Molecular mechanisms of hepcidin regulation in sea bass (Dicentrarchus labrax)

Cloning and expression analysis of Janus activated kinase family genes from spotted seabass (Lateolabrax maculatus)

Janus kinases (JAKs) are important components of the JAK-STAT signaling pathway and play vital roles in innate immunity, autoimmune diseases, and inflammation. However, information about JAKs remains largely unknown in the spotted seabass, a fish species of Perciformes with great commercial value in the aquaculture industry. The aims of this study are to obtain the complete cDNA sequences of JAKs (JAK1, JAK2A, JAK2B, JAK3 and TYK2) from spotted seabass and to investigate their roles upon stimulation with lipopolysaccharides (LPS) and Edwardsiella tarda, using RT-PCR, PCR and qRT-PCR methods. All five JAK genes from the spotted seabass, each encode more than 1100 amino acids residues. JAK1 and JAK3 consist of 24 exons and 23 introns, whereas JAK2A, JAK2B and TYK2 consist of 23 exons and 22 introns. Furthermore, these five spotted seabass JAKs share high sequence identities with those of other fish species in protein domain analysis, synteny analysis, and phylogenetic analysis. Moreover, these five JAK genes were ubiquitously expressed in all tissues examined from healthy fish, and inducible expressions of JAKs were observed in the intestine, gill, head kidney, and spleen following LPS treatment or E. tarda infection. These findings indicate that all these JAK genes are involved in the antibacterial immunity of the spotted seabass and provide a basis for further understanding the mechanism of JAKs antibacterial response in the spotted sea bass.

Assessing the role of ulvan as immunonutrient in Solea senegalensis

Immunonutrition is a promising and viable strategy for the development of prophylactic measures in aquaculture. Ulvan, a sulphated marine polysaccharide from green seaweeds, has many biological activities including the immunomodulatory ones. The aim of this study was to assess the short and long-term effects of an ulvan-rich extract obtained from U. ohnoi as immunonutrient in Senegalese sole juveniles. In this work, an ulvan-rich extract from Ulva ohnoi has been obtained by the hot water method and isolated by ethanol precipitation. The FTIR analysis revealed that the ulvan-rich extact had very similar characteristics to previously published ulvan spectra. The total sulfate and protein content was 24.85 ± 3.98 and 0.91 ± 0.04 %, respectively. In vitro assays performed in Senegalese sole (Solea senegalensis) macrophages showed that the ulvan obtained in this study did not compromise the cell viability at concentrations up to 1 mg ml-1 and expression levels of lyg, irf1, il6, il10, c7, tf and txn were significantly upregulated in a concentration dependent-manner. Finally, S. senegalensis juveniles were fed basal diets and diets supplemented with the ulvan-rich extract at ratios 1 and 2 % for 30 days and then, challenged with Photobacterium damselae subsp. piscicida (Phdp). Thereafter, ulvan was withdrawn from the diet and all juveniles were fed the basal diet for 30 days. At 30 days post withdrawal (dpw), juveniles were challenged with Phdp. The expression profiles of a set of genes related to the immune system in spleen were evaluated as well as the lysozyme, peroxidase and bactericidal activity in plasma. Dietary effects of 1 % ulvan resulted in a boost of the immune response and increased disease resistance at short-term whereas juveniles fed diets supplemented with 2 % ulvan showed a significant decrease in the bactericidal activity and lack of protection against Phdp. At long-term (30 days after the withdrawal of ulvan), an improved response was observed in juveniles previously fed 1 % ulvan.

Synthetic Antimicrobial Peptides Fail to Induce Leucocyte Innate Immune Functions but Elicit Opposing Transcriptomic Profiles in European Sea Bass and Gilthead Seabream

