Molecular characterization and immune response expression of the QM gene from the scallop Chlamys farreri

Molecular Mechanisms Underlying Vibrio Tolerance in Ruditapes philippinarum Revealed by Comparative Transcriptome Profiling

The clam Ruditapes philippinarum is an important species in the marine aquaculture industry in China. However, in recent years, the aquaculture of R. philippinarum has been negatively impacted by various bacterial pathogens. In this study, the transcriptome libraries of R. philippinarum showing different levels of resistance to challenge with Vibrio anguillarum were constructed and RNA-seq was performed using the Illumina sequencing platform. Host immune factors were identified that responded to V. anguillarum infection, including C-type lectin domain, glutathione S-transferase 9, lysozyme, methyltransferase FkbM domain, heat shock 70 kDa protein, Ras-like GTP-binding protein RHO, C1q, F-box and BTB/POZ domain protein zf-C2H2. Ten genes were selected and verified by RT-qPCR, and nine of the gene expression results were consistent with those of RNA-seq. The lectin gene in the phagosome pathway was expressed at a significantly higher level after V. anguillarum infection, which might indicate the role of lectin in the immune response to V. anguillarum. Comparing the results from R. philippinarum resistant and nonresistant to V. anguillarum increases our understanding of the resistant genes and key pathways related to Vibrio challenge in this species. The results obtained here provide a reference for future immunological research focusing on the response of R. philippinarum to V. anguillarum infection.

A QM protein from Bombyx mori negatively regulates prophenoloxidase activation and melanization by interacting with Jun protein

The QM gene that encodes for the ribosomal protein L10 was firstly identified from human tumour cells as a tumour suppressor. In this study, a QM gene was identified in silkworm Bombyx mori (BmQM) and its immunomodulatory function was explored. BmQM messenger RNA (mRNA) and protein were highly expressed in the silk gland and fat body, and expressed in all stages of silkworm growth. After challenged with four different microorganisms, the expression levels of BmQM mRNA in fat body or haemocytes were significantly upregulated compared with the control. After knock-down of BmQM gene, the expressions of some immune genes (PGRPS6, Gloverin0, Lysozyme and Moricin) were affected, and the transcripts of prophenoloxidase1 and prophenoloxidase2 have different degrees of change. The phenoloxidase activity was significantly reduced when the purified recombinant BmQM protein was injected. Recombinant BmQM protein inhibited systemic melanization and suppressed prophenoloxidase activation stimulated by Micrococcus luteus, but it did not affect phenoloxidase activity. Far-western blotting assays showed that the BmQM protein interacted with silkworm BmJun protein, which negatively regulates AP-1 expression. Our results indicated that BmQM protein could affect some immune gene expression and negatively regulate the prophenoloxidase-activating system, and it may play an important role in regulation of the innate immunity in insects.

Investigating the natural resistance of blackfoot p-a%%KERN_ERR%%ua Haliotis iris to abalone viral ganglioneuritis using whole transcriptome analysis

The natural resistance of New Zealand blackfoot p-a%%%%%%%%%%%%%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%KERN_ERR%%ua Haliotis iris to infection by haliotid herpesvirus-1 (HaHV-1) and to the disease abalone viral ganglioneuritis was investigated in experimentally challenged p-aua using high throughput RNA-sequencing. HaHV-1-challenged p-aua up-regulated broad classes of genes that contained chitin-binding peritrophin-A domains, which seem to play diverse roles in the p-aua immune response. The p-aua also up-regulated vascular adhesion protein-1 (VAP-1), an important adhesion molecule for lymphocytes, and chitotriosidase-1 (CHIT-1), an immunologically important gene in mammalian immune systems. Moreover, several blood coagulation pathways were dysregulated in the p-aua, possibly indicating viral modulation. We also saw several indications that neurological tissues were specifically affected by HaHV-1, including the dysregulation of beta-1,4-N-acetylgalactosaminyltransferase (B4GALNT), GM2 ganglioside, neuroligin-4 and the Notch signalling pathway. This research may support the development of molecular therapeutics useful to control and/or manage viral outbreaks in abalone culture.

