Adaptive evolution of hepcidin genes in antarctic notothenioid fishes

Characterization, Expression, and Functional Analysis of the Northern Snakehead (Channa argus) Hepcidin

Hepcidin, an antimicrobial peptide (AMP), is a well-conserved molecule present in various species such as fish, amphibians, birds, reptiles, and mammals. It exhibits broad-spectrum antimicrobial activity and holds a significant role in the innate immune system of host organisms. The northern snakehead (Channa argus) has become a valuable freshwater fish in China and Asia. In this investigation, the cDNA encoding the hepcidin gene of northern snakehead was cloned and named caHep. The amino acid sequences and protein structure of caHep are similar to those of hepcidins from other fish. The eukaryotic expression product of the caHep gene showed broad-spectrum antibacterial activity. Scanning electron microscope analysis indicated that the caHep peptide inhibited bacterial growth by damaging their cell membranes. Lipopolysaccharide (LPS) injection induced significant expression of caHep, implying the involvement of caHep in the innate immune response of northern snakeheads. This investigation showed that the caHep peptide is potentially a robust antibacterial drug against bacterial diseases in aquaculture animals.

In silico molecular and functional characterization of a dual function antimicrobial peptide, hepcidin (GIFT-Hep), isolated from genetically improved farmed tilapia (GIFT, Oreochromis niloticus)

BACKGROUND

Antimicrobial peptides (AMPs), innate immune response molecules in organisms, are also known for their dual functionality, exemplified by hepcidin-an immunomodulator and iron regulator. Identifying and studying various AMPs from fish species can provide valuable insights into the immune profiles of aquaculturally significant fish, which can be made use of in its culture.

RESULTS

Hepcidin, a dual-function antimicrobial peptide, was isolated from the gill tissue of Genetically Improved Farmed Tilapia (GIFT-Hep). GIFT-Hep consists of a 90 amino acid pre-propeptide with a 24-mer signal, a 40-mer propeptide, and a 26-mer mature peptide region. The mature peptide had a molecular weight of 3015.61 Da, a theoretical pI of 8.78, a net charge of +4.25, and a protein-binding potential of 2.06 kcal/mol. Four disulfide bonds were formed by eight cysteine residues in the mature region. The presence of positively charged arginine residues renders the peptide 50% hydrophobic. Molecular analysis of GIFT-Hep revealed the presence of a furin propeptide convertase motif, RX(K/R)R, which facilitates trimming of the peptide to yield the mature GIFT-Hep. The hypothetical iron regulatory sequence, QSHLSL, was also identified in the mature peptide. In silico predictions about the characteristics of GIFT-Hep, such as charge, hydrophobicity, high surface accessibility, transmembrane helical regions, hydrophobic faces, hot spots, and cell-penetrating properties, suggest that the peptide functions as an iron regulatory antimicrobial agent.

CONCLUSIONS

This study reports a hepcidin antimicrobial peptide with both HAMP1 and HAMP2 properties isolated from genetically improved farmed tilapia, and further evaluation of the properties will prove the feasibility of GIFT-Hep being used as a therapeutant in aquaculture.

Identification of antibacterial activity of LEAP2 from Antarctic icefish Chionodraco hamatus

Liver-expressed antimicrobial peptide 2 (LEAP2) is a small peptide, which is consisted of signal peptide, pro-peptide and the bioactive mature peptide. Mature LEAP2 is an antibacterial peptide with four highly conserved cysteines forming two intramolecular disulfide bonds. Chionodraco hamatus, an Antarctic notothenioid fish that lives in the coldest water, has white blood unlike most fish of the world. In this study, the LEAP2 coding sequence was cloned from C. hamatus, including a 29 amino acids signal peptide and mature peptide of 46 amino acids. High levels of LEAP2 mRNA were detected in the skin and liver. Mature peptide was obtained by chemical synthesis in vitro, displayed selective antimicrobial activities against Escherichia coli, Aeromonas hydrophila, Staphylococcus aureus and Streptococcus agalactiae. Liver-expressed antimicrobial peptide 2 showed bactericidal activity by destroying the cell membrane integrity and robustly combined with bacterial genomic DNA. In addition, overexpression of the Tol-LEAP2-EGFP in zebrafish larva showed stronger antimicrobial activity in C. hamatus than in zebrafish, accompanied by lower bacterial load and expression of pro-inflammatory factors. This is the first demonstration of the antimicrobial activity of LEAP2 from C. hamatus, which is of useful value in improving resistance to pathogens.

Antimicrobial peptide hepcidin contributes to restoration of the intestinal flora after Aeromonas hydrophila infection in Acrossocheilus fasciatus

Hepcidin is a cysteine-rich antimicrobial peptide that serves an important role in the immunity system of fishes. It exhibits antibacterial, antifungal, antiviral, and antitumor activities. However, the exact role of fish hepcidin in the regulation of the intestinal flora still remains a mystery. In our study, we sequenced and characterized hepcidin from the liver of Acrossocheilus fasciatus. Phylogenetic tree analysis showed that A. fasciatus hepcidin and Gobiocypris rarus hepcidin were the most closely related, and both belonged to the fish HAMP1 cluster. Studies conducted on in vivo tissue distribution showed that the expression of hepcidin was highest in healthy A. fasciatus liver. Aeromonas hydrophila infection was confirmed by the increased expression of pro-inflammatory cytokine genes and bacterial loads in A. fasciatus tissues. After A. hydrophila infection, hepcidin expression significantly increased in the liver, spleen, and head kidney. In vitro antibacterial assays showed that hepcidin exhibits strong broad spectrum antibacterial activity. Furthermore, we examined the regulatory effect of hepcidin on the intestinal flora and found that A. fasciatus hepcidin restored the reduced diversity and compositional changes in intestinal flora caused by A. hydrophila infection. Our results suggest that hepcidin could regulate the intestinal flora in fishes; however, the underlying mechanisms need to be explored in greater detail.

