Transcriptome profiling of red swamp crayfish (Procambarus clarkii) hepatopancreas in response to lipopolysaccharide (LPS) infection

Transcriptome-based network analysis reveals hub immune genes and pathways of hepatopancreas against LPS in Amphioctopus fangsiao

The hepatopancreas is the biggest digestive organ in Amphioctopus fangsiao (A. fangsiao), but also undertakes critical functions like detoxification and immune defense. Generally, pathogenic bacteria or endotoxin from the gut microbiota would be arrested and detoxified in the hepatopancreas, which could be accompanied by the inevitable immune responses. In recent years, studies related to cephalopods immune have been increasing, but the molecular mechanisms associated with the hepatopancreatic immunity are still unclear. In this study, lipopolysaccharide (LPS), a major component of the cell wall of Gram-negative bacteria, was used for imitating bacteria infection to stimulate the hepatopancreas of A. fangsiao. To investigate the immune process happened in A. fangsiao hepatopancreas, we performed transcriptome analysis of hepatopancreas tissue after LPS injection, and identified 2615 and 1943 differentially expressed genes (DEGs) at 6 and 24 h post-injection, respectively. GO and KEGG enrichment analysis showed that these DEGs were mainly involved in immune-related biological processes and signaling pathways, including ECM-receptor interaction signaling pathway, Phagosome signaling pathway, Lysosome signaling pathway, and JAK-STAT signaling pathways. The function relationships between these DEGs were further analyzed through protein-protein interaction (PPI) networks. It was found that Mtor, Mapk14 and Atm were the three top interacting DEGs under LPS stimulation. Finally, 15 hub genes involving multiple KEGG signaling pathways and PPI relationships were selected for qRT-PCR validation. In this study, for the first time we explored the molecular mechanisms associated with hepatopancreatic immunity in A. fangsiao using a PPI networks approach, and provided new insights for understanding hepatopancreatic immunity in A. fangsiao.

From the fat body to the hemolymph: Profiling tick immune and storage proteins through transcriptomics and proteomics

Ticks are blood-feeding arachnids that are known to transmit various pathogenic microorganisms to their hosts. During blood feeding, ticks activate their metabolism and immune system to efficiently utilise nutrients from the host's blood and complete the feeding process. In contrast to insects, in which the fat body is known to be a central organ that controls essential metabolic processes and immune defense mechanisms, the function of the fat body in tick physiology is still relatively unexplored. To fill this gap, we sought to uncover the repertoire of genes expressed in the fat body associated with trachea (FB/Tr) by analyzing the transcriptome of individual, partially fed (previtellogenic) Ixodes ricinus females. The resulting catalog of individual mRNA sequences reveals a broad repertoire of transcripts encoding proteins involved in nutrient storage and distribution, as well as components of the tick immune system. To gain a detailed insight into the secretory products of FB/Tr specifically involved in inter-tissue transport and humoral immunity, the transcriptomic data were complemented with the proteome of soluble proteins in the hemolymph of partially fed female ticks. Among these proteins, the hemolipoglyco-carrier proteins were predominant. When comparing immune peptides and proteins from the fat body with those produced by hemocytes, we found that the fat body serves as a unique producer of certain immune components. Finally, time-resolved transcriptional regulation of selected immune transcripts from the FB/Tr was examined in response to experimental challenges with model microbes and analyzed by RT-qPCR. Overall, our data show that the fat body of ticks, similar to insects, is an important metabolic tissue that also plays a remarkable role in immune defense against invading microbes. These findings improve our understanding of tick biology and its impact on the transmission of tick-borne pathogens.

Evolution and expression analysis of carotenoid cleavage oxygenase gene family in Chinese mitten crab Eriocheir sinensis

Carotenoid cleavage oxygenase (CCO) plays a pivotal role in various biological activities, including antioxidant and immune functions in animals. This paper investigates the evolution and expression of CCO genes based on three chordates and 27 arthropods. Aquatic animals exhibit a higher abundance of CCO genes. Despite this, research on CCO in crustaceans has been notably limited, with a complete absence of any previous studies on the CCO genes for the Chinese mitten crab (Eriocheir sinensis). In this study, six CCO genes were identified in the E. sinensis genome database. Results reveal that the evolution of the CCO gene family in Crustacea is primarily characterized by purifying selection, with a preference for employing similar codons. EsCCO1 and EsCCO3 were mainly expressed in the epidermal layer, and EsCCO4 was mainly expressed in the hindgut. Meanwhile, EsCCO5 and EsCCO6 were mainly expressed in the hepatopancreas and endometrium. A notable detail that different EsCCO genes demonstrate distinct expression patterns within various tissues of E. sinensis. The findings of this study offer fundamental insights that could serve as a basis for further exploration into the functions and regulatory mechanisms of CCO genes in crustacean species.

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.

