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Insulin is a key hormone for the regulation of metabolism in vertebrates. Insulin is produced by pancreatic islet cells in response to elevated glucose levels and leads to the uptake of glucose by tissues such as liver and adipose tissue to store energy. Insulin also has additional functions in regulating development. Previous work has shown that the proglucagon gene, which encodes hormones counter regulating insulin, is duplicated in teleost fish, and that the peptide hormones encoded by these genes have diversified in function. I sought to determine whether similar processes have occurred to insulin genes in these species. Searches of fish genomes revealed an unexpected diversity of insulin genes. A triplication of the insulin gene occurred at the origin of teleost fish, however one of these three genes, insc, has been lost in most teleost fish lineages. The two other insulin genes, insa and insb, have been retained but show differing levels of selective constraint suggesting that they might have diversified in function. Intriguingly, a duplicate copy of the insa gene, which I named insab, is found in many fish. The coding sequence encoded by insab genes is under weak selective constraint, with its predicted protein sequences losing their potential to be processed into a two-peptide hormone. However, these sequences have retained perfectly conserved cystine residues, suggesting that they maintain insulin's three-dimensional structure and therefore might modulate the processing and secretion of insulin produced by the other genes. [ABSTRACT FROM AUTHOR]

Orexin A (OXA) and neuropeptide Y (NPY) are two hypothalamic neuropeptides involved in the regulation of feeding behavior and food intake in all vertebrates. Accumulating evidences document that they undergo age‐related modifications, with consequences on metabolism, sleep/wake disorders and progression of neurodegenerations. The present study addressed the age related changes in expression and distribution of orexin A (its precursor is also known as hypocretin—HCRT) and NPY, and their regulation by food intake in the short‐lived vertebrate model Nothobranchius furzeri. Our experiments, conducted on male specimens, show that: (a) HCRT and OXA and NPY mRNA and protein are localized in neurons of diencephalon and optic tectum, as well as in numerous fibers projecting through the entire neuroaxis, and are colocalized in specific nuclei; (b) in course of aging, HCRT and NPY expressing neurons are localized also in telencephalon and rhombencephalon; (c) HCRT expressing neurons increased slightly in the diencephalic area of old animals and in fasted animals, whereas NPY increased sharply; (d) central HCRT levels are not regulated neither in course of aging nor by food intake; and (e) central NPY levels are augmented in course of aging, and regulated by food intake only in young. These findings represent a great novelty in the study of central orexinergic and NPY‐ergic systems in vertebrates', demonstrating an uncommon and unprecedented described regulation of these two orexigenic neuropeptides. The central regulation of the two orexigenic hypothalamic neuropeptides, orexin A (and its precursor hypocretin—HCRT) and neuropeptide Y (NPY), was investigated in the short‐lived annual killifish Nothobranchius furzeri in course of aging. HCRT levels are not regulated neither in course of aging nor by food intake, whereas NPY levels are augmented in course of aging, and regulated by food intake only in young. These findings represent a great novelty in the study of central orexinergic and NPY‐ergic systems in vertebrates', and demonstrate an uncommon and unprecedented described regulation of these two orexigenic neuropeptides. [ABSTRACT FROM AUTHOR]

The mitochondrial gene cytochrome c oxidase I (COI) is commonly used for DNA barcoding in animals. However, most of the COI barcode nucleotides are conserved and sequences longer than about 650 base pairs increase the computational burden for species identification. To solve this problem, we propose a decision theory-based COI SNP tagging (DCST) approach that focuses on the discrimination of species using single nucleotide polymorphisms (SNPs) as the variable nucleotides of the sequences of a group of species. Using the example of 126 teleost mackerel fish species (order: Scombriformes), we identified 281 SNPs by alignment and trimming of their COI sequences. After decision rule making, 49 SNPs in 126 fish species were determined using the scoring system of the DCST approach. These COI-SNP barcodes were finally transformed into one-dimensional barcode images. Our proposed DCST approach simplifies the computational complexity and identifies the most effective and fewest SNPs to resolve or discriminate species for species tagging. [ABSTRACT FROM AUTHOR]

Studies using fish fin as a model to understand the nuance of epimorphosis are gaining interest of lately. This study illustrates for the first time the daily changes in the tissue architecture of regenerating tail fin of Poecilia latipinna. Wound epithelium is formed within 24 hpa that eventually gets stratified into apical epithelial cap by 48 hpa. In the subsequent day, proliferating cells accumulate in front of each fin-ray marking the beginning of blastema. Distally these cells express signs of cartilage condensation by 4 dpa. However, ossification and subsequent transformation of actinotrichia to lepidotrichia was observed on 5 dpa. Subsequently, the regenerate grew at variable rate until it achieved the original size on 25 dpa. This result would serve as a worthwhile standard reference for further explorative studies that demand manipulation of a regulatory signal at a defined time point. [ABSTRACT FROM AUTHOR]

• Inhibition of BMP signaling reduced the rate of proliferation and hence, the proper organization of blastema. • BMP signaling regulates the extent of apoptosis during blastema formation. • LDN193189 caused dysregulation of extra cellular matrix remodeling in the regenerating caudal fin. Bone morphogenetic proteins play a pivotal role in the epimorphic regeneration in vertebrates. Blastema formation is central to the epimorphic regeneration and crucially determines its fate. Despite an elaborate understanding of importance of Bone morphogenetic protein signaling in regeneration, its specific role during the blastema formation remains to be addressed. Regulatory role of BMP signaling during blastema formation was investigated using LDN193189, a potent inhibitor of BMP receptors. The study involved morphological observation, in vivo proliferation assay by incorporation of BrdU, comet assay, qRT-PCR and western blot. Blastemal outgrowth was seen reduced due to LDN193189 treatment, typified by dimensional differences, reduced number of proliferating cells and decreased levels of PCNA. Additionally, proapoptotic markers were found to be upregulated signifying a skewed cellular turnover. Further, the cell migration was seen obstructed and ECM remodeling was disturbed as well. These findings were marked by differential transcript as well as protein expressions of the key signaling and regulatory components, their altered enzymatic activities and other microscopic as well as molecular characterizations. Our results signify, for the first time, that BMP signaling manifests its effect on blastema formation by controlling the pivotal cellular processes possibly via PI3K/AKT. Our results indicate the pleiotropic role of BMPs specifically during blastema formation in regulating cell migration, cell proliferation and apoptosis, and lead to the generation of a molecular regulatory map of determinative molecules. [ABSTRACT FROM AUTHOR]

Abstract Teleost fish possess all the necessary elements to mount an adaptive immune response. Despite this, the important physiological and structural differences between the mammalian and the teleost fish immune system, anticipate significant changes regarding how this response is coordinated and executed. B cells are key players in adaptive immune responses through the production of antibodies. However, recent studies performed in mammals and other species including fish point to many additional functions of B cells within both the adaptive and the innate immune system, in many occasions taking part in the crosstalk between these two arms of the immune response. Furthermore, it should be taken into account that fish B cells share many functional and phenotypical features with innate B cell populations from mammals, which will surely condition their response to antigens. Concerning viral infections, although most studies undertaken to date in fish have been focused on characterizing antibody production, some recent studies have demonstrated that fish B cells are able to interact with viruses at different levels. In this sense, in the current review, we have tried to provide an overview of what is currently known regarding the role of teleost B cells in antiviral immunity. Highlights • There are important differences regarding how B cell responses are coordinated and executed in fish compared to mammals. • Fish B cells share many functional and phenotypical features with innate B cell populations from mammals. • Fish B cells seem to directly interact with viruses. • Fish B cells play different roles in the response to viral infections. [ABSTRACT FROM AUTHOR]

