Extracellular DNA traps in a ctenophore demonstrate immune cell behaviors in a non-bilaterian

The formation of extracellular DNA traps (ETosis) is a first response mechanism by specific immune cells following exposure to microbes. Initially characterized in vertebrate neutrophils, cells capable of ETosis have been discovered recently in diverse non-vertebrate taxa. To assess the conservation of ETosis between evolutionarily distant non-vertebrate phyla, we observed and quantified ETosis using the model ctenophore Mnemiopsis leidyi and the oyster Crassostrea gigas. Here we report that ctenophores - thought to have diverged very early from the metazoan stem lineage - possess immune-like cells capable of phagocytosis and ETosis. We demonstrate that both Mnemiopsis and Crassostrea immune cells undergo ETosis after exposure to diverse microbes and chemical agents that stimulate ion flux. We thus propose that ETosis is an evolutionarily conserved metazoan defense against pathogens.

Climate change can impair bacterial pathogen defences in sablefish via hypoxia-mediated effects on adaptive immunity

Low-oxygen levels (hypoxia) in aquatic habitats are becoming more common because of global warming and eutrophication. However, the effects on the health/disease status of fishes, the world's largest group of vertebrates, are unclear. Therefore, we assessed how long-term hypoxia affected the immune function of sablefish, an ecologically and economically important North Pacific species, including the response to a formalin-killed Aeromonas salmonicida bacterin. Sablefish were held at normoxia or hypoxia (100% or 40% air saturated seawater, respectively) for 6-16 weeks, while we measured a diverse array of immunological traits. Given that the sablefish is a non-model organism, this involved the development of a species-specific methodological toolbox comprised of qPCR primers for 16 key immune genes, assays for blood antibacterial defences, the assessment of blood immunoglobulin (IgM) levels with ELISA, and flow cytometry and confocal microscopy techniques. We show that innate immune parameters were typically elevated in response to the bacterial antigens, but were not substantially affected by hypoxia. In contrast, hypoxia completely prevented the ∼1.5-fold increase in blood IgM level that was observed under normoxic conditions following bacterin exposure, implying a serious impairment of adaptive immunity. Since the sablefish is naturally hypoxia tolerant, our results demonstrate that climate change-related deoxygenation may be a serious threat to the immune competency of fishes.

Further evidence from common garden rearing experiments of heritable traits separating lean and siscowet lake charr (Salvelinus namaycush) ecotypes

Genetic evidence of selection for complex and polygenically regulated phenotypes can easily become masked by neutral population genetic structure and phenotypic plasticity. Without direct evidence of genotype‐phenotype associations it can be difficult to conclude to what degree a phenotype is heritable or a product of environment. Common garden laboratory studies control for environmental stochasticity and help to determine the mechanism that regulate traits. Here we assess lipid content, growth, weight, and length variation in full and hybrid F₁ crosses of deep and shallow water sympatric lake charr ecotypes reared for nine years in a common garden experiment. Redundancy analysis (RDA) and quantitative‐trait‐loci (QTL) genomic scans are used to identify associations between genotypes at 19,714 single nucleotide polymorphisms (SNPs) aligned to the lake charr genome and individual phenotypes to determine the role that genetic inheritance plays in ecotype phenotypic diversity. Lipid content, growth, length, and weight differed significantly among lake charr crosses throughout the experiment suggesting that pedigree plays a large roll in lake charr development. Polygenic scores of 15 SNPs putatively associated with lipid content and/or condition factor indicated that ecotype distinguishing traits are polygenically regulated and additive. A QTL identified on chromosome 38 contained >200 genes, some of which were associated with lipid metabolism and growth, demonstrating the complex nature of ecotype diversity. The results of our common garden study further indicate that lake charr ecotypes observed in nature are predetermined at birth and that ecotypes differ fundamentally in lipid metabolism and growth.

The Influence of Life History on the Response to Parasitism: Differential response to non-lethal sea lamprey parasitism by two lake charr ecomorphs

The energetic demands of stressors like parasitism require hosts to reallocate energy away from normal physiological processes to survive. Life history theory provides predictions about how hosts will reallocate energy following parasitism, but few studies provide empirical evidence to test these predictions. We examined the sub-lethal effects of sea lamprey parasitism on lean and siscowet lake charr, two ecomorphs with different life history strategies. Leans are shorter lived, faster growing, and reach reproductive maturity earlier than siscowets. Following a parasitism event of 4 days, we assessed changes to energy allocation by monitoring endpoints related to reproduction, energy storage, and growth. Results indicate that lean and siscowet lake charr differ considerably in their response to parasitism. Severely parasitized leans slightly increased their reproductive effort and maintained growth and energy storage, consistent with expectations based on life history that leans are less likely to survive parasitism and have shorter lifespans than siscowets making investing in immediate reproduction more adaptive. Siscowets nearly ceased reproduction following severe parasitism and showed evidence of altered energy storage, consistent with a strategy that favors maximizing long-term reproductive success. These findings suggest that life history can be used to generalize stressor response between populations and can aid management efforts.

