) provides insights into its immune adaptation and hypoxia tolerance

BACKGROUND

The introduction of non-native species is a primary driver of biodiversity loss in freshwater ecosystems. The redclaw crayfish (Cherax quadricarinatus) is a freshwater species that exhibits tolerance to hypoxic stresses, fluctuating temperatures, high ammonia concentration. These hardy physiological characteristics make C. quadricarinatus a popular aquaculture species and a potential invasive species that can negatively impact tropical and subtropical ecosystems. Investigating the genomic basis of environmental tolerances and immune adaptation in C. quadricarinatus will facilitate the development of management strategies of this potential invasive species.

RESULTS

We constructed a chromosome-level genome of C. quadricarinatus by integrating Nanopore and PacBio techniques. Comparative genomic analysis suggested that transposable elements and tandem repeats drove genome size evolution in decapod crustaceans. The expansion of nine immune-related gene families contributed to the disease resistance of C. quadricarinatus. Three hypoxia-related genes (KDM3A, KDM5A, HMOX2) were identified as being subjected to positive selection in C. quadricarinatus. Additionally, in vivo analysis revealed that upregulating KDM5A was crucial for hypoxic response in C. quadricarinatus. Knockdown of KDM5A impaired hypoxia tolerance in this species.

CONCLUSIONS

Our results provide the genomic basis for hypoxic tolerance and immune adaptation in C. quadricarinatus, facilitating the management of this potential invasive species. Additionally, in vivo analysis in C. quadricarinatus suggests that the role of KDM5A in the hypoxic response of animals is complex.

Toxic mechanisms of nanoplastics exposure at environmental concentrations on juvenile red swamp crayfish (Procambarus clarkii): From multiple perspectives

Nanoplastics pollution has emerged as a global issue due to its widespread potential toxicity. This study delved in to toxic effects of nanoplastics on juvenile P. clarkii and molecular mechanisms from perspectives of growth, biochemical, histopathological analysis and transcriptome level for the first time. The findings of this study indicated that nanoplastics of different concentrations have varying influence mechanisms on juvenile P. clarkii. Nanoplastics have inhibitory effects on growth of juvenile P. clarkii, can induce oxidative stress. The biochemical analysis and transcriptome results indicated that 10 mg/L nanoplastics can activate the antioxidant defense system and non-specific immune system in juvenile P. clarkii, and affect energy metabolism and oxidative phosphorylation. While 20 mg/L and 40 mg/L have a destructive influence on the immune function in juvenile P. clarkii, leading to lipid peroxidation and oxidative damage, and induce apoptosis, can affect ion transport and osmotic pressure regulation. The findings of this study can offer foundational data for delving further into impacts of nanoplastics on crustaceans and toxicity mechanism.

Isolation and characterization of a lectin-like chitinase from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii

A lectin was isolated from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii by affinity chromatography using mucin-sepharose matrix. The purity of the isolated lectin was confirmed in native gradient PAGE that showed a single protein band of ∼37.9 kDa. In SDS-PAGE also one band of ∼43.3 kDa molecular weight was observed that indicated the protein to be a monomer. The band from the SDS-PAGE gel was identified through mass spectrometry as chitinase 1. The purified chitinase (50 μg/ml) hemagglutinated rabbit RBCs and, mucin and glucose inhibited hemagglutination with minimum concentrations of 0.1 mg/ml and 100 mM, respectively. Bacterial agglutination with Gram -ve Vibrio harveyi, Aeromonas sobria and Escherichia coli was also observed by this protein. Thus, chitinase 1 showed lectin-like properties besides its chitin hydrolytic activity. In western blot with hepatopancreas sample, rabbit antiserum against chitinase 1 cross-reacted to two additional proteins namely, chitinase 1C and obstructor E (a chitin-binding protein, CBP), besides its specific reactivity. An indirect ELISA was developed with the antiserum to quantify chitinases/CBP in hepatopancreas and serum samples of M. rosenbergii. The assay was used in samples from juvenile prawns following V. harveyi challenge. At 72 h post-challenge, significantly higher levels of chitinases/CBP were quantified in the hepatopancreas of the challenged group (1.8 ± 0.2 mg/g tissue) compared to the control (1.2 ± 0.1 mg/g tissue). This study suggests that the chitinase 1 protein with lectin-like properties is possibly induced at the protein level and can be putatively involved in the innate immune response of M. rosenbergii.

In vitro immune analysis of serum from the hemolymph of the anomuran crab Albunea symmysta (Linnaeus, 1758) displayed diversified reactions

The present investigation aims to substantiate that serum from the hemolymph of anomuran crab Albunea symmysta encompasses multiple immunological reactions in in vitro condition. The serum highly agglutinated human O erythrocytes in the presence of Ba2+. Distinct and unique sugar binding capacity of serum towards laminarin, N-acetyl sugars and higher binding specificity towards a glycoprotein, fetuin was inferred. In vitro enhancement of melanin synthesis due to enhanced oxidation of 3, 4-dihydroxy-dl-phenylalanine (dl-DOPA) by preincubation of nonself molecules with serum phenoloxidase (PO) was documented. Similarly, dl-DOPA oxidation by serum PO was reduced when preincubated with chemical inhibitors and copper chelators. Further, the crab serum lysed the vertebrate erythrocytes with maximum hemolysis against chicken and it unveiled dependency on divalent cation, serum concentration, ionic strength, pH, temperature and time interval. Occurrence of maximum hemolysis at a concentration of 30 µl, pH 8.0, temperature 37 °C and time interval of 60 min in the presence of Ba2+ were documented. Interestingly, serum hemolysis was reduced by different osmoprotectants suggesting a colloid-osmotic mechanism involving in hemolysis. It was observed that A. symmysta serum had antimicrobial activity against Gram-positive Staphylococcus aureus and fungal pathogen Candida albicans. The serum showed higher glycan content, potent lysozyme and free radical scavenging activity suggesting the existence of potential immune molecules of therapeutic use. These results clearly demonstrated the diversified immunogenicity of A. symmysta serum confirming a highly conserved non-specific immunity of crustaceans.

A novel exoskeletal-derived C-type lectin facilitates phagocytosis of hemocytes in the oriental river prawn Macrobrachium nipponense

C-type lectins (CTLs) execute critical functions in multiple immune responses of crustaceans as a member of pattern recognition receptors (PRRs) family. In this study, a novel CTL was identified from the exoskeleton of the oriental river prawn Macrobrachium nipponense (MnLec3). The full-length cDNA of MnLec3 was 1150 bp with an open reading frame of 723 bp, encoding 240 amino acids. MnLec3 protein contained a signal peptide and one single carbohydrate-recognition domain (CRD). MnLec3 transcripts were widely distributed at the exoskeleton all over the body. Significant up-regulation of MnLec3 in exoskeleton after Aeromonas hydrophila challenged suggested the involvement of MnLec3 as well as the possible function of the exoskeleton in immune response. In vitro tests with recombinant MnLec3 protein (rMnLec3) manifested that it had polysaccharide binding activity, a wide spectrum of bacterial binding activity and agglutination activity only for tested Gram-negative bacteria (Escherichia coli, Vibrio anguillarum and A. hydrophila). Moreover, rMnLec3 significantly promoted phagocytic ability of hemocytes against A. hydrophila in vivo. What's more, MnLec3 interference remarkably impaired the survivability of the prawns when infected with A. hydrophila. Collectively, these results ascertained that MnLec3 derived from exoskeleton took an essential part in immune defense of the prawns against invading bacteria as a PRR.