Abstract A combination of previous studies and the present study indicated species-specific debromination of polybromodiphenyl ethers (PBDEs) in teleost fish. Three situations of debromination were found, namely rapid debromination represented by debromination of BDE 99 to BDE 47 observed in common carp, tilapia, crucian carp, and oscar fish; slow debromination represented by debromination of BDE 99 to BDE 49 observed in the abovementioned fish and rainbow trout, salmon, and snakehead; and no or minor debromination observed in catfish. The results of experiments on cofactors, inhibitors, and substrate competitors indicated that activities of outer ring deiodinase of 3, 3′, 5′-triiodothyronine (type I deiodinase), which cannot be inhibited by 6-propyl-2-thiouracil, were responsible for the rapid debromination, and the outer ring deiodinase of thyroxine (type II deiodinase) regulated the slow debromination. The debromination of BDE 99 to BDE 49 was more common, but occurred at a much lower rate (approximately 100 times lower) than the debromination of BDE 99 to BDE 47. This was because the activity of type II deiodinase was nearly two orders of magnitude lower than that of type I deiodinase in the fish species studied. Further studies on debromination of PBDEs and properties of deiodinase in more species are needed to confirm the hypothesis. Graphical abstract Image 1 Highlights • Different pathways and rates in PBDE debromination were observed among fish. • Three situations on debromination of PBDE exist among teleost fish. • Slow debromination (BDE 99 to 49) was mainly regulated by type II deiodinases (DI). • Type I DI non-inhibited by PTU was responsible for rapid debromination (BDE99 to 47). • Slow debromination was more common but at much lower extent than rapid debromination. Differences in deiodinase activity among fish species are responsible for the species-specific debromination of PBDEs in teleost fish. [ABSTRACT FROM AUTHOR]

Periods of food deprivation of several months are common events for fishes and in such conditions, fitness will be determined by their capacity to maximize food encounters while minimizing predation risk. In this context, the propensity to take risks and the willingness to associate with conspecifics are particularly important as they contribute to alleviating the trade-off between predation avoidance and foraging efficiency. This study examined to what extent food deprivation modulates fish risk-taking and social behaviours, as well as the relationship between them. To address these issues, juvenile European sea bass were either fed daily with a maintenance ration or food deprived for a period of 3 weeks. Risk taking and sociability were assessed through measurements of fish willingness to explore a novel environment, and to interact with a novel object or a conspecific. Multivariate analysis allowed the identification of three behaviours: risk taking, exploratory activity and solitariness. Food-deprived fish interacted less with conspecifics than control fish; however, no difference in terms of risk taking and exploratory patternswas observed. Finally, the relationship between risk taking and solitariness was influenced by feeding status. When food-deprived, fish with a higher propensity to take risk displayed increased solitariness, while when fed normally, they interacted more with conspecifics. [ABSTRACT FROM AUTHOR]

Why sex chromosomes turn over and remain undifferentiated in some taxa, whereas they degenerate in others, is still an area of ongoing research. The recurrent occurrence of homologous and homomorphic sex chromosomes in distantly related taxa suggests their independent evolution or continued recombination since their first emergence. Fishes display a great diversity of sex-determining systems. Here, we focus on sex chromosome evolution in haplochromines, the most species-rich lineage of cichlid fishes. We investigate sex-specific signatures in the Pseudocrenilabrus philander species complex, which belongs to a haplochromine genus found in many river systems and ichthyogeographic regions in northern, eastern, central, and southern Africa. Using whole-genome sequencing and population genetic, phylogenetic, and read-coverage analyses, we show that one population of P. philander has an XX–XY sex-determining system on LG7 with a large region of suppressed recombination. However, in a second bottlenecked population, we did not find any sign of a sex chromosome. Interestingly, LG7 also carries an XX–XY system in the phylogenetically more derived Lake Malawi haplochromine cichlids. Although the genomic regions determining sex are the same in Lake Malawi cichlids and P. philander, we did not find evidence for shared ancestry, suggesting that LG7 evolved as sex chromosome at least twice in haplochromine cichlids. Hence, our work provides further evidence for the labile nature of sex determination in fishes and supports the hypothesis that the same genomic regions can repeatedly and rapidly be recruited as sex chromosomes in more distantly related lineages. [ABSTRACT FROM AUTHOR]

Background: Diet is a major determinant of intestinal microbiome composition. While studies have evaluated microbiome responses to diet variation, less is understood of how the act of feeding influences the microbiome, independent of diet type. Here, we use the clownfish Premnas biaculeatus, a species reared commonly in ornamental marine aquaculture, to test how the diversity, predicted gene content, and gene transcription of the microbiome vary over a two-day diurnal period with a single daily feeding event. This study used fish fed four times daily, once daily, or every three days prior to the diurnal period, allowing us also to test how feeding frequency affected microbiome diversity. The amount of time between feedings had no affect on baseline diversity of the microbiome. In contrast, the act of feeding itself caused a significant short term change in the microbiome, with microbiome diversity, predicted gene content, and gene transcription varying significantly between time points immediately before and 1.5 hours post feeding. Variation was driven by abundance shifts involving exact sequence variants (ESVs), with one ESV identified as Photobacterium sp. increasing from <0.5% of sequences immediately pre-feeding to 34% at 1.5 hours post-feeding. Other ESVs from a range of microbial groups also increased dramatically after feeding, with the majority also detected in the food. One ESV identified as Clostridium perfringens represented up to 55% of sequences but did not vary significantly over the diurnal period and was not detected in the food. Post-feeding samples were enriched in transcripts and predicted genes for social interactions, cell motility, and coping with foreign DNA, whereas time points farther from feeding were enriched in genes of diverse catabolic and biosynthetic functions. These results confirm feeding as a significant destabilizing force in clownfish intestinal microbiomes, likely due to both input of cells attached to food and stimulation of resident microbes. Microbes such as Photobacterium may episodically transition from environmental reservoirs to growth in the gut, likely in association with food particles. This transition may be facilitated by functions for navigating a new environment and interacting with neighboring microbes and host cells. Other taxa, such as Clostridium, are comparatively stable intestinal members and less likely to be affected by passing food. Conclusions about microbiome ecology may therefore differ based on when samples were collected relative to the last feeding. [ABSTRACT FROM AUTHOR]