Antimicrobial peptides (AMPs) are promising molecules in diverse fields, including aquaculture. AMPs possess lytic effects on a wide range of pathogens, resulting in a potential replacement for traditional antimicrobials in aquaculture. In addition, they also have modulatory effects on host immune responses. Thus, the objective of this work was to evaluate the immunomodulatory capability of three known synthetic AMPs derived from European sea bass, NK-lysin (Nkl), hepcidin (Hamp), and dicentracin (Dic), in head-kidney cell suspensions from European sea bass and gilthead seabream. The tested peptides were neither cytotoxic for European sea bass nor gilthead seabream cells and failed to modulate the respiratory burst and phagocytosis activities. However, they modified the pattern of transcription of immune-related genes differently in both species. Peptides were able to promote the expression of marker genes for anti-inflammatory (il10), antiviral (mx, irf3), cell-mediated cytotoxicity (nccrp1, gzmb), and antibody responses (ighm) in European sea bass, with the Nkl peptide being the most effective. Contrary to this, the effects of those peptides on gilthead seabream mainly resulted in the suppression of immune responses. To conclude, European sea bass-derived peptides can be postulated as potential tools for immunostimulation in European sea bass fish farms, but more efforts are required for their universal use in other species.

Early innate immune responses in European sea bass (Dicentrarchus labrax L.) following Tenacibaculum maritimum infection

Introduction

The marine aquaculture industry has been witnessing a worldwide emergence of tenacibaculosis, a poorly understood bacterial disease caused by Tenacibaculum maritimum that affects commercially important fish. So far, knowledge on the T. maritimum virulence mechanisms is scarce and the pathogen-host interaction operating in tenacibaculosis remain to be disclosed. This study aimed at contributing to a better understanding of this disease, by evaluating the early innate immune response triggered in European sea bass (Dicentrarchus labrax) by a bath-challenge with T. maritimum.

Methods

Groups of sea bass were bath-challenged with T. maritimum (challenged fish) or mock-challenged. Undisturbed fish were used as controls (time 0). Samples of blood, liver and mucosal organs (skin, gills and posterior-intestine) were collected at 0 h (control) and at 6, 24, 48 and 72 h post-challenge (n=12). Mucosal organs were used for analyzing the expression of immune-related genes by RT-qPCR, as well as blood samples for assessing haematological and innate humoral parameters and liver for oxidative stress assessment.

Results

An increased expression of il-1β, il8, mmp9 and hamp1 was detected in all mucosal organs of infected fish when compared with control and mock-challenged fish, suggesting a pro-inflammatory response against T. maritimum transversal to all organs. The faster induction of these pro-inflammatory genes was observed in the gills. Regarding the systemic response, challenged fish presented neutrophilia, monocytosis, signs of anemia, and a decrease of bactericidal and lysozyme activities in plasma. Almost no variations were observed regarding hepatic oxidative stress.

Discussion/Conclusions

The present study suggests that T. maritimum induces a local innate immune response upon bath infection not only in the skin of European sea bass, but also in the gills and posterior-intestine, likely triggered by the T. maritimum's capacity to adhere, colonize and damage these organs that can function as entry ways to bacteria, leading ultimately to the seen host's systemic response.

Molecular characterization of HEPCIDIN-1 (HAMP1) gene in red-bellied pacu (Piaractus brachypomus)

Hepcidins are cysteine-rich peptides, which participate in iron metabolism regulation, the inflammatory and antimicrobial response. This study characterizes the hepcidin-1 (HAMP1) gene, its transcript expression in different tissues, as well as its regulation in a model of brain injury in Piaractus brachypomus. Bioinformatic analysis was carried out to determine conserved domains, glycosylation sites and protein structure of HAMP1, and probability that HAMP1 corresponds to an antimicrobial peptide (AMP). Relative gene expression of the P. brachypomus HAMP1 gene was determined by qPCR from cDNA of several tissues, a brain injury model, an organophosphate sublethal toxicity model and anesthetic experiment using the 2^-ΔΔCt method. HAMP1 ORF encodes for a 91 aa pre-prohepcidin conformed for a prodomain with 42 aa and mature peptide of 25 aa. Mature domain was determined as an AMP. HAMP1 transcript is expressed in all the tissues, being higher in the spleen and liver. HAMP1 mRNA level was upregulated in the brain injury group, as well as in the olfactory bulb, optic chiasm and telencephalon of red-bellied pacu brain exposed to an organophosphate. In anesthetic experiment, HAMP1 mRNA level was upregulated in the liver and gills. HAMP1 gene of P. brachypomus may be involved in the inflammatory, antimicrobial, hypoxia and stress oxidative response.