Exposure to polystyrene nanoplastics induces apoptosis, autophagy, histopathological damage, and intestinal microbiota dysbiosis of the Pacific whiteleg shrimp (Litopenaeus vannamei)

Nanoplastics (NPs) are widely distributed environmental pollutants that can disrupt intestinal immunity of crustaceans. In this study, the effects of NPs on gut immune enzyme activities, cell morphology, apoptosis, and microbiota diversity of Litopenaeus vannamei were investigated. L. vannamei was exposed to five concentrations of NPs (0, 0.1, 1, 5, and 10 mg/L) for 28 days. The results showed that higher concentrations of NPs damaged the intestinal villi, promoted formation of autophagosomes, increased intestinal non-specific immunoenzyme activities, and significantly increased apoptosis at 10 mg/L. In response to exposure to NPs, the expression levels of ATG3, ATG4, ATG12, Caspase-3, p53, and TNF initially increased and then decreased. In addition, the concentration of NPs was negatively correlated to the expression levels of the genes of interest and intestinal enzyme activities, suggesting that exposure to NPs inhibited apoptosis and immune function. The five dominant phyla of the gut microbiota (Proteobacteria, Firmicutes, Bacteroidetes, Acidobacteria, and Actinomycetes) were similar among groups exposed to different concentrations of NPs, but the abundances tended to differ. Notably, exposure to NPs increased the abundance of pathogenic bacteria. These results confirm that exposure to NPs negatively impacted intestinal immune function of L. vannamei. These findings provide useful references for efficient breeding of L. vannamei.

Prometryn exposure disrupts the intestinal health of Eriocheir sinensis: Physiological responses and underlying mechanism

Most toxicity studies of prometryn in non-target aquatic animals have focused on hepatotoxicity, cardiotoxicity, embryonic developmental and growth toxicity, while studies on the molecular mechanisms of intestinal toxicity of prometryn are still unknown. In the current study, the intestinal tissues of the Chinese mitten crab (Eriocheir sinensis) were used to uncover the underlying molecular mechanisms of stress by 96-h acute in vivo exposure to prometryn. The results showed that prometryn activated the Nrf2-Keap1 pathway and up-regulated the expression of downstream antioxidant genes. Prometryn induced the expression of genes associated with non-specific immunity and autophagy, and induced apoptosis through the MAPK pathway. Interestingly, the significant up-or down-regulation of the above genes mainly occurred at 12 h- 24 h after exposure. Intestinal flora sequencing revealed that prometryn disrupted the intestinal normal barrier function mainly by reducing beneficial bacteria abundance, which further weakened the intestinal resistance to exogenous toxicants and caused an inflammatory response. Correlation analyses found that differential flora at the genus level had potential associations with gut stress-related genes. In conclusion, our study contributes to understanding the molecular mechanisms behind the intestinal stress caused by herbicides on aquatic crustaceans.

Differential molecular responses of hemolymph and hepatopancreas of swimming crab, Portunus trituberculatus, infected with Ameson portunus (Microsporidia)

Ameson portunus (Microsporidia) has caused serious economic losses to the aquaculture industry of swimming crab, Portunus trituberculatus. The hemolymph and hepatopancreas are the main immune organs of P. trituberculatus, and the main sites of A. portunus infection. Elucidating the response characteristics of hemolymph and hepatopancreas to microsporidian infection facilitates the development of microsporidiosis prevention and control strategy. This study performed comparative transcriptomic analysis of hemolymph (PTX/PTXA) and hepatopancreas (PTG/PTGA) of P. trituberculatus uninfected and infected with A. portunus. The results showed that there were 223 and 1309 differentially expressed genes (DEGs) in PTX/PTXA and PTG/PTGA, respectively. The lysosome pathway was significantly enriched after the invasion of the hemolymph by A. portunus. Also, immune-related genes were all significantly up-regulated in the hemolymph and hepatopancreas, suggesting that the invasion by A. portunus may activate host immune responses. Unlike hemolymph, antioxidant and detoxification-related genes were also significantly up-regulated in the hepatopancreas. Moreover, metabolism-related genes were significantly down-regulated in the hepatopancreas, suggesting that energy synthesis, resistance to pathogens, and regulation of oxidative stress were suppressed in the hepatopancreas. Hemolymph and hepatopancreas have similarity and tissue specificity to microsporidian infection. The differential genes and pathways identified in this study can provide references for the prevention and control of microsporidiosis.

Diversity of MrTolls and their regulation of antimicrobial peptides expression during Enterobacter cloacae infection in Macrobrachium rosenbergii

Toll/Toll-like receptor (TLR) is an important pattern recognition receptor that plays an important role in the immunity of animals. Six Toll genes were identified in Macrobrachium rosenbergii, namely, MrToll, MrToll1, MrToll2, MrToll3, MrToll4, and MrToll5. SMART analysis showed that all six Tolls have a transmembrane domain, a TIR domain, and different number of LRR domains. The phylogenetic tree showed that six Tolls were located in six different branches. Among these six Tolls, only MrToll4 contains the QHR motif, which is similar to insect Toll9. MrToll4 belongs to V-type/scc Toll with only one LRRCT domain. MrToll1 and MrToll5 are classical P-type/mcc Toll with two LRRCT domains and an LRRNT. MrTolls were distributed in the hemocytes, heart, hepatopancreas, gills, stomach, and intestine. During the infection of Enterobacter cloacae, the expression level of MrToll and MrToll1-4 was upregulated in the intestine of M. rosenbergii. RNA interference experiments showed that the expression of most antimicrobial peptide (AMP) genes was negatively regulated by MrTolls during E. cloacae infection. On the contrary, crustin (Cru) 3 and Cru4 were inhibited after the knockdown of MrToll, and Cru1 and Cru4 were significantly downregulated with the knockdown of MrToll4 during E. cloacae challenge. These results suggest that MrTolls may be involved in the regulation of AMP expression in the intestine during E. cloacae infection.

