A low-density lipoprotein receptor-related protein (LRP)-like molecule identified from Chlamys farreri participated in immune response against bacterial infection

Molecular analyses of the gill symbiosis of the bathymodiolin mussel Gigantidas platifrons

Although the deep-sea bathymodiolin mussels have been intensively studied as a model of animal-bacteria symbiosis, it remains challenging to assess the host-symbiont interactions due to the complexity of the symbiotic tissue-the gill. Using cold-seep mussel Gigantidas platifrons as a model, we isolated the symbiont harboring bacteriocytes and profiled the transcriptomes of the three major parts of the symbiosis-the gill, the bacteriocyte, and the symbiont. This breakdown of the complex symbiotic tissue allowed us to characterize the host-symbiont interactions further. Our data showed that the gill's non-symbiotic parts play crucial roles in maintaining and protecting the symbiosis; the bacteriocytes supply the symbiont with metabolites, control symbiont population, and shelter the symbiont from phage infection; the symbiont dedicates to the methane oxidation and energy production. This study demonstrates that the bathymodiolin symbiosis interacts at the tissue, cellular, and molecular level, maintaining high efficiency and harmonic chemosynthetic micro niche.

Transcriptome analysis of hemocytes from the white shrimp Litopenaeus vannamei with the injection of dopamine

As a crucial neuroendocrine-immune factor, dopamine (DA) could regulate the immune system of Litopenaeus vannamei. To understand the immune mechanisms and regulatory pathways of DA in L. vannamei, the transcriptome analysis of hemocytes of L. vannamei with injection of DA (10^-6 mol/shrimp) at 3 and 12 h were performed in this study. Moreover, quantitative real-time PCR (qPCR) method was applied to validate the accuracy of transcriptome sequencing and analyze the expression pattern of candidate differentially expressed genes (DEGs) at different time points (0, 3, 6, 12, and 24 h) after DA injection. The results showed that a total of 51382 unigenes with a N50 length of 2341 bp were generated. And 1397 and 457 DEGs were obtained by comparative transcriptome at 3 and 12h respectively. Moreover, the results of functional annotation and enriched pathway showed that the DEGs were involved in phagosome (ko04145), lysosome (ko04142), Endocytosis (ko04144), and NOD-like receptor signaling pathway (ko04621). Besides, the Pearson's correlation coefficient (R) between transcriptome sequencing and qPCR was 0.845, which confirmed the reliability of the transcriptome sequencing results and the accuracy of assembly. Furthermore, the expression pattern of 15 candidate DEGs, containing 9 up-regulated and 6 down-regulated DEGs at 3 h, indicated the regulation of DA in physiological functions especially in the immune system. Therefore, these results revealed that DA induced the expressions of membrane receptors or proteins, activated intracellular signaling pathways, regulated cellular and humoral immune systems, controlled antioxidation and apoptosis, and was involved in the regulation of neuroendocrine system. These findings are helpful to promote the understanding on the effects of biogenic amines on physiological functions and regulatory networks of crustacean, and offer a substantial material and foundation for researching the immune response of crustacean.

A novel calreticulin-related molecule that interacts with bacteria and enhances host resistance against bacterial infection in black rockfish, Sebastes schlegeli

Calreticulin (CRT) is a highly conserved and multi-functional protein with diverse localizations. CRT has lectin-like properties and possesses important immunological activities in mammalian. In teleost, very limited studies on CRT immunologic function have been documented. In the present study, a CRT homologue (SsCRT) was cloned, identified and characterized from black rockfish, Sebastes schlegeli, an important aquaculture species in East Asia. The full length of SsCRT cDNA is 2180 bp and encoded a polypeptide of 425 amino acids. SsCRT contains a signal peptide, three distinct structural and functional domains (N-, P- and C-domains), and an endoplasmic reticulum (ER) retrieval signal sequence (KDEL). The deduced amino acid sequence of SsCRT shares 89-92% overall sequence identities with the CRT proteins of several fish species. SsCRT was distributed ubiquitously in all the detected tissues and was highly expressed in the spleen, muscle and liver. After the infection of fish extracellular bacterial pathogen Vibrio anguillarum and intracellular bacterial pathogen Edwardsiella tarda, the mRNA transcripts of SsCRT in spleen, liver, and head kidney were significantly up-regulated. The expression patterns were time-dependent and tissue-dependent. Recombinant SsCRT (rSsCRT) exhibited apparent binding activities against different bacteria and PAMPs. In vivo studies showed that the expressions of multiple immune-related genes such as TNF13B, IL-1β, IL-8, SAA, Hsp70, and ISG15 in head kidney were significantly enhanced when black rockfish were treated with rSsCRT. Furthermore, rSsCRT reduced pathogen dissemination and replication in fish kidney and spleen. These results indicated that SsCRT served as an immune receptor to recognize and eliminate the invading pathogens, which played a vital role in the immune response of Sebastes schlegeli. These findings provide new insights into understanding the roles of CRT proteins in immune response and pathogen infection in teleost.