A novel serum spherical lectin from lamprey reveals a more efficient mechanism of immune initiation and regulation in jawless vertebrates

The innate immune system is the body's first line of defense against pathogens and involves antibody and complement system-mediated antigen removal. Immune-response-related complement molecules have been identified in lamprey, and the occurrence of innate immune response via the mannose-binding lectin-associated serine proteases of the lectin cascade has been reported. We have previously shown that lamprey (Lampetra japonica) serum can efficiently and specifically eliminate foreign pathogens. Therefore, we aimed to understand the immune mechanism of lamprey serum in this study. We identified and purified a novel spherical lectin (LSSL) from lamprey serum. LSSL had two structural calcium ions coordinated with conserved amino acids, as determined through cryogenic electron microscopy. LSSL showed high binding capacity with microbial and mammalian glycans and demonstrated agglutination activity against bacteria. Phylogenetic analysis revealed that LSSL was transferred from phage transposons to the lamprey genome via horizontal gene transfer. Furthermore, LSSL was associated with mannose-binding lectin-associated serine protease 1 and promoted the deposition of the C3 fragment on the surface of target cells upon binding. These results led us to conclude that LSSL initiates and regulates agglutination, resulting in exogenous pathogen and tumor cell eradication. Our observations will give a greater understanding of the origin and evolution of the complement system in higher vertebrates and lead to the identification of novel immune molecules and pathways for defense against pathogens and tumor cells.

Massive gene expansion of hepcidin, a host defense peptide, in gilthead seabream (Sparus aurata)

Host defense peptides (HDP) are among the most ancient immune molecules in animals and clearly reflect an ancestral evolutionary history involving pathogen-host interactions. Hepcidins are a very widespread family of HDPs among vertebrates and are especially diverse in teleosts. We have investigated the identification of new hepcidins in gilthead seabream (Sparus aurata), a fish farmed in the Mediterranean. Targeted gene predictions supported with expressed sequence tags (ESTs) derived from Hidden Markov Models were used to find the hamp genes in the seabream genome. The results revealed a massively clustered hamp duplication on chromosome 17. In fact, the seabream genome contains the largest number of hepcidin copies described in any vertebrate. The evolutionary history of hepcidins in seabream, and vertebrates generally, clearly indicates high adaptation in teleosts and novel subgroups within hepcidin type II. Furthermore, basal hepcidin gene expression analysis indicates specific-tissue expression profiles, while the presence and distribution of transcription factor binding sites (TFBS) in hamp promoters as well as their transcription profile upon bacterial challenge indicates different immune roles depending on the type of hepcidin and tissue. This massive duplication of HDP genes in a bony fish could point to a far more specific and adaptive innate immune system than assumed in the classic concept of immunity in mammals. Hence, a new world of knowledge regarding hepcidins in fish and vertebrates is being initiated.

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.

Hepcidin Gene Co-Option Balancing Paternal Immune Protection and Male Pregnancy

Viviparity has originated independently more than 150 times in vertebrates, while the male pregnancy only emerged in Syngnathidae fishes, such as seahorses. The typical male pregnancy seahorses have closed sophisticated brood pouch that act as both uterus and placenta, representing an excellent model system for studying the evolutionary process of paternal immune protection. Phylogenetic analysis indicated that the hampII gene family has multiple tandem duplicated genes and shows independent lineage-specific expansion in seahorses, and they had the highest ratio of nonsynonymous substitutions to synonymous substitutions (dN/dS) in the seahorse phylogenetic branch. The expression levels of hampIIs in the brood pouch placenta were significantly higher during pregnancy than non-pregnancy. Both LPS stimulation test in vivo and cytotoxicity test in vitro proved the immunological protection function of hampIIs against pathogen infection in seahorse. Besides, seahorse hampII peptides exhibit weaker antibacterial function, but stronger agglutination and free endotoxin inhibition. We assumed that the modified immunological function seemed to be a trade-off between the resistance to microbial attack and offspring protection. In brief, this study suggests that the rapid co-option of hampIIs contributes to the evolutionary adaption to paternal immune care during male pregnancy.

Identification of Antibacterial Activity of Hepcidin From Antarctic Notothenioid Fish

Hepcidin is a small peptide composed of signal peptide, propeptide, and the bioactive mature peptide from N terminal to C terminal. Mature hepcidin is an antibacterial peptide and iron regulator with eight highly conserved cysteines forming four intramolecular disulfide bonds, giving it a β sheet hairpin-like structure. Hepcidin homologs are found in a variety of vertebrates, especially fish, and their diversity may be associated with different habitats and different levels of pathogens. Dissostichus mawsoni, an Antarctic notothenioid fish that lives in the coldest water unlike most places of the world, with at least two hepcidin variants with eight cysteines. We confirmed the formation process of activated mature hepcidins from D. mawsoni in Chinese hamster ovary (CHO) cell line, obtained recombinant hepcidin protein from prokaryotes, and characterized its binding ability and antibacterial activity against varying bacteria. The expression of hepcidin in CHO cell line showed that the prepropeptide of Dmhep_8cysV1 and Dmhep_8cysV2 cleavage into smaller mature peptide. The antibacterial assay and flow cytometry showed that Dmhep_8cysV1, Dmhep_8cysV2, and Drhep bound to different bacteria and killed them with different minimum inhibitory concentration. These data suggest that hepcidin plays an important role in the innate immunity of D. mawsoni and is of great value in improving resistance to pathogens.

A hepatic antimicrobial peptide, hepcidin from Indian major carp, Catla catla: molecular identification and functional characterization

Background

Increase of antibiotic resistance in pathogenic microbes necessitated novel molecules for curing infection. Antimicrobial peptides (AMPs) are the gene-encoded evolutionarily conserved small molecules with therapeutic value. AMPs are considered as an alternative drug for conventional antibiotics. Hepcidin, the cysteine-rich antimicrobial peptide, is an important component in innate immune response. In this study, we identified and characterized hepcidin gene from the fish, Catla catla (Indian major carp) and termed it as Cc-Hep.

Results

Open reading frame of Cc-Hep consists of 261 base pair that encodes 87 amino acids. Cc-Hep is synthesized as a prepropeptide consisting of 24 amino acid signal peptide, 36 amino acid propeptide, and 26 amino acid mature peptide. Sequence analysis revealed that Cc-Hep shared sequence similarity with hepcidin from Sorsogona tuberculata. Phylogenetic analysis indicated that Cc-Hep was grouped with HAMP2 family. Structure analysis of mature Cc-Hep identified two antiparallel beta sheets stabilized by four disulphide bonds and a random coil. The mature peptide region of Cc-Hep has a charge of + 2, isoelectric value 8.23 and molecular weight 2.73 kDa.