Fish immunology research is at a pivotal point with the increasing availability of functional immunoassays and major advances in omics approaches. However, studies on fish B cells and their distinct subsets remain a challenge due to the limited availability of differentially expressed surface markers. To address this constraint, cell surface proteome of Atlantic salmon IgM+ B cells were analyzed by mass spectrometry and compared to surface proteins detected from two adherent salmon head kidney cell lines, ASK and SSP-9. Out of 21 cluster of differentiation (CD) molecules identified on salmon IgM+ B cells, CD22 and CD79A were shortlisted as potential markers based on the reported B cell-specific surface expression of their mammalian homologs. Subsequent RT-qPCR analyses of flow cytometry-sorted subpopulations from head kidney leukocytes confirmed that both cd22 and cd79a genes were highly expressed in IgM+ lymphoid cells but were observed in barely detectable levels in IgM− non-lymphoid suspension and adherent cells. Similarly, significantly high cd22 and cd79a mRNA levels were observed in IgM+ or IgT+ lymphoid cells from the spleen and peritoneal cavity, but not in their corresponding IgM− IgT− non-lymphoid fractions. This suggests that the B cell restrictive expression of CD22 and CD79A extend down to the transcription level, which was consistent across different lymphoid compartments and immunoglobulin isotypes, thus strongly supporting the potential of CD22 and CD79A as pan-B cell markers for salmon. In addition, this study provides novel information on the salmon B cell surface protein repertoire, as well as insights on B cell evolution. Further investigation of the identified salmon CD molecules, including development of immunological tools for detection, will help advance our understanding of the dynamics of salmon B cell responses such as during infection, vaccination, or immunostimulation. [ABSTRACT FROM AUTHOR]

Teleost fish are excellent models to study the phylogeny of the slc34 gene family, Slc34-mediated phosphate (Pi) transport and how Slc34 transporters contribute Pi homeostasis. Fish need to accumulate Pi from the diet to sustain growth. Much alike in mammals, intestinal uptake in fish is partly a paracellular and partly a Slc34-mediated transcellular process. Acute regulation of Pi balance is achieved in the kidney via a combination of Slc34-mediated secretion and/or reabsorption. A great plasticity is observed in how various species perform and combine the different processes of secretion and reabsorption. A reason for this diversity is found in one or two whole genome duplication events followed by potential gene loss; consequently, teleosts exhibit distinctly different repertoires of Slc34 transporters. Moreover, due to habitats with vastly different salinity, teleosts face the challenge of either preserving water in a hyperosmotic environment (seawater) or excreting water in hypoosmotic freshwater. An additional challenge in understanding teleost Pi homeostasis are the genome duplication and retention events that diversified peptide hormones such as parathyroid hormone and stanniocalcin. Dietary Pi and non-coding RNAs also regulate the expression of piscine Slc34 transporters. The adaptive responses of teleost Slc34 transporters to e.g. Pi diets and vitamin D are informative in the context of comparative physiology, but also relevant in applied physiology and aquaculture. In fact, Pi is essential for teleost fish growth but it also exerts significant adverse consequences if over-supplied. Thus, investigating Slc34 transporters helps tuning the physiology of commercially valuable teleost fish in a confined environment. [ABSTRACT FROM AUTHOR]

Immunoglobulins are globulins with antibody activity or antibody-like structures, and fish were the first vertebrates to develop immunoglobulins. There are three major types of immunoglobulins (IgM, IgD and IgZ) in teleost fish, which play an important role in resisting pathogen infection. For fish, the intestinal tract is not only the place for nutrient digestion but also the largest endocrine organ. The intestinal mucosal barrier system can block pathogenic microorganisms and toxins and is important for immunologic defense. Therefore, the study of the molecular mechanism of fish immunoglobulin in intestinal mucosa is of great significance to the selection of immune prevention strategies for fish diseases. At present, information on the immune system of intestinal mucosa in fish is scarce, and there are still many problems in the function of newly identified antibodies, which need further research. In this study, we have summarized current knowledge about the types, gene structure, biological function, and immune response of immunoglobulins in teleost fish, and intestinal mucosal immune tissue of fish. The scientific questions in this field were also presented according to the progress from the latest research in fish immunology. The aim of present study is to provide a theoretical basis for the study of fish immunology. [ABSTRACT FROM AUTHOR]

The dorsal portion of the descending octaval nucleus (dDO), the main first-order auditory nucleus in jawed fish, includes four lateral and three medial neuronal populations that project to the auditory midbrain. One medial population and one lateral population contain neurons that receive a remarkably large axon terminal from the utricular branch of the octaval nerve. Immunocytochemistry for connexin 35 (Cx35) was used to determine whether this connection includes electrical synapses. Although Cx35 was not localized to these large contacts, it was observed in the three other lateral dDO populations. Another first-order nucleus, the dorsal portion of the anterior octaval nucleus (dAO), primitively projects to the auditory midbrain in jawed fishes and contains neurons positive for Cx35. Utricular branch terminals were coincident with some Cx35 puncta in dDO and dAO. The results are discussed in light of what is known about the occurrence of electrical synapses in first-order auditory and vestibular nuclei in fish and tetrapods. [ABSTRACT FROM AUTHOR]

Periods of food deprivation up to several months are common features for fishes and in such conditions, fitness will be determined by their capacity to maximize food encounter while minimizing predation risk. In this context, the propensity to take risk and the willingness to associate with conspecifics are particularly important as they contribute to alleviating the tradeoff between predation avoidance and foraging efficiency. This study examined to what extent food deprivation modulates fish risk-taking and social behaviours, as well as the relationship between them. To address these issues juvenile European sea bass were either fed daily with a maintenance ration or food-deprived during 3 weeks. Risk-taking and sociability were assessed through measurements of fish willingness to explore a novel environment, to interact with a novel object or a conspecific. Multivariate analysis allowed the identification of three behaviours, risk-taking, exploratory activity and solitariness. Food-deprived fish interacted less with conspecifics than control fish. After food-deprivation, no difference in terms of risk-taking and exploratory patterns was observed. Finally, the relationship between risky-taking and solitariness was influenced by the feeding status. When food-deprived fish with higher propensity to take risk displayed increased solitariness while, when fed normally they interacted more with conspecifics. [ABSTRACT FROM AUTHOR]

The number of farmed fish in the world has increased considerably. Aquaculture is a growing industry that will in the future provide a large portion of fishery products. Moreover, in recent years, the number of teleost fish used as animal models for scientific research in both biomedical and ecological fields has increased. Therefore, it is increasingly important to implement measures designed to enhance the welfare of these animals. Currently, a number of European rules exist as requirements for the establishment, care and accommodation of fish maintained for human purposes. As far as (teleost) fish are concerned, the fact that the number of extant species is much greater than that of all other vertebrates must be considered. Of further importance is that each species has its own specific physical and chemical requirements. These factors make it difficult to provide generalized recommendations or requirements for all fish species. An adequate knowledge is required of the physiology and ecology of each species bred. This paper integrates and discusses, in a single synthesis, the current issues related to fish welfare, considering that teleosts are target species for both aquaculture and experimental models in biological and biomedical research. We first focus on the practical aspects, which must be considered when assessing fish welfare in both research and aquaculture contexts. Next, we address husbandry and the care of fish housed in research laboratories and aquaculture facilities in relation to their physiological and behavioural requirements, as well as in reference to the suggestions provided by European regulations. Finally, to evaluate precisely which parameters described by Directive 2010/63/EU are reported in scientific papers, we analysed 82 articles published by European researchers in 2014 and 2015. This review found that there is a general lack of information related to the optimal environmental conditions that should be provided for the range of species covered by this directive. [ABSTRACT FROM AUTHOR]