Characterization of Erythroferrone in a Teleost Fish (Dicentrarchus labrax) With Two Functional Hepcidin Types: More Than an Erythroid Regulator

Erythroferrone is a recently identified erythroid regulator produced by erythroblasts in the mammalian bone marrow and extramedullary sites, known to be induced in conditions of anemia or blood loss. Iron metabolism is affected by erythroferrone through its capacity to inhibit hepcidin production, leading to the increase of iron availability required for erythropoiesis. However, little is known about erythroferrone function in other vertebrates, in particular teleost fish, that unlike mammals, present two different functional types of hepcidin, one type mostly involved in iron metabolism and the other in antimicrobial response. The study of erythroferrone evolution and its biological role in teleost fish can give us valuably new insights into its function. To address these questions, we characterized erythroferrone in the European sea bass (Dicentrarchus labrax), a species presenting two hepcidin types, and evaluated variations in its expression levels in response to different experimental conditions. During experimental anemia, erythroferrone responds by increasing its expression and suppressing hepcidin production, following the pattern observed in mammals, but it is not influenced by iron overload. However, during bacterial infection, erythroferrone is downregulated and hepcidin levels increase. Furthermore, administration of Hamp1 but not of Hamp2 peptides suppresses erythroferrone expression. In conclusion, in dual hepcidin teleost fish erythroferrone seems to only interact with type 1 hepcidin, known to be involved in iron homeostasis, but not with type 2, which has an almost exclusive antimicrobial role.

The Era of Antimicrobial Peptides: Use of Hepcidins to Prevent or Treat Bacterial Infections and Iron Disorders

The current treatments applied in aquaculture to limit disease dissemination are mostly based on the use of antibiotics, either as prophylactic or therapeutic agents, with vaccines being available for a limited number of fish species and pathogens. Antimicrobial peptides are considered as promising novel substances to be used in aquaculture, due to their antimicrobial and immunomodulatory activities. Hepcidin, the major iron metabolism regulator, is found as a single gene in most mammals, but in certain fish species, including the European sea bass (Dicentrarchus labrax), two different hepcidin types are found, with specialized roles: the single type 1 hepcidin is involved in iron homeostasis trough the regulation of ferroportin, the only known iron exporter; and the various type 2 hepcidins present antimicrobial activity against a number of different pathogens. In this study, we tested the administration of sea bass derived hepcidins in models of infection and iron overload. Administration with hamp2 substantially reduced fish mortalities and bacterial loads, presenting itself as a viable alternative to the use of antibiotics. On the other hand, hamp1 seems to attenuate the effects of iron overload. Further studies are necessary to test the potential protective effects of hamp2 against other pathogens, as well as to understand how hamp2 stimulate the inflammatory responses, leading to an increased fish survival upon infection.

Iron metabolism: an emerging therapeutic target underlying the anti-cancer effect of quercetin

Iron, an essential micronutrient for all kinds of cells, is essential for the balance of body internal environment. Notably, cancer cells exhibit a strong dependence on iron and require a large amount of iron for proliferation. A growing number of studies suggested that iron metabolism imbalance and subsequent excess iron accumulation are closely related to the occurrence and progression of cancer. Precisely, excess iron promotes the development of cancer due to the pro-oxidative nature of iron and its damaging effects on DNA. Simultaneously, tumor cells acquire large amounts of iron to maintain rapid growth and proliferation. Therefore, targeting iron metabolism may provide a new way for the treatment of cancer. Quercetin, a natural flavonoid, has long been regarded as potential drug for cancer treatments owing to its anti-inflammatory, antioxidant and anti-tumor effects. It is proven that quercetin possesses a high iron-chelating capacity, depriving cancer cells of iron or altering iron metabolism. Herein, we conduct a review on the mechanisms of iron imbalance in tumors and the role of quercetin in iron chelation, which will provide insight into the potential for quercetin as an anti-cancer drug.