Conclusion

Functional characterization predicted antibacterial, antioxidant, and anticancer potential of Cc-Hep, which can be explored in aquaculture or human health care.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

COVID-19 and iron dysregulation: distant sequence similarity between hepcidin and the novel coronavirus spike glycoprotein

The spike glycoprotein of the SARS-CoV-2 virus, which causes COVID-19, has attracted attention for its vaccine potential and binding capacity to host cell surface receptors. Much of this research focus has centered on the ectodomain of the spike protein. The ectodomain is anchored to a transmembrane region, followed by a cytoplasmic tail. Here we report a distant sequence similarity between the cysteine-rich cytoplasmic tail of the coronavirus spike protein and the hepcidin protein that is found in humans and other vertebrates. Hepcidin is thought to be the key regulator of iron metabolism in humans through its inhibition of the iron-exporting protein ferroportin. An implication of this preliminary observation is to suggest a potential route of investigation in the coronavirus research field making use of an already-established literature on the interplay of local and systemic iron regulation, cytokine-mediated inflammatory processes, respiratory infections and the hepcidin protein. The question of possible homology and an evolutionary connection between the viral spike protein and hepcidin is not assessed in this report, but some scenarios for its study are discussed.

Immunomodulatory function of antimicrobial peptide EC-Hepcidin1 modulates the induction of inflammatory gene expression in primary cells of Caspian Trout (Salmo trutta caspius Kessler, 1877)

Hepcidins, a group of antimicrobial peptides (AMPs), play a key role in the innate immune system of fishes and act against different pathogens. In this study, antimicrobial and immune-inflammatory activity of a synthetic EC-hepcidin1, previously identified from orange-spotted grouper, were evaluated. EC-hepcidin1 showed weak activity against the zoonotic fish pathogen Streptococcus iniae (MIC 100 μg mL^-1 and MBC 150 μg mL^-1). To study the effect of AMPs in general, and EC-hepcidin1 in particular, a primary cell culture (SC) from the fin tissue of the Caspian Trout (Salmo trutta caspius) was established. The neutral Red method on SC cells revealed that EC-hepcidin1 has no or very low cytotoxic properties. Treatment of cells with either EC-hepcidin1 (150 μg mL^-1) or fish pathogen Streptococcus iniae (MOI = 10) and a mixture of both resulted in the up-regulation of gene expression of MHC-UBA, IL-6, and TNFα indicating the modulatory function on inflammatory processes. These findings indicate that EC-hepcidin1 might act as a candidate for modulation of the innate immune system in S. iniae-based infection.

The genomic basis for colonizing the freezing Southern Ocean revealed by Antarctic toothfish and Patagonian robalo genomes

Background

The Southern Ocean is the coldest ocean on Earth but a hot spot of evolution. The bottom-dwelling Eocene ancestor of Antarctic notothenioid fishes survived polar marine glaciation and underwent adaptive radiation, forming >120 species that fill all water column niches today. Genome-wide changes enabling physiological adaptations and the rapid expansion of the Antarctic notothenioids remain poorly understood.

Results

We sequenced and compared 2 notothenioid genomes—the cold-adapted and neutrally buoyant Antarctic toothfish Dissostichus mawsoni and the basal Patagonian robalo Eleginops maclovinus, representing the temperate ancestor. We detected >200 protein gene families that had expanded and thousands of genes that had evolved faster in the toothfish, with diverse cold-relevant functions including stress response, lipid metabolism, protein homeostasis, and freeze resistance. Besides antifreeze glycoprotein, an eggshell protein had functionally diversified to aid in cellular freezing resistance. Genomic and transcriptomic comparisons revealed proliferation of selcys–transfer RNA genes and broad transcriptional upregulation across anti-oxidative selenoproteins, signifying their prominent role in mitigating oxidative stress in the oxygen-rich Southern Ocean. We found expansion of transposable elements, temporally correlated to Antarctic notothenioid diversification. Additionally, the toothfish exhibited remarkable shifts in genetic programs towards enhanced fat cell differentiation and lipid storage, and promotion of chondrogenesis while inhibiting osteogenesis in bone development, collectively contributing to the achievement of neutral buoyancy and pelagicism.

Conclusions

Our study revealed a comprehensive landscape of evolutionary changes essential for Antarctic notothenioid cold adaptation and ecological expansion. The 2 genomes are valuable resources for further exploration of mechanisms underlying the spectacular notothenioid radiation in the coldest marine environment.

Chondrostean sturgeon hepcidin: An evolutionary link between teleost and tetrapod hepcidins

Hepcidin, a cysteine-rich antimicrobial peptide (AMP), plays key roles as a regulatory hormone in iron homeostasis, providing a link between iron metabolism and innate immunity. Unlike many other AMPs displaying a high degree of sequence variability among closely related organisms, hepcidin is highly conserved from teleosts to mammals. However, little is known about the early ancestry of hepcidins in the vertebrate lineage. Here, we first report potential a prototype hepcidin from the Siberian sturgeon Acipenser baerii, a primitive chondrostean species. The A. baerii hepcidin (AbHAMP) gene showed a tripartite exon-intron organization, which encoded a precursor protein comprised of three structural signatures containing eight cysteine residues, a common structure in vertebrate hepcidin genes and proteins. mRNA expression by iron-overloading and bacterial infection and antibacterial activity revealed that AbHAMP might play a role in iron metabolism regulator in the liver, and in direct and/or indirect host immune response in the kidney against invading pathogen. Comparison of gene and protein sequences reveled that AbHAMP possesses intermediate characteristics between tetrapodian and teleostean hepcidins (HAMP1s). Phylogenetically, AbHAMP had a closer genetic affiliation to tetrapodian orthologs than to teleostean orthologs, suggesting that the structures of this chondrostean hepcidin may closely reflect the structures of an evolutionarily ancestral form that might have evolved into extant hepcidins in tetrapods and teleosts, respectively. Based on the identification of hepcidin from the chondrostean group, the emergence of the common ancestral hepcidin should be traced back to in early Osteichthyes: no later than sarcopterygian (lobe-finned fishes) - actinopterygian (ray-finned fishes) split.