New insights into the regulation mechanism of red claw crayfish (Cherax quadricarinatus) hepatopancreas under air exposure using transcriptome analysis

Red claw crayfish (Cherax quadricarinatus) is an important freshwater shrimp species worldwide with enormous economic value. Waterless transportation is an inherent feature of red claw crayfish transportation. However, the high mortality of red claw crayfish is a severe problem in the aquaculture of crayfish after waterless transportation. In this study, we investigated the responses of the hepatopancreas from the red claw crayfish undergoing air exposure stress and normal conditions on transcriptome levels. We used Illumina-based RNA sequencing (RNA-Seq) to perform a transcriptome analysis from the hepatopancreas of red claw crayfish challenged by air exposure. An average of 57,148,800 clean reads per library was obtained, and 33,567 unigenes could be predicted and classified according to their homology with matches in the National Center for Biotechnology Information (NCBI) non-redundant protein sequences (Nr), Gene Ontology (GO), a manually annotated and reviewed protein sequence database (Swiss-Prot), protein families (Pfam), Clusters of Orthologous Groups (COG) of proteins, and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. 690 and 3407 differentially expressed genes (DEGs) were identified between the two stress stages of the red claw crayfish. More DEGs were identified in 12 h, indicating that gene expressions were largely changed at 12 h. Some immune-related pathways and genes were identified according to KEGG and GO enrichment analysis. A total of 12 DEGs involved in immune response and trehalose mechanism were verified by quantitative real-time-polymerase chain reaction (qRT-PCR). The results indicated that the red claw crayfish might counteract the stress of air exposure at the transcriptomic level by increasing expression levels of antioxidant-, immune-, and trehalose metabolism-related genes. These transcriptome results from the hepatopancreas provide significant insights into the influence mechanism of air exposure to the trehalose mechanism and immune response in the red claw crayfish.

Acute toxicity, biochemical and transcriptomic analysis of Procambarus clarkii exposed to avermectin

BACKGROUND

Pesticides are extensively applied globally. Pesticide residues induce calamitous effects on the environment and untargeted organisms. Public concerns for the safety of freshwater organisms and the challenges posed by aquatic contaminants remain high. In the present study, the acute toxicity of avermectins (AVMs) to the crayfish, Procambarus clarkii was evaluated. We also evaluated the potential effects of AVM on the biochemical and transcriptomic status of the hepatopancreas and gastrointestinal tract in P. clarkii.

RESULTS

The 24, 48, 72, 96 h median lethal concentrations (LC₅₀ ) of AVM on crayfish were 2.626, 1.162, 0.723, 0.566 mg L^-1 , respectively. The crayfish were then exposed to 0.65 mg L^-1 of AVM for 96 h. AVM significantly altered biochemical parameters including AChE and CAT activities in the hepatopancreas, and AChE, SOD and Na + -K + -ATPase activities in the gastrointestinal tract at several time points. Furthermore, transcriptomic analysis identified 953 and 1851 differentially-expressed genes (DEGs) in the hepatopancreas and gastrointestinal tract, respectively. KEGG enrichment showed that the gene expression profiles of the hepatopancreas and gastrointestinal tract were distinct from each other. The DEGs in the hepatopancreas were mostly enriched with stress-response pathways, while the majority of the DEGs in the gastrointestinal tract belonged to metabolism-related pathways.

CONCLUSION

We demonstrated that the AVM induced acute toxicity, oxidative stress, osmoregulation disturbance, neurotoxicity and transcriptome imbalance in crayfish. These findings unraveled the detrimental effects of AVMs exposure on crayfish. © 2022 Society of Chemical Industry.

Coastal degradation impacts on green turtle's (Chelonia mydas) diet in southeastern Brazil: Nutritional richness and health