RADSex: A computational workflow to study sex determination using restriction site-associated DNA sequencing data

The study of sex determination and sex chromosome organization in nonmodel species has long been technically challenging, but new sequencing methodologies now enable precise and high-throughput identification of sex-specific genomic sequences. In particular, restriction site-associated DNA sequencing (RAD-Seq) is being extensively applied to explore sex determination systems in many plant and animal species. However, software specifically designed to search for and visualize sex-biased markers using RAD-Seq data is lacking. Here, we present RADSex, a computational analysis workflow designed to study the genetic basis of sex determination using RAD-Seq data. RADSex is simple to use, requires few computational resources, makes no prior assumptions about the type of sex-determination system or structure of the sex locus, and offers convenient visualization through a dedicated R package. To demonstrate the functionality of RADSex, we re-analysed a published data set of Japanese medaka, Oryzias latipes, where we uncovered a previously unknown Y chromosome polymorphism. We then used RADSex to analyse new RAD-Seq data sets from 15 fish species spanning multiple taxonomic orders. We identified the sex determination system and sex-specific markers in six of these species, five of which had no known sex-markers prior to this study. We show that RADSex greatly facilitates the study of sex determination systems in nonmodel species thanks to its speed of analyses, low resource usage, ease of application and visualization options. Furthermore, our analysis of new data sets from 15 species provides new insights on sex determination in fish.

The rise and fall of the ancient northern pike master sex-determining gene

The understanding of the evolution of variable sex determination mechanisms across taxa requires comparative studies among closely related species. Following the fate of a known master sex-determining gene, we traced the evolution of sex determination in an entire teleost order (Esociformes). We discovered that the northern pike (Esox lucius) master sex-determining gene originated from a 65 to 90 million-year-old gene duplication event and that it remained sex linked on undifferentiated sex chromosomes for at least 56 million years in multiple species. We identified several independent species- or population-specific sex determination transitions, including a recent loss of a Y chromosome. These findings highlight the diversity of evolutionary fates of master sex-determining genes and the importance of population demographic history in sex determination studies. We hypothesize that occasional sex reversals and genetic bottlenecks provide a non-adaptive explanation for sex determination transitions.

Reproductive life history of sablefish (Anoplopoma fimbria) from the U.S. Washington coast

Sablefish (Anoplopoma fimbria) is a marine groundfish that supports valuable fisheries in the North Pacific Ocean and holds promise for marine aquaculture. Limited information is available, however, about its reproductive biology. This study aimed to characterize the complete reproductive cycle, including seasonal changes in gonadal development (macroscopic and histological), plasma sex steroid levels (17β-estradiol -E2-, and 11-ketotestosterone -11KT-), gonadosomatic and hepatosomatic indices (GSI, and HSI), and condition factor (K) of female and male sablefish captured off the Washington coast. Adult fish (209 females, 159 males) were caught by longline monthly from August 2012 to August 2013. Early signs of recruitment of ovarian follicles into secondary growth, indicated by oocytes containing small yolk granules and cortical alveoli, were first observed in March. Oogenesis progressed during spring and summer, and fully vitellogenic follicles were first observed in July. Vitellogenic growth was correlated with increases in plasma E2, GSI, HSI and K. Periovulatory females, indicated by fully-grown oocytes with migrating germinal vesicles and hydrated oocytes, were found from November to February. At this stage, plasma E2 and GSI reached maximal levels. In males, proliferating cysts containing spermatocytes were first observed in April. Testicular development proceeded during spring and summer, a period during which all types of male germ cells were found. The first clusters of spermatozoa appeared in July, concomitant with a 5.2-fold increase in GSI. Spermiating males were observed from November to April; at this time, spermatids were absent or greatly reduced, and testis lobules were filled with spermatozoa. The highest levels of plasma 11KT were found in males at this stage. Postspawning ovaries and testes, and basal steroids levels were found in fish captured from February to April. These results suggest that sablefish in coastal Washington initiate their reproductive cycle in March/April and spawn primarily in January/February.

