Identification and expression analysis of immune-related genes linked to Rel/NF-κB signaling pathway under stresses and bacterial challenge from the small abalone Haliotis diversicolor

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 2,615 and 1,943 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.

Utilisation of probiotics for disease management in giant freshwater prawn (Macrobrachium rosenbergii): Administration methods, antagonistic effects and immune response

The giant freshwater prawn (Macrobrachium rosenbergii) is a high-yielding prawn variety well-received worldwide due to its ability to adapt to freshwater culture systems. Macrobrachium rosenbergii is an alternative to shrimp typically obtained from marine and brackish aquaculture systems. However, the use of intensive culture systems can lead to disease outbreaks, particularly in larval and post-larval stages, caused by pathogenic agents such as viruses, bacteria, fungi, yeasts and protozoans. White tail disease (viral), white spot syndrome (viral) and bacterial necrosis are examples of economically significant diseases. Given the increasing antibiotic resistance of disease-causing microorganisms, probiotics have emerged as promising alternatives for disease control. Probiotics are live active microbes that are introduced into a target host in an adequate number or dose to promote its health. In the present paper, we first discuss the diseases that occur in M. rosenbergii production, followed by an in-depth discussion on probiotics. We elaborate on the common methods of probiotics administration and explain the beneficial health effects of probiotics as immunity enhancers. Moreover, we discuss the antagonistic effects of probiotics on pathogenic microorganisms. Altogether, this paper provides a comprehensive overview of disease control in M. rosenbergii aquaculture through the use of probiotics, which could enhance the sustainability of prawn culture.

Transcriptomic responses to thermal stress in hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂)

China is the world’s largest abalone producing country. Currently, summer mortality caused by high temperature, is one of the biggest challenges for abalone aquaculture industry. The hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂) was conferred on the “new variety”. It has heterosis for thermal tolerance and has been cultured at large-scale in southern China. In this study, a transcriptome analysis was performed to identify the related genes in this hybrid abalone under thermal stress and recovery stage. Compared to control group (18°C), a total of 75, 2173, 1050, 1349, 2548, 494, and 305 differentially expressed genes (DEGs) were identified at 21°C, 24°C, 27°C, 30°C, 32°C, 29°C, and 26°C, respectively. In this study, 24°C is the critical temperature at which the abalone is subjected to thermal stress. With the temperature rising, the number of stress-responsive genes increased. During the temperature recovering to the optimum, the number of stress-responsive genes decreased gradually. Thus, this hybrid abalone has a rapid response and strong adaptability to the temperature. Under the thermal stress, the abalone triggered a complicated regulatory network including degrading the misfolded proteins, activating immune systems, negative regulation of DNA replication, and activating energy production processes. The more quickly feedback regulation, more abundant energy supply and more powerful immune system might be the underlying mechanisms to fight against thermal stress in this hybrid abalone. These findings could provide clues for exploring the thermal-response mechanisms in abalone. The key genes and pathways would facilitate biomarker identification and thermal-tolerant abalone breeding studies.

Transcriptomic analysis and discovery of genes involving in enhanced immune protection of Pacific abalone (Haliotis discus hannai) in response to the re-infection of Vibrio parahaemolyticus