Identification and expression of the hepcidin gene from brown trout (Salmo trutta) and functional analysis of its synthetic peptide

Hepcidin, a hepatic antimicrobial peptide, is a key player of the nonspecific immune system. The structure of hepcidin gene from brown trout (Bthepc) has been characterized at the molecular level. The 1158-bp mRNA generates a coding sequence (CDS) of 267 bp, which encodes an 88-amino acid protein. Molecular evolution analysis classified Bthepc to the family Salmonidae. Amino acid sequence homologies between Bthepc and hepcidin in other species such as Oncorhynchus mykiss, Salmo salar, and Hucho taimen were found to be 93.18%, 96.59%, and 92.05% respectively. The mature peptide and the signal peptide of Bthepc are made of 25 and 24 amino acids, respectively. Similar to the other species, eight conserved cysteines in the mature peptide of Bthepc are held together by four disulphide bonds. Expression profiling of Bthepc indicated its highest expression in the liver. Further, iron levels or inflammation did not induce the age-dependent expression of Bthepc. Bthepc mRNA expression analysis in six immune tissues (liver, gill, spleen, skin, head kidney and intestine) indicated different levels of increase when challenged with Aeromonas salmonicida and Aeromonas hydrophila. The antimicrobial activity of synthetic Bthepc to typical pathogens was verified in vitro. In addition, Bthepc showed moderate haemolytic activity to mammalian erythrocytes. The antimicrobial activity of Bthepc was attributed to the disruption of the bacterial outer membrane integrity, which was evident from our scanning electron microscopy results. In summary, hepcidin gene of brown trout was characterized, and its antimicrobial activity was verified on different levels.

Hepcidin cDNA evolution in vertebrates

Hepcidin, belonging to the β-defensin family, was isolated for the first time from plasma and human urine. It is a cationic peptide, rich in cysteine bound with four disulfide bridges, which plays a major role in innate immunity and iron homeostasis. Some vertebrate species have multiple hepcidin homolog genes and each contains only one copy that functions as an iron regulator except hepcidin sequences in the pigeon (Columba livia). The aim of this chapter is to investigate the molecular evolution of several hepcidin gene from searches of the literature and public genomic databases from 17 different species, all among the vertebrates.

Mudskipper (Boleophthalmus pectinirostris) Hepcidin-1 and Hepcidin-2 Present Different Gene Expression Profile and Antibacterial Activity and Possess Distinct Protective Effect against Edwardsiella tarda Infection

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in fish immunity against pathogens. Most fish species have two or more hepcidin homologs that have distinct functions. This study investigated the immune functions of mudskipper (Boleophthalmus pectinirostris) hepcidin-1 (BpHep-1) and hepcidin-2 (BpHep-2) in vitro and in vivo. Upon infection with Edwardsiella tarda, the expression of BpHep-1 and BpHep-2 mRNA in immune tissues was significantly upregulated, but the expression profiles were different. Chemically synthesized BpHep-1 and BpHep-2 mature peptides exhibited selective antibacterial activity against various bacterial species, and BpHep-2 exhibited a stronger antibacterial activity and broader spectrum than BpHep-1. BpHep-1 and BpHep-2 both inhibited the growth of E. tarda in vitro, with the latter being more effective than the former. In addition, both peptides induced hydrolysis of purified bacterial genomic DNA (gDNA) or gDNA in live bacteria. In vivo, an intraperitoneal injection of 1.0 μg/g BpHep-2 significantly improved the survival rate of mudskippers against E. tarda infection compared with 0.1 μg/g BpHep-2 or 0.1 and 1.0 μg/g BpHep-1. Similarly, only BpHep-2 treatment effectively reduced the tissue bacterial load in E. tarda-infected mudskippers. Furthermore, treatment with 1.0 or 10.0 μg/ml BpHep-2 promoted the phagocytic and bactericidal activities of mudskipper monocytes/macrophages (MO/MФ). However, only the highest dose (10.0 μg/ml) of BpHep-1 enhanced phagocytosis, and BpHep-1 exerted no obvious effects on bactericidal activity. In conclusion, BpHep-2 is a stronger bactericide than BpHep-1 in mudskippers, and acts not only by directly killing bacteria but also through an immunomodulatory function on MO/MФ.

Characterization, expression, and functional analysis of the hepcidin gene from Brachymystax lenok

Hepcidin, a cysteine-rich antimicrobial peptide, is an important effector molecule in the innate immune system. Recently, Brachymystax lenok has become to be a valuable cold-water fish in China, particularly as the wild resources are rapidly declining. In this study, the hepcidin gene of Brachymystax lenok (Blhepc) has been cloned. The 870-bp mRNA contains a coding sequence (CDS) of 267 bp that encodes 88 amino acid residues. Amino acid sequence identities of Blhepc with hepcidin in Oncorhynchus mykiss, Salmo salar, and Hucho taimen were found to be 93.18%, 89.77% and 93.18%, respectively. Phylogenetic analysis indicated that Blhepc was clustered in the family Salmonidae. The putative signal peptide and the mature peptide contained 24 and 25 amino acid residues, respectively. The RXXR motif for recruitment of propeptide convertase was identified upstream of the mature peptide of Blhepc by sequence analysis. The N-terminal amino acid residues of the mature Blhepc peptide were Q-SH-L, a structure involved in regulating iron metabolism. Eight conserved cysteine residues in the mature peptide were held together by four disulfide bonds. Expression profiling of Blhepc indicated its highest level in the liver; its expression was stronger in males than in similar-aged females. Moreover, its expression in the liver increased significantly with age. Expression of Blhepc in six immune tissues showed increase in various degrees when challenged with Aeromonas salmonicida and Aeromonas hydrophila. A synthetic Blhepc mature peptide was validated to have significant antimicrobial activity against gram-negative and gram-positive bacteria and fungi in vitro. These results show that Blhepc may be an important component in the innate immunity of Brachymystax lenok, which could provide antimicrobial activities against invading pathogens.