Two novel calreticulin-related molecules with microbial binding and phagocytosis enhancing capacity in the half-smooth tongue sole, Cynoglossus semilaevis

Calreticulin (CRT) is highly conserved chaperone located in the endoplasmic reticulum. It plays important roles in innate immunity. Although various immune-related functions of CRT have been reported in vertebrates and invertebrates, information on the potential functions of teleost CRT is very limited. In the present study, we characterized two calreticulin-related molecules from tongue sole (Cynoglossus semilaevis), calreticulin-like1 and calreticulin-like2 (CsCRTL1 and CsCRTL2). CsCRTL1and CsCRTL2 contain signature CRT motifs that are highly conserved in different species. CsCRTL1and CsCRTL2 were expressed in liver, head kidney, brain, spleen, heart, muscle, skin, intestine and gills. The expression levels of CsCRTL1and CsCRTL2 were highest in liver and spleen, respectively. After stimulation by Vibrio anguillarum and Streptococcus agalactiae, CsCRTL1 and CsCRTL2 were significantly up-regulated. The expression patterns depended on the tissue type, pathogen type, and infection time. The recombinant proteins rCsCRTL1and rCsCRTL2 bound to different pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and to different bacteria, such as Gram-negative bacteria V. anguillarum and Gram-positive bacteria Staphylococcus aureus. Moreover, rCsCRTL1and rCsCRTL2 significantly enhanced the killing of V. anguillarum by tongue sole macrophages. Our results indicate that CsCRTL1and CsCRTL2 play important roles in antibacterial immunity of tongue sole.

An invertebrate-specific miRNA targeted the ancient cholinergic neuroendocrine system of oyster

Acetylcholine (ACh) is the main neurotransmitter in the cholinergic neuroendocrine system and plays an indispensable role in modulating diverse immune responses. As important transporters in choline uptake, choline transporter-like proteins (CTLs) can control ACh synthesis and release indirectly in multiple organisms. In this study, cgi-miR-2d, an invertebrate-specific miRNA in oyster Crassostrea gigas, is proved to repress the synthesis/release of ACh by targeting CgCTL1 and choline uptake in haemocytes during the early stage of pathogen infection. In short, an opposite expression pattern between CgCTL1 and cgi-miR-2d is observed during Vibrio splendidus infection, accompanied by changes in haemolymph ACh. In addition, the expression level of CgCTL1 is found to be significantly repressed after cgi-miR-2d overexpression in vivo, while both haemocyte choline and haemolymph ACh are also decreased simultaneously, similar to the finding in CgCTL1 knock-down assay. As a result, the expression of two tumour necrosis factor-like proteins and the bacteriostatic activity of oyster haemocytes are found to be altered significantly by either gain-of-function cgi-miR-2d or knock-down of CgCTL1. To our knowledge, this is the first miRNA identified in invertebrates that can target the ancient cholinergic system and augment immune response during infection.

Transcriptome analysis of the immune reaction of the pearl oyster Pinctada fucata to xenograft from Pinctada maxima

The pearl oyster Pinctada maxima exhibits great difficulty to culture pearls through nuclear insertion with an allograft, but it is easy for P. fucata to culture pearls after allografting. If P. fucata could be used as a surrogate mother to culture P. maxima pearls, it would benefit the pearl culture industry of P. maxima. However, this is blocked by the immune rejection of P. fucata against P. maxima mantle grafts. In this study, the immune responses of P. fucata hemocyte to allograft and xenograft were investigated after transplantation by transcriptome analysis. In total, 107.93 Gb clean reads were produced and assembled using the reference genome of P. fucata. Gene Ontology Term enrichment and KEGG enrichment analyses indicated that apoptosis, hippo signaling pathway, oxidation-reduction, MAPK signaling pathway, ribosome, protein processing in endoplasmic reticulum, purine metabolism, NF-kappa B signaling pathway, oxidative phosphorylation, Ras signaling pathway, and ubiquitin mediated proteolysis were involved in response to transplantation. Many genes related to oxidation-reduction reactions, the MAPK signaling pathway, and apoptosis were identified by comparison of the allograft group and the xenograft group at 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h post-transplantation. Among them, the expression levels of NADH dehydrogenase, succinate dehydrogenase and other dehydrogenases were increased significantly in the xenograft groups compared with allograft groups at 0 h post transplantation, indicating that a respiratory burst of neutrophils occurred immediately after xenograft transplantation. Additionally, HSP70 was highly expressed from 0 h to 96 h in the xenograft groups, indicating an oyster immune response to the xenograft. The genes enriched in the ribosome and hippo-signaling pathways were also identified, and expression patterns of these DEGs were different as compared between transplantation and control groups. Finally, altered expression levels of 10 randomly selected immune-related DEGs were confirmed by quantitative real-time PCR. These results indicated that oxidation-reduction is likely the key factor responsible for immune rejection to transplantation. The findings should provide some new insight into the molecular mechanism of immune rejection of the host against xenograft, and thus benefit to development of immunosuppressive reagents to facilitate effective xenograft pearling.