This study evaluated the influence of environmental degradation on the nutritional value of the main marine macrophytes consumed by green sea turtles (Chelonia mydas) in areas with different degrees of urbanization. Macrophyte assemblages in the highly urbanized area (HUa) showed lower richness compared to the lightly urbanized area (LUa) (Mann-Whitney U test: 10.0 ± 3.6 SD genera and 11.9 ± 4.2 taxa per transect vs. 20.1 ± 7.0 genera and 23.5 ± 9.2 taxa per transect) respectively. Also, diet was poorer with 4.0 ± 1.6 genera per turtle (vs. 8.5 ± 4.0 in HUa) and less diverse with Shannon index of diversity = 0.45 ± 0.29 (vs. 0.64 ± 0.46 in LUa). Body condition was similar in both areas. About half of individuals were classified as having normal body condition, 14-15% as underweight and 23-34% as being emaciated. Fibropapillomatosis prevalence (χ² = 8.720; n = 222; df = 1; p = 0.003) was higher in the HUa but, in affected animals, severity was marginally non-significant (χ² = 5.721; n = 82; df = 2; p = 0.057). Significant differences in energy content (kcal) were detected between areas in both summer (S) and winter (W). All ANOVAs on total lipids (F = 22.15 [S] and 30.39 [W]), total water-soluble proteins (F = 327.65 [S] and 64.42 [W]) and total carbohydrates (F = 70.90 [S] and 27.62 [W]) showed high significance (p < 0.001). Carotenoids concentration yielded significant results for Halodule in summer and Hypnea in winter (ANOVAs, F = 39.42 and 13.07, respectively). For both, tests revealed that concentration was higher in LUa than HUa. High levels of phycobiliproteins and proteins in this area probably reflect nitrogen accumulation. Frequency and severity of fibropapillomatosis suggest that urbanization-caused alterations in species diversity and in chemical composition of marine plants affect green turtles' health. LIGHT ABSTRACT: The use of coastal areas by humanity is widespread and increasing. The impacts caused to the coastal environment, be it terrestrial, estuarine or marine, are important and affect numerous species. Our study evaluated the influence of environmental degradation on the nutritional value of the main algae eaten by the green turtle, one of the very few marine megaherbivores (those herbivores with body mass above 10 kg). Diet in the highly urbanized area was richer in proteins, lipids and carbohydrates (sugars) and lower in carotenoids (photosynthetic and photoprotectant pigments in algae and plants; precursors of vitamin A involved in oxygen transport in animals-animals do not synthetize such molecules). High levels in phycobiliproteins (photosynthetic pigments present in some algae) and proteins in the highly urbanized area probably result from organic pollution and nitrogen accumulation in coastal waters. Nitrogen compounds dissolved in water are a threat to vertebrates due to its toxicity and negative effects on the immune system. Our results suggest that algae chemical composition and severity of fibropapillomatosis (tumors caused by a herpesvirus in green sea turtles) are directly related through environmental alterations caused by urbanization.

Pathogen of Vibrio harveyi infection and C-type lectin proteins in whiteleg shrimp (Litopenaeus vannamei)

Diseases caused by Vibrio harveyi in shrimps have gradually become one group of the most serious threats to shrimp production, while related molecular mechanisms of infections with Vibrio harveyi are still not known well in shrimps. Here, we performed proteomic sequencing of hepatopancreas in whiteleg shrimps (Litopenaeus vannamei) infected with exogenous Vibrio harveyi, and subsequent functional annotation and calculation of differentially expressed proteins (DEPs) in this study. A total of 145 DEPs were obtained, among them 36 were up-regulated and 109 were down-regulated after the infection. Meanwhile, our results showed that after the infection of Vibrio harveyi, expression levels of a variety of C-type lectins (CTLs) were changed significantly. In-depth functional domain analysis and spatial structure prediction of these CTLs revealed that amino acid sequences and spatial structures of the C-type lectin domain (CTLD) shared by the CTL-S and IML proteins were variant, suggesting differential functions between the two CTLs. In summary, various members of the CTL family have different epidemic responses to Vibrio harveyi infection, which provides a theoretical guidance for deep-going investigations on practical immunity reactions and pathogen infections in shrimps.

Molecular characterization and functional analysis of the lysosomal cathepsin D-like gene in red swamp crayfish, Procambarus clarkii

Aspartic proteinases are one of the four families of proteinase enzymes that are widely present in living organisms. They are involved in various physiological events, such as protein degradation, development, and host defense. However, the characterization and functional roles of aspartic proteinases remain to be elucidated in crustaceans. Here, we characterized a fragment of cathepsin D-like cDNA from red swamp crayfish, Procambarus clarkii (Pc-cathepsin D-like). The open reading frame of the Pc-cathepsin D-like gene contained 1152 bp, encoding a protein of 383 amino acid residues. We also evaluated the immunological role of the Pc-cathepsin D-like gene in vivo. Spatial distribution analysis revealed that the Pc-cathepsin D-like mRNA was high in the hepatopancreas, followed by the gut, gills, and hemocytes of P. clarkii. The expression levels of the Pc-cathepsin D-like gene increased following challenge with viral (polyinosinic: polycytidylic acid) and bacterial (lipopolysaccharides, peptidoglycan) PAMPs compared with PBS injection. The suppression of the Pc-cathepsin D-like gene by RNA interference significantly increased the expression of immune-associated genes. These results showed that the Pc-cathepsin D-like gene has an essential biological role in innate immune responses because it regulates the expression of immune-associated genes.

Differentially expressed genes involved in immune pathways from yellowhead catfish (Tachysurus fulvidraco) after poly (I:C) challenge

Yellowhead catfish (Tachysurus fulvidraco) is an important aquaculture fish species in China with a high market value. Infectious diseases pose serious threats in farmed fish species, and although vaccines can prevent certain infections, they rely on potent adjuvants. In this study, we analyzed the transcriptomic profiles of spleens from poly (I:C)-treated T. fulvidraco. We obtained 46,362,922 reads corresponding to 490,926 transcripts and 318,059 genes. Gene annotation using different databases and subsequent differential gene expression analyses led to the identification of 5587 differentially expressed genes (DEGs), of which 2473 were up-regulated and 3114 were down-regulated in poly (I:C)-treated fish. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of DEGs revealed the significant dysregulation of immune- and cancer-related genes in the spleens of poly (I:C)-treated fish. Notably, several components of JAK-STAT, MAPK, and p53 signaling pathways were significantly dysregulated in response to poly (I:C) treatment. Quantitative real-time PCR (qRT-PCR) analysis of 11 randomly selected immune response genes confirmed the reliability of our findings. In conclusion, our findings provide novel insight into the immune responses of T. fulvidraco and suggest that poly (I:C) may represent a promising adjuvant of fish vaccines.