Abstract The use of anesthetic in fish farming is a traditional practice which aims to reduce the stress caused by transport and handling. However, anesthesia-induction protocols are commonly established and implemented without proper physiological/behavioral evaluation. Additionally, concentration and time of exposure to the anesthetic are often set without considering species-specific responses. The fat snook (Centropomus parallelus) is a fish with great potential for aquaculture. Given its remarkable euryhalinity, it can grow in fresh- or seawater. Most studies on fat snook anesthesia tested natural compounds (essential oils) instead of traditional anesthetics. However, the use of benzocaine is much more common in the commercial sector, as it is easy to obtain and of relatively low cost. The present study aimed at analyzing the effects benzocaine exposure on glucose and cortisol plasma levels (two traditional stress markers in teleost fish), as well as on plasma osmolality, chloride and magnesium, (indicators of osmo-ionic allostasis) in animals acclimated to different salinities. Results showed that while osmo-ionic allostasis was strictly maintained across the treatments, time of anesthesia had a strong positive relationship to plasma cortisol and glucose, regardless the salinity of exposure and acclimation. The results are discussed as they relate to anesthesia protocols and how stress response generated by time of anesthesia may challenge farming flexibility. [ABSTRACT FROM AUTHOR]

Highlights • Evidence for brain systems specialized in defensive behavior in fish are reviewed. • Telencephalic and habenular circuits represent a "high road" for defensive behavior. • Hypothalamic circuits organize neuroendocrine and neurovegetative outputs. • The optic tectum mediate fast escape responses via projections to the central gray and/or the brainstem escape network. Abstract Defensive behavior is a function of specific survival circuits, the "aversive brain system", that are thought to be conserved across vertebrates, and involve threat detection and the organization of defensive responses to reduce or eliminate threat. In mammals, these circuits involve amygdalar and hypothalamic subnuclei and midbrain circuits. The increased interest in teleost fishes as model organisms in neuroscience created a demand to understand which brain circuits are involved in defensive behavior. Telencephalic and habenular circuits represent a "forebrain circuit" for threat processing and organization of responses, being important to mounting appropriate coping responses. Specific hypothalamic circuits organize neuroendocrine and neurovegetative outputs, but are the less well-studied in fish. A "midbrain circuit" is represented by projections to interneurons in the optic tectum which mediate fast escape responses via projections to the central gray and/or the brainstem escape network. Threatening stimuli (especially visual stimuli) can bypass the "high road" and directly activate this system, initiating escape responses. Increased attention to these circuits in an evolutionary framework is still needed. [ABSTRACT FROM AUTHOR]

Applying genome-wide computational-based approaches (using the draft genome sequence published in recent years) and following a set of strict filtering criteria, a total of 48 potentially conserved microRNAs belonging to 30 families were identified from economically important fish tuna (Thunnus orientalis). Using BLAST and RNA hybrid program a total of 19 potential miRNA targets were also identified in this study, which includes a number of signaling molecules (serine/threonine-protein kinase, GTPase activating protein etc.) and transcription factors (F-box protein, zinc finger protein etc.). This study provides the basis for gaining a better understanding of miRNA-mediated gene regulatory processes in fishes. [ABSTRACT FROM AUTHOR]

The adult human heart cannot repair itself after injury and, instead, forms a permanent fibrotic scar that impairs cardiac function and can lead to incurable heart failure. The zebrafish, amongst other organisms, has been extensively studied for its innate capacity to repair its heart after injury. Understanding the signals that govern successful regeneration in models such as the zebrafish will lead to the development of effective therapies that can stimulate endogenous repair in humans. To date, many studies have investigated cardiac regeneration using a reverse genetics candidate gene approach. However, this approach is limited in its ability to unbiasedly identify novel genes and signalling pathways that are essential to successful regeneration. In contrast, drawing comparisons between different models of regeneration enables unbiased screens to be performed, identifying signals that have not previously been linked to regeneration. Here, we will review in detail what has been learnt from the comparative approach, highlighting the techniques used and how these studies have influenced the field. We will also discuss what further comparisons would enhance our knowledge of successful regeneration and scarring. Finally, we focus on the Astyanax mexicanus, an intraspecies comparative fish model that holds great promise for revealing the secrets of the regenerating heart.

Fish are ectothermic and small changes in water temperature could greatly affect reproduction. The two-spotted goby is a small semi-pelagic species that uses visual and acoustic displays to mate. Here, we studied the effect of temperature (16 and 20 °C) on acoustic and visual courtship and associated reproductive success in 39 males. Temperature influenced male visual courtship performed outside the nest, but it did not influence calling rate and the number of laid eggs. Interestingly, the number of sounds (drums) was the sole predictor of spawning success. These findings suggest that exposure to different temperatures within the species' natural range affect courtship behaviour but not its reproductive success. We propose that finding the link between acoustic behaviour and reproduction in fishes offers the opportunity to monitor fish sounds both in the lab and in nature to learn how they respond to environmental changes and human impacts, namely global warming. • We studied the effect of temperature on breeding behaviour in the two-spotted goby. • Temperature affected male visual courtship but did not influence acoustic courtship. • Temperature had no effect on the likelihood of spawning or the number of eggs. • Male acoustic activity (number of drums) was the only predictor of spawning success. • Fish courtship sounds can be used to monitor responses to environmental changes. [ABSTRACT FROM AUTHOR]

There is accumulating evidence demonstrated that long noncoding RNAs (lncRNA) act as gene regulators in various biological processes, including innate immunity, in which lncRNAs could play their regulatory roles by interacting with miRNAs. Compared with mammals, there is little attention paid to the mechanism of the lncRNA-miRNA regulatory network in teleost fish. Herein, we found a long noncoding RNAs LTCONS4500 that could function as a positive regulator of the immune response in miiuy croaker (Miichthys miiuy). Specifically, we found that the expression of LTCONS4500 could be upregulated by gram-negative bacteria, such as Vibrio anguillarum and Vibrio harveyi. Upregulated LTCONS4500 could promote the expression of inflammatory cytokines. Further study showed that LTCONS4500 could act as a competing endogenous RNA (ceRNA) to interact with miR-3570-5p to facilitate MyD88 expression and thus enhance antibacterial immune responses. Our data suggests the function and mechanism of lncRNAs in antibacterial immune responses of teleost fish, which will enrich the gene regulatory network of vertebrates. • Long noncoding RNA LTCONS4500 functions as a positive regulator in antibacterial immune responses of miiuy croaker. • LTCONS4500 has a positive regulatory effect on MyD88. • LTCONS4500 can serve as a competitive endogenous RNA (ceRNA) for miR-3570-5p, promoting antibacterial immune response. [ABSTRACT FROM AUTHOR]