Characterization of a Lipopolysaccharide- and Beta-1,3-Glucan Binding Protein (LGBP) from the Hepatopancreas of Freshwater Prawn, Macrobrachium rosenbergii, Possessing Lectin-Like Activity

The study focuses on the isolation, characterization, and expression analysis of a lectin from the hepatopancreas of Macrobrachium rosenbergii. The protein was isolated by affinity chromatography on a melibiose-agarose column. The molecular weight of the native protein was found to be ~120 kDa which consists of a single polypeptide of ~39.5 kDa. On mass spectrometric analysis, the protein was identified as lipopolysaccharide- and beta-1,3-glucan binding protein (LGBP). LGBP showed hemagglutination with rabbit RBC like a lectin and its carbohydrate-binding specificity was determined by the hemagglutination inhibition test. The protein also showed antibacterial activity against two Gram-negative bacteria Vibrio harveyi and Aeromonas sobria, and one Gram positive bacteria Bacillus cereus in the disc diffusion test. Rabbit antiserum was raised against the purified LGBP and used to develop a sandwich ELISA system for quantitation of the protein in hepatopancreas and serum samples of M. rosenbergii. The expression of the LGBP transcripts in muscle, hepatopancreas, and gill tissues from M. rosenbergii juveniles at 72 h post-challenge of V. harveyi was not modulated as noticed in qPCR analysis. However, significant increases in the concentrations of LGBP protein in hepatopancreas (5.23 ± 0.45 against 3.43 ± 0.43 mg/g tissue in control) and serum (1.08 ± 0.14 against 0.61 ± 0.08 µg/ml in control) were observed in the challenged group of prawns in ELISA suggesting its putative role against bacterial infections. The study for the first time characterized the native LGBP of M. rosenbergii showing a multifunctional role in immunity.

The copepod Eurytemora affinis as a relevant species to assess estuarine sediment toxicity: Effects on gene expression and swimming behavior

Compared to freshwater ecosystems, the health status of estuarine waters remains little studied despite their importance for many species. They represent a zone of interest for Human settlements that make them the final sink of pollution in both the water column and sediment. Once in sediments, pollutants could represent a threat to benthic as well as pelagic estuarine species through resuspension events. In the Seine estuary, the copepod Eurytemora affinis has been previously presented as a relevant species to assess resuspended sediment contamination through fitness-related effects at the individual level. The aim of the present study was to use E. affinis copepods to assess estuarine sediment-derived elutriates toxicity at environmental concentrations of particles using a molecular (i.e. transcriptomics) and a behavioral approach. Two sites along the Seine estuary were sampled. The analysis of sediments reveals that both sites have the same granulometric composition and close contamination profiles with the detection of PCBs, PAHs and pyrethroid insecticides. The transcriptomic analysis reveals that exposure to elutriates from both sites triggers the dysregulation of genes involved in biological function as defense response, immunity, ecdysone pathway or neurotoxicity with 66% and 36% of shared genes at the highest concentration for Tancarville and Fatouville. This analysis also reveals a higher count of dysregulated genes in the Fatouville site compared to the Tancarville (271 vs 148) despite their close contamination profile. These results emphasize the molecular approach sensitivity to assess environmental matrix toxicity with E. affinis. The analysis of the swimming behavior of E. affinis did not highlight significant effects after elutriate exposure. However, our strategy to assess E. affinis swimming behavior allows the discrimination of basal swimming behavior i.e. dark/light velocity changes and strong thigmotaxis behavior. Thus, it represents a promising standardized tool to assess copepods swimming behavior in ecotoxicological studies.

Role of crustacean female sex hormone in regulating immune response in the mud crab, Scylla paramamosain

Crustacean female sex hormone (CFSH) is responsible for sexual differentiation in crustaceans. The CFSH exhibited an interleukin-17 domain homologous to vertebrate IL-17, a family of inflammatory cytokines that play vital roles in immune defense. However, the immunoregulation of CFSH in crustaceans is a mystery. Therefore, this study aimed to investigate the immune regulatory roles of CFSH and CFSHR in the mud crab Scylla paramamosain. This study's immunofluorescence result revealed that Sp-CFSHR was highly expressed in granulocytes and semi-granulocytes but had moderate expression in hyalinocytes. The expression level of Sp-CFSH transcript in eyestalk ganglia and Sp-CFSHR in hemocytes were significantly up-regulated by the Poly (I:C) stimulation but significantly down-regulated in response to the lipopolysaccharide (LPS) stimulation. In our study, in vitro experiment exhibited that the nuclear transcription factors NF-κB signaling molecules (Sp-Dorsal and Sp-Relish), Sp-STAT, apoptosis-related gene Sp-IAP, and phagocytosis related gene (Sp-Rab5) expressions were significantly increased in hemocytes by recombinant CFSH (rCFSH) in vitro, but the pro-inflammatory cytokine gene (Sp-IL-16) expression was significantly suppressed. Finally, the rCFSH injection significantly up-regulated Sp-Dorsal, Sp-Relish, Sp-IAP, Sp-Caspase, Sp-ALF2, and C-type lectin (Sp-CTL-B) expressions in hemocytes as well as enhanced the bacterial clearance of the mud crab. In conclusion, our results suggested that CFSH may be a counterpart of vertebrate IL-17 in crustaceans that can enhance innate immunity to defense against Vibrionaceae infection via the NF-κB and/or JAK-STAT signaling pathways. This study provides the first evidence that CFSH is involved in the immunoregulation in crustaceans and enriches the insight of neuroendocrine-immune regulatory system, which providing new ideas for disease prevention in the mud crab industry.

Research progress of pattern recognition receptors in red swamp crayfish (Procambarus clarkii)

Though Procambarus clarkii (red swamp crayfish) is a lower invertebrate, it has nonetheless developed a complex innate immune system. The crayfish farming industry has suffered considerable economic losses in recent years as a consequence of bacterial and viral diseases. Hence, perhaps the most effective ways to prevent microbial infections in P. clarkii are to examine and elucidate its innate immunity. The first step in the immune response is to recognize pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs). PRRs are expressed mainly on immune cell surfaces and recognize at least one PAMP. Thence, downstream immune responses are activated and pathogens are phagocytosed. To date, the PRRs identified in P. clarkii include Toll-like receptors (TLRs), lectins, fibrinogen-related proteins (FREPs), and β-1,3-glucan-binding proteins (BGRPs). The present review addresses recent progress in research on PRRs and aims to provide guidance for improving immunity and preventing and treating infectious diseases in P. clarkii.

mARC dependent NO synthesis activates CanA-Relish-AMPs signal pathway in Eriocheir sinensis during nitrite stress

As a signal molecule, nitric oxide (NO) can induce the production of antimicrobial peptides (AMPs) in invertebrate innate immunity and is produced through NO synthase (NOS) oxidation or nitrite reduction. Although the role of NOS-derived NO has been extensively studied, studies on nitrite-dependent NO are relatively scarce. In this study, we identified a mitochondrial amidoxime reducing component (mARC), a kind of nitrite reductase, in Eriocheir sinensis. Under nitrite stress, the expression level of EsmARC in the intestine of E. sinensis increased, and the production of NO increased. Furthermore, EsmARC knockdown resulted in a remarkable decrease in NO concentration. These findings indicate that nitrite stress induces the expression of mARC, which promotes the production of NO in E. sinensis. In addition, the expression levels of AMPs in the intestine were upregulated under nitrite stress. Moreover, EsmARC knockdown resulted in the downregulated expression of AMPs. EsmARC plays a positive role in the synthesis of AMPs under nitrite stress. Calcineurin subunit A (CanA) is a serine/threonine protein phosphatase involved in the process by which NO regulates the expression of AMPs. EsCanA knockdown significantly inhibited the transcription of EsRelish and the expression of AMPs under nitrite stress, and EsRelish silencing resulted in the downregulated expression levels of AMPs under nitrite stress. These results indicate that nitrite stress activates the CanA-Relish-AMP pathway in E. sinensis. In summary, mARC-dependent NO synthesis activates the CanA-Relish-AMP signal pathway in E. sinensis during nitrite stress. This research provides novel insights into the relationship between nitrite stress and NO-dependent immune signal activation in crustaceans.