Effects of the sulfated polysaccharide ulvan from Ulva ohnoi on the modulation of the immune response in Senegalese sole (Solea senegalensis)

Sulfated polysaccharides derived from green seaweeds exhibit many beneficial biological activities and have great potential to be used as nutraceutical in aquaculture. In this work, we evaluated the effects of the sulfated polysaccharide ulvan from Ulva ohnoi on Senegalese sole (Solea senegalensis) juveniles at the transcriptomic level. Cytotoxicity assay performed in liver primary cell cultures from sole determined that the different ulvan concentrations assayed did not impair cell viability. Juveniles were intraperitoneally (IP) injected with ulvan (0.5 mg/fish) followed by a challenge with Photobacterium damselae subsp. piscicida (Phdp) at 7 days. RNASeq analyses at 2 days post injection (dpi) revealed that 402 transcripts were differentially expressed in liver between ulvan IP injected and control groups before the challenge. Genes related to bacterial and antiviral defence, complement system, chemokines, proteasomes and antigen presentation were upregulated in ulvan treated groups. A detailed expression analysis of sixteen genes related to innate and adaptive immune system was performed in two systemic tissues: liver and spleen. Ulvan injection provoked the upregulation of tlr22 and a transient inflammatory response was initiated in both liver and spleen at 2 dpi. As consequence, expression of acute phase proteins, antimicrobial peptides and complement genes was induced. Moreover, expression of mhcI, mhcII, psmb10 and bcl6 was also induced 2 dpi. At 2 dpi with Phdp, inflammatory cytokines and genes related to bacterial and antiviral defense, iron metabolism, complement system and antigen presentation were differentially modulated in survival juveniles previously IP injected with ulvan. Moreover, mortality was retarded in ulvan treated juveniles. These results provide new evidence about the role of ulvan as a bioactive compound with immunomodulatory activity in Senegalese sole as well as its possible use as vaccine adjuvant against Phdp. This is the first published study that evaluates the transcriptomic response of Senegalese sole IP injected with ulvan.

Expression and functional analysis of Nile tilapia transferrin receptors (TfRs) in host resistance to pathogenic bacteria and iron ion metabolism

Transferrin receptors (TfRs) play an essential role in iron-withholding strategy, and are involved in immune response against bacterial infection. In this study, the transferrin receptor 1 (OnTfR1) and transferrin receptor 2 (OnTfR2) genes are identified and characterized in Nile tilapia (Oreochromis niloticus). The open reading frames of OnTfR1 and OnTfR2 are 2220 and 2343 bp of nucleotide sequence, encoding 739 and 780 amino acids, respectively. The deduced proteins of OnTfR1 and OnTfR2 are highly homologous to those of other species, containing three conserved TfR superfamily domains (PA TfR domain, M28 TfR domain and TfR dimer domain). Expression analyses of OnTfRs in the healthy tilapia reveal that the OnTfR1 and OnTfR2 transcripts are the most abundant in the liver. The in vivo studies show that the expressions of OnTfRs are significantly up-regulate in liver and spleen, following infections of Streptococcus agalactiae and Aeromonas hydrophila. In addition, the in vitro studies reveal that the up-regulations of OnTfR expressions are also significant in monocytes/macrophages and hepatocytes upon the stimulations of S. agalactiae and A. hydrophila. Moreover, the iron ion (Fe³⁺) could significantly increase the expressions of OnTfRs in monocytes/macrophages and hepatocytes. Taken together, the present study indicates that OnTfRs may be involved in host defense against bacterial infection and possess the function of combining or transporting iron ions in Nile tilapia.

Transcriptomic analysis of dead end knockout testis reveals germ cell and gonadal somatic factors in Atlantic salmon

Background

Sustainability challenges are currently hampering an increase in salmon production. Using sterile salmon can solve problems with precocious puberty and genetic introgression from farmed escapees to wild populations. Recently sterile salmon was produced by knocking out the germ cell-specific dead end (dnd). Several approaches may be applied to inhibit Dnd function, including gene knockout, knockdown or immunization. Since it is challenging to develop a successful treatment against a gene product already existing in the body, alternative targets are being explored. Germ cells are surrounded by, and dependent on, gonadal somatic cells. Targeting genes essential for the survival of gonadal somatic cells may be good alternative targets for sterility treatments. Our aim was to identify and characterize novel germ cell and gonadal somatic factors in Atlantic salmon.

Results

We have for the first time analysed RNA-sequencing data from germ cell-free (GCF)/dnd knockout and wild type (WT) salmon testis and searched for genes preferentially expressed in either germ cells or gonadal somatic cells. To exclude genes with extra-gonadal expression, our dataset was merged with available multi-tissue transcriptome data. We identified 389 gonad specific genes, of which 194 were preferentially expressed within germ cells, and 11 were confined to gonadal somatic cells. Interestingly, 5 of the 11 gonadal somatic transcripts represented genes encoding secreted TGF-β factors; gsdf, inha, nodal and two bmp6-like genes, all representative vaccine targets. Of these, gsdf and inha had the highest transcript levels. Expression of gsdf and inha was further confirmed to be gonad specific, and their spatial expression was restricted to granulosa and Sertoli cells of the ovary and testis, respectively. Finally, we show that inha expression increases with puberty in both ovary and testis tissue, while gsdf expression does not change or decreases during puberty in ovary and testis tissue, respectively.