Comparative transcriptome analysis of the gills of Procambarus clarkii provide novel insights into the response mechanism of ammonia stress tolerance

Procambarus clarkii is an important model crustacean organism in many researches. Ammonia nitrogen is one of common contaminants in aquatic environment, influencing the health of aquatic organisms. The primary objective of this study was to investigate molecular mechanisms on ammonia stress in gills of P. clarkii to provide new insights into the strategies of aquatic animals in responding to high concentration of ammonia in the environment. Procambarus clarkii were randomly assigned into two groups (ammonia stress group, AG; control group, CG), and gill samples were dependently excised from AG and CG. Then response mechanisms on ammonia stress were investigated based on transcriptome data of P. clarkii. 9237 differentially expressed genes were identified in ammonia stress group. The genes of ion transport enzymes (NKA and SLC6A5S) were significantly up-regulated. Whereas the immune-related genes (e.g. MAP3K7, HSP70, HSP90A, CTSF, CTSL1, CHI and CTL4) and pathways were significantly up-regulated, which played an important role in reacting to ammonia stress. Procambarus clarkii may enhance immune defense to counteract ammonia toxicity by the up-regulation of immune-related genes and signaling pathways. The activities of ion transport enzymes are changed to mobilise signal transduction and ion channel regulation for adapting to ammonia environment. These previous key genes play an important role in resistance to ammonia stress to better prepare for survival in high concentration of ammonia.

Transcriptome analysis of immune-related genes in Sesarmops sinensis hepatopancreas in reaction to peptidoglycan challenge

Sesarmops sinensis is a dominant omnivorous crab species, which plays an important ecological function in salt marsh ecosystems. To better understand its immune system and immune related genes under pathogen infection, the transcriptome was analyzed by comparing the data of S. sinensis hepatopancreas stimulated by PBS and PGN. A set of assembly and annotation identified 39,039 unigenes with an average length of 1105 bp, obtaining 1300 differentially expressed genes (DEGs) in all, which included 466 remarkably up-regulated unigenes and 834 remarkably down-regulated unigenes. In addition, based on mensurable real time-polymerase chain reaction and high-throughput sequencing, several immune responsive genes were found to be markedly up-regulated under PGN stimulation. In conclusion, in addition to enriching the existing transcriptome data of S. sinensis, this study also clarified the immune response of S. sinensis to PGN stimulation, which will help us to further understand the crustacean's immune system.

Molecular characterization of a heat shock protein 21 (Hsp21) from red swamp crayfish, Procambarus clarkii in response to immune stimulation

Small heat shock proteins are a molecular chaperone and implicated in various physiological and stress processes in animals. However, the immunological functions of Hsp genes remain to elucidate in the crustaceans, particularly in red swamp crayfish, Procambarus clarkii. Here we report the cloning of heat shock protein 21 from the P. clarkii (hereafter Pc-Hsp21). The open reading frame of Pc-Hsp21 was 555 base pairs, encoding a protein of 184 amino acid residues with an alpha-crystallin family domain. Quantitative real-time PCR (qRT-PCR) analysis revealed a constitutive transcript expression of Pc-Hsp21 in the tested tissue, with the highest in hepatopancreas. The transcript abundance for this gene enhanced in hepatopancreas following immune challenge with the lipopolysaccharide, peptidoglycan, and poly I:C compared to the control group. The depletion of Pc-Hsp21 by double-stranded RNA altered transcript expression profiles of several genes in hepatopancreas, genes involved in the crucial immunological pathways of P. clarkii. These results suggest that Pc-Hsp21 plays an essential biological role in the microbial stress response by modulating the expression of immune-related genes in P. clarkii.