Integrated analysis of a miRNA-mRNA network related to immunity and autophagy in Macrobrachium rosenbergii infected with Aeromonas hydrophila

MicroRNAs (miRNAs) are a group of RNAs that regulate gene expression in the post-transcriptionally. miRNAs can regulate numerous processes, such as the immune response, due to their dynamic expression patterns. The giant freshwater prawn Macrobrachium rosenbergii is a major freshwater aquaculture prawn that is attacked by various bacteria, including Aeromonas hydrophila. For this study, we performed an analysis of the miRNA and mRNA transcriptome analysis of M. rosenbergii which was infected with A. hydrophila. We identified 56 differentially expressed miRNAs (DEMs) and 1542 differentially expressed mRNAs. Furthermore, an integrated analysis of miRNA-mRNA expression led to the identification of 729 differentially predicted target genes (DETGs) of the DEMs. Multiple functional categories related to immunity, apoptosis, and autophagy were found to be enriched in the DETGs. During the infection of M. rosenbergii by A. hydrophila, an elaborate regulatory network involving Toll and immune deficiency (IMD) signaling, mitogen-activated protein kinase (MAPK) signaling, lysosome, and cell apoptosis was formed by a complex interplay of 40 crucial DEMs and 22 DETGs, all associated with the immune and autophagy pathway. The findings suggest that infection with A. hydrophila triggers intricate responses in both miRNA and mRNA, significantly impacting immune and autophagy processes in M. rosenbergii.

A novel tumor necrosis factor receptor-associated factor 6 (TRAF6) gene from Macrobrachiumrosenbergii involved in antibacterial defense against Aeromonas hydrophila

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an adapter protein that triggers downstream cascades mediated by both TNFR and the interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) superfamily. TRAF6 is involved in various biological processes, including innate and adaptive immunity. In the present study, a homolog of TRAF6 from Macrobrachium rosenbergii (MrTRAF6) was identified and characterized. The full-length cDNA of MrTRAF6 consisted of 2,114 nucleotides with an open reading frame (ORF) of 1,695 nucleotides encoding a 564-amino acid protein that contained a conserved TRAF family motif including two RING-type zinc fingers and a C-terminal meprin and TRAF homology (MATH) domain. The putative amino sequence of MrTRAF6 shared 45.5-97.3% identity with TRAF6s from other crustacean species with the highest identity to Macrobrachium nipponense TRAF6. Phylogenetic analysis revealed that MrTRAF6 was closely related to TRAF6 of invertebrates and clustered with crustaceans. According to gene expression analysis, the MrTRAF6 transcript demonstrated broad expression in all tissues tested, with the highest expression level in gill and the lowest in muscle tissues. Upon immune challenge with Aeromonas hydrophila, significant upregulation of MrTRAF6 expression was found in the gill, hepatopancreas, hemocyte, and muscle. Furthermore, an RNA interference assay showed that silencing MrTRAF6 by dsRNA could reduce the expression of mannose-binding lectin (MBL) and crustin, but no significant change was detected in anti-lipopolysaccharide factor 5 (ALF5) levels. In addition, the cumulative mortality rate of MrTRAF6-silenced M. rosenbergii was significantly increased after A. hydrophila infection. These findings indicated that MrTRAF6 is involved in antibacterial activity and plays a critical role in the innate immune response of M. rosenbergii.

Microplastics in feed cause sublethal changes in the intestinal microbiota and a non-specific immune response indicator of the freshwater crayfish Procambarus clarkii (Decapoda: Cambaridae)

Microplastics (MP) are a hazardous pollutant of global concern that threatens aquatic ecosystems and public health. We used the invasive, cosmopolitan, and environmentally versatile red swamp crayfish Procambarus clarkii as a model to study the effects of MP on the intestinal microbiome. Crayfish collected from the environment were compared with specimens exposed to recycled Polyethylene terephthalate (rPET) MP in feed (30%) for 96 h in the laboratory and a control group. We analyzed the 16S rRNA of the intestinal bacteria by PCR-DGGE and high-throughput sequencing. MP exposure caused dysbiosis of the intestinal microbiota, with an increase in Alphaproteobacteria and Actinobacteria. We detected higher abundance of opportunistic genera such as Klebsiella, Acinetobacter, Hydromonas, Pseudomonas, Gemmobacter, and Enterobacter on MP fed organisms. Moreover, MP exposure reduced the abundance of Clostridia and Bateroidetes, which are important for immune system development and pathogen prevention. Furthermore, MP exposure decreased the phenoloxidase (PO) immune response in crayfish. There was a significant difference in the richness of intestinal bacterial communities after consumption of food contaminated with MP, likely increasing the abundance of opportunistic bacteria in the intestinal microbiota. Our results suggest that MP alter the gut microbial composition and impair the health of P. clarkii.

Immune functions of pattern recognition receptors in Lepidoptera

Pattern recognition receptors (PRRs), as the "sensors" in the immune response, play a prominent role in recognizing pathogen-associated molecular patterns (PAMPs) and initiating an effective defense response to pathogens in Lepidoptera. It is becoming increasingly clear that damage-associated molecular patterns (DAMPs) normally play a physiological role within cells; however, when exposed to extracellular, they may become "part-time" critical signals of the immune response. Based on research in recent years, we review herein typical PRRs of Lepidoptera, including peptidoglycan recognition protein (PGRP), gram-negative binding protein (GNBP), β-1,3-glucan recognition protein (βGRP), C-type lectin (CTL), and scavenger receptor (SR). We also outline the ways in which DAMPs participate in the immune response and the correlation between PRRs and immune escape. Taken together, these findings suggest that the role of PRRs in insect innate immunity may be much greater than expected and that it is possible to recognize a broader range of signaling molecules.

Duox mediated ROS production inhibited WSSV replication in Eriocheir sinensis under short-term nitrite stress

Nitrite stress and white spot syndrome virus (WSSV) infection are major problems threatening the sustainable and healthy development of Eriocheir sinensis. Some studies have found that nitrite stress can lead to the production of reactive oxygen species (ROS), whereas synthetic ROS plays a vital role in the signaling pathway. However, whether nitrite stress influences the infection of crabs by WSSV remains unclear. NADPH oxidases, including NOX1-5 and Duox1-2, are important for ROS production. In the present study, a novel Duox gene (designated as EsDuox) was identified from E. sinensis. The studies found that nitrite stress could increase the expression of EsDuox during WSSV infection and decrease the transcription of the WSSV envelope protein VP28. Moreover, nitrite stress could increase the production of ROS, and the synthesis of ROS relied on EsDuox. These results indicated a potential "nitrite stress-Duox activation-ROS production" pathway that plays a negative role in WSSV infection in E. sinensis. Further studies found that nitrite stress and EsDuox could promote the expression of EsDorsal transcriptional factor and antimicrobial peptides (AMPs) during WSSV infection. Moreover, the synthesis of AMPs was positively regulated by EsDorsal in the process of WSSV infection under nitrite stress. Furthermore, EsDorsal played an inhibitory role in the replication of WSSV under nitrite stress. Our study reveals a new pathway for "nitrite stress-Duox activation-ROS production-Dorsal activation-AMP synthesis" that is involved in the defense against WSSV infection in E. sinensis during short-term nitrite stress.

