Differential expressions of HSP70 gene between golden and brown noble scallops Chlamys nobilis under heat stress and bacterial challenge

Tissue-specific, temporal, and core gene-dependent expression patterns of Hsp70s reveal functional allocation in Chlamys farreri under heat stress

Heat shock proteins 70 KDa (Hsp70s) engage in a broad spectrum of cellular functions in response to various stressors. Marine bivalves face substantial threats from the rising seawater temperature attributed to global warming. In the present study, expression patterns of Hsp70s in Zhikong scallop Chlamys farreri (CfHsp70s) were determined in embryos and larvae at all developmental stages, in healthy adult tissues, and across four various tissues exposed to high temperature for acute and chronic periods through in silico analysis. Spatiotemporal expressions suggested CfHsp70s performed specific functional differentiations in scallop's development and growth. Regulatory expression patterns of CfHsp70s, characterized by predominant down-regulation in the mantle, gill and hemocytes, as well as contrasting up-regulation in the heart, suggest differential functional allocation of CfHsp70s among tissues in response to heat stress. Particularly, a core set of 14 CfHsp70s, especially the nine members of the Hsp70B2s, characterized by gene expansion, intron-less structure, shorter gene length, preference for hydrophilic amino acids, and coordinated expression profiles, was predominantly responsible for the inducible up-regulations observed across all four tissue types. Collectively, the tissue-specific, temporal and core gene-dependent expression patterns of CfHsp70s illustrate the functional allocation and molecular evolution of Hsp70 family members in Zhikong scallops.

The HSP70 and IL-1β of Nile tilapia as molecular adjuvants can enhance the immune protection of DNA vaccine against Streptococcus agalactiae infection

Globally, streptococcal disease caused by Streptococcus agalactiae is known for its high mortality rate, which severely limits the development of the tilapia breeding industry. As a third-generation vaccine, DNA vaccines have shown great application prospects in the prevention and control of aquatic diseases, but their low immunogenicity limits their development. The combination of DNA vaccines and molecular adjuvants proved to be an effective method for inducing protective immunity. This study constructed recombinant plasmids encoding tilapia HSP70 and IL-1β genes (pcHSP70 and pcIL-1β) to verify their effectiveness as molecular adjuvants for S. agalactiae DNA vaccine (pcSIP) in the immunized tilapia model. The results revealed that serum-specific IgM production, enzyme activities, and immune-related gene expression in tilapia immunized with pcSIP plus pcHSP70 or pcIL-1β were significantly higher than those in tilapia immunized with pcSIP alone. It is worth noting that combination with molecular adjuvants improved the immune protection of DNA vaccines, with a relative percentage survival (RPS) of 51.72% (pcSIP plus pcHSP70) and 44.83% (pcSIP plus pcIL-1β), respectively, compared with that of pcSIP alone (24.14%). Thus, our study indicated that HSP70 and IL-1β in tilapia are promising molecular adjuvants of the DNA vaccine in controlling S. agalactiae infection.

The attachment factors and attachment receptors of human noroviruses

Human noroviruses (HuNoVs) are the leading etiological agent causing the worldwide outbreaks of acute epidemic non-bacterial gastroenteritis. Histo-blood group antigens (HBGAs) are commonly acknowledged as cellular receptors or co-receptors for HuNoVs. However, certain genotypes of HuNoVs cannot bind with any HBGAs, suggesting potential additional co-factors and attachment receptors have not been identified yet. In addition, food items, such as oysters and lettuce, play an important role in the transmission of HuNoVs. In the past decade, a couple of attachment factors other than HBGAs have been identified and analyzed from foods and microbiomes. Attachment factors exhibit potential as inhibitors of viral binding to receptors on host cells. Therefore, it is imperative to further characterize the attachment factors for HuNoVs present in foods to effectively control the spread of HuNoVs within the food chain. This review summarizes the potential attachment factors/receptors of HuNoVs in humans, foods, and microbiome.