Acute inflammation is crucial to the immune responses of fish. The process protects the host from infection and is central to induction of subsequent tissue repair programs. Activation of proinflammatory signals reshapes the microenvironment within an injury/infection site, initiates leukocyte recruitment, promotes antimicrobial mechanisms and contributes to the resolution of inflammation. Inflammatory cytokines and lipid mediators are primary contributors to these processes. Uncontrolled or persistent induction results in delayed tissue healing. The kinetics by which inducers and regulators of acute inflammation exert their actions is essential for understanding the pathogenesis of fish diseases and identifying potential treatments. Although, a number of these are well-conserved across, others are not, reflecting the unique physiologies and life histories of members of this unique animal group. • Acute inflammation is critical for host protective immune responses. • This process entails immune cell recruitment and release of inflammatory mediators. • Inflammation control is essential to avoid tissue injury. • Many components are well conserved across teleost fish and mammals. • Inflammation is associated with innate and adaptive immune components. [ABSTRACT FROM AUTHOR]

• A novel intergenic lncRNA (linc-93.2) was identified in the head kidney primary macrophages of common carp (Cyprinus carpio) with 3,619 bp full-length. • Linc-93.2 localized to the nucleus of primary macrophages, with the highest expression level in spleen followed by head kidney. • Its expression pattern is similar to majority of the predicted cis- and trans- target genes following lipopolysaccharide (LPS) or bisphenol A (BPA) challenges. • Linc-93.2 was involved in BPA-mediated immunotoxicity via NF-κB and estrogen receptor (ER) pathway. Increasing evidence suggests that long non-coding RNAs (lncRNAs) play pivotal roles in various biological processes. However, current studies on lncRNAs mostly focus on mammalian species, with little research on the functional roles of lncRNAs in teleost fish. Here, we identified a novel intergenic lncRNA (linc-93.2) in the head kidney primary macrophages of common carp (Cyprinus carpio) after exposure to a typical environmental endocrine disrupting chemical, bisphenol A (BPA). As a result, linc-93.2 was more than 3,619 bp in length and predominantly localized to the nucleus of primary macrophages other than cytoplasm, with the highest expression level in spleen followed by head kidney among different organs. Bioinformatic analysis predicted a cis -target gene, dennd1b , and 20 trans -target genes including hsp70, gna13 and rasgap , were potentially regulated by linc-93.2; NFκB and estrogen receptor (ERα) binding sites were located in the promoter region upstream of its transcription start site, which together suggested the involvement of linc-93.2 in immune and neurological functions in fish. Based on that, the expression level of linc-93.2 was determined in macrophages following acute lipopolysaccharide (LPS) and BPA treatments, both of which significantly induced linc-93.2 and IL-1β expression in cells. Moreover, a NF-κB inhibitor PDTC significantly reduced linc-93.2 expression in macrophages, but co-exposure of macrophages to PDTC with BPA or LPS could significantly rescue linc-93.2 expression, consistent with the observation on that LPS or BPA alone significantly induced both linc-93.2 and its target gene expression. Interestingly, linc-93.2 and its target gene expression was significantly suppressed by an ER antagonist ICI 182,780, however, the co-exposure of macrophages to ICI 182,780 with BPA failed to attenuate their declined expression. Overall, the current study demonstrated that linc-93.2, a novel immune-related lncRNA, may participate in the immune processes of common carp macrophages via the NF-κB and ER pathway. The results presented in this study enhance our understanding of the immunotoxin mechanisms of BPA in teleost fish. [ABSTRACT FROM AUTHOR]

Streptococcus agalactiae (Sta) of Lancefield group B is the primary etiological agent of bacterial meningitis in Nile tilapia and newborn humans. Thus, the study of this disease is of fundamental importance for aquaculture and human medicine. Additionally, elucidation of the mechanisms involved in the host–pathogenic response is important for the success of new therapies. In the present study, we elucidated important aspects of the innate immune response in the brain tissue of Nile tilapia (Oreochromis niloticus) infected by Sta. The neuroinflammatory process in the meninges started with the migration of MHC class II and CD68 + cells, production of TNF-alpha, and the effective immune response to Sta was mediated by the increased iNOs+. In conclusion, the present study brings a partial understanding of the pathophysiological and neuroinflammatory mechanisms in meningitis in Sta infected tilapia, enabling important advances in the therapy of this disease as well as the possibility of using this biological model to understand human meningitis.

Infectious pancreatic necrosis virus (IPNv) is a worldwide etiologic agent of one disease that causes severe economic losses in several species of fish, mainly in young salmonids. Its genome consists of two linear double-stranded RNA segments that encode five viral proteins. Teleost fish respond to infectious agents, mainly through the components of innate immunity. This response to viral infections is initiated, conducted, and coordinated by pathogen recognition receptors (PRRs), which can detect the presence of microorganisms through the identification of molecular patterns associated with pathogens (PAMPs). Heterologous PRR molecules have been found in salmonids, even in teleost fish. NOD-like receptors (NLRs) are a multigenic family of cytoplasmic molecules involved in immunity and apoptosis; these receptors have been little studied in fish. However, they have recently been linked to antiviral defense. There is no information that relates the expression of NOD-like receptors with IPNv infection. Thus, the objective of this study was to analyze the gene expression of several members of subfamily A of the NLRs (NOD1, NOD2, NLR-C3, NLR-C5, and NLR-X1) in response to IPNv infection by real-time quantitative PCR (RT-qPCR) and cellular models used in vitro and ex vivo. The expression analysis revealed that CHSE-214 cells, infected with IPNv, show a positive regulation of the NLRs, with the NLRX1 gene being the one with the highest expression. A similar result was obtained when primary cultures of head kidney of rainbow trout were infected with IPNv, but in this case, the most stimulated receptor was found to be NLR-C5. Overall, the results suggest that NLRs could play a key role in the regulation of defense mechanisms of salmonids against viral pathogens and justify the exploration of the precise molecular mechanism related to the immune system of the NLRs in these fish.

Tumor necrosis factor ligand superfamily members such as B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) have been identified in mammals as key regulators of B cell homeostasis and activation. However, the immune functions of APRIL are not as well defined as those of BAFF. Furthermore, while BAFF is present in all vertebrates, APRIL is missing in some animal groups, suggesting that BAFF has compensated the functions of APRIL in these species. In this context, we thought of great interest to explore the effects of APRIL on teleost B cells, given that APRIL appears for the first time in evolution in bony fish. Thus, in this study, we have performed an extensive analysis of the effect of APRIL on B cells using rainbow trout (Oncorhynchus mykiss) as a model species. Our results demonstrate that APRIL induces a specific proliferation of IgM+ B cells by itself and increases IgM secretion without promoting a terminal differentiation to plasma cells. APRIL also increased the levels of surface MHC II and augmented the capacity of these cells to process antigen, effects that were exclusively exerted on IgM+ B cells. Although our results point to a highly conserved role of APRIL on B cell homeostasis and activation throughout evolution, some specific differential effects have been observed in fish in comparison to the effects of APRIL previously described in mammals. Finally, the effects that APRIL induces on rainbow trout IgM+ B cells described in this paper have been compared with those previously reported in response to BAFF.