Antioxidation, immunity and hepatopancreatic histology of red swamp crayfish (Procambarus clarkii) subjected to low-temperature aerial exposure stress and re-immersion

Desiccation is a stressful situation that decapods often experience during live transportation. This study investigated the effects of low-temperature aerial exposures (LTAEs) (dry exposure (DL) and moist exposure (ML) at 6 °C) and re-immersion on the antioxidative and immune responses and hepatopancreatic histopathology in P. clarkii. Compared to the control group (normally feeding at 24.0 °C water temperature), the crayfish under LTAEs showed overall severe hepatopancreatic oxidative damage, with significantly increased malondialdehyde (MDA) contents and significantly reduced total antioxidant capacity (T-AOC), and oxidant damage was not fully recovered even after 12 h of re-immersion; the expression of hsp70 was significantly increased within 24-48 h of stress and re-immersion. The activity of hemolymphatic acid phosphatase (ACP) was significantly increased during 24-48 h of the stress and at 12 h of re-immersion; the activity of aspartic aminotransferase (AST) and alanine aminotransferase (ALT) was significantly increased throughout the experiment; and the gene expression of proPO or TLR was significantly increased during 12-48 h of the stress. Severe histopathological changes (lumen dilatation, vacuolation of epithelial cells and reduced cell numbers) were observed in hepatopancreas at 48 h of stress and 12 h of re-immersion. These results indicated that 48 h of low-temperature aerial exposure stress stimulated the non-specific immunity but adversely affected the antioxidation and hepatopancreatic histomorphology of P. clarkii, whereas 12 h of re-immersion was not sufficient to restore crayfish from stress to a normal state.

Identification of acid phosphatase (ShACP) from the freshwater crab Sinopotamon henanense and its expression pattern changes in response to cadmium

Acid phosphatase(ACP) is an important immune enzyme in crustacean humoral immunity. At present, the research on ACP mainly focuses on the biochemical properties of the enzyme, while few studies on gene expression. In this study, ShACP was cloned and the effect of cadmium stress on the expression and function of ShACP in the freshwater crab Sinopotamon henanense was studied. Analysis of the ShACP sequence and tissue distribution results showed that the cDNA sequence of ShACP was 1629 bp, including 48 bp 5' untranslated region, 1209 bp open reading frame region, and 372 bp 3' untranslated region, encoding 402 amino acids. ShACP contained multiple phosphorylation sites and mainly played a role in the hemolymph. Under low-concentration cadmium stress, the body improved immunity by enhancing the expression of ShACP, while high-concentration cadmium stress inhibited the expression of ShACP. ShACP can promote the phagocytosis of hemocytes, while cadmium stress reduced the phagocytosis of hemocytes. This study provides a theoretical basis for further research on the immune system of crabs and is of great significance for the study of crustacean immune responses under heavy metal stress.

Impact of Titanium Dioxide-Graphene Oxide (TiO2-GO) Composite Nanoparticle on the Juveniles of the Giant River Prawn, Macrobrachium rosenbergii: Physio-Biochemistry and Transcriptional Response

Nanomaterials are used in many fields, resulting in inevitably releasing into the aquatic environment. The presence of nanomaterials, including TiO₂-GO in the aquatic environment, can be toxic to aquatic organisms. However, few studies have focused on the effects of TiO₂-GO composite nanoparticle on crustaceans. In the present study, the giant river prawn Macrobrachium rosenbergii juveniles were exposed to two concentrations of TiO₂-GO composite nanoparticle (0.1 and 0.5 mg/L). The effects of TiO₂-GO composite exposure on activities of digestive and antioxidant-related enzymes and expressions of growth and immune-related genes at the transcriptome were studied. The results showed that the survival rate and growth performance were not negatively affected by TiO₂-GO composite at the two exposure levels. Nevertheless, exposure to TiO₂-GO composite causes an effect on the activities of digestive and antioxidant enzymes in the juvenile prawns. The enzyme activities of CAT, SOD, GSH-Px, AMS, TPS, and LPS in the 0.1 mg/L TiO₂-GO composite experimental group were markedly reduced than those in the control group. Additionally, the expression level of genes involved in growth and immunity was significantly affected by TiO₂-GO composite. After exposure to the 0.1 mg/L TiO₂-GO composite, the mRNA expression level of MSTN was significantly increased, but the level of EcR, Raptor, and CaBP was significantly decreased. However, the mRNA levels of the CTL, TLR, JAK, and STAT were significantly increased after exposure to the 0.5 mg/L concentration of TiO₂-GO composite. Furthermore, to understand the molecular mechanism of M. rosenbergii under TiO₂-GO composite exposure, RNA-Seq was employed to analyze the changes of the muscle and hepatopancreas transcriptome. Compared with the control group, we identified 5166 and 4784 differentially expressed genes (DEGs) in the muscle and hepatopancreas, respectively (p < 0.05). Based on gene ontology and KEGG analysis, significant differences were observed in the DEGs involved in activity and binding, metabolism, immune response, and environmental information processing. These results showed that exposure to TiO₂-GO composite nanoparticle led to the changes of enzyme activity and gene expression, suggesting that TiO₂-GO composite existing in aquatic environments would disrupt the physiology of M. rosenbergii. This study will serve as a foundation for subsequent research into the evaluation of nanomaterial toxicity on crustacean species.

Bovine lactoferricin on non-specific immunity of giant freshwater prawns, Macrobrachium rosenbergii

This study aimed to investigate the effects of dietary Bovine lactoferricin (LFcinB) on the growth performance and non-specific immunity in Macrobrachium rosenbergii. Five experimental diets were 1.0‰ Bovine lactoferricin (LCB1); 1.5‰ Bovine lactoferricin (LCB1.5); 2.0‰ Bovine lactoferricin (LCB2); 2.5‰ Bovine lactoferricin (LCB2.5); the control group, basal diet without Bovine lactoferricin. A total of 600 prawns were randomly assigned to 5 groups in triplicate in 15 tanks for an 8-week feeding trial. The results showed the final weight, weight gain rate, specific growth rate and survival rate of prawns in the treatment groups were significantly improved versus the control (P < 0.05). The feed conversion ratio was reduced significantly in treatment groups compared to the control (P < 0.05). Compared with the control, alkaline phosphatase (AKP), acid phosphatase (ACP), lysozyme (LZM), catalase (CAT), superoxide dismutase (SOD) activities in the hepatopancreas of the treatment groups were significantly enhanced, and malondialdehyde (MDA) content was reduced significantly (P < 0.05). Compared with the control, the relative expression levels of AKP, ACP, LZM, CAT, SOD, Hsp70, peroxiredoxin-5, Toll, dorsal and relish genes were significantly higher among treatment groups, except for the AKP gene in the LCB1 group and the Hsp70 gene in the LCB1.5 group (P < 0.05). Compared with the control, the relative expression levels of TOR, 4E-BP, eIF4E1α and eIF4E2 genes were significantly enhanced in the LCB1.5 group (P < 0.05). When resistance against Vibrio parahaemolyticus in prawn is considered, higher doses of Bovine lactoferricin show better antibacterial ability. The present study indicated that dietary Bovine lactoferricin could significantly improve the growth performance and improve the antioxidative status of M. rosenbergii. The suitable addition level is 1.5 g/kg. LFcinB has great potential as a new feed additive without the threat of drug resistance.