Dimethylsulfoniopropionate (DMSP) Increases Survival of Larval Sablefish, Anoplopoma fimbria

High concentrations of dimethylsulfoniopropionate (DMSP), a chemical compound released by lysed phytoplankton, may indicate high rates of grazing by zooplankton and may thus be a foraging cue for planktivorous fishes. Previous studies have shown that some planktivorous fishes and birds aggregate or alter locomotory behavior in response to this chemical cue, which is likely adaptive because it helps them locate prey. These behavioral responses have been demonstrated in juveniles and adults, but no studies have tested for effects on larval fish. Larvae suffer from high mortality rates and are vulnerable to starvation. While larvae are generally thought to be visual predators, they actually have poor vision and cryptic prey. Thus, larval fish should benefit from a chemical cue that provides information on prey abundance. We reared larval sablefish, Anoplopoma fimbria, for one week and supplemented feedings with varying concentrations of DMSP to test the hypothesis that DMSP affects larval survival. Ecologically relevant DMSP concentrations increased larval survival by up to 70 %, which has implications for production in aquaculture and recruitment in nature. These results provide a new tool for increasing larval production in aquaculture and also suggest that larvae may use DMSP as an olfactory cue. The release of DMSP may be a previously unappreciated mechanism through which phytoplankton affect larval survival and recruitment.

An Enriched European Eel Transcriptome Sheds Light upon Host-Pathogen Interactions with Vibrio vulnificus

Infectious diseases are one of the principal bottlenecks for the European eel recovery. The aim of this study was to develop a new molecular tool to be used in host-pathogen interaction experiments in the eel. To this end, we first stimulated adult eels with different pathogen-associated molecular patterns (PAMPs), extracted RNA from the immune-related tissues and sequenced the transcriptome. We obtained more than 2x10⁶ reads that were assembled and annotated into 45,067 new descriptions with a notable representation of novel transcripts related with pathogen recognition, signal transduction and the immune response. Then, we designed a DNA-microarray that was used to analyze the early immune response against Vibrio vulnificus, a septicemic pathogen that uses the gills as the portal of entry into the blood, as well as the role of the main toxin of this species (RtxA1₃) on this early interaction. The gill transcriptomic profiles obtained after bath infecting eels with the wild type strain or with a mutant deficient in rtxA1₃ were analyzed and compared. Results demonstrate that eels react rapidly and locally against the pathogen and that this immune-response is rtxA1₃-dependent as transcripts related with cell destruction were highly up-regulated only in the gills from eels infected with the wild-type strain. Furthermore, significant differences in the immune response against the wild type and the mutant strain also suggest that host survival after V. vulnificus infection could depend on an efficient local phagocytic activity. Finally, we also found evidence of the presence of an interbranchial lymphoid tissue in European eel gills although further experiments will be necessary to identify such tissue.

High-throughput sequencing and pathway analysis reveal alteration of the pituitary transcriptome by 17α-ethynylestradiol (EE2) in female coho salmon, Oncorhynchus kisutch

Considerable research has been done on the effects of endocrine disrupting chemicals (EDCs) on reproduction and gene expression in the brain, liver and gonads of teleost fish, but information on impacts to the pituitary gland are still limited despite its central role in regulating reproduction. The aim of this study was to further our understanding of the potential effects of natural and synthetic estrogens on the brain-pituitary-gonad axis in fish by determining the effects of 17α-ethynylestradiol (EE2) on the pituitary transcriptome. We exposed sub-adult coho salmon (Oncorhynchus kisutch) to 0 or 12 ng EE2/L for up to 6 weeks and effects on the pituitary transcriptome of females were assessed using high-throughput Illumina(®) sequencing, RNA-Seq and pathway analysis. After 1 or 6 weeks, 218 and 670 contiguous sequences (contigs) respectively, were differentially expressed in pituitaries of EE2-exposed fish relative to control. Two of the most highly up- and down-regulated contigs were luteinizing hormone β subunit (241-fold and 395-fold at 1 and 6 weeks, respectively) and follicle-stimulating hormone β subunit (-3.4-fold at 6 weeks). Additional contigs related to gonadotropin synthesis and release were differentially expressed in EE2-exposed fish relative to controls. These included contigs involved in gonadotropin releasing hormone (GNRH) and transforming growth factor-β signaling. There was an over-representation of significantly affected contigs in 33 and 18 canonical pathways at 1 and 6 weeks, respectively, including circadian rhythm signaling, calcium signaling, peroxisome proliferator-activated receptor (PPAR) signaling, PPARα/retinoid x receptor α activation, and netrin signaling. Network analysis identified potential interactions between genes involved in circadian rhythm and GNRH signaling, suggesting possible effects of EE2 on timing of reproductive events.