Conclusions

This study contributes with transcriptome data on salmon testis tissue with and without germ cells. We provide a list of novel and known germ cell- and gonad somatic specific transcripts, and show that the expression of two highly active gonadal somatic secreted TGF-β factors, gsdf and inha, are located within granulosa and Sertoli cells.

Distinct herpesvirus resistances and immune responses of three gynogenetic clones of gibel carp revealed by comprehensive transcriptomes

Background

Gibel carp is an important aquaculture species in China, and a herpesvirus, called as Carassius auratus herpesvirus (CaHV), has hampered the aquaculture development. Diverse gynogenetic clones of gibel carp have been identified or created, and some of them have been used as aquaculture varieties, but their resistances to herpesvirus and the underlying mechanism remain unknown.

Results

To reveal their susceptibility differences, we firstly performed herpesvirus challenge experiments in three gynogenetic clones of gibel carp, including the leading variety clone A⁺, candidate variety clone F and wild clone H. Three clones showed distinct resistances to CaHV. Moreover, 8772, 8679 and 10,982 differentially expressed unigenes (DEUs) were identified from comparative transcriptomes between diseased individuals and control individuals of clone A⁺, F and H, respectively. Comprehensive analysis of the shared DEUs in all three clones displayed common defense pathways to the herpesvirus infection, activating IFN system and suppressing complements. KEGG pathway analysis of specifically changed DEUs in respective clones revealed distinct immune responses to the herpesvirus infection. The DEU numbers identified from clone H in KEGG immune-related pathways, such as “chemokine signaling pathway”, “Toll-like receptor signaling pathway” and others, were remarkably much more than those from clone A⁺ and F. Several IFN-related genes, including Mx1, viperin, PKR and others, showed higher increases in the resistant clone H than that in the others. IFNphi3, IFI44-like and Gig2 displayed the highest expression in clone F and IRF1 uniquely increased in susceptible clone A⁺. In contrast to strong immune defense in resistant clone H, susceptible clone A⁺ showed remarkable up-regulation of genes related to apoptosis or death, indicating that clone A⁺ failed to resist virus offensive and evidently induced apoptosis or death.

Conclusions

Our study is the first attempt to screen distinct resistances and immune responses of three gynogenetic gibel carp clones to herpesvirus infection by comprehensive transcriptomes. These differential DEUs, immune-related pathways and IFN system genes identified from susceptible and resistant clones will be beneficial to marker-assisted selection (MAS) breeding or molecular module-based resistance breeding in gibel carp.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3945-6) contains supplementary material, which is available to authorized users.

Synthetic hepcidin from fish: Uptake and protection against Vibrio anguillarum in sea bass (Dicentrarchus labrax)

The generation of a variety of new therapeutic agents to control and reduce the effects of pathogen in aquaculture is urgently needed. The antimicrobial peptides (AMPs) are one of the major components of the innate defenses and typically have broad-spectrum antimicrobial activity. However, absorption and distributions of exogenous AMPs for therapeutics application on farmed fish species need to be studied. Previous studies in our laboratory have shown the properties of hepcidin as an effective antimicrobial peptide produced in fish in response to LPS and iron. Therefore, we decided to investigate the antimicrobial activity of four synthetic variants of hepcidin against Vibrio anguillarum in vitro, and using the more effective peptide we demonstrated the pathogen's ability to protect against the infection in European Sea bass. Additionally the uptake of this peptide after ip injection was demonstrated, reaching its distribution organs such as intestine, head kidney, spleen and liver. The synthetic peptide did not show cytotoxic effects and significantly reduced the accumulated mortalities percentage (23.5%) compared to the European Sea bass control (72.5%) at day 21. In conclusion, synthetic hepcidin shows antimicrobial activity against V. anguillarum and the in vivo experiments suggest that synthetic hepcidin was distributed trough the different organs in the fish. Thus, synthetic hepcidin antimicrobial peptide could have high potential for therapeutic application in farmed fish species.