Traditionally, invertebrates were thought to lack immune memory owing to a lack of acquired immune-related factors such as immunoglobulin. Nonetheless, with the in-depth consideration of invertebrate immune priming, scholars have gradually realized that the immune defenses of invertebrates are more complex than previously imagined. In the current investigation, the survival rate of Vibrio parahaemolyticus re-infected Haliotis discus hannai (VV group) was significantly different from the other groups (p < 0.05), indicating that an enhanced immune response may commence after first exposure to the same strain of V. parahaemolyticus. The transcriptome profiles of hemocytes obtained 102,052 unigenes, and 27,449 of them were annotated successfully. Venn diagram analysis showed that 2832 DEGs commonly responded to the first and second immune responses. 1734 "immune response genes" and 1460 "potential immune-enhancing genes" were also identified. A comparison of both "immune response genes" and "potential immune-enhancing genes" revealed 1019 immune-enhancing regulatory genes and 281 essential immune-enhancing genes. According to the KEGG enrichment analysis results of ERGs and EEGs, classical immune-related signaling pathways, such as NF-kappa B signaling pathway, NOD-like receptor signaling pathway, IL-17 signaling pathway, and TLR signaling pathway were significantly enriched, indicating that they were all involved in the response to V. parahaemolyticus re-infection and were likely dominant in the immune enhancement process of H. discus hannai hemocytes. The intermolecular interactions generated by Cytoscape after re-infection of V. parahaemolyticus appear more intuitively to demonstrate that hemocytes regulation was not an independent process, but rather an intricate regulatory network. H. discus hannai demonstrated enhanced immunological activity after re-infection with V. parahaemolyticus, showing immune memory in hemocytes. The current study's findings have broadened the study of immune enhancement in invertebrates and laid the framework for future research into the molecular mechanism of immune enhancement in abalones.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

Background

Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone’s cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry.

The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.

Results

The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB).

Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.

Conclusions

Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs).

The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08611-8.

Long-read RNA sequencing of Pacific abalone Haliotis discus hannai reveals innate immune system responses to environmental stress

Haliotis discus hannai is a commercially important mollusk species, and the abalone aquaculture sector has been jeopardized by deteriorating environmental circumstances such as bacterial infection and thermal stress during the hot summers. However, due to a paucity of genetic information, such as transcriptome resources, our understanding of their stress adaptation is restricted. In this research, using single-molecule long-read (SMRT) sequencing technology, a library composed of ten tissues (i.e., haemocytes, gills, muscle, hepatopancreas, digestive tract, mantle, mucous gland, ovary, testis and head) was constructed and sequenced. In all, 41,855 high-quality unique transcripts, among which 24,778 were successfully annotated. Additionally, 13,463 SSRs, 1,169 transcription factors, and 18,124 lncRNAs were identified in H. discus hannai transcriptome. Furthermore, multiple immune-related transcripts were identified according to KEGG annotation, and a portion of these transcripts were mapped into several classical immune-related pathways, including the PI3K-AKT signaling pathway and Toll-like receptor signaling pathway. Additionally, 24 typical sequences related to the immunity pathway were detected by RT-PCR; the results showed that most of the immune-related genes showed significantly high expression at 72 h after bacterial challenges and thermal stress, especially the expression level of genes in gills was significantly higher than that in haemocytes under V. parahaemolyticus stress at 24 h. At the same time. The analysis of alternative splicing identified several innate immunity-related functions genes, including CD109 and caspase 2. These results suggest that the complex immune system, particularly the powerful innate immunity system, was crucial for H. discus hannai response to numerous environmental challenges.

Differentially expressed lncRNAs involved in immune responses of Haliotis diversicolor and H. discus hannai challenged with Vibrio parahaemolyticus

Although many studies have shown that lncRNA, a non-coding RNA with a length of more than 200 bases, is involved in various biological functions, including the immune process, stress process, and cell development process. However, the function of lncRNA in abalone, especially in immunity, has been rarely studied. H. discus hannai and H. diversicolor are two main aquaculture abalone, and their growth is easily affected by the main pathogen Vibrio parahaemolyticus. Through rigorous screening procedures for transcripts in this study, we found that lncRNAs were 34,240, 23,022 in Haliotis diversicolor and H. discus hannai injected with V. parahaemolyticus, respectively. We also identified the unique and common lncRNAs and mRNAs of two abalone species for the first time; the shared lncRNAs and mRNAs in Haliotis diversicolor and H. discus hannai were 2352 and 13,165, respectively. Then gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the differentially expressed target genes of common and unique lncRNAs has shown that common lncRNAs could be widely involved in the biological processes of stress and cell development in both abalone species. In contrast, unique lncRNAs are linked to the Toll-like receptor, NF-kappaB signaling pathway of H. diversicolor, and pattern recognition receptors and lectins immune-related pathways of H. discus hannai. The co-expression network shows that some immune-related genes, such as INFK1, INFK2, CASP2, CASP8, IRAK1, lectin C, were closely related to lncRNAs. Further, we identified the targeted relationship between some immune-related genes and lncRNAs by qRT-PCR, through which we showed that the expression trend between targeted genes, such as INFK1 and Lnc7057, lectin C and Lnc6943, Lnc5637, and PLCG1 and Lnc1692, were consistent. In general, our results showed that lncRNA expression was induced in the two species of abalone after being infected with V. parahaemolyticus, and lncRNA was involved in the immune response of abalone by targeting coding genes.