Luteinizing hormone stimulation of in vitro ovulation in brook trout (Salvelinus fontinalis) involves follicle contraction and activation of proteolytic genes

Luteinizing hormone (LH) is an essential hormone for the stimulation of the ovulatory process in vertebrates. However, little is known in fish regarding the different mechanisms induced by LH during ovulation that facilitate the rupture of the follicle wall and the subsequent expulsion of the mature oocyte. In this study, the effects of salmon LH (sLH) on in vitro ovulation were investigated in brook trout (Salvelinus fontinalis) isolated follicles. sLH significantly stimulated in vitro ovulation and contraction of brook trout preovulatory follicles. In order to investigate the possible involvement of proteolytic events in the ovulatory action of LH, the expression of genes known to have a crucial role in the degradation of follicle wall structure was examined. Our results show that sLH clearly stimulated the mRNA expression levels of matrix metalloproteinases (MMPs; including mmp2 and mmp19) and other enzymes with proteolytic action during ovulation, such as a disintegrin and metalloproteinase with thrombospondin-like motifs 1 (adamts1) and plasminogen (plg), in brook trout preovulatory follicles. In addition, the expression of mmp2, adamts1 and plg increased in brook trout follicles during the progression of LH-induced ovulation. Interestingly, the expression of tissue inhibitor of matrix metalloproteinase 2 (timp2), a known regulator of MMP2 activity, paralleled that of mmp2, suggesting the existence of a controlled mechanism of MMP2 action. Therefore, the known increase in proteolytic activity during ovulation in fish could be the result of the stimulation of the expression of proteolytic enzymes by LH in preovulatory follicles. We propose that LH may stimulate ovulation in brook trout follicles by stimulating proteolysis of the follicle wall and by stimulating follicle contraction.

Effects of methylmercury on epigenetic markers in three model species: mink, chicken and yellow perch

We previously reported that methylmercury (MeHg) exposure is associated with DNA hypomethylation in the brain stem of male polar bears. Here, we conveniently use archived tissues obtained from controlled laboratory exposure studies to look for evidence that MeHg can disrupt DNA methylation across taxa. Brain (cerebrum) tissues from MeHg-exposed mink (Neovison vison), chicken (Gallus gallus) and yellow perch (Perca flavescens) were analyzed for total Hg levels and global DNA methylation. Tissues from chicken and mink, but not perch, were also analyzed for DNA methyltransferase (DNMT) activity. In mink we observed significant reductions in global DNA methylation in an environmentally-relevant dietary exposure group (1 ppm MeHg), but not in a higher group (2 ppm MeHg). DNMT activity was significantly reduced in all treatment groups. In chicken or yellow perch, no statistically significant effects of MeHg were observed. Dose-dependent trends were observed in the chicken data but the direction of the change was not consistent between the two endpoints. Our results suggest that MeHg can be epigenetically active in that it has the capacity to affect DNA methylation in mammals. The variability in results across species may suggest inter-taxa differences in epigenetic responses to MeHg, or may be related to differences among the exposure scenarios used as animals were exposed to MeHg through different routes (dietary, egg injection), for different periods of time (19-89 days) and at different life stages (embryonic, juvenile, adult).

Identification of ovarian gene expression patterns during vitellogenesis in Atlantic cod (Gadus morhua)

Follicular maturational competence and ovulatory competence in teleost fish refer to the ability of the ovarian follicle to undergo final oocyte maturation and ovulation, respectively, in response to gonadotropin stimulation and other external cues. Some gene products related to competence acquisition are likely synthesized during vitellogenic growth, as these follicles gain in vivo responsiveness to exogenous gonadotropin stimulation and can be induced to undergo maturation and ovulation. In Atlantic cod (Gadus morhua), gonadotropin responsiveness has been shown to be oocyte size-dependent, and only ovaries containing late-stage vitellogenic follicles can be induced to ovulate. The purpose of the present study was to compare gene expression patterns between mid (unresponsive) and late (responsive) vitellogenic ovaries to identify genes involved in gonadotropin responsiveness and the acquisition of maturational and ovulatory competencies. Representational difference analysis was conducted in