Novel insights into iron regulation and requirement in marine medaka Oryzias melastigma

Iron (Fe) is an essential trace element for marine fish. However, our knowledge of Fe requirements at different development stages of marine fish is still limited. Here, we reported the efficient Fe absorption strategies adopted by larval fish under different dietary Fe supplementary levels (i.e., 0-640 mg/kg). Biokinetically, the larval fish controlled their dietary Fe assimilation efficiency (AE, 1.6-18.5%), and enhanced their waterborne Fe uptake (ca. 2.5 fold change of uptake rate constant) once the dietary Fe was deficient (i.e., 27.4 mg Fe/kg feed). Transcriptionally, the expression of hepcidin1 (hep1; Fe regulator; i.e., 2.3-15.7 fold change) in larval fish was positively correlated with the Fe supplementary levels. Comparatively, the female adult fish were poor in assimilating the added Fe source (i.e., ferric form) with similar life-sustainable levels of Fe (i.e., 0.046-0.12 μg/g/d assimilated for Fe supplementary levels of 27.4, 162 and 657 mg Fe/kg feed). The overall feeding experiments suggested that dietary net Fe flux sufficient for the normal growth of larval medaka was 0.71-1.75 μg/g/d (i.e., 83.9 mg Fe/kg feed), consistent with the modeled value (i.e., 1.09-2.16 μg/g/d). In female adults, the estimated essential net Fe flux was 0.88-0.90 μg/g/d.

Hepcidin-Dependent Regulation of Erythropoiesis during Anemia in a Teleost Fish, Dicentrarchus labrax

Anemia is a common disorder, characterized by abnormally low levels of red blood cells or hemoglobin. The mechanisms of anemia development and response have been thoroughly studied in mammals, but little is known in other vertebrates, particularly teleost fish. In this study, different degrees of anemia were induced in healthy European sea bass specimens (Dicentrarchus labrax) and at pre-determined time points hematological parameters, liver iron content and the expression of genes involved in iron homeostasis and hematopoiesis, with particular attention on hepcidins, were evaluated. The experimental anemia prompted a decrease in hamp1 expression in all tested organs, in accordance to an increased need for iron absorption and mobilization, with slight increases in hamp2 in the kidney and intestine. The liver was clearly the major organ involved in iron homeostasis, decreasing its iron content and showing a gene expression profile consistent with an increased iron release and mobilization. Although both the spleen and head kidney are involved in erythropoiesis, the spleen was found to assume a more preponderant role in the recovery of erythrocyte levels. The intestine was also involved in the response to anemia, through the increase of iron transporting genes. Administration of Hamp1 or Hamp2 mature peptides showed that only Hamp1 affects hematological parameters and liver iron content. In conclusion, the molecular mechanisms of response to anemia present in sea bass are similar to the ones described for mammals, with these results indicating that the two hepcidin types from teleosts assume different roles during anemia.

Receptor-Mediated Drug Delivery Systems Targeting to Glioma

Glioma has been considered to be the most frequent primary tumor within the central nervous system (CNS). The complexity of glioma, especially the existence of the blood-brain barrier (BBB), makes the survival and prognosis of glioma remain poor even after a standard treatment based on surgery, radiotherapy, and chemotherapy. This provides a rationale for the development of some novel therapeutic strategies. Among them, receptor-mediated drug delivery is a specific pattern taking advantage of differential expression of receptors between tumors and normal tissues. The strategy can actively transport drugs, such as small molecular drugs, gene medicines, and therapeutic proteins to glioma while minimizing adverse reactions. This review will summarize recent progress on receptor-mediated drug delivery systems targeting to glioma, and conclude the challenges and prospects of receptor-mediated glioma-targeted therapy for future applications.