Effect of dietary replacement of fish meal by poultry by-product meal on the growth performance, immunity, and intestinal health of juvenile red swamp crayfish, procambarus clarkia

The present study was conducted to investigate the dietary replacement of fish meal with poultry by-product meal (PBM) on the growth performance, immunity, antioxidant properties, and intestinal health of red swamp crayfish (Procambarus clarkia). A diet containing 20% fish meal (FM) and complex plant ingredients as the main protein resources was set as the FM group (crude protein 32%, crude lipid 6%). Four diets replacing 25%, 50%, 75%, and 100% fish meal of the FM diet with PBM were set as the PBM25, PBM50, PBM75, and PBM100 groups, respectively. Compared to the FM group, the PBM100 diet significantly decreased growth performance and feed utilization of crayfish, while markedly increasing the activity of serum aspartate aminotransferase. The immune response was depressed in crayfish fed the PBM100 diet as the activities of serum lysozyme and phenoloxidase, gene expression of anti-lipopolysaccharide factors (alf), cyclophilin A (cypa), crustin, and hemocyanin-1 (hep-1) in hepatopancreas were remarkably decreased. The activities of antioxidases and expression of antioxidant-relevant genes in the hepatopancreas were not influenced by PBM inclusion. Crayfish fed different diets exhibited no obvious symptoms of enteritis, but the PBM100 diet destructed intestinal morphology by significantly decreasing the average length of longitudinal ridges. The α-diversity and overall community structure were not significantly influenced but variations were found in the relative abundance of some genera by PBM inclusion. In summary, CAP could successfully replace 75% dietary FM in a basal diet containing 20% fish meal, while higher CAP level compromised growth performance, immunity, and intestinal histology of crayfish.

Integrated analysis of mRNA and microRNA transcriptome related to immunity and autophagy in shrimp hemocytes infected with Spiroplasma eriocheiris

In recent years, the industry in charge of the cultivation of Macrobrachium nipponense (M.nipponense) has suffered significant economic losses due to an infectious pathogen called Spiroplasma eriocheiris (S.eriocheiris). There has therefore been a need to identify the key immune and autophagy genes that respond to M.nipponense's infection with S. eriocheiris to analyze its immune response mechanism and the regulation of related microRNAs (miRNAs). In this study, the mRNA and miRNA transcriptome of M.nipponense's hemocytes were analyzed at different stages of infection. This analysis employed the second and third-generation sequencing technologies. In the mRNA transcriptome, 1656 genes were expressed in healthy and susceptible M.nipponense. 892 of these were significantly up-regulated, while 764 were down-regulated. 118 genes with significant differences in autophagy, endocytosis, lysosome, Toll, IMD, and VEGF pathways were obtained from the transcriptome. In the miRNA transcriptome, 312 miRNAs (Conserved: 112, PN-type: 18, PC-type: 182) were sequenced. 74 were significantly up-regulated, and 57 were down-regulated. There were 25 miRNAs involved in regulating the Toll and IMD pathways, 41 in endocytosis, 30 in lysosome, and 12 in the VEGF pathway. An integrated analysis of immune-related miRNAs and mRNAs showed that miRNAs with significant differences (P < 0.05) such as ame-miR-29b-3p, dpu-miR-1and PC-3p-945_4074, had corresponding regulatory relationships with 118 important immune genes such as Relish, Dorsal, Caspase-3, and NF-κB. This study obtained the key immune and autophagy-related genes and corresponding regulatory miRNAs in M. nipponense's hemocytes in response to an infection by S.eriocheiris. The results can provide vital data that further reveals the defense mechanism of M.nipponense's immune system against S.eriocheiris. It can also help further comprehension and interpretation of M.nipponense's resistance mechanism to the invading S.eriocheiris, and provide molecular research information for the realization of host-directed therapies (HDT) for M.nipponense.

Comparative transcriptomics reveals the immune dynamics during the molting cycle of swimming crab Portunus trituberculatus

Molting is one of the most important biological processes of crustacean species, and a number of molecular mechanisms facilitate this complex procedure. However, the understanding of the immune mechanisms underlying crustacean molting cycle remains very limited. This study performed transcriptome sequencing in hemolymph and hepatopancreas of the swimming crab (Portunus trituberculatus) during the four molting stages: post-molt (AB), inter-molt (C), pre-molt (D), and ecdysis (E). The results showed that there were 78,572 unigenes that were obtained in the hemolymph and hepatopancreas of P. trituberculatus. Further analysis showed that 98 DEGs were involved in immunity response of hemolymph and hepatopancreas, and most of the DEGs participated in the process of signal transduction, pattern recognition proteins/receptors, and antioxidative enzymes system. Specifically, the key genes and pathway involved in signal transduction including the GPCR126, beta-integrin, integrin, three genes in mitogen-activated protein kinase (MAPK) signaling cascade (MAPKKK10, MAPKK4, and p38 MAPK), and four genes in Toll pathway (Toll-like receptor, cactus, pelle-like kinase, and NFIL3). For the pattern recognition proteins/receptors, the lowest expression level of 11 genes was found in the E stage, including C-type lectin receptor, C-type lectin domain family 6 member A and SRB3/C in the hemolymph, and hepatopancreatic lectin 4, C-type lectin, SRB, Down syndrome cell adhesion molecule homolog, Down syndrome cell adhesion molecule isoform, and A2M. Moreover, the expression level of copper/zinc superoxide dismutase isoform 4, glutathione peroxidase, glutathione S-transferase, peroxiredoxin, peroxiredoxin 6, and dual oxidase 2 in stage C or stage D significantly higher than that of stage E or stage AB. These results fill in the gap of the continuous transcriptional changes that are evident during the molting cycle of crab and further provided valuable information for elucidating the molecular mechanisms of immune regulation during the molting cycle of crab.

Polystyrene microplastics induced male reproductive toxicity and transgenerational effects in freshwater prawn

Microplastics have become pervasive environmental pollutants, especially in freshwater rivers and lakes. However, how freshwater prawns' reproductive system is affected by polystyrene microplastics (PS-MPs) remains incompletely understood. Thus, the present study aimed to determine the effect of PS-MPs on the male reproductive system and offspring larval immunity in oriental river prawn. Acute exposure to PS-MPs decreased the survival rate and heart rate of prawn larvae. After chronic exposure to PS-MPs (2 and 20 mg/L) for four weeks, the oxidative stress generation in testis tissue indicated a negative impact on male prawn testicular function. PS-MPs disrupted testicular germ cell quality and caused sex hormone imbalance, leading to reduced hatching success and survival of F1 larvae, despite not being exposed to PS-MPs. Steroidogenic gene expression was altered and apoptosis-related genes had higher expression in the gonads after parental exposure to PS-MPs. Decreased immunity-related enzyme activities were observed in F1 larvae with/without continued PS-MPs exposure, compared with those in untreated prawns. A concentration-dependent increase in bioaccumulation of PS-MPs in different tissues of larval offspring was observed. Thus, PS-MPs had multiple effects on male reproductive dysfunction and transgenerational toxicity in prawns. Our findings provide a novel insight into the reproductive toxicity mechanism of microplastics in freshwater crustaceans.