Transcriptomic profiling of the thermal tolerance in two subspecies of the bay scallop Argopecten irradians

The bay scallop is a eurythermal species with high economic value and now represents the most cultured bivalve species in China. Two subspecies of the bay scallop, the northern subspecies Argopecten irradians irradians Korean population (KK) and the southern subspecies Argopecten irradians concentricus (MM), exhibited distinct adaptations to heat stress. However, the molecular mechanism of heat resistance of the two subspecies remains unclear. In this study, we compared the transcriptomic responses of the two subspecies to heat stress and identified the involved differentially expressed genes (DEGs) and pathways. More DEGs were found in the KK than in the MM when exposed to high temperatures, indicating elevated sensitivity to thermal stress in the KK. Enrichment analysis suggests that KK scallops may respond to heat stress more swiftly by regulating GTPase activity. Meanwhile, MM scallops exhibited higher resistance to heat stress mainly by effective activation of their antioxidant system. Chaperone proteins may play different roles in responses to heat stress in the two subspecies. In both subspecies, the expression levels of antioxidants such as GST were significantly increased; the glycolysis process regulated by PC and PCK1 was greatly intensified; and both apoptotic and anti-apoptotic systems were significantly activated. The pathways related to protein translation and hydrolysis, oxidoreductase activity, organic acid metabolism, and cell apoptosis may also play pivotal roles in the responses to heat stress. The results of this study may provide a theoretical basis for marker-assisted breeding of heat-resistant strains.

Genome-wide identification of the HSP70 genes in Pacific oyster Magallana gigas and their response to heat stress

Heat shock protein 70 (HSP70), the most prominent and well-characterized stress protein in animals, plays an important role in assisting animals in responding to various adverse conditions. In the present study, a total of 113 HSP70 gene family members were identified in the updated genome of Magallana gigas (designated MgHSP70) (previously known as Crassostrea gigas). There were 75, 12, 11, and 8 HSP70s located in the cytoplasm, nucleus, mitochondria, and endoplasmic reticulum, respectively, and 7 HSP70s were located in both the nucleus and cytoplasm. Among 113 MgHSP70 genes, 107 were unevenly distributed in 8 chromosomes of M. gigas with the greatest number in chromosome 07 (61 genes, 57.01%). The MgHSP70 gene family members were mainly assigned into five clusters, among which the HSPa12 subfamily underwent lineage-specific expansion, consisting of 89 members. A total of 68 MgHSP70 genes (60.18%) were tandemly duplicated and formed 30 gene pairs, among which 14 gene pairs were under strong positive selection. In general, the expression of MgHSP70s was tissue-specific, with the highest expression in labial palp and gill and the lowest expression in adductor muscle and hemocytes. There were 35, 31, and 47 significantly upregulated genes at 6, 12, and 24 h after heat shock treatment (28 °C), respectively. The expression patterns of different tandemly duplicated genes exhibited distinct characteristics after shock treatment, indicating that these genes may have different functions. Nevertheless, genes within the same tandemly duplicated group exhibit similar expression patterns. Most of the tandemly duplicated HSP70 gene pairs showed the highest expression levels at 24 h. This study provides a comprehensive description of the MgHSP70 gene family in M. gigas and offers valuable insights into the functions of HSP70 in the mollusc adaptation of oysters to environmental stress.

Expansion of the HSP70 gene family in Tegillarca granosa and expression profiles in response to zinc toxicity

Zinc (Zn) is an essential micronutrient in organisms and an abundant element in the Earth's crust. Trace amounts of Zn released from natural sources can enter aquatic ecosystems through weathering and erosion. Zn accumulates in organisms, and when its intracellular concentration exceeds a certain level, it can induce oxidative stress and trigger oxidative stress-mediated heat shock protein (HSP) modulation. HSP70 is the most evolutionarily conserved among the HSP families. Despite extensive research on HSP70 genes in bivalves, the HSP70 gene family of Tegillarca granosa is still poorly characterized. We identified 65 HSP70 genes belonging to 6 families in the T. granosa genome, with 50 HSPa12 and 11 HSPa B2 genes highly expanded. On chromosome 11, 39 HSP70 (60%) genes were identified, and the HSPa12A genes were highly duplicated. A total of 527 and 538 differentially expressed genes were identified in the gills and mantle based on Zn exposure, respectively. The Gene Ontology of cellular anatomical entities was significantly enriched with upregulated differentially expressed genes in the gills and mantle. Eight of the 11 HSPa B2 genes were upregulated in both tissues. Most of the genes identified in both tissues were involved in "protein homeostasis" and "inhibition of apoptosis," which are associated with the HSP70 family's resistance to extrinsic and intrinsic stress. Hence, this study identified that the HSP70 gene family plays a vital role in the adaptation of aquatic organisms to heavy metal (e.g., Zn) stress in contaminated environments by compiling the different physiological responses to preserve homeostasis.

Molecular Mechanism Based on Histopathology, Antioxidant System and Transcriptomic Profiles in Heat Stress Response in the Gills of Japanese Flounder

As an economically important flatfish in Asia, Japanese flounder is threatened by continuously rising temperatures due to global warming. To understand the molecular responses of this species to temperature stress, adult Japanese flounder individuals were treated with two kinds of heat stress—a gradual temperature rise (GTR) and an abrupt temperature rise (ATR)—in aquaria under experimental conditions. Changes in histopathology, programmed cell death levels and the oxidative stress status of gills were investigated. Histopathology showed that the damage caused by ATR stress was more serious. TUNEL signals confirmed this result, showing more programmed cell death in the ATR group. In addition, reactive oxygen species (ROS) levels and the 8-O-hDG contents of both the GTR and ATR groups increased significantly, and the total superoxide dismutase (T-SOD) activities and total antioxidant capacity (T-AOC) levels decreased in the two stressed groups, which showed damage to antioxidant systems. Meanwhile, RNA-seq was utilized to illustrate the molecular mechanisms underyling gill damage. Compared to the control group of 18 °C, 507 differentially expressed genes (DEGs) were screened in the GTR group; 341 were up-regulated and 166 were down-regulated, and pathway enrichment analysis indicated that they were involved in regulation and adaptation, including chaperone and folding catalyst pathways, the mitogen-activated protein kinase signaling (MAPK) pathway and DNA replication protein pathways. After ATR stress, 1070 DEGs were identified, 627 were up-regulated and 423 were down-regulated, and most DEGs were involved in chaperone and folding catalyst and DNA-related pathways, such as DNA replication proteins and nucleotide excision repair. The annotation of DEGs showed the great importance of heat shock proteins (HSPs) in protecting Japanese flounder from heat stress injury; 12 hsp genes were found after GTR, while 5 hsp genes were found after ATR. In summary, our study records gill dysfunction after heat stress, with different response patterns observed in the two experimental designs; chaperones were activated to defend heat stress after GTR, while replication was almost abandoned due to the severe damage consequent on ATR stress.

Transcriptome analysis reveals potential key immune genes of Hong Kong oyster (Crassostrea hongkongensis) against Vibrio parahaemolyticus infection

Hong Kong oyster (Crassostrea hongkongensis) is one of the main species of economic shellfish cultivated in the coastal areas of southern China. The cultivation of this shellfish may be adversely impacted by Vibrio parahaemolyticus, a harmful pathogenic bacterium for many mariculture species, as it usually exists on the surface of Hong Kong oysters. Although previous studies have discovered that oysters rely on non-specific immune system to fight pathogen invasion, the genes corresponding to the complex immune system against Vibrio is still not fully elucidated. Therefore, we conducted a transcriptome analysis on the gill from Hong Kong oysters at two time points (i.e., 12 h and 24 h after V. parahaemolyticus or PBS challenge) to identify potential immune genes against V. parahaemolyticus infection. A total of 61779 unigenes with the average length of 1221 bp were obtained, and the annotation information of 39917 unigenes were obtained from Nr, SwissProt, KEGG and COG/KOG. After a pairwise comparison between V. parahaemolyticus or PBS challenge at the two time points, three groups of differentially expressed genes induced by V. parahaemolyticus were captured and analyzed. GO and KEGG analyses showed that multiple immune-related genes played an important role in pathogen infection, including HSP70, PCDP3 and TLR4. Furthermore, genes annotation indicated that LITAF, TNFSF10, Duox2 and big defensin family are also involved in immune regulation. Our study provides a reference for further exploration the molecular mechanism that defenses the pathogen infection regarding the identified immune-related genes in Hong Kong oysters.

Oyster Heat Shock Protein 70 Plays a Role in Binding of Human Noroviruses

Human noroviruses (HuNoVs) are important foodborne pathogens causing acute gastroenteritis. Oysters are an important vehicle for the transmission of HuNoVs. Histo-blood group antigen (HBGA)-like substances are considered the primary ligands for bioaccumulation of HuNoVs in oyster tissues. In this study, proteinaceous ligands for specific binding of HuNoVs were mined from oyster tissues using a bacterial cell surface display system. The macromolecular target was captured and identified in proteomic analysis. The distribution of viral particles, oyster heat shock protein 70 (oHSP 70), and type A HBGA (positive control) in oyster tissue was investigated by multiplex immunofluorescence assays after artificial contamination with HuNoVs (GII.4). Our results demonstrated that oHSP 70 is a candidate vital ligand for specific binding of HuNoVs in oyster tissues. In addition, P proteins (GI.1 and GII.4) and viral particles (GI.1 and GII.4) were captured by recombinant oHSP 70 in an enzyme-linked immunosorbent assay with a sample signal/negative signal of 7.8, 6.3, 17.0, and 8.8, respectively. The findings suggested that oHSP 70 plays an important role in the binding of these foodborne viruses. IMPORTANCE Human noroviruses (HuNoVs) are the most important pathogen for nonbacterial epidemic gastroenteritis cases. Foodborne transmission plays an important role in HuNoVs infection. Oysters, filter-feeding epibenthic bivalves, can be contaminated by fecal discharge in harvest water. A new proteinaceous ligand for HuNoVs other than HBGA is identified in oyster tissues. The significance of our research is in identifying and verifying the ligands in oyster tissues for HuNoV binding. Our data will allow a better understanding of HuNoV attachment in and transmission by oysters, leading to the control of undesired foodborne disease.

Molecular cloning, expression HSP70 and its response to bacterial challenge and heat stress in Microptenus salmoides

The gene encoding HSP70 was isolated from Microptenus salmoides by homologous cloning and rapid amplification of cDNA ends (RACE). The HSP70 transcripts were 2116 bp long and contained 1953 open reading frames encoding proteins of 650 amino acids with a molecular mass of 71.2 kDa and theoretical isoelectric point of 5.22. The qRT-PCR analysis showed that the HSP70 gene was differentially expressed in various tissues under normal conditions, and the highest HSP70 level was observed in the spleen and the lowest levels in the muscle and heart. The clear time-dependent expression level of HSP70 was observed after bacterial challenge and heat stress. A significant increase in HSP70 expression level was detected and reached a maximum at 3 h and 6 h in liver, spleens and gill tissues after Aeromonas hydrophila infection and heat stress, respectively (P < 0.05). As time progressed, the expression of HSP70 transcript was downregulated and mostly dropped back to the original level at 48 h. The concentration of cortisol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) increased as the time of stress progressed, with the highest level found on 3 h and later declined rapidly and reached to the control levels at the 48 h. Those results suggested that HSP70 was involved in the immune response to bacterial challenge and heat stress. The cloning and expression analysis of the HSP70 provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides.

Identification and molecular characterization of peroxiredoxin 6 from noble scallop Chlamys nobilis revealing its potent immune response and antioxidant property

The 1-cyseine peroxiredoxin (Prx6) is an importantly antioxidant enzyme that protects cells from oxidative damage caused by excessive production of reactive oxygen species (ROS). In this study, we described the molecular characteristics of the noble scallop Chlamys nobilis peroxiredoxin 6 (designed as CnPrx6), immune responses and DNA protection activity of the recombinant protein. The complete ORF (696 bp) of CnPrx6 encoded a polypeptide (25.5 kDa) of 231 amino acids, harboring a conserved peroxidase catalytic center (⁴¹PVCTTE⁴⁶) and the catalytic triads putatively involved in peroxidase and phospholipase A2 activities. The deduced amino acid sequence of CnPrx6 shared a relatively high amino acid sequence similarity (more than 50%). The qRT-PCR revealed that the CnPrx6 mRNA was constitutively expressed in all examined tissues, with the highest expression observed in adductor. Upon immunological challenge with Vibrio parahaemolyticus, lipopolysaccharides (LPS) and polyinosinic-polycytidylic acid (Poly I:C), the expression level of CnPrx6 mRNA was significantly up-regulated (P < 0.05). Furthermore, there was a significant difference (P < 0.05) in the expression level of CnPrx6 between golden and brown scallops. The purified recombinant CnPrx6 protein protected the supercoiled plasmid DNA from metal-catalyzed ROS damage. Taken together, these results indicated that the CnPrx6 may play an important role in modulating immune responses and minimizing DNA damage in noble scallop Chlamys nobilis.

Roles of Carotenoids in Invertebrate Immunology

Carotenoids are biologically active pigments that are well-known to enhance the defense and immunity of the vertebrate system. However, in invertebrates, the role of carotenoids in immunity is not clear. Therefore, this study aims to review the scientific evidence for the role of carotenoids in invertebrate immunization. From the analysis of published literatures and recent studies from our laboratory, it is obvious that carotenoids are involved in invertebrate immunity in two ways. On the one hand, carotenoids can act as antioxidant enzymes to remove singlet oxygen, superoxide anion radicals, and hydroxyl radicals, thereby reducing SOD activity and reducing the cost of immunity. In some organisms, carotenoids have been shown to promote SOD activity by up-regulating the expression of the ZnCuSOD gene. Carotenoids, on the other hand, play a role in the expression and regulation of many genes involved in invertebrate immunity, including thioredoxins (TRX), peptidoglycan recognition receptor proteins (PGRPs), ferritins, prophenoloxidase (ProPO), vitellogenin (Vg), toll-like receptor (TLRs), heat shock proteins (HSPs), and CuZnSOD gene. The information in this review is very useful for updating our understanding of the progress of carotenoid research in invertebrate immunology and to help identify topics for future topics.

Effects of thermal stress on mortality and HSP90 expression levels in the noble scallops Chlamys nobilis with different total carotenoid content

The noble scallop Chlamys nobilis is an economically important marine bivalve cultivated in the southern sea of China since the 1980s. Unfortunately, mass mortality of this scallop species often occurs in summer. The present study was conducted to investigate whether the expression of heat shock protein 90 (HSP90) and level of carotenoids could enhance high-temperature stress resistance in scallop. First, the HSP90 homolog of C. nobilis (designated CnHSP90) was identified and cloned. The complete cDNA sequence of CnHSP90 was 2631 bp, including a 2181-bp open reading frame (ORF) encoding a 726 amino acid polypeptide with five HSP90 family signatures, and sharing high homology with members of the HSP90 family. CnHSP90 was ubiquitously expressed in all examined tissues including the intestine, kidney, adductor, mantle, gill, and gonad, with the highest in the gonad. Golden and brown scallops, which contain significantly different total carotenoid content (TCC), were subjected to acute thermal challenge, and the LTE50 (semi-lethal temperature at 36 h heat shock) and LTI50 (semi-lethal time after heat shock) as well as the correlation between CnHSP90 gene expression and TCC were determined. The LTE50 of golden scallop (32.14 °C) was higher than that of brown scallops (31.19 °C), with longer LTI50 at all tested temperatures, indicating that golden scallops were more resistant to thermal stress than brown scallops. Similarly, the mRNA expression levels of CnHSP90 in gill of golden scallops were significantly higher (P < 0.05) than that of brown scallops at 6, 12, 24, and 36 h, with a strong positive correlation between CnHSP90 expression level and TCC. This suggests that both carotenoids and HSP90 levels could improve thermal resistance in the noble scallops.