Immune state correlates with histopathological level and reveals molluscan health in populations of Modiolus kurilensis by integral health index (IHI)

Quantitative analysis of the histopathological and immune parameters of bivalve Modiolus kurilensis collected from water areas with different level of ecotoxicological stress was performed. Significant differences between samples from polluted and non-polluted sites were revealed for total haemocyte count; percentage of agranulocytes; size and internal complexity of agranulocytes and granulocytes; phagocytic activity; percentage of NBT-positive cells; hemolytic activity and plasma protein concentration; percentage of the optical density of haemolymph major polypeptide bands at 55 kDa, 78 kDa, and 124 kDa; concretion coverage area in the kidney tubules; thickness of the tubular basement membrane; nephrocyte shape; and karyopyknosis of the kidneys; and hypervacuolisation; necrosis; karyopyknosis; haemocyte infiltration; fibrosis; and invasion of the digestive gland. Analysis of the global histopathological condition index based on the weighted indices also revealed that both the digestive gland and kidneys showed significantly greater histopathological changes in the bivalves collected from polluted water. Bivalve histopathology is an established tool in aquatic toxicology. However, it reflects a morphological picture of change, which, as a rule, can be clearly recorded only at the later stages of pathology, and in some cases, indicates an adaptation to stressors within the physiological norm. In this respect, a promising and highly sensitive biomarker of the functional state of bivalves, in terms of norm and pathology as well as their habitat, is the evaluation of immune status in combination with morphological changes. However, the use of different methods and scales of assessment and the diagnosis of biomarkers, characterised by different profiles of the stress response, makes it difficult to compare the results of different studies. We propose a reliable and powerful system for assessing the physiological state of bivalve molluscs, expressed in the integral health index (IHI) and based on the standardisation of the numerical values for all parameters that have significant differences between animals collected from impacted and non-impacted water areas. In our study, IHI calculated in three variants (for histopathological parameters, for immunological parameters, and in combination) showed the most significant differences in each of the cases, but the strongest difference (-4.07) was in calculating the total IHI, which included both the immune and histopathological parameters (p = 0.00005).

Primary culture of Zhikong scallop Chlamys farreri hemocytes as an in vitro model for studying host-pathogen interactions

Primary cultured cells can be a useful tool in studies on physiology, virology, and toxicology. Hemocytes play an important role in animal rapid response to pathogen invasion. In this study, an appropriate medium for primary culture of hemocytes of the bivalve Chlamys farreri was developed by adding 5% fetal bovine serum and 1% C. farreri serum to Leibovitz L-15 medium. These primary cultured hemocytes were maintained for more than 40 d in vitro and were classified into 3 types: (1) granulocytes containing numerous granules in the cytoplasm, (2) hyalinocytes with no or few granules, (3) a small percentage of macrophage-like cells. Furthermore, the primary cultured hemocytes were observed to be sensitive to bacterial and viral challenges. These hemocytes could phagocytose the bacterium Vibrio anguillarum, and presented cytopathic effects on the extracellular products (ECPs) of V. anguillarum; the mRNA level of QM, which plays an important role in immune response, also significantly increased 12 h after infection. When these hemocytes were challenged with ostreid herpesvirus 1 (OsHV-1), virus particles and empty capsids in the cells infected for 48 h were observed by transmission electron microscopy, and the QM mRNA level increased significantly at 12 h and 24 h following OsHV-1 challenge. This primary culture system is available for C. farreri hemocytes which can be used in the future to study host-pathogen interactions.