Lipopolysaccharide (LPS) is the major component of the outer membrane of Gram-negative bacteria. This molecule can induce strong immune response and various biological effects. In mammals, TLR4 can recognize LPS and induce inflammatory response. However, the innate receptor in fish for recognizing LPS remains ambiguous. LPS can invade the cytoplasm via outer membrane vesicles produced by Gram-negative bacteria and could be detected by intracellular receptor caspase-11 in mammals, so, there may also exist the intracellular receptors that can recognize LPS in fish. NOD1 is a member of NOD-like receptors family and can recognize the iE-DAP in the cytoplasm in mammals. In fish, NOD1 can also respond to infection of Gram-negative bacteria and may play an important role in the identification of bacterial components. In this study, to study whether NOD1 is a recognition receptor for LPS, we detected the expression of NOD1 and several cytokines at transcript levels to determine whether LPS can induce inflammatory response in teleost fish and NOD1 can respond to LPS. Then, we perform the binding analysis between NOD1 and ultrapure LPS by using Streptavidin pulldown assay and enzyme-linked immunosorbent assay to prove that NOD1 can be combined with LPS, and using dual luciferase reporter gene assay to verify the signal pathways activated by NOD1. Next, through cell viability analysis, we proved that LPS-induced cytotoxicity can be mediated by NOD1 in fish. The results showed that NOD1 can identify LPS and activate the NF-κB signal pathway by recruiting RIPK2 and then promoting the expression of inflammatory cytokines to induce the resistance of organism against bacterial infection.

In the last decade, several studies have been focused on revealing the microRNA (miRNA) repertoire and determining their functions in farm animals such as poultry, pigs, cattle, and fish. These small non-protein coding RNA molecules (18–25 nucleotides) are capable of controlling gene expression by binding to messenger RNA (mRNA) targets, thus interfering in the final protein output. MiRNAs have been recognized as the main regulators of biological features of economic interest, including body growth, muscle development, fat deposition, and immunology, among other highly valuable traits, in aquatic livestock. Currently, the miRNA repertoire of some farmed fish species has been identified and characterized, bringing insights about miRNA functions, and novel perspectives for improving health and productivity. In this review, we summarize the current advances in miRNA research by examining available data on Neotropical and other key species exploited by fisheries and in aquaculture worldwide and discuss how future studies on Neotropical fish could benefit from this knowledge. We also make a horizontal comparison of major results and discuss forefront strategies for miRNA manipulation in aquaculture focusing on forward-looking ideas for forthcoming research.

The insulin-like growth factor (Igf) binding protein (Igfbp) family has a broad range of physiological functions and a fascinating evolutionary history. This review focuses on the Igfbps of teleost fishes, where genome duplication events have diversified gene repertoire, function, and physiological regulation—with six core Igfbps expanded into a family of over twenty genes in some lineages. In addition to briefly summarizing the current state of knowledge on teleost Igfbp evolution, function, and expression-level regulation, we highlight gaps in our understanding and promising areas for future work.

B-cell antigen receptor (BCR) or antibody diversity arises from somatic recombination of immunoglobulin (Ig) gene segments and is concentrated within the Ig heavy (H) chain complementarity-determining region 3 (CDR-H3). We performed high-throughput sequencing of the expressed antibody heavy-chain repertoire from adult torafugu. We found that torafugu use between 70 and 82% of all possible V (variable), D (diversity), and J (joining) gene segment combinations and that they share a similar frequency distribution of these VDJ combinations. The CDR-H3 sequence repertoire observed in individuals is biased with the preferential use of a small number of VDJ, dominated by sequences containing inserted nucleotides. We uncovered the common CDR-H3 amino-acid (aa) sequences shared by individuals. Common CDR-H3 sequences feature highly convergent nucleic-acid recombination compared with private ones. Finally, we observed differences in repertoires between IgM and IgT, including the unequal usage frequencies of V gene segment and the biased number of nucleotide insertion/deletion at VDJ junction regions that leads to distinct distributions of CDR-H3 lengths.

It is now widely recognized that neutrophils are sophisticated cells that are critical to host defense and the maintenance of homeostasis. In addition, concepts such as neutrophil plasticity are helping to define the range of phenotypic profiles available to cells in this group and the physiological conditions that contribute to their differentiation. Herein, we discuss key features of the life of a teleost neutrophil including their development, migration to an inflammatory site, and contributions to pathogen killing and the control of acute inflammation. The potent anti-microbial mechanisms elicited by these cells in bony fish are a testament to their long-standing evolutionary contributions in host defense. In addition, recent insights into their active roles in the control of inflammation prior to induction of apoptosis highlight their importance to the maintenance of host integrity in these early vertebrates. Overall, our goal is to summarize recent progress in our understanding of this cell type in teleost fish, and to provide evolutionary context for the contributions of this hematopoietic lineage in host defense and an efficient return to homeostasis following injury or infection.

The brown meagre Sciaena umbra, an iconic demersal fish species in Mediterranean coastal habitats, is particularly vulnerable to fishing pressure and presents a worrying population decline. Fish numbers and sizes were surveyed by visual census at Scandola (Corsica) in and outside reserve zones subject to increasing levels of protection, including unprotected zones (UP) where all fishing activities are permitted, buffer zones (BZ) subject to partial protection and a totally protected no-take integral reserve zone (IR). The numerical abundance, individual size and biomass of the brown meagre were found to increase with levels of reserve protection. The abundance of the larger size classes and the numbers of fish per shoal were significantly lower in unprotected zones. A comparison with similar censuses performed in 1983 showed a significant increase of S. umbra abundance in IR, but no difference in UP. That increasing levels of protection resulted in increased abundance and biomass of the brown meagre suggested a prominent role of fishing, particularly spearfishing, activities in the persistence of its low abundance in the unprotected zones. As a consequence, protective action for the brown meagre (including a ban on both spearfishing and recreational hook-and-line fishing) has been introduced in France since January 2014.

Pattern recognition receptors can recognize pathogens, and then cells are induced to produce pro-inflammatory cytokines and interferon by multiple signaling pathways. Nevertheless, excessive inflammation disrupts immune homeostasis, thereby inducing autoimmune and inflammatory diseases. Thus, the regulation of immune responses is extremely important for host to keep homeostasis. In this study, we found that miR-19a plays a negative regulator in MyD88-mediated NF-κB signaling pathway by targeting MyD88 in miiuy croaker. Furthermore, over-expression of miR-19a in macrophages suppresses the expression of MyD88 and its downstream signaling genes of IRAK1, IRAK4 and TRAF6, whereas, the inhibitor of miR-19a has opposite effect. This study can increase our knowledge and help us to furthermore understand miRNAs regulatory mechanism in teleost fish. [ABSTRACT FROM AUTHOR]