Regulatory effect of heat shock transcription factor-1 gene on heat shock proteins and its transcriptional regulation analysis in small abalone Haliotis diversicolor

Background

The effects of diverse stresses ultimately alter the structures and functions of proteins. As molecular chaperones, heat shock proteins (HSPs) are a group of highly conserved proteins that help in the refolding of misfolded proteins and the elimination of irreversibly damaged proteins. They are mediated by a family of transcription factors called heat shock factors (HSFs). The small abalone Haliotis diversicolor is a species naturally distributed along the southern coast of China. In this study, the expression of HdHSF1 was inhibited by RNAi in hemocytes in order to further elucidate the regulatory roles of HdHSF1 on heat shock responsive genes in abalone. Meanwhile, to understand the transcriptional regulation of the HdHSF1 gene, the 5′-upstream regulatory region of HdHSF1 was characterized, and the relative promoter activity was examined by dual-luciferase reporter gene assay system in HEK293T cell lines.

Results

After the inhibition of the H. diversicolor HSF1 gene (HdHSF1) by dsRNA (double-stranded RNA), the expression of most heat shock related-genes was down-regulated (p < 0.05). It indicated the importance of HdHSF1 in the heat shock response of H. diversicolor. Meanwhile, 5′-flanking region sequence (2633 bp) of the HdHSF1 gene was cloned; it contained a putative core promoter region, TATA box, CAAT box, CpG island, and many transcription elements. In HEK293T cells, the 5′-flanking region sequence can drive expression of the enhanced green fluorescent protein (EGFP), proving its promoter function. Exposure of cells to the high-temperature (39 °C and 42 °C) resulted in the activation of HdHSF1 promoter activity, which may explain why the expression of the HdHSF1 gene participates in heat shock response. Luciferase activity of different recombinant plasmids, which contained different truncated promoter fragments of the HdHSF1 gene in HEK293T cells, revealed the possible active regions of the promoter. To further identify the binding site of the critical transcription factor in the region, an expression vector with the site-directed mutation was constructed. After being mutated on the GATA-1 binding site, we found that the luciferase activity was significantly increased, which suggested that the GATA-1 binding site has a certain weakening effect on the activity of the HdHSF1 promoter.

Conclusions

These findings suggest that GATA-1 may be one of the transcription factors of HdHSF1, and a possible signaling pathway mediated by HdHSF1 may exist in H. diversicolor to counteract the adverse effects of heat shock stress.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12860-020-00323-9.