Molecular characterization of a hepcidin homologue in starry flounder (Platichthys stellatus) and its synergistic interaction with antibiotics

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in host immunity against pathogenic organisms. Most fish hepcidins exert bactericidal activities against a wide range of pathogens. In this study, we identified a cDNA sequence encoding a hepcidin homologue (PsHepcidin) in the starry flounder Platichthys stellatus. The predicted amino acid sequence of PsHepcidin comprises a signal peptide and a prodomain, which are followed by the mature peptide. Sequence analysis revealed that PsHepcidin belongs to the fish HAMP2 cluster and that it is closely related to mudskipper hepcidin-2. Expression of PsHepcidin mRNA was detected in all examined immune-related tissues, with the highest transcript levels being found in the liver. In response to lipopolysaccharide treatment, PsHepcidin was significantly up-regulated in the liver, kidney, and spleen in a time-dependent manner. Chemically synthesized mature peptides of PsHepcidin were found to exhibit broad antimicrobial activity in vitro. We also investigated the combined effect of PsHepcidin and conventional antibiotics and found that these combinations showed synergistic effects against most of the examined bacterial strains. Collectively, the results of this study indicate that PsHepcidin exhibits potent antibacterial activity both independently and when used in combination with conventional antibiotics.

Nutritional Immunity Triggers the Modulation of Iron Metabolism Genes in the Sub-Antarctic Notothenioid Eleginops maclovinus in Response to Piscirickettsia salmonis

Iron deprivation is a nutritional immunity mechanism through which fish can limit the amount of iron available to invading bacteria. The aim of this study was to evaluate the modulation of iron metabolism genes in the liver and brain of sub-Antarctic notothenioid Eleginops maclovinus challenged with Piscirickettsia salmonis. The specimens were inoculated with two P. salmonis strains: LF-89 (ATCC^® VR-1361™) and Austral-005 (antibiotic resistant). Hepatic and brain samples were collected at intervals over a period of 35 days. Gene expression (by RT-qPCR) of proteins involved in iron storage, transport, and binding were statistically modulated in infected fish when compared with control counterparts. Specifically, the expression profiles of the transferrin and hemopexin genes in the liver, as well as the expression profiles of ferritin-M, ferritin-L, and transferrin in the brain, were similar for both experimental groups. Nevertheless, the remaining genes such as ferritin-H, ceruloplasmin, hepcidin, and haptoglobin presented tissue-specific expression profiles that varied in relation to the injected bacterial strain and sampling time-point. These results suggest that nutritional immunity could be an important immune defense mechanism for E. maclovinus against P. salmonis injection. This study provides relevant information for understanding iron metabolism of a sub-Antarctic notothenioid fish.

Coordination of Bactericidal and Iron Regulatory Functions of Hepcidin in Innate Antimicrobial Immunity in a Zebrafish Model

Hepcidin acts as both an antimicrobial peptide and a hormonal regulator of iron homeostasis; however, the biological significance of this dual-function in immune reactions remains elusive. In this study, we provide experimental evidence regarding the coordination of this dual-function in the innate antimicrobial immunity using a zebrafish model. The transcription of hepcidin gene was significantly upregulated in liver by Aeromonas hydrophila (A.h) DNA stimulation, which was accompanied by an increase of hepcidin protein and a decrease of iron concentration in serum. Thus, an enhanced bactericidal activity against A.h and Escherichia coli and inhibitory effects on A.h growth and OmpA expression were observed in A.h cells, the latter of which made the bacterium more susceptible to complement attack. The enhanced bacteriostatic activities in serum following the stimulation were dramatically impaired by neutralizing hepcidin or restoring iron to the samples. Immuno-protection assay showed that zebrafish administrated with A.h DNA or designed CpG-ODNs had a significantly enhanced defence against A.h and Vibrio alginolyticus infections, which was also eliminated by the neutralization of hepcidin. Results indicate that the induction of hepcidin leads to the decrease of iron in circulation, which eventually limits iron availability to invading microorganisms, thus contributing to host defence.

Molecular Characterisation of a Novel Isoform of Hepatic Antimicrobial Peptide, Hepcidin (Le-Hepc), from Leiognathus equulus and Analysis of Its Functional Properties In Silico

Hepcidin represents a family of cysteine-rich antimicrobial peptides that are mainly expressed in the liver of living organisms. In this study, we have identified and characterised a novel isoform of hepcidin from the common pony fish, Leiognathus equulus (Le-Hepc). A 261-bp fragment cDNA coding for 86 amino acids was obtained. Homologous analysis showed that Le-Hepc belongs to the hepcidin super family and shares sequence identity with other known fish pre-propeptide hepcidin sequences. The ORF encodes for a 24-amino acid (aa) signal peptide coupled to a 36-aa prodomain followed by a 26-aa mature peptide. The mature peptide region has a calculated molecular weight of 2.73 kDa, a net positive charge of +2 and a theoretical pI of 8.23. Phylogenetic analysis of Le-Hepc showed a strong relationship with other fish hepcidin sequences and clustered into HAMP2 group hepcidins. Secondary structural analysis indicated that Le-Hepc mature peptide contains two antiparallel β-sheets strengthened by four disulphide bonds formed by eight conserved cysteine residues. The physicochemical properties of the peptide and its structural parameters are in agreement with characteristic features of an antimicrobial peptide. This is the first report of an antimicrobial peptide from the common pony fish, L. equulus.

Neofunctionalization of zona pellucida proteins enhances freeze-prevention in the eggs of Antarctic notothenioids

The mechanisms by which the eggs of the Antarctic notothenioid fishes avoid freezing are not fully understood. Zona pellucida proteins (ZPs) are constituents of the chorion which forms a protective matrix surrounding the egg. Here we report occurrence of freezing temperature-related gene expansion and acquisition of unusual ice melting-promoting (IMP) activity in a family of Antarctic notothenioid ZPs (AnnotoZPs). Members of AnnotoZPs are shown to bind with ice and non-colligatively depress the melting point of a solution in a range of 0.26 to 0.65 °C at a moderate concentration. Eggs of zebrafishes expressing an AnnotoZP transgene show improved melting point depression and enhanced survival in freezing conditions. Mutational analyses in a representative AnnotoZP indicate the ZP domain and patches of acidic residues are essential structures for the IMP activity. AnnotoZPs, therefore, represent a group of macromolecules that prevent freezing by a unique ZP-ice interaction mechanism distinct from the known antifreeze proteins.