Identification and functional characterization of a novel member of low-density lipoprotein receptor-related protein (LRP)-like family in amphioxus

Low-density lipoprotein receptor-related protein (LRP) is a group of important endocytic receptors contributing to binding ligands and maintaining internal environment. In this study, we identified a soluble LRP-like molecule in the amphioxus B. japonicum, BjLRP, with an uncharacterized domain structure combination of LY-EGF-CRD-EGF-CRD. It was mainly expressed in the gill, muscle, notochord and testis, and was significantly up-regulated following the challenge with bacteria. Recombinant BjLRP was capable of interacting with both Gram-negative and positive bacteria as well as PAMPs including lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN). Interestingly, recombinant LY peptide was also able to bind to the Gram-negative and positive bacteria as well as the PAMPs LPS, LTA and PGN. By contrast, none of recombinant EGF1, EGF2, CRD1 and CRD2 had affinity to the bacteria and the PAMPs. In addition, BjLRPΔLY had no affinity to the PAMPs, although BjLRPΔLY showed slight affinity to the bacteria. These suggest that the interaction of BjLRP with the bacteria and PAMPs was primarily attributable to the LY domain. It is clear that BjLRP is a novel pattern recognition protein capable of identifying and interacting with invading bacteria in amphioxus.

Identification and characterization of a novel calreticulin involved in the immune response of the Zhikong scallop, Chlamys farreri

Calreticulin (CRT) is a multifunctional calcium-binding chaperone shared among vertebrates and invertebrates. In this study, a novel CRT (CfCRT) was identified in the Zhikong scallop Chlamys farreri by rapid amplification of cDNA ends. The full-length cDNA was composed of 1345 bp, which included a 1158 bp open reading frame, a 25 bp 5'-untranslated region (UTR) and a 162 bp 3'-UTR. The predicted molecular mass of CfCRT was 44.8 kDa. CfCRT contained three highly conserved domains (N-, P- and C-domains) essential to the function of CRT. BLAST analysis revealed significant sequence similarity (73%-92%) with CRT proteins from other mollusks. The mRNA transcripts of CfCRT were present in all the tested tissues of Zhikong scallops, with the higher expression level in the hemocytes and mantle. After stimulation by Vibrio anguillarum, the mRNA transcript of CfCRT in hemocytes was significantly upregulated. Recombinant plasmid pBCRT was successfully expressed in Escherichia coli BL21 (DE3). The recombinant (r)CfCRT protein could bind to the surface of several bacteria including the Gram-negative bacteria V. anguillarum, E. coli, and the Gram-positive bacterium Staphylococcus aureus. Moreover, rCfCRT was able to suppress their growth significantly. These results indicate that CfCRT might act as an immune effector in Zhikong scallop innate immunity.

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.

The immune system and its modulation mechanism in scallop

Scallops are a cosmopolitan family of bivalves, and some of them are highly prized as dominant aquaculture species. In the past decades, there have been increasing studies on the basic biology and immunology of scallops, and this review summarizes the research progresses of immune system and its modulation mechanism in scallop. As invertebrate, scallops lack adaptive immunity and they have evolved an array of sophisticated strategies to recognize and eliminate various invaders by employing a set of molecules and cells. It is evident that basic immune reactions such as immune recognition, signal transduction, and effector synthesis involved in immune response are accomplished in a variety of ways. They rely upon an extensive repertoire of phagocytosis, apoptosis and encapsulation of the circulating hemocytes for eliminating invasive pathogens, as well as the production of immune effectors that are active against a large range of pathogens or sensitive for the environmental stress. Furthermore, the molecular constitutions, metabolic pathways and immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, enkephalinergic system and NO system in scallop are also discussed, which can be taken as an entrance to better understand the origin and evolution of the neuroendocrine-immune regulatory network in lower invertebrates.