The involvement of crustaceans toll-like receptors in pathogen recognition

Crustacean species are considered as a major sector in the aquaculture industry that plays a fundamental role in the world's economy. However, with a wide range of various epidemic diseases in the industry, studies of immune-related genes such as toll-like receptor genes are of great importance. Recently, the TLR in crustacean species has been described to perform a vital role in defense of crustacean against the pathogens. Meanwhile, many TLR genes from crustacean were characterized, and their contribution discovered in innate immunity against several pathogens. This review was aimed to present an overview of the crustacean TLRs including structural features that contained three major domains: a leucine-rich repeat (LRR) domains, a transmembrane area (TM), and a conserved region called Toll/interleukin-1 receptor (TIR) domain. The tissue distribution patterns of TLR genes, which act as a guide for future research on which TLR gene or genes that can be expressed, at which tissue or tissues. We also described recent works on the expression of the TLR gene that evaluated the immune function after pathogen stimulation in shrimp, crab, and crayfish. Furthermore, we recommended a prospective for future investigation plan that might contribute to the development and management systems in the global crustacean aquaculture industry. Lastly, we assumed that a clear understanding of the expression pattern and biological function of crustacean TLR genes could serve as a baseline for future immunological studies.

Immunity-related genes and signaling pathways under hypoxic stresses in Haliotis diversicolor: a transcriptome analysis

Due to increased temperatures and aquaculture density, thermal and hypoxia stresses have become serious problems for the aquaculture of abalone Haliotis diversicolor. Stresses lead to immunosuppression, which can cause severe negative impacts on aquaculture farms. To study the mechanism of immunosuppression after hypoxia stress and bacterial challenge, transcriptomes of H. diversicolor hemocytes involved in immunity were profiled. A total of 307,395,572 clean reads were generated and assembled into 99,774 unigenes. KEGG analysis indicated that 225 unigenes with immunologic function were mapped into immune-related pathways. Expression of 41 unigenes measured by quantitative real-time PCR (qRT-PCR) showed consistent results with that of transcriptome analysis. When exposure challenge of Vibrio parahaemolyticus, it is indicated that the PI3K-AKT, MAPK, NF-κB and P53 signal pathways were involved in the hypoxia-induced immunosuppression of H. diversicolor. Furthermore, when the AKT gene (HdAKT) was inhibited by double-stranded RNA (dsRNA), expression levels of HdAKT was lower than the blank and control group in hemocytes at 4 h, 12 h and 24 h (p < 0.05).

Time course analysis of immunity-related gene expression in the sea cucumber Apostichopus japonicus during exposure to thermal and hypoxic stress

Temperature and dissolved oxygen concentration are important abiotic factors that can limit the growth and survival of sea cucumbers by affecting their immune systems. As global warming intensifies, sea cucumbers are increasingly exposed to adverse environmental conditions, which can cause severe economic losses and limit the sustainable development of sea cucumber aquaculture. It is therefore important to better understand how sea cucumbers respond to environmental stress, especially with regard to its effects on immunity. In the present study, the time series of immunity-related gene expression in sea cucumbers under thermal and hypoxic stresses were analyzed separately. The expression trends of 17 genes related to the nuclear factor κB (NF-κB) pathway, the protease family, the complement system, heat shock proteins (HSPs) and the transferrin family during exposure to two stresses at eight time points were concluded. These genes have interconnected roles in stress defense. The expression levels of genes relating to the NF-κB pathways and HSPs were strongly affected in the sea cucumber thermal stress response, while melanotransferrin (Mtf), ferritin (Ft) and mannan-binding C-type lectin (MBCL) were affected by hypoxia. In contrast, complement factor B (Bf), myosin V (Mys) and serine protease inhibitor (SPI) were not that sensitive during the initial period of environmental stress. Similar expression patterns under both thermal and hypoxic stress for certain genes, including an increase in Hsp90 and decreases in lysozyme (Lys), major yolk protein (MYP) and cathepsin C (CTLC) were observed in sea cucumbers. Conversely, NF-κB and Hsp70 were differentially affected by the two stress treatments. Lysozyme-induced immune defense was inconstant in sea cucumbers coping with stress. A gene ontology (GO) analysis of the selected genes revealed that the most co-involved terms related to immunity and iron ion. Our analysis suggests that sea cucumbers demonstrate complex and varied immune responses to different types of stresses. This dynamic image of the immune responses and stress tolerance of sea cucumbers provides new insights into the adaptive strategies of holothurians in adverse environments.