Expansion of capacities for iron transport and sequestration reflects plasma volumes and heart mass among white-blooded notothenioid fishes

The family Channichthyidae or “icefishes” (suborder Notothenioidei) represents the only vertebrates lacking hemoglobin (Hb) as adults. Several icefish species also do not express cardiac myoglobin (Mb). We address how levels of proteins involved in iron (Fe) processing (transport, sequestration, and export) vary among white- and red-blooded notothenioids, and whether absence of Hb and/or Mb in channichthyids is accompanied by expansion of contents of Fe-binding proteins to protect against unchaperoned Fe. Levels of transferrin (Tf), ferritin (Ft), ceruloplasmin (Cp), and non-heme Fe were quantified in plasma, serum, and/or nonhematopoietic tissues (cardiac ventricle, skeletal muscle, and liver) from species of white-blooded ( Chaenocephalus aceratus, Champsocephalus gunnari, Chionodraco rastrospinosus, Pseudochaenichthys georgianus) (the first two species not expressing Mb) and red-blooded ( Notothenia coriiceps, Gobionotothen gibberifrons) notothenioids. We also measured levels of ascorbate (Asc), a mediator of Fe uptake. While plasma concentrations of Tf and tissue levels of Asc are similar among species, concentrations of plasma Asc are lower in white-blooded species. Concentrations of Ft and non-heme Fe and activities of Cp are also generally reduced in icefishes compared with red-blooded notothenioids. The presence of cardiac Mb in some icefish species does not appear to influence levels of proteins involved in Fe processing. To address further the question of Fe sequestration within a physiological context, we account for well-characterized differences in blood volume and heart mass among white- and red-blooded notothenioids. We report that total contents of plasma Tf are greater, while ventricle non-heme Fe is at least at parity in white- vs. red-blooded species.

Identification of prohormones and pituitary neuropeptides in the African cichlid, Astatotilapia burtoni

Background

Cichlid fishes have evolved remarkably diverse reproductive, social, and feeding behaviors. Cell-to-cell signaling molecules, notably neuropeptides and peptide hormones, are known to regulate these behaviors across vertebrates. This class of signaling molecules derives from prohormone genes that have undergone multiple duplications and losses in fishes. Whether and how subfunctionalization, neofunctionalization, or losses of neuropeptides and peptide hormones have contributed to fish behavioral diversity is largely unknown. Information on fish prohormones has been limited and is complicated by the whole genome duplication of the teleost ancestor. We combined bioinformatics, mass spectrometry-enabled peptidomics, and molecular techniques to identify the suite of neuropeptide prohormones and pituitary peptide products in Astatotilapia burtoni, a well-studied member of the diverse African cichlid clade.

Results

Utilizing the A. burtoni genome, we identified 148 prohormone genes, with 21 identified as a single copy and 39 with at least 2 duplicated copies. Retention of prohormone duplicates was therefore 41 %, which is markedly above previous reports for the genome-wide average in teleosts. Beyond the expected whole genome duplication, differences between cichlids and mammals can be attributed to gene loss in tetrapods and additional duplication after divergence. Mass spectrometric analysis of the pituitary identified 620 unique peptide sequences that were matched to 120 unique proteins. Finally, we used in situ hybridization to localize the expression of galanin, a prohormone with exceptional sequence divergence in cichlids, as well as the expression of a proopiomelanocortin, prohormone that has undergone an additional duplication in some bony fish lineages.

Conclusion

We characterized the A. burtoni prohormone complement. Two thirds of prohormone families contain duplications either from the teleost whole genome duplication or a more recent duplication. Our bioinformatic and mass spectrometric findings provide information on a major vertebrate clade that will further our understanding of the functional ramifications of these prohormone losses, duplications, and sequence changes across vertebrate evolution. In the context of the cichlid radiation, these findings will also facilitate the exploration of neuropeptide and peptide hormone function in behavioral diversity both within A. burtoni and across cichlid and other fish species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2914-9) contains supplementary material, which is available to authorized users.

Transcriptomic responses to low temperature stress in the Manila clam, Ruditapes philippinarum

The Manila clam, Ruditapes philippinarum, is an economically important shellfish in marine aquaculture, with a broad thermal tolerance. The ability to cope with cold stress is quite important for the survival of aquatic species under natural conditions. A cold-tolerant clam that can survive the winter at temperatures below 0 °C might extend our understanding of the mechanisms underlying the response to cold stress. In this study, the transcriptional response of the Manila clam to cold stress (-1 °C) was characterized using RNA sequencing. The transcriptomes of a cold-treatment (O) group of clams, which survived under cold stress, and the control group (OC2), which was not subjected to cold stress, were sequenced with the Illumina HiSeq platform. In all, 148,593 unigenes were generated. Compared with the unigene expression profile of the control group, 1760 unigenes were up regulated and 2147 unigenes were down regulated in the O group. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that signal transduction, mitochondrial metabolism, cellular component organization or biogenesis, and energy production processes were the most highly enriched pathways among the genes that were differentially expressed under cold stress. All these pathways could be assigned to the following biological functions in the cold-tolerant Manila clam: signal response to cold stress, antioxidant response, cell proliferation, and energy production.

The New Antimicrobial Peptide SpHyastatin from the Mud Crab Scylla paramamosain with Multiple Antimicrobial Mechanisms and High Effect on Bacterial Infection

SpHyastatin was first identified as a new cationic antimicrobial peptide in hemocytes of the mud crab Scylla paramamosain. Based on the amino acid sequences deduced, it was predicted that this peptide was composed of two different functional domains, a proline-rich domain (PRD) and a cysteine-rich domain (CRD). The recombinant product of SpHyastatin displayed potent antimicrobial activities against the human pathogen Staphylococcus aureus and the aquatic animal pathogens Aeromonas hydrophila and Pseudomonas fluorescens. Compared with the CRD of SpHyastatin, the PRD presented better antimicrobial and chitin binding activities, but both regions were essential for allowing SpHyastatin complete antimicrobial activity. The binding properties of SpHyastatin to different microbial surface molecules suggested that this might be an initial and crucial step for performing its antimicrobial activities. Evaluated using propidium iodide uptake assays and scanning electron microscopy images, the antimicrobial mechanism of SpHyastatin was found to be prone to disrupt cell membrane integrity. Interestingly, SpHyastatin exerted its role specifically on the surface of S. aureus and Pichia pastoris whereas it directly killed P. fluorescens through simultaneous targeting the membrane and the cytoplasm, indicating that SpHyastatin could use different antimicrobial mechanisms to kill different species of microbes. As expected, the recombinant SpHyastatin increased the survival rate of crabs challenged with Vibrio parahaemolyticus. In addition, SpHyastatin could modulate some V. parahaemolyticus-responsive genes in S. paramamosain.