Identification and functional characterization of C-type lectins and crustins provide new insights into the immune response of Portunus trituberculatus

A meticulous understanding of the immune characteristics of aquaculture animals is the basis for developing precise disease prevention and control strategies. In this study, four novel C-type lectins (PtCTL-5, PtCTL-6, PtCTL-7 and PtCTL-8) including a single carbohydrate-recognition domain (CRD), and four novel crustins (Ptcrustin-1, Ptcrustin-2, Ptcrustin-3 and Ptcrustin-4) with a single whey acidic protein (WAP) domain were identified from the swimming crab Portunus trituberculatus. Tissue distribution analysis indicated that most of the target genes were predominantly expressed in the hepatopancreas in all examined tissues, except for Ptcrustin-1 which were mainly expressed in the gills. Our results showed that the eight genes displayed various transcriptional profiles across different tissues. In hemocytes, the PtCTL-7 responded quickly to Vibrio alginolyticus and exhibited much more strongly up-regulation than other three PtCTLs. The Ptcrustin-1 rapidly responded to V. alginolyticus within 3 h in all the three tested tissues. Furthermore, recombinant proteins of PtCTL-5 and PtCTL-8 were successfully obtained, and both of them displayed bacterial binding activities toward V. alginolyticus, V. harveyi and Staphylococcus aureus, and only showed antibacterial activity against V. harveyi. These findings provided new insights into the diverse immune response of P. trituberculatus and laid theoretical foundations for the development of precise disease prevention and control strategies in P. trituberculatus farming. Moreover, the specific anti-V. harveyi activities exhibited by rPtCTL-5 and rPtCTL-8 suggested their promising application prospects for controlling diseases caused by V. harveyi.

Physiological and muscle tissue responses in Litopenaeus vannamei under hypoxic stress via iTRAQ

White L. vannamei have become the most widely cultivated shrimp species worldwide. Cultivation of L. vannamei is one of the predominant sectors in China’s aquaculture industry. This study focused on the physiological and biochemical responses, differential protein expression, and expression characteristics of the related crucial functional protein genes under low oxygen conditions among different strains of L. vannamei. It was found that 6 h of hypoxic stress caused a significant reduction in the total hemocyte number in both strains, while the hypoxia-sensitive strain showed a stronger reduction. In contrast, the hemocyanin concentration showed only an overall upward trend. Proteomic analysis of L. vannamei muscle tissue revealed 3,417 differential proteins after 12 h of hypoxic stress. Among them, 29 differentially expressed proteins were downregulated and 244 were upregulated in the hypoxia-sensitive strain. In contrast, there were only 10 differentially expressed proteins with a downregulation pattern and 25 with an upregulation pattern in the hypoxia-tolerant strain. Five protein genes that responded significantly to hypoxic stress were selected for quantitative real-time PCR analysis, namely, hemocyanin, chitinase, heat shock protein 90 (HSP 90), programmed death protein, and glycogen phosphorylase. The results showed that the gene expression patterns were consistent with proteomic experimental data except for death protein and glycogen phosphorylase. These results can enrich the general knowledge of hypoxic stress in L. vannamei and the information provided differentially expressed proteins which may be used to assist breeding programs of L. vannamei of new strains with tolerance to hypoxia.

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

A novel type I Crustin from Exopalaemon carinicauda: Antimicrobial ability related to conserved cysteine

Crustins are a kind of antibacterial peptides (AMP) existing in crustaceans, and their antibacterial abilities are considered to be related to the conserved WAP domain. In this study, a novel type I Crustin gene was identified in Exopalaemon carinicauda, named EcCru. The deduced amino acid sequence revealed that the conserved cysteine at position 7 in the WAP domain was replaced by aspartic acid. The gene is 405 bp in length, encoding 134 amino acids, and is mainly distributed in gills and hepatopancreas. After Vibrio parahaemolyticus and Aeromonas hydrophila stimulation, the expression of EcCru was significantly up-regulated within 12 h, and then returned to normal levels. The recombinant protein was obtained using the Pichia pastoris expression system, and the recombinant protein had neither antibacterial activity against gram-positive or gram-negative bacteria. But the antibacterial ability emerged when Asp¹⁰¹ was mutated to Cys. Notably, we also obtained a mutant that had a deletion at the 6 th conserved Cys in the WAP domain, and this mutant had antibacterial ability against gram-positive bacteria Bacillus subtilis and B. cereus. This indicates that the conserved cysteine with different positions in WAP domain can have different effects on the antibacterial ability of Crustins.

Gastrointestinal Microbiota of Spiny Lobster: A Review

The gastrointestinal (GI) microbiota is a group of complex and dynamic microorganisms present in the GI tract of an organism that live in symbiosis with the host and benefit the host with various biological functions. The communities of GI microbiota are formed by various aerobic, anaerobic, and facultatively anaerobic bacteria in aquatic species. In spiny lobsters, common GI microorganisms found in the GI tract are Vibrio, Pseudomonas, Bacillus, Micrococcus, and Flavobacterium, where the structure and abundance of these microbes are varied depending on the environment. GI microbiotas hold an important role and significantly affect the overall condition of spiny lobsters, such as secreting digestive enzymes (lipase, protease, and cellulase), helping in digesting food intake, providing nutrition and synthesising vitamins needed by the host system, and protecting the host against infection from pathogens and diseases by activating an immune mechanism in the GI tract. The microorganisms in the water column, sediment, and diet are primarily responsible for altering, manipulating, and shaping GI microbial structures and communities. This review also highlights the possibilities of isolating the indigenous GI microbiota as a potential probiotic strain and introducing it to spiny lobster juveniles and larvae for better health management.

Time-Course of the Innate Immune Response of the Terrestrial Crustacean Porcellio scaber After Injection of a Single Dose of Lipopolysaccharide

Invertebrates, including crustaceans, rely on cellular and humoral immune responses to protect against extrinsic and intrinsic factors that threaten their integrity. Recently, different immune parameters have been increasingly used as biomarkers of effects of pollutants and environmental change. Here, we describe the dynamics of the innate immune response of the terrestrial crustacean Porcellio scaber to injection of a single dose of lipopolysaccharide (LPS), an important molecular surface component of the outer membrane of Gram-negative bacteria. The aim was to provide a basis for interpretation of change in immune parameters as a result of different challenges, including microplastics and nanoplastics exposure. Changes in total and differential numbers of hemocytes, hemocyte viability, and humoral immune parameters (i.e., phenoloxidase-like activity, nitric oxide levels) were assessed at different times (3, 6, 12, 24, 48 h). An injection of 0.5 μg/μL LPS into the body of P. scaber resulted in a rapid decrease (3 h after LPS injection) in the total number of hemocytes and reduced viability of the hemocytes. This was accompanied by changed proportions of the different hemocyte types, as a decrease in the numbers of semigranulocytes and granulocytes, and a marked increase in the numbers of hyalinocytes. In addition, phenoloxidase-like activity and nitric oxide levels in the hemolymph were increased at 3 h and 6 h, respectively, after the LPS challenge. Forty-eight hours after LPS injection, the immune parameters in the hemolymph of P. scaber had returned to those before the LPS challenge. This suggests that the innate immune system successfully protected P. scaber from the deleterious effects of the LPS challenge. These data indicate the need to consider the dynamics of innate immune responses of P. scaber when effects of infections, pollutants, or environmental changes are studied. We also propose an approach to test the immunocompetence of organisms after different challenges in ecotoxicity studies, based on the dynamics of their immune responses.