Thifluzamide induces the toxic effects on zebrafish (Danio rerio) via inhibition of succinate dehydrogenase (SDH)

Thifluzamide is widely used in treatment of rice diseases and has potential toxicity on aquatic organism. Although previous studies have focused on the toxic effect of thifluzamide in zebrafish, no consistent conclusions have been reached. To help to elucidate the toxic mechanism, qualities of liver and mitochondria were evaluated. The global changes in the transcriptome of zebrafish after exposure to thifluzamide were measured. Based on this, the expression and activities of chitinase and succinate dehydrogenase (SDH) were further assayed. And the targeted site of thifluzamide in zebrafish was confirmed by dock study and co-exposure study. Here we report that developmental inhibition was observed along with presence of liver and mitochondrial damage. The expression of SDHa-d and genes related to mitochondrial DNA (mtDNA) replicate and mitochondrial complexes were significantly altered. And, as the top differentially expressed genes, the expression of chia.1-6 did show apparent changes, but differences of chitinase activity between exposure groups and the controls did not reach significance. In line with that, dock study showed that the binding potentials of thifluzamide toward zebrafish chitinase and SDH exhibited in the following order: SDH> chitinase. And sdhb-sdhc-sdhd (Qp site) showed the highest binding activity toward thifluzamide. The joint exposure (thifluzamide + Q10) significantly improved the survival of zebrafish compared with single thifluzamide exposure. These results indicate that SDH, especially Qp-site, may be the target of thifluzamide in zebrafish and inhibition of SDH activity may be at least in partial responsible for the toxicity of thifluzamide in zebrafish. In addition, the antagonistic effect of Q10 on thifluzamide toxicity in zebrafish suggests that Q10 may be a useful adjunct to detoxification.

B-type allatostatin modulates immune response in hepatopancreas of the mud crab Scylla paramamosain

B-type allatostatin (AST-B) is a pleiotropic neuropeptide, widely found in arthropods. However, the information about its immune effect in crustaceans is unknown. In this study, we identified the nervous tissue as the main site for Sp-AST-B expression, while its receptor gene (Sp-AST-BR) is widely expressed in various tissues, including the hepatopancreas. This suggests the peptide's potential role in diverse physiological processes in the mud crab Scylla paramamosain. In situ hybridization revealed that Sp-AST-BR is mainly localized in the F-cell of hepatopancreas. Furthermore, we found a significant up-regulation of Sp-AST-BR transcripts in the hepatopancreas following exposure to lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid (Poly (I:C)). Results from in vitro and in vivo experiments revealed that treatment with a synthetic AST-B peptide mediated significant upregulation in expression of AST-BR, nuclear factor-κB (NF-κB) pathway components (Dorsal and Relish), pro-inflammatory cytokine (IL-16) and antimicrobial peptides (AMPs) in the hepatopancreas. In addition, AST-B treatment mediated significant elevation of nitric oxide (NO) production and enhanced the bacteriostasis capacity of the hepatopancreas tissue in vitro. Taken together, these findings reveal the existence of a basic neuroendocrine-immune (NEI) network in crabs, and indicate that AST-B could couple with its receptor to trigger downstream signaling pathways and induce immune responses in the hepatopancreas.

Short neuropeptide F enhances the immune response in the hepatopancreas of mud crab (Scylla paramamosain)

Short neuropeptide F (sNPF), a highly conserved neuropeptide, displays pleiotropic functions on multiple aspects of physiological processes, such as feeding, metabolic stress, locomotion, circadian clock and reproduction. However, to date there has no any report on the possible immunoregulation of sNPF in crustaceans. In the present study, we found that the Sp-sNPF was mainly expressed in the nervous tissue in the mud crab Scylla paramamosain, while the sNPF receptor gene (Sp-sNPF-R) was expressed in a wide variety of tissues, including the hepatopancreas. In situ hybridization further showed that the Sp-sNPF-R positive signal mainly localized in the F-cells of the hepatopancreas. Moreover, the Sp-sNPF-R transcription could be significantly up-regulated after the challenge of bacteria-analog LPS or virus-analog Poly (I:C). Both in vitro and in vivo experiments showed that the synthetic sNPF peptide significantly increased the gene expressions of sNPF-R, nuclear factor-κB (NF-κB) signaling genes and antimicrobial peptides (AMPs) in the hepatopancreas. Simultaneously, the administration of sNPF peptide in vitro also increased the concentration of nitric oxide (NO) and the bacteriostasis of the culture medium of hepatopancreas. These results indicated that sNPF up-regulated hepatopancreas immune responses, which may bring new insight into the neuroendocrine-immune regulatory system in crustacean species, and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

Heat shock protein 20 from Procambarus clarkii is involved in the innate immune responses against microbial infection

Small heat shock proteins (shsps) are conserved across invertebrate species. They are implicated in the modulation of various biological processes, such as immune responses, abiotic stress tolerance metamorphosis, and embryonic development. Herein, we identified a heat shock protein 20 from the red swamp crayfish, Procambarus clarkii (named as Pc-Hsp20), and performed in vivo studies to elucidate its physiological functions in the innate immunity. The open reading frame of Pc-Hsp20 was 609 base pair, encoding a protein of 202 amino acid residues with a hsp20/alpha crystallin family domain. Pc-Hsp20 was ubiquitously expressed in various tissues; however, it was highest in the hepatopancreas. The challenge with immune elicitors remarkably enhanced the transcript level of Pc-Hsp20 in the hepatopancreas when compared with the control. Administration of double-stranded RNA could significantly reduce expression of the Pc-Hsp20 mRNAs, and most of the immune-related genes expression enhanced with a variable concentration in the hepatopancreas. Altogether, these results suggest that Pc-Hsp20 may participate in innate immunity against microbial pathogens.