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.

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.

Antimicrobial activity of trout hepcidin

Hepcidin is an antimicrobial peptide and a hormone produced mostly the liver. It is a cysteine-rich peptide with a highly conserved β-sheet structure. Recently, we described the hepcidin expression in liver of rainbow trout and its inducibility by iron overloading and lipopolysaccharide (LPS). Thus, in this work, we focused in analyzing the importance of the peptide conformation associated to its oxidative state in the antimicrobial activity. This peptide showed a α-helix conformation in reduced state and the characteristic β-sheet conformation in the oxidized state. Antimicrobial activity assays showed that the oxidized peptide is more effective than the reduced peptide against Escherichia coli and the important salmon fish pathogen Piscirickettsia salmonis. In addition, confocal analysis of P. salmonis culture exposed to trout hepcidin coupled with rhodamine revealed the intracellular location of this peptide and Sytox permeation assay showed that membrane disruption is not the mechanism of its antimicrobial action. Moreover, a conserved ATCUN motif was detected in the N-terminus of this peptide. This sequence has been described as a small metal-binding site that has been implicated in DNA cleavage. In this work we proved that this peptide is able to induce DNA hydrolysis in the presence of ascorbate and CuCl2. When the same experiments were carried out using a variant with truncated N-terminus no DNA hydrolysis was observed. Our results suggest that correct folding of hepcidin is required for its antimicrobial activity and most likely the metal-binding site (ATCUN motif) present in its N-terminus is involved in the oxidative damage to macromolecules.

Antimicrobial peptides from fish

Antimicrobial peptides (AMPs) are found widely distributed through Nature, and participate in the innate host defense of each species. Fish are a great source of these peptides, as they express all of the major classes of AMPs, including defensins, cathelicidins, hepcidins, histone-derived peptides, and a fish-specific class of the cecropin family, called piscidins. As with other species, the fish peptides exhibit broad-spectrum antimicrobial activity, killing both fish and human pathogens. They are also immunomodulatory, and their genes are highly responsive to microbes and innate immuno-stimulatory molecules. Recent research has demonstrated that some of the unique properties of fish peptides, including their ability to act even in very high salt concentrations, make them good potential targets for development as therapeutic antimicrobials. Further, the stimulation of their gene expression by exogenous factors could be useful in preventing pathogenic microbes in aquaculture.

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.

Genome evolution in the cold: Antarctic icefish muscle transcriptome reveals selective duplications increasing mitochondrial function

Antarctic notothenioids radiated over millions of years in subzero waters, evolving peculiar features, such as antifreeze glycoproteins and absence of heat shock response. Icefish, family Channichthyidae, also lack oxygen-binding proteins and display extreme modifications, including high mitochondrial densities in aerobic tissues. A genomic expansion accompanying the evolution of these fish was reported, but paucity of genomic information limits the understanding of notothenioid cold adaptation. We reconstructed and annotated the first skeletal muscle transcriptome of the icefish Chionodraco hamatus providing a new resource for icefish genomics (http://compgen.bio.unipd.it/chamatusbase/, last accessed December 12, 2012). We exploited deep sequencing of this energy-dependent tissue to test the hypothesis of selective duplication of genes involved in mitochondrial function. We developed a bioinformatic approach to univocally assign C. hamatus transcripts to orthology groups extracted from phylogenetic trees of five model species. Chionodraco hamatus duplicates were recorded for each orthology group allowing the identification of duplicated genes specific to the icefish lineage. Significantly more duplicates were found in the icefish when transcriptome data were compared with whole-genome data of model species. Indeed, duplicated genes were significantly enriched in proteins with mitochondrial localization, involved in mitochondrial function and biogenesis. In cold conditions and without oxygen-carrying proteins, energy production is challenging. The combination of high mitochondrial densities and the maintenance of duplicated genes involved in mitochondrial biogenesis and aerobic respiration might confer a selective advantage by improving oxygen diffusion and energy supply to aerobic tissues. Our results provide new insights into the genomic basis of icefish cold adaptation.

Molecular cloning, recombinant expression, and antimicrobial activity of EC-hepcidin3, a new four-cysteine hepcidin isoform from Epinephelus coioides

Hepcidin, a cysteine-rich antimicrobial peptide, is widespread in fish and shows multiple activities, including antimicrobial, antivirus, and antitumor. Here, a new four-cysteine hepcidin isoform gene, EC-hepcidin3, was cloned from the marine-cultured orange-spotted grouper (Epinephelus coioides). The complete cDNA sequence consisted of 603 bases with an open reading frame (ORF) of 270 bases. The genomic DNA sequence was composed of two introns and three exons, and its 312-bp upstream region had multiple putative transcription factor binding sites. Soluble recombinant protein EC-proHep3 containing a His-tag at the C-terminus was obtained from expression plasmid pET-28a/EC-proHep3 in Escherichia coli Rosetta. It was purified by immobilized metal affinity chromatography (IMAC), and it showed antibacterial activity in vitro. Kinetic studies indicated that recombinant EC-proHep3 has strong, rapid activity against Staphylococcus aureus and Pseudomonas stutzeri. The results indicate that EC-hepcidin3 might be an effective component in the innate immune system of groupers.