Effects of dietary carbohydrate/lipid ratios on non-specific immune responses, antioxidant capacity, hepatopancreas and intestines histology, and expression of TLR-MAPK/NF-κB signaling pathway-related genes of Procambarus clarkii

To investigate the effects of dietary carbohydrate/lipid (CHO: L) ratios on non-specific immune responses, antioxidant capacity, and expression of TLR-MAPK/NF-κB signaling pathway-related genes of red swamp crayfish (Procambarus clarkii). Four isonitrogenous and isoenergetic diets containing different CHO: L ratios were formulated. The results showed that the group with a CHO: L ratio of 5.94 had better growth performance (P < 0.05). The highest T-AOC, CAT, and SOD activities and the lowest MDA content in hemolymph and hepatopancreas were observed in the group with a CHO: L ratio of 5.94 (P < 0.05). The lowest activities of ALT, AST, ACP, AKP, and ALB in the hemolymph were observed in CHO: L ratio 5.94 group (P < 0.05), while the highest LZM activity, TP, and GLB content were observed in CHO: L 5.94 group (P < 0.05). The highest mRNA expression levels of tlr3, myd88, and mapk3, and the lowest mRNA expression levels of nf-kb α, nf-kb β, nf-kb p105, and traf6 were observed in the CHO: L of 5.94 group (P < 0.05). The highest mRNA expression levels of immune-related genes were observed in the CHO: L of 5.94 group (P < 0.05). Overall, these results indicated that the optimum dietary CHO: L ratio is vital in promoting growth and enhancing antioxidants and immunity to maintain red swamp crayfish's intestinal and hepatopancreas health status. In conclusion, the diets with a CHO:L ratio of 5.94 (approximately 36.23% carbohydrate and 6.10% lipid) is optimal for juvenile red swamp crayfish's physiological condition and health status.

Yorkie Negatively Regulates the Expression of Antimicrobial Proteins by Inducing Cactus Transcription in Prawns Macrobrachium nipponense

The Hippo signaling pathway controls organ size and immune system in Drosophila and mammals. Yorkie acts as a transcriptional co-activator in the Hippo pathway and cross-talks with other essential pathways. In this study, a Yorkie gene and two Cactus isoforms (designated as MnYorkie, MnCactus-a, and MnCactus-b, respectively) were isolated and characterized from oriental river prawns (Macrobrachium nipponense). Results showed that MnYorkie includes 1620 bp open reading frame and encodes a protein of 539 amino acids (aa). MnCactus-a (377 aa) and MnCactus-b (471 aa) were produced by alternative splicing. MnYorkie and MnCactus were continuously expressed in all selected tissues. Upon Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Vibrio parahaemolyticus stimulation, the mRNA levels of MnYorkie and MnCactus in hemocytes and intestines underwent time-dependent enhancement. RNA interference studies showed that MnYorkie silencing remarkably downregulated the transcription of MnCactus but upregulated the expression of seven immune-related genes. In addition, MnYorkie silencing in vivo decreased the susceptibility of prawns to bacterial challenge. After S. aureus and V. parahaemolyticus infection, the survival rate of prawns increased significantly from 2 to 6 days, which corresponded to the period of MnYorkie knockdown. All these findings suggested that MnYorkie in the Hippo pathway might exhibit remarkable biological roles in the immune defense of M. nipponense by negatively regulating the expression of immune-related genes and promoting the transcription of MnCactus.

Effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the non-specific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.

Host Controls of Within-Host Disease Dynamics: Insight from an Invertebrate System

AbstractWithin-host processes (representing the entry, establishment, growth, and development of a parasite inside its host) may play a key role in parasite transmission but remain challenging to observe and quantify. We develop a general model for measuring host defenses and within-host disease dynamics. Our stochastic model breaks the infection process down into the stages of parasite exposure, entry, and establishment and provides associated probabilities for a host's ability to resist infections with barriers and clear internal infections. We tested our model on Daphnia dentifera and the parasitic fungus Metschnikowia bicuspidata and found that when faced with identical levels of parasite exposure, Daphnia patent (transmitting) infections depended on the strength of internal clearance. Applying a Gillespie algorithm to the model-estimated probabilities allowed us to visualize within-host dynamics, within which signatures of host defense could be clearly observed. We also found that early within-host stages were the most vulnerable to internal clearance, suggesting that hosts have a limited window during which recovery can occur. Our study demonstrates how pairing longitudinal infection data with a simple model can reveal new insight into within-host dynamics and mechanisms of host defense. Our model and methodological approach may be a powerful tool for exploring these properties in understudied host-parasite interactions.

Effects of nonylphenol exposure on histological changes, apoptosis and time-course transcriptome in gills of white shrimp Litopenaeus vannamei

Nonylphenol (NP) is considered as one of the persistent organic pollutants (POPs) in the environment. Pacific white shrimp Litopenaeus vannamei is the predominant species in China, which is frequently affected by environmental pollutants. However, potential toxicity mechanism of NP in shrimp has not been comprehensively studied. To explore the physiological changes and molecular mechanism involved in NP exposure of shrimp, we analyzed histological alterations, apoptosis and transcriptional responses of L.vannamei subjected to NP. Results indicated that significant changes in the histoarchitecture of the gills were observed after NP exposure for 3, 12 and 48 h. Apoptosis was also detected in a time-dependent manner. Numerous differentially expressed genes (DEGs) were obtained at 3 h, 12 h and 48 h after exposure. On the basis of the expression patterns over the time course, these DEGs were classified into 12 clusters. GO and KEGG enrichment analysis of these DEGs was carried out and a dynamic and global view was obtained in shrimp after NP exposure on a transcriptome level. In addition, 15 DEGs involved in immune response, apoptosis, DNA repair, osmoregulation etc. were selected for qRT-PCR validation. The expression patterns of these DEGs kept a well consistent with the high-throughput data at different timepoints, which confirmed the accuracy and reliability of the transcriptome data. All the results demonstrated that NP exposure might lead to impairments of biological functions in gills, alter immune and antioxidant response, compromise DNA repair and anti-apoptosis abilities of shrimp, cause severe histopathological changes and eventually trigger apoptosis. The present study enriched the information on the toxicity mechanism of crustaceans in response to NP exposure.