Fluoxetine suppresses the immune responses of blood clams by reducing haemocyte viability, disturbing signal transduction and imposing physiological stress

The antidepressant fluoxetine (FLX), a selective serotonin reuptake inhibitor, is widely prescribed for the treatment of depression and anxiety disorders. Nowadays, measurable quantities of FLX have been frequently detected in the aquatic ecosystems worldwide, which may pose a potential threat to aquatic organisms. Although the impacts of FLX exposure on immune responses are increasingly well documented in mammals, they remain poorly understood in aquatic invertebrates. Therefore, to gain a better understanding of the ecotoxicological effects of FLX, the impacts of waterborne FLX exposure on the immune responses of blood clam, Tegillarca granosa, were investigated in this study. Results obtained showed that both cellular and humoural immune responses in T. granosa were suppressed by exposure to waterborne FLX, as indicated by total counts of haemocytes (THC), phagocytic rate, and activities of superoxide dismutases (SOD) and catalase (CAT), suggesting that waterborne FLX renders blood clams more vulnerable to pathogen challenges. To ascertain the mechanisms explaining how waterborne FLX affects immune responses, haemocyte viabilities, intracellular Ca²⁺ levels, in vivo concentrations of neurotransmitters, physiological stress conditions (as indicated by in vivo concentrations of cortisol), and expressions of key regulatory genes from Ca²⁺ and neurotransmitter signal transduction, as well as immune-related signalling pathways, were examined after 10 days of FLX exposure by blood clams via 1, 10 and 100 μg/L waterborne FLX. The results obtained indicated that immune response suppression caused by waterborne FLX could be due to (i) inhibited haemocyte viabilities, which subsequently reduce the THC; (ii) altered intracellular Ca²⁺ and neurotransmitter concentrations, which lead to constrained phagocytosis; and (iii) aggravated physiological stress, which thereafter hampers immune-related NFκB signalling pathways.

Responses of HSP70 Gene to Vibrio parahaemolyticus Infection and Thermal Stress and Its Transcriptional Regulation Analysis in Haliotis diversicolor

Heat-shock protein 70 (HSP70) is a molecular chaperone that plays critical roles in cell protein folding and metabolism, which helps to protect cells from unfavorable environmental stress. Haliotis diversicolor is one of the most important economic breeding species in the coastal provinces of south China. To date, the expression and transcriptional regulation of HSP70 in Haliotis diversicolor (HdHSP70) has not been well characterized. In this study, the expression levels of HdHSP70 gene in different tissues and different stress conditions were detected. The results showed that the HdHSP70 gene was ubiquitously expressed in sampled tissues and was the highest in hepatopancreas, followed by hemocytes. In hepatopancreas and hemocytes, the HdHSP70 gene was significantly up-regulated by Vibrio parahaemolyticus infection, thermal stress, and combined stress (Vibrio parahaemolyticus infection and thermal stress combination), indicating that HdHSP70 is involved in the stress response and the regulation of innate immunity. Furthermore, a 2383 bp of 5'-flanking region sequence of the HdHSP70 gene was cloned, and it contains a presumed core promoter region, a CpG island, a (TG)39 simple sequence repeat (SSR), and many potential transcription factor binding sites. The activity of HdHSP70 promoter was evaluated by driving the expression of luciferase gene in HEK293FT cells. A series of experimental results indicated that the core promoter region is located between -189 bp and +46 bp, and high-temperature stress can increase the activity of HdHSP70 promoter. Sequence-consecutive deletions of the luciferase reporter gene in HEK293FT cells revealed two possible promoter activity regions. To further identify the binding site of the key transcription factor in the two regions, two expression vectors with site-directed mutation were constructed. The results showed that the transcriptional activity of NF-1 site-directed mutation was significantly increased (p < 0.05), whereas the transcriptional activity of NF-κB site-directed mutation was significantly reduced. These results suggest that NF-1 and NF-κB may be two important transcription factors that regulate the expression of HdHSP70 gene.