Genomic characterization, phylogeny and gene regulation of g-type lysozyme in sole (Solea senegalensis)

The g-type lysozyme is a key protein of the innate immune system to fight bacterial infections. In this study we cloned and characterized the gene encoding for g-type lysozyme in Senegalese sole (Solea senegalensis). The deduced amino acid sequence comprised 195 residues containing the three conserved catalytic residues and two cysteines. A BAC analysis revealed that the gene is structured in 5 exons and 4 introns. Also, two polyadenylation signals that generate two cDNAs differing in 3'-UTR length were detected. Promoter analysis showed the presence of the main cis-acting elements involved in the transcriptional regulation of the gene. At genomic level, the g-type lysozyme was associated with mucolipin 1 and the peptidoglycan recognition protein 2 conforming a cluster of antidefensive genes with a well-conserved synteny across Percomorpha. FISH analysis using the BAC clone revealed a single hybridization signal located in an acrocentric chromosome pair. The phylogenetic analysis confirmed that the g-type lysozyme represents a complex group in fish that has been shaped by gene duplications and diversification with several positions under Darwinian selection. Expression analysis in juvenile tissues indicated that transcript levels were higher in gills, spleen and heart. During development, gene expression activated just at the beginning of metamorphosis, increasing progressively until climax. Hormonal treatments demonstrated that this gene was regulated positively by thyroid hormones during development and negatively by dexamethasone. In contrast, no response was observed after all-trans retinoic acid or 4-diethylaminobenzaldehyde treatments. Finally, treatments using lipopolysaccharide, lipoteichoic acid, peptidoglycan, zymosan and poly(I:C) activated gene expression in a time- and tissue-specific manner. Taken together, data indicate that g-type lysozyme is a high evolutionary conserved gene that diversified to adapt to changing environment and pathogen conditions. Gene expression can be activated by diverse pathogen stimuli and modulated by physiological factors with important consequences for the aquaculture of this species.

A fish antimicrobial peptide, tilapia hepcidin TH2-3, shows potent antitumor activity against human fibrosarcoma cells

As part of a continuing search for potential anticancer drug candidates from antimicrobial peptides of marine organisms, tilapia (Oreochromis mossambicus) hepcidin TH2-3 was evaluated in several tumor cell lines. The results indicated that TH2-3, a synthetic 20-mer antimicrobial peptide, specifically inhibited human fibrosarcoma cell (HT1080 cell line) proliferation and migration. The way in which TH2-3 inhibited HT1080 cell growth was then studied. TH2-3 inhibited HT1080 cell growth in a concentration-dependent manner according to an MTT analysis, which was confirmed by a soft-agar assay and AO/EtBr staining. Scanning electron microscopy revealed that TH2-3 caused lethal membrane disruption in HT1080 cancer cells, and a wound healing assay supported that TH2-3 decreased the migration of HT1080 cells. In addition, c-Jun mRNA expression was downregulated after treatment with TH2-3 for 48-96 h compared to the untreated group. These findings suggest a mechanism of cytotoxic action of TH2-3 and indicate that TH2-3 may be a promising chemotherapeutic agent against human fibrosarcoma cells.

Cloning and expression of a hepcidin gene from a marine fish (Pseudosciaena crocea) and the antimicrobial activity of its synthetic peptide

Hepcidin gene is widely expressed in various fish, suggesting that this antimicrobial peptide is a very important component in the innate immune system. Large yellow croaker (Pseudosciaena crocea) is one of the important economic species of marine-cultured fish but knowledge of its innate immune mechanism is lacking. In this study, we characterize a P. crocea hepcidin gene named as PC-hepc. It consists of an open reading frame of 258 bases encoding 85 amino acids and has a conserved sequence in common with other known hepcidins. The genomic DNA of PC-hepc contains three exons and two introns, the same organization as other reported hepcidins, indicating that PC-hepc is one member of the hepcidin family in fish. The tissue-specific expression of PC-hepc gene in normal fish and the expression pattern in LPS-challenged fish at the time course of stimulation were investigated. The expression of PC-hepc mRNA was significantly increased in the spleen, heart and stomach but not significantly induced in the liver after LPS challenge. An interesting finding is the demonstration of high amounts of PC-hepc transcripts in the kidney in normal fish and their maintenance through 48h exposure to LPS challenge. The synthetic PC-hepc demonstrated a rather wide spectrum of antimicrobial activity in vitro against bacteria and fungi tested, and particularly showed strong activity against the principal fish pathogens, Aeromonas hydrophila, Vibrio parahaemloyticus, Vibrio alginolyticus and Vibrio harvryi. The study indicates that PC-hepc may play a role with a tissue-specific mode in the innate immunity of P. crocea.

Transcriptomic and genomic evolution under constant cold in Antarctic notothenioid fish

The antifreeze glycoprotein-fortified Antarctic notothenioid fishes comprise the predominant fish suborder in the isolated frigid Southern Ocean. Their ecological success undoubtedly entailed evolutionary acquisition of a full suite of cold-stable functions besides antifreeze protection. Prior studies of adaptive changes in these teleost fishes generally examined a single genotype or phenotype. We report here the genome-wide investigations of transcriptional and genomic changes associated with Antarctic notothenioid cold adaptation. We sequenced and characterized 33,560 ESTs from four tissues of the Antarctic notothenioid Dissostichus mawsoni and derived 3,114 nonredundant protein gene families and their expression profiles. Through comparative analyses of same-tissue transcriptome profiles of D. mawsoni and temperate/tropical teleost fishes, we identified 177 notothenioid protein families that were expressed many fold over the latter, indicating cold-related up-regulation. These up-regulated gene families operate in protein biosynthesis, protein folding and degradation, lipid metabolism, antioxidation, antiapoptosis, innate immunity, choriongenesis, and others, all of recognizable functional importance in mitigating stresses in freezing temperatures during notothenioid life histories. We further examined the genomic and evolutionary bases for this expressional up-regulation by comparative genomic hybridization of DNA from four pairs of Antarctic and basal non-Antarctic notothenioids to 10,700 D. mawsoni cDNA probes and discovered significant to astounding (3- to >300-fold, P < 0.05) Antarctic-specific duplications of 118 protein-coding genes, many of which correspond to the up-regulated gene families. Results of our integrative tripartite study strongly suggest that evolution under constant cold has resulted in dramatic genomic expansions of specific protein gene families, augmenting gene expression and gene functions contributing to physiological fitness of Antarctic notothenioids in freezing polar conditions.