The red swamp crayfish, Procambarus clarkii cathepsin C, participates in the innate immune response to the viral and bacterial pathogens

The cathepsin C, a lysosomal cysteine protease, involves the modulation of immune and inflammatory responses in living organisms. However, the knowledge on cathepsin C in red swamp crayfish (Procambarus clarkii), a freshwater crustacean with economic values, remained unclear. In the present study, we provide identification and molecular characterization of cathepsin C from P. clarkii. (Hereafter Pc-cathepsin C). The Pc-cathepsin C cDNA contained a 1356 bp open reading frame that encoded a protein of 451 amino acid residues. The deduced amino acid sequence comprised of cathepsin C exclusion domain and pept_C1 domain, and also catalytic residues (Cys²⁴⁸, His³⁹⁵ and Asn⁴¹⁷). Analysis of the transcriptional patterns of the Pc-cathepsin C gene revealed that it was broadly distributed in various tissues of P. clarkii, and it was more abundant in the hepatopancreas and gut. Following a challenge with viral and bacterial pathogen-associated molecular patterns, the expression of Pc-cathepsin C was strongly enhanced at different time points. The knockdown of Pc-cathepsin C, altered the expression of immune-responsive genes, suggesting its immunoregulatory role in P. clarkii. This study has identified and provided the immunoregulatory function of Pc-cathepsin C, which will contribute to further investigation of the molecular mechanism of cathepsin C in crustaceans.

A Possible Role of Crustacean Cardioactive Peptide in Regulating Immune Response in Hepatopancreas of Mud Crab

Crustacean cardioactive peptide (CCAP), a cyclic amidated non-apeptide, is widely found in arthropods. The functions of CCAP have been revealed to include regulation of heart rate, intestinal peristalsis, molting, and osmotic pressure. However, to date, there has not been any report on the possible involvement of CCAP in immunoregulation in crustaceans. In this study, a CCAP precursor (designated as Sp-CCAP) was identified in the commercially important mud crab Scylla paramamosain, which could be processed into four CCAP-associated peptides and one mature peptide (PFCNAFTGC-NH₂). Bioinformatics analysis indicated that Sp-CCAP was highly conserved in crustaceans. RT-PCR results revealed that Sp-CCAP was expressed in nerve tissues and gonads, whereas the Sp-CCAP receptor gene (Sp-CCAPR) was expressed in 12 tissues of S. paramamosain, including hepatopancreas. In situ hybridization further showed that an Sp-CCAPR-positive signal is mainly localized in the F-cells of hepatopancreas. Moreover, the mRNA expression level of Sp-CCAPR in the hepatopancreas was significantly up-regulated after lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid [Poly (I:C)] challenge. Meanwhile, the mRNA expression level of Sp-CCAPR, nuclear transcription factor NF-κB homologs (Sp-Dorsal and Sp-Relish), member of mitogen-activated protein kinase (MAPK) signaling pathway (Sp-P38), pro-inflammatory cytokines factor (Sp-TNFSF and Sp-IL16), and antimicrobial peptide (Sp-Lysozyme, Sp-ALF, Sp-ALF4, and Sp-ALF5) in the hepatopancreas were all up-regulated after the administration of synthetic Sp-CCAP mature peptide both in vivo and in vitro. The addition of synthetic Sp-CCAP mature peptide in vitro also led to an increase in nitric oxide (NO) concentration and an improved bacterial clearance ability in the hepatopancreas culture medium. The present study suggested that Sp-CCAP signaling system might be involved in the immune responses of S. paramamosain by activating immune molecules on the hepatopancreas. Collectively, our findings shed new light on neuroendocrine-immune regulatory system in arthropods and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

Identification and functional characterization of the astacidin family of proline-rich host defence peptides (PcAst) from the red swamp crayfish (Procambarus clarkii, Girard 1852)

This study reports the identification of four novel proline-rich antimicrobial peptides (PR-AMP) from the transcriptome of the red swamp crayfish Procambarus clarkii. The newly identified putative peptides (PcAst-1b, -1c, -2 and -3), which are related with the previously identified hemocyte-specific PR-AMP astacidin-1, are encoded by the multi-genic astacidin gene family. The screening of available and proprietary transcriptomes allowed to define the taxonomical range of distribution of this gene family to Astacoidea and Parastacoidea. The antimicrobial properties of three synthetic PcAst peptides (PcAst-1a, -1b/c and -2), were characterized against reference bacteria or multidrug resistant clinical isolates, and their cytotoxicity was evaluated towards human transformed cell lines. The antimicrobial activity ranged from potent and broad-spectrum, in low-salt medium, to poor, whereas it was generally low in full nutrient broth. No significant toxic effects were observed on cultured human cells. RNA-seq data from 12 different tissues indicated a strong specificity for haemocytes under naïve physiological condition, with moderate expression (5-fold lower) in gills. Quantitative real time PCR revealed a rapid (within 2 h) and significant up-regulation of PcAst-1a (Astacidin 1) and PcAst-2 expression in response to LPS injection. Due to the variation in antimicrobial potency and inducibility, the roles of the other astacidins (PcAst-1b, -1c and -3) need to be further investigated to determine their significance to the immune responses of the red swamp crayfish.