HFE gene: Structure, function, mutations, and associated iron abnormalities

The hemochromatosis gene HFE was discovered in 1996, more than a century after clinical and pathologic manifestations of hemochromatosis were reported. Linked to the major histocompatibility complex (MHC) on chromosome 6p, HFE encodes the MHC class I-like protein HFE that binds beta-2 microglobulin. HFE influences iron absorption by modulating the expression of hepcidin, the main controller of iron metabolism. Common HFE mutations account for ~90% of hemochromatosis phenotypes in whites of western European descent. We review HFE mapping and cloning, structure, promoters and controllers, and coding region mutations, HFE protein structure, cell and tissue expression and function, mouse Hfe knockouts and knockins, and HFE mutations in other mammals with iron overload. We describe the pertinence of HFE and HFE to mechanisms of iron homeostasis, the origin and fixation of HFE polymorphisms in European and other populations, and the genetic and biochemical basis of HFE hemochromatosis and iron overload.

Antimicrobial Peptides as Mediators of Innate Immunity in Teleosts

Antimicrobial peptides (AMPs) have been identified throughout the metazoa suggesting their evolutionarily conserved nature and their presence in teleosts is no exception. AMPs are short (18–46 amino acids), usually cationic, amphipathic peptides. While AMPs are diverse in amino acid sequence, with no two AMPs being identical, they collectively appear to have conserved functions in the innate immunity of animals towards the pathogens they encounter in their environment. Fish AMPs are upregulated in response to pathogens and appear to have direct broad-spectrum antimicrobial activity towards both human and fish pathogens. However, an emerging role for AMPs as immunomodulatory molecules has become apparent—the ability of AMPs to activate the innate immune system sheds light onto the multifaceted capacity of these small peptides to combat pathogens through direct and indirect means. Herein, this review focuses on the role of teleost AMPs as modulators of the innate immune system and their regulation in response to pathogens or other exogenous molecules. The capacity to regulate AMP expression by exogenous factors may prove useful in modulating AMP expression in fish to prevent disease, particularly in aquaculture settings where crowded conditions and environmental stress pre-dispose these fish to infection.

The Megalobrama amblycephala transferrin and transferrin receptor genes: molecular cloning, characterization and expression during early development and after Aeromonas hydrophila infection

Both transferrin (TF) and transferrin receptor (TFR) play vital roles in iron homeostasis, which is essential for cellular growth and survival. Besides, TF and TFR are also reported to be involved in immune response against bacterial infection. In the present study, we cloned and characterized the Tf and TfR genes in Megalobrama amblycephala. The M. amblycephala Tf gene contained 17 exons and 16 introns, encoding 651 amino acids, while the M. amblycephala TfR gene contained 18 exons and 17 introns, encoding 768 amino acids. In healthy fish, Tf mRNA was most abundant in the liver, and TfR was highly expressed in the blood and brain. During early development, the expression of Tf increased from 12 hpf (hour post fertilization) to 26 hpf, followed by a diminution at 32 hpf, then increased significantly to the peak level at 2 dph (day post hatching). The expression pattern of TfR was similar to that of Tf, fluctuating from 0 hpf to 32 hpf and dramatically increasing to the peak at 2 dph. Additionally, both Tf and TfR genes responded to Aeromonas hydrophila infection, by increasing their expression in the liver, spleen and kidney at both mRNA and protein levels, indicating that they were involved in M. amblycephala immune response. Immunohistochemical analysis and Prussian blue staining verified the internalization of TF-receptor system with bound-iron in the liver of M. amblycephala.

RNA-seq analysis reveals significant transcriptome changes in turbot (Scophthalmus maximus) suffering severe enteromyxosis

Background

Enteromyxosis caused by the intestinal myxozoan parasite Enteromyxum scophthalmi is a serious threat for turbot (Scophthalmus maximus, L.) aquaculture, causing severe catarrhal enteritis leading to a cachectic syndrome, with no therapeutic options available. There are still many aspects of host-parasite interaction and disease pathogenesis that are yet to be elucidated, and to date, no analysis of the transcriptomic changes induced by E. scophthalmi in turbot organs has been conducted. In this study, RNA-seq technology was applied to head kidney, spleen and pyloric caeca of severely infected turbot with the aim of furthering our understanding of the pathogenetic mechanisms and turbot immune response against enteromyxosis.