Gene expression of key ion transporters (the Na+/K+-ATPase NKA, the Na+, K+-2Cl− cotransporter NKCC1, and CFTR) in the gills, opercular inner epithelium, and pseudobranch of European seabass juveniles (Dicentrarchus labrax) were studied after acute transfer up to 4 days from seawater (SW) to freshwater (FW). The functional remodeling of these organs was also studied. Handling stress (SW to SW transfer) rapidly induced a transcript level decrease for the three ion transporters in the gills and operculum. NKA and CFTR relative expression level were stable, but in the pseudobranch, NKCC1 transcript levels increased (up to 2.4-fold). Transfer to FW induced even more organ-specific responses. In the gills, a 1.8-fold increase for NKA transcript levels occurs within 4 days post transfer with also a general decrease for CFTR and NKCC1. In the operculum, transcript levels are only slightly modified. In the pseudobranch, there is a transient NKCC1 increase followed by 0.6-fold decrease and 0.8-fold CFTR decrease. FW transfer also induced a density decrease for the opercular ionocytes and goblet cells. Therefore, gills and operculum display similar trends in SW-fish but have different responses in FW-transferred fish. Also, the pseudobranch presents contrasting response both in SW and in FW, most probably due to the high density of a cell type that is morphologically and functionally different compared to the typical gill-type ionocyte. This pseudobranch-type ionocyte could be involved in blood acid-base regulation masking a minor osmotic regulatory capacity of this organ compared to the gills. [ABSTRACT FROM AUTHOR]

A neuromodulatory role for dopamine has been reported for magnocellular neuroendocrine cells in the mammalian hypothalamus. We examined its potential role as a local intercellular messenger in the neuroendocrine Dahlgren cell population of the caudal neurosecretory system (CNSS) of the euryhaline flounder Paralichthys olivaceus . In vitro application of dopamine (DA) caused an increase in electrical activity (firing frequency, recorded extracellularly) of Dahlgren cells, recruitment of previously silent cells, together with a greater proportion of cells showing phasic (irregular) activity. The dopamine precursor, levodopa (L-DOPA), also increased firing frequency, cell recruitment and enhanced bursting and tonic activity. The effect of dopamine was blocked by the D1, D5 receptor antagonist SCH23390, but not by the D2, D3, D4 receptor antagonist amisulpride. Transcriptome sequencing revealed that all DA receptors (D1, D2, D3, D4, and D5) were present in the flounder CNSS. However, quantitative RT-PCR revealed that D5 receptor mRNA expression was significantly increased in the CNSS following dopamine superfusion. These findings suggest that dopamine may modulate CNSS activity in vivo , and therefore neurosecretory output, through D5 receptors. [ABSTRACT FROM AUTHOR]

microRNAs (miRNAs) are highly conserved, small non-coding endogenous molecule, and can participate in a variety of biological processes in organisms such as development, growth and immune response. Dual-Specificity Phosphatases (DUSPs) are enzymes that can remove phosphate groups from phosphatases. Research found that DUSP1 is an important molecule in the process of MAPK regulation. However, as a significant regulatory factor, the study of DUSP1 was very few in fish. Consequently, in this study, the regulatory role of miRNAs on DUSP1 has been verified through dual-luciferase reporter assay and western blotting analysis. Furethermore, we found that miR-375 mimics and pre-miR-375 plasmid can negatively regulate the target gene DUSP1 in miiuy croaker through combining with 3'untranslated region of DUSP1 gene. These experiment results directly indicate the negative regulatory function of miR-375 to DUSP1. Moreover, miR-375 can negatively regulate NF-κB signaling pathway via target to DUSP1. This study can increase our knowledge and help us to understand complexity of genomic and complex gene expression regulatory networks in teleost fish. [ABSTRACT FROM AUTHOR]

Thyroid hormones (THs) play important roles in the regulation of many biological processes of vertebrates, such as growth, metabolism, morphogenesis and reproduction. An increasing number of studies have been focused on the involvement of THs in the male reproductive system of vertebrates, in particular of fish. Therefore, this mini-review aims to summarize the main findings on THs role in male reproductive system of fish, focusing on sex differentiation, testicular development and spermatogenesis. The existing data in the literature have demonstrated that THs exert their roles at the different levels of the hypothalamic-pituitary-gonadal (HPG) axis. In general a positive correlation has been shown between THs and fish reproductive status; where THs are associated with testicular development, growth and maturation. Recently, the molecular mechanisms underlying the role of THs in spermatogenesis have been unraveled in zebrafish testis. THs promote germ cell proliferation and differentiation by increasing a stimulatory growth factor of spermatogenesis produced by Sertoli cells. In addition, THs enhanced the gonadotropin-induced androgen release in zebrafish testis. Next to their functions in the adult testis, THs are involved in the gonadal sex differentiation through modulating sex-related gene expression, and testicular development via regulation of Sertoli cell proliferation. In conclusion, this mini-review showed that THs modulate the male reproductive system during the different life stages of fish. The physiological and molecular mechanisms showed a link between the thyroid and reproduction, suggesting a possibly co-evolution and interdependence of these two systems. [ABSTRACT FROM AUTHOR]

Abstract: Nucleotide‐binding and oligomerization domain (NOD)‐like receptors (NLRs) are a group of intracellular pathogen recognition receptors (PRRs) that play key roles in pathogen recognition and subsequent activation of innate immune signalling pathways. Expressions of several NLR subfamily members, including NOD1, NOD2, NLR‐C3, NLR‐C5 and NLR‐X1 have been reported in many different teleost fish species. These receptors are activated by a variety of ligands, including lipopolysaccharides (LPS), peptidoglycans (PGN) and polyinosinic‐polycytidylic acid [Poly(I:C)]. Synthetic dsRNA and bacterial or viral infections are known to stimulate these receptors both in vitro and in vivo. In this review, we focus on the identification, expression and function of teleost NLRs in response to bacterial or viral pathogens. Additionally, NLR ligand specificity and signalling pathways involved in the recognition of bacterial or viral stimuli are also summarized. This review focuses on current knowledge in this area and provides future perspectives regarding topics in need of additional investigation. Understanding the response of innate immune system to bacterial or viral infections in diverse species could inform the development of more effective therapies and vaccines. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor ligand superfamily members such as B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) have been identified in mammals as key regulators of B cell homeostasis and activation. However, the immune functions of APRIL are not as well defined as those of BAFF. Furthermore, while BAFF is present in all vertebrates, APRIL is missing in some animal groups, suggesting that BAFF has compensated the functions of APRIL in these species. In this context, we thought of great interest to explore the effects of APRIL on teleost B cells, given that APRIL appears for the first time in evolution in bony fish. Thus, in this study, we have performed an extensive analysis of the effect of APRIL on B cells using rainbow trout (Oncorhynchus mykiss) as a model species. Our results demonstrate that APRIL induces a specific proliferation of IgM+ B cells by itself and increases IgM secretion without promoting a terminal differentiation to plasma cells. APRIL also increased the levels of surface MHC II and augmented the capacity of these cells to process antigen, effects that were exclusively exerted on IgM+ B cells. Although our results point to a highly conserved role of APRIL on B cell homeostasis and activation throughout evolution, some specific differential effects have been observed in fish in comparison to the effects of APRIL previously described in mammals. Finally, the effects that APRIL induces on rainbow trout IgM+ B cells described in this paper have been compared with those previously reported in response to BAFF. [ABSTRACT FROM AUTHOR]