Proteomic analysis of differentially expressed proteins in the lipopolysaccharide-stimulated hepatopancreas of the freshwater crayfish Procambarus clarkii

Procambarus clarkii is one of the most important aquatic invertebrates in China and has high commercial value. However, aquaculture has suffered great economic loss due to outbreaks of infectious diseases in P. clarkii. To identify red swamp crayfish related proteins involved in the response to bacterial infection, we analysed immune-related proteins following lipopolysaccharide (LPS) stimulation by quantitative proteomics. The proteome of the hepatopancreas of P. clarkii challenged with LPS and phosphate-buffered saline was analysed to evaluate the immune response. Based on liquid chromatography coupled with tandem mass spectrometry, 16 upregulated and 29 downregulated proteins were identified. A Gene Ontology analysis demonstrated 5 biological process, 11 cellular component, and 6 molecular function subcategories. The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis indicated that the identified proteins were mainly involved in metabolism, phagosome, and ribosome. Real-time quantitative reverse transcription-PCR revealed that eight immune-related genes were upregulated after LPS stimulation compared to the control. Taken together, the data enhance our understanding of the immune response of crayfish to LPS.

Comparative transcriptome analysis of the gills of Procambarus clarkii provides novel insights into the immune-related mechanism of copper stress tolerance

The red-swamp crayfish (Procambarus clarkii) is the most important economic shrimp species in China, and is an important model crustacean organism in many fields of research. In crustaceans, gills interface directly with the ambient environment and thus play a vital role in the toxicology. In the context of increasing environmental heavy metal pollution, the relationship between copper (Cu²⁺) stress and the immune response of P. clarkii has recently received considerable attention. However, impact of Cu²⁺ on the crayfish immune system is still not fully understood. In this study, we used Illumina sequencing technology to perform a transcriptome analysis of the gills of P. clarkii after 24 h of Cu²⁺ treatment. A total of 37,226,812 unigenes were assembled, and 1943 unigenes were significantly differentially expressed between the control and Cu²⁺ treatment groups. Functional categorization of differentially expressed genes (DEGs) revealed that genes related to antioxidant activity, detoxication, metabolic processes, biosynthetic processes, and immune system processes were differentially regulated during Cu²⁺ stress. In addition, DEGs in the immune system were classified as being related to the MAPK signaling pathway, purine metabolism, Toll and Imd signaling pathway, PI3K-Akt signaling pathway and Hippo signaling pathway. Five genes (CuZnSOD, CAT, IDH1, PHYH and DECR2) were significantly up-regulated in the peroxisome pathway, which plays an important role in reacting to oxidative stress. Importantly, qRT-PCR validation of the results for seven genes chosen at random (NDK, ATP6L, ATP5C1, RPS14, RPL22e, CTSF and HSP90A) confirmed the Illumina sequencing results. This study provides a valuable starting point for further studies to elucidate the molecular basis of the immune system's response to Cu²⁺ stress in crayfish.

New insight into the molecular basis of Fe (III) stress responses of Procambarus clarkii by transcriptome analysis

Iron in excess can have toxic effects on living organisms. In China, the freshwater crayfish Procambarus clarkii is a source of aquatic food with high-quality protein and has significant commercial value. P. clarkii shows oxidative stress on exposure to heavy metals, and antioxidant enzymes, such as ubiquitination enzymes and proteasomes, play important roles in oxidative stress. To understand the antioxidant defense system of P. clarkii, we analyzed the hepatopancreas transcriptomes of P. clarkii after stimulation with FeCl₃. In total, 5199 differentially expressed genes (DEGs) were identified (2747 upregulated and 2452 downregulated). GO analysis revealed that these DEGs belonged to 16 cellular component, 16 molecular function, and 19 biological process subcategories. A total of 1069 DEGs were classified into 25 categories by using COG. Some antioxidant defense pathways, such as "Ubiquitin mediated proteolysis" and "Glutathione metabolism," were identified using KEGG. In addition, quantitative real time-PCR (qRT-PCR) substantiated the up-regulation of a random selection of DEGs including antioxidant and immune defense genes. We obtained information for P. clarkii transcriptome databases and new insights into the responses of P. clarkii hepatopancreas to heavy metals.