Integrative transcriptome analysis and discovery of genes involving in immune response of hypoxia/thermal challenges in the small abalone Haliotis diversicolor

In recent years, the abalone aquaculture industry has been threatened by the deteriorating environmental conditions, such as hypoxia and thermal stress in the hot summers. It is necessary to investigate the molecular mechanism in response to these environmental challenges, and subsequently understand the immune defense system. In this study, the transcriptome profiles by RNA-seq of hemocytes from the small abalone Haliotis diversicolor after exposure to hypoxia, thermal stress, and hypoxia plus thermal stress were established. A total of 103,703,074 clean reads were obtained and 99,774 unigenes were assembled. Of the 99,774 unigenes, 47,154 and 20,455 had homologous sequences in the Nr and Swiss-Prot protein databases, while 16,944 and 10,840 unigenes could be classified by COG or KEGG databases, respectively. RNAseq analysis revealed that the differentially expressed genes (DEGs) after challenges of hypoxia, thermal stress, or hypoxia plus thermal stress were 24,189, 29,165 and 23,665, among which more than 3000 genes involved in at least 230 pathways, including several classical immune-related pathways. The genes and pathways that were involved in immune response to hypoxia/thermal challenges were identified by transcriptome analysis and further validated by quantitative real-time PCR and RNAi technology. The findings in this study can provide information on H. diversicolor innate immunity to improve the abalone aquaculture industry, and the analysis of the potential immune-related genes in innate immunity signaling pathways and the obtained transcriptome data can provide an invaluable genetic resource for the study of the genome and functional genes.

Heat shock cognate 70 gene in Haliotis diversicolor: responses to pathogen infection and environmental stresses and its transcriptional regulation analysis

Heat shock cognate 70 (HSC70) is a class of highly conserved proteins which functions as a molecular chaperon, participates in tolerance processes, and is involved in protein folding, degradation, targeting, translocation, and protein complex remodeling. In this study, the mRNA expression level of the Haliotis diversicolor HSC70 (HdHSC70) gene was detected by quantitative real-time PCR in different tissues and under different stresses. The results showed that the HdHSC70 gene was ubiquitously expressed in seven selected tissues. The highest expression level was detected in gills (P < 0.05). The expression level of the HdHSC70 gene was significantly upregulated by thermal stress, hypoxia stress, Vibrio parahaemolyticus infection, and combined thermal and hypoxia stress. The upregulation occurred at the early stage of stress. These results indicated that the HdHSC70 is an important component in the immune system of H. diversicolor and is involved in the early stress response. Meanwhile, 5'-flanking region sequence (2013 bp) of the HdHSC70 gene was cloned; it contains a putative core promoter region, heat shock element, CpG, and transcription elements including NF-1, Sp1, Oct-1, interferon consensus sequence binding protein (ICSBP), etc. In HEK 293T cells, the 5'-flanking region sequence is able to drive expression of the enhanced green fluorescent protein (EGFP), proving its promoter function. The promoter activity increased after high-temperature treatment, which may be the immediate reason why the expression of the HdHSC70 gene was significantly upregulated by thermal stress. After the ICSBP-binding site was mutated, we found the luciferase activity significantly reduced, which suggested that the ICSBP-binding site has a certain enhancement effect on the activity of the HdHSC70 promoter.

PI3K-AKT signaling pathway is involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor

The PI3K-AKT signal pathway has been found to be involved in many important physiological and pathological processes of the innate immune system of vertebrates and invertebrates. In this study, the AKT (HdAKT) and PI3K (HdPI3K) gene of small abalone Haliotis diversicolor were cloned and characterized for the important status of PI3K and AKT protein in PI3K-AKT signaling pathway. The full length cDNAs of HdAKT and HdPI3K are 2126 bp and 6052 bp respectively, encoding proteins of 479 amino acids and 1097 amino acids, respectively. The mRNA expression level of fourteen genes in the PI3K-AKT signaling pathway were detected by quantitative real-time PCR. The results showed that all these fourteen genes were ubiquitously expressed in seven selected tissues. Meanwhile, HdAKT was expressed in haemocytes with the highest expression level (p < 0.05) next in hepatopancreas (p < 0.05). On the other hand, the expression level of HdPI3K in haemocytes was higher than other tissues. Under normal condition, the gene expression level of HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members were significantly up-regulated by Vibrio parahaemolyticus infection which demonstrated that HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members play a role in the innate immune system of abalone. The mRNA expression of these genes in gills, haemocytes and hepatopancreas was significantly down-regulated after the Vibrio parahaemolyticus stimulation with environment stimulation (thermal, hypoxia and thermal & hypoxia). These results indicate that the dual/multiple stresses defeat the immune system and lead to immunosuppression in abalone. PI3K-AKT signaling pathway may be involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor.

Dietary choline regulates antibacterial activity, inflammatory response and barrier function in the gills of grass carp (Ctenopharyngodon idella)

An 8-week feeding trial was conducted to determine the effects of graded levels of choline (197-1795 mg/kg) on antibacterial properties, inflammatory status and barrier function in the gills of grass carp. The results showed that optimal dietary choline supplementation significantly improved lysozyme and acid phosphatase activities, complement component 3 (C3) content, and the liver expressed antimicrobial peptide 2 and Hepcidin mRNA levels in the gills of fish (P < 0.05). In addition, appropriate dietary choline significantly decreased the oxidative damage, which might be partly due to increase copper, zinc superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) activities and increased glutathione content in the gills of fish (P < 0.05). Moreover, appropriate dietary choline significantly up-regulated the mRNA levels of interleukin 10 and transforming growth factor β1, Zonula occludens 1, Occludin, Claudin-b, c, 3 and 12, inhibitor of κBα, target of rapamycin, Cu/Zn-SOD, CAT, GR, GPx, GST and NF-E2-related factor 2 in the gills of fish (P < 0.05). Conversely, appropriate dietary choline significantly down-regulated the mRNA levels of pro-inflammatory cytokines, tumor necrosis factor α, interleukin 8, interferon γ, interleukin 1β, and related signaling factors, nuclear factor kappa B p65, IκB kinase β, IκB kinase γ, myosin light chain kinase and Kelch-like-ECH-associated protein 1a (Keap1a) in the gills of fish (P < 0.05). However, choline did not have a significant effect on the mRNA levels of IκB kinase α, Claudin-15 and Keap1b in the gills of fish. Collectively, appropriate dietary choline levels improved gill antibacterial properties and relative gene expression levels of tight junction proteins, and decreased inflammatory status, as well as up-regulated the mRNA levels of related signaling molecules in the gills of fish. Based on gill C3 content and AHR activity, the dietary choline requirements for young grass carp (266.5-787.1 g) were estimated to be 1191.0 and 1555.0 mg/kg diet, respectively.

NMR-based metabolomic analysis of Haliotis diversicolor exposed to thermal and hypoxic stresses

Haliotis diversicolor is a commercially important cultured shellfish. It is also an important marine model organism for environmental science. High temperature accompanied with hypoxia frequently induces diseases or even death to abalones. In present study, (1)H NMR spectroscopy together with pattern recognition methods was used to investigate the responses of muscle and gill of H. diversicolor to thermal and hypoxic stresses. It was found that obvious gender-, time- and tissue-specific metabolic responses were induced by thermal and hypoxic stresses. In combination with the changes of H. diversicolor in physiological features, the dual-modal stresses were suggested to mainly cause the disturbance in energy metabolism and osmotic balance in muscle and gill tissues with different mechanisms. Further, the corresponding correlation networks and metabolic pathways derived from the characteristic metabolites were used to assess the major metabolic functions of these characteristic metabolites. These findings shed some lights on the metabolic influences of environmental stresses on marine organisms.