Concerns about the welfare of production animals have extended from farm animals to fish, but an overview of the impact of especially capture fisheries on fish welfare is lacking. This review provides a synthesis of 85 articles, which demonstrates that research interest in fish welfare in capture fisheries has increased over time and that research has focused more on trawls and hooks than on purse seines, gillnets, traps and seines. We found that various gear characteristics, fish characteristics and context variables affect external injuries and mortality. Although the influence of gear characteristics on injuries and mortality can by nature not be compared across gear types, synthesis of the articles reviewed shows that fish characteristics and context variables influence injuries and mortality across gear types. In terms of fish characteristics, decreasing fish length and certain fish species were associated with higher mortality. In terms of context variables, greater capture depth and a longer fishing duration were associated with more injuries and higher mortality, whereas a large change in water temperature, a longer duration of air exposure and a high density in the net were associated with higher mortality. These relations provide options to reduce injuries and mortality from commercial capture fisheries. Implementation of such options, however, would require analysis of potential trade-offs between welfare benefits, and ecological and economic consequences. [ABSTRACT FROM AUTHOR]

Teleost fish are unique in having type I and type II interferons (IFNs) only, and the type I IFNs are classified into Group one and Group two based on the presence of two or four cysteines respectively, and are further classified into seven subgroups. In the present study, three distinct type I IFNs, IFNc, IFNd and IFNh, have been identified in the genome sequences of a perciform fish, the mandarin fish Siniperca chuatsi . These IFNs are induced following the stimulation of Polyinosinic polycytidylic acid (poly(I:C)) and Resiquimod (R848) either in vivo or in vitro . But, the infectious spleen and kidney necrosis virus (ISKNV) infection caused a delayed response of IFNs, which may be resulted from the viral inhibition of type I IFN production and related signalling. The three receptor subunits, cytokine receptor family B 1 (CRFB1), CRFB2 and CRFB5 are also expressed in a similar manner as observed for the IFNs, and IFNc, IFNd and IFNh use preferentially the receptor complex, CRFB2 and CRFB5, CRFB1 and CRFB5, CRFB1 and CRFB5 respectively for their effective signalling in the induction of IFN-stimulated genes (ISGs). Moreover, the IFNs are able to induce their own expression, and also the IRF3 and IRF7 expression, leading to the amplification of IFN cascade. It is further revealed that these three IFNs are transcribed differently by IRF7 and IRF3. The composition, function, signalling and transcription of type I IFNs have been investigated in detail in a teleost fish. [ABSTRACT FROM AUTHOR]

Motivated by studies of speech deficits in humans, several studies over the past two decades have investigated the potential role of a forkhead domain transcription factor, FoxP2, in the central control of acoustic signaling/vocalization among vertebrates. Comparative neuroanatomical studies that mainly include mammalian and avian species have mapped the distribution of FoxP2 expression in multiple brain regions that imply a greater functional significance beyond vocalization that might be shared broadly across vertebrate lineages. To date, reports for teleost fish have been limited in number and scope to nonvocal species. Here, we map the neuroanatomical distribution of FoxP2 mRNA expression in a highly vocal teleost, the plainfin midshipman (Porichthys notatus). We report an extensive overlap between FoxP2 expression and vocal, auditory, and steroid-signaling systems with robust expression at multiple sites in the telencephalon, the preoptic area, the diencephalon, and the midbrain. Label was far more restricted in the hindbrain though robust in one region of the reticular formation. A comparison with other teleosts and tetrapods suggests an evolutionarily conserved FoxP2 phenotype important to vocal-acoustic and, more broadly, sensorimotor function among vertebrates. [ABSTRACT FROM AUTHOR]

Phagocytosis evolved from a fundamental nutrient acquisition mechanism in primitive unicellular amoeboids, into a dynamic and complex component of innate immunity in multicellular organisms. To better understand the cellular mechanisms contributing to phagocytic processes across vertebrates, our research has focused on characterizing the involvement of innate immune proteins originally identified in channel catfish (Ictalurus punctatus) called leukocyte immune-type receptors (IpLITRs). These unique teleost proteins share basic structural as well as distant phylogenetic relationships with several immunoregulatory proteins within the mammalian immunoglobulin superfamily. In the present study, we use a combination of live-cell confocal imaging and high-resolution scanning electron microscopy to further examine the classical immunoreceptor tyrosine-based activation motif (ITAM)-dependent phagocytic pathway mediated by the chimeric construct IpLITR 2.6b/IpFcRγ-L and the functionally diverse immunoreceptor tyrosine-based inhibitory motif-containing receptor IpLITR 1.1b. Results demonstrate that IpLITR 1.1b-expressing cells can uniquely generate actin-dense filopodia-like protrusions during the early stages of extracellular target interactions. In addition, we observed that these structures retract after contacting extracellular targets to secure captured microspheres on the cell surface. This activity was often followed by the generation of robust secondary waves of actin polymerization leading to the formation of stabilized phagocytic cups. At depressed temperatures of 27°C, IpLITR 2.6b/IpFcRγ-L-mediated phagocytosis was completely blocked, whereas IpLITR 1.1b-expressing cells continued to generate dynamic actin-dense filopodia at this lower temperature. Overall, these results provide new support for the hypothesis that IpLITR 1.1b, but not IpLITR 2.6b/IpFcRγ-L, directly triggers filopodia formation when expressed in representative myeloid cells. This also offers new information regarding the directed ability of immunoregulatory receptor-types to initiate dynamic membrane structures and provides insights into an alternative ITAM-independent target capture pathway that is functionally distinct from the classical phagocytic pathways. [ABSTRACT FROM AUTHOR]

Lipopolysaccharide (LPS) is the major component of the outer membrane of Gram-negative bacteria. This molecule can induce strong immune response and various biological effects. In mammals, TLR4 can recognize LPS and induce inflammatory response. However, the innate receptor in fish for recognizing LPS remains ambiguous. LPS can invade the cytoplasm via outer membrane vesicles produced by Gram-negative bacteria and could be detected by intracellular receptor caspase-11 in mammals, so, there may also exist the intracellular receptors that can recognize LPS in fish. NOD1 is a member of NOD-like receptors family and can recognize the iE-DAP in the cytoplasm in mammals. In fish, NOD1 can also respond to infection of Gram-negative bacteria and may play an important role in the identification of bacterial components. In this study, to study whether NOD1 is a recognition receptor for LPS, we detected the expression of NOD1 and several cytokines at transcript levels to determine whether LPS can induce inflammatory response in teleost fish and NOD1 can respond to LPS. Then, we perform the binding analysis between NOD1 and ultrapure LPS by using Streptavidin pulldown assay and enzyme-linked immunosorbent assay to prove that NOD1 can be combined with LPS, and using dual luciferase reporter gene assay to verify the signal pathways activated by NOD1. Next, through cell viability analysis, we proved that LPS-induced cytotoxicity can be mediated by NOD1 in fish. The results showed that NOD1 can identify LPS and activate the NF-κB signal pathway by recruiting RIPK2 and then promoting the expression of inflammatory cytokines to induce the resistance of organism against bacterial infection. [ABSTRACT FROM AUTHOR]