Comparative proteomic investigation of Marsupenaeus japonicus hepatopancreas challenged with Vibrio parahaemolyticus and white spot syndrome virus

This study aimed to use isobaric tags (IBTs) to investigate the immune response of the hepatopancreas of Marsupenaeus japonicas infected with Vibrio parahaemolyticus or white spot syndrome virus (WSSV). Liquid chromatography-tandem mass spectrometry and protein sequencing identified 1005 proteins. Among them, 109 proteins were upregulated and 94 were downregulated after V. parahaemolyticus infection. After WSSV infection, 130 proteins were identified as differentially abundant, including 88 that were upregulated and 42 were downregulated. Fifty-four proteins were identified as differentially abundant after both V. parahaemolyticus and WSSV infection. A number of proteins related to cytoskeletal processes, including actin and myosin, and apoptosis-related proteins were upregulated in shrimp after V. parahaemolyticus and WSSV infection, indicating that phagocytosis and apoptosis may be involved in the response to in V. parahaemolyticus or WSSV infection. Quantitative real-time PCR was carried out to verify the reliability of the proteomic data. These data provide a basis to characterize the immunity-related processes of shrimp in response to infection with WSSV or V. parahaemolyticus.

Involvement of gamma interferon inducible lysosomal thiol reductase in the innate immune responses of red swamp crayfish, Procambarus clarkii

The Gamma interferon inducible lysosomal thiol reductase (GILT) plays a key biological role in the immune responses and involves in the processing of class II MHC-restricted antigen by stimulating disulfide bond reduction in mammals. To determine the biological function of GILT in the innate immune system of crustaceans, we sequenced and cloned GILT gene from red swamp crayfish, Procambarus clarkii (Pc-GILT). The deduced amino acid sequence of Pc-GILT contained the putative conserved structures of the GILT family proteins: the GILT signature (CQHGX2ECX2NX4C) sequence and the active site (CXXS) motif. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis suggested that a recombinant Pc-GILT protein was successfully expressed in Escherichia coli (E. coli). Quantitative real-time PCR analysis showed that Pc-GILT transcript level was highest in the hepatopancreas followed by the gut, heart and muscles. Additionally, we analyzed the transcription level of Pc-GILT gene in hepatopancreas of red swamp crayfish under biotic stress conditions. The expression of Pc-GILT gene upregulated after viral (poly I:C) and bacterial (peptidoglycan, lipopolysaccharide) infection. The suppression of Pc-GILT by double stranded RNA influenced the transcript levels of various immune-related genes. These observations indicate that the Pc-GILT probably plays a key biological role in the innate immune responses of red swamp crayfish, since it modulates the expression of genes associated with immune pathways.

Transcriptome-wide identification of differentially expressed genes in Procambarus clarkii in response to chromium challenge

Because of the high protein content and rich meat quality of crayfish Procambarus clarkii, it has become widely popular in China in recent years and has a high economic value. When P. clarkii is stimulated by heavy metals, it reacts to oxidation. P. clarkii has evolved antioxidant defense systems, including antioxidant enzymes such as catalase (CAT). The hexavalent form of Cr (VI) is a pathogenic factor that is of particular concern in aqueous systems because of its great toxicity to living organisms. In this study, we characterized the transcriptome of P. clarkii using a RNA sequencing method and performed a comparison between K₂Cr₂O₇-treated samples and controls. In total, 34,237 unigenes were annotated. We identified 5098 significantly differentially expressed genes (DEGs), including 2536 and 2562 were significantly up-regulated and down-regulated, respectively. In addition, quantitative real time-PCR (qRT-PCR) confirmed the up-regulation of a random selection of DEGs. Our results contribute to a more comprehensive understanding of the antioxidant defense system used by P. clarkii in response to heavy metal stress.

Identification and molecular characterization of a novel anti-lipopolysaccharide factor (ALF) from red swamp crayfish, Procambarus clarkii

Anti-lipopolysaccharide factors are a group of small proteins with broad spectrum antiviral property and antibacterial activity. Herein, we obtained the genomic sequence of the Procambarus clarkii anti-lipopolysaccharide factor (PcALF) gene by using polymerase chain reaction to investigate its expression pattern in various tissues and in the immune tissues (Hepatopancreas) following exposure to pathogens. The deduced protein of PcALF was conserved; it displayed the signal peptides and putative lipo-polysaccharide binding domain, particularly the two conserved cysteine amino acid residues at both ends of the domain. The recombinant protein of PcALF was successfully expressed in Escherichia coli and rabbit anti-PcALF polyclonal antibodies were prepared. The qRT-PCR analysis showed unequal distribution of PcALF transcript in the examined tissues, however the transcript level was greatest in hepatopancreas. The challenge with peptidoglycan (PGN), lipo-polysaccharide (LPS) and Poly I:C significantly enhanced expression level of PcALF in hepatopancreas when compared with the PBS control. RNA interference of PcALF affected the mRNA expression levels of immune-related genes. Taken together, our data suggested that PcALF is an inducible protein and could play a key biological role in the innate immune defense of P. clarkii.