Results

A huge amount of information was generated with more than 23,000 identified genes in the three organs, amongst which 4,762 were differently expressed (DE) between infected and control fish. Associate gene functions were studied based on gene ontology terms and available literature, and the most interesting DE genes were classified into five categories: 1) immune and defence response; 2) apoptosis and cell proliferation; 3) iron metabolism and erythropoiesis; 4) cytoskeleton and extracellular matrix and 5) metabolism and digestive function. The analysis of down-regulated genes of the first category revealed evidences of a connexion failure between innate and adaptive immune response, especially represented by a high number of DE interferon-related genes in the three organs. Furthermore, we found an intense activation of local immune response at intestinal level that appeared exacerbated, whereas in kidney and spleen genes involved in adaptive immune response were mainly down-regulated. The apoptotic machinery was only clearly activated in pyloric caeca, while kidney and spleen showed a marked depression of genes related to erythropoiesis, probably related to disorders in iron homeostasis. The genetic signature of the causes and consequences of cachexia was also demonstrated by the down-regulation of the genes encoding structural proteins and those involved in the digestive metabolism.

Conclusions

This transcriptomic study has enabled us to gain a better understanding of the pathogenesis of enteromyxosis and identify a large number of DE target genes that bring us closer to the development of strategies designed to effectively combat this pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1149) contains supplementary material, which is available to authorized users.

Molecular characterization, phylogeny and expression of a hepcidin gene in the blotched snakehead Channa maculata

A hepcidin-like gene (cmHep) was cloned and characterized from the liver of the blotched snakehead Channa maculata. The complete cmHep cDNA was 756 bp in length, containing an open reading frame of 270 bp (encoding 89 amino acids), flanked by 210 bp and 276 bp of 5' and 3' untranslated regions, respectively. The deduced peptide of 89 amino acids consisted of 24 aa, 40 aa and 25 aa for signal peptide, prodomain and mature peptide, respectively. The mature peptide had eight cysteines at the identical conserved positions in common with most of other known hepcidins in vertebrates. cmHepc gene displayed a tripartite structure (three exons interrupted by two introns), which organisation was conserved between the blotched snakehead and other fish species. Phylogenetic analysis of hepcidins from C. maculata and other vertebrates showed that major phylogenetic grouping of fish hepcidin coincided with the current euteleosts classification, indicating the multiphyletic evolution of hepcidin in the teleosts. In the Acanthopterygii subclade, there were two distinct additional subclades named as HAMP-Ac1 and HAMP-Ac2. The blotched snakehead hepcidin was in the group HAMP-Ac1, which has the hypothetical iron regulatory sequence [Q-S/I-H-L/I-S/A] motif in N-terminal of mature peptide. The RT-PCR showed cmHep mRNA transcripts were widely distributed in all tissues tested in the blotched snakehead including the liver, gill, intestine, spleen, head kidney and peripheral white blood cell. The most abundant of cmHep mRNA was detected in liver. A significant up-regulation of cmHep expression was detected only in head kidney at 24h post-challenge with Vibrio parahaemolyticus in blotched snakehead adults, no significant differences found in liver, gill, intestine and spleen. The cmHep expression was up-regulated in spleen, head kidney and intestine at 24h post-injection with LPS in blotched snakehead juveniles, liver cmHep expression was not altered. Iron overloading and poly I:C stimulation down-regulated cmHep expression in liver, but did not significantly change cmHep expression in spleen, head kidney and intestine in blotched snakehead juveniles.

Molecular Characterisation and Phylogenetic Analysis of a Novel Isoform of Hepatic Antimicrobial Peptide, Hepcidin (Zc-hepc1), from the Coral Fish Moorish idol, Zanclus cornutus (Linnaeus, 1758)

Hepcidin is a family of short cysteine-rich antimicrobial peptides (AMPs) participating in various physiological functions with inevitable role in host immune responses. Present study deals with identification and characterisation of a novel hepcidin isoform from coral fish Zanclus cornutus. The 81 amino acid (aa) preprohepcidin obtained from Z. cornutus consists of a hydrophobic aa rich 22 mer signal peptide, a highly variable proregion of 35 aa and a bioactive mature peptide with 8 conserved cysteine residues which contribute to the disulphide back bone. The mature hepcidin, Zc-hepc1 has a theoretical isoelectric point of 7.46, a predicted molecular weight of 2.43 kDa and a net positive charge of +1. Phylogenetic analysis grouped Z. cornutus hepcidin with HAMP2 group hepcidins confirming the divergent evolution of hepcidin-like peptide in fishes. Zc-hepc1 can attain a β-hairpin-like structure with two antiparallel β-sheets. This is the first report of an AMP from the coral fish Z. cornutus.