Viruses infecting marine molluscs

Although a wide range of viruses have been reported in marine molluscs, most of these reports rely on ultrastructural examination and few of these viruses have been fully characterized. The lack of marine mollusc cell lines restricts virus isolation capacities and subsequent characterization works. Our current knowledge is mostly restricted to viruses affecting farmed species such as oysters Crassostrea gigas, abalone Haliotis diversicolor supertexta or the scallop Chlamys farreri. Molecular approaches which are needed to identify virus affiliation have been carried out for a small number of viruses, most of them belonging to the Herpesviridae and birnaviridae families. These last years, the use of New Generation Sequencing approach has allowed increasing the number of sequenced viral genomes and has improved our capacity to investigate the diversity of viruses infecting marine molluscs. This new information has in turn allowed designing more efficient diagnostic tools. Moreover, the development of experimental infection protocols has answered some questions regarding the pathogenesis of these viruses and their interactions with their hosts. Control and management of viral diseases in molluscs mostly involve active surveillance, implementation of effective bio security measures and development of breeding programs. However factors triggering pathogen development and the life cycle and status of the viruses outside their mollusc hosts still need further investigations.

Identification of a new calreticulin homolog from Yesso scallop (Patinopecten yessoensis) and its role in innate immunity

Calreticulin (CRT) is a multifunctional and highly conserved Ca²⁺-binding protein shared among vertebrates and invertebrates. In this study, we cloned and characterized a CRT gene, PyCRT, from Yesso scallop, Patinopecten yessoensis. The full-length cDNA of PyCRT was 1830 bp, including a 1242 bp open reading frame (ORF), a 29 bp 5'-untranslated region and a 559 bp 3'-untranslated region. PyCRT was consisted of three distinct structural and functional domains (N-, P- and C-domains), a signal peptide and an endoplasmic reticulum (ER) retrieval signal sequence (HDEL). Tissue specific expression analysis showed that PyCRT was distributed widely in Yesso scallop, and was highly expressed in the mantle and hemocytes. After Vibrio anguillarum challenge, the expression of PyCRT in hemocytes had a significant increase and reached the maximum level at 12 h post-infection. We also demonstrated for the first time in mollusc that the recombinant PyCRT (rPyCRT) could bind to the Gram-negative bacterium V. anguillarum, Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. Our results suggested that the CRT gene from Yesso scallop possessed immune-related regulatory functions in the innate immune system in scallops.

Identification and characterization of a ferritin gene involved in the immune defense response of scallop Chlamys farreri

Scallop Chlamys farreri is an important aquaculture species in northern China. However, its mass mortality caused by several pathogens can result in great economic loss and negative impacts to the sustainable development of the scallop industry. Thus, improving the overall understanding of immune response mechanisms involved in host-pathogen interactions is necessary. Ferritins are conserved molecules in organisms that are involved in diverse biological processes, such as mediating host-pathogen responses. In this study, we report a novel ferritin gene from C. farreri (denoted as CfFER). The full length of CfFER is 848 bp and contains a 5'-UTR of 113 bp, a 3'-UTR of 219 bp, and a complete open reading frame (ORF) of 516 bp. The ORF encodes a polypeptide of 171 amino acid residues with a molecular weight of approximately 19.95 kDa and an isoelectric point of 5.07. The CfFER protein exhibited typical ferritin structures, namely, a ferroxidase diiron center, a ferrihydrite nucleation center, and an iron-binding response signature. Phylogenetic analysis revealed that CfFER was closely related to other mollusk ferritin proteins. Expression of CfFER in different tissues was analyzed by quantitative real-time PCR, and results showed that CfFER was ubiquitously expressed in all examined tissues. The highest and lowest expression levels of CfFER were measured in the muscle and hemocyte, respectively. The relative mRNA expression of CfFER in response to bacterial (Vibrio anguillarum) and viral (acute viral necrobiotic virus) challenges sharply increased by ca. 5-fold about12 h post-infection (hpi) and then normalized at 48 hpi. Western blot analysis with polyclonal antibodies generated from the recombinant product of CfFER also demonstrated the presence of ferritin protein in hemocytes. These findings strongly suggest that CfFER is involved in the immune response of C. farreri and protection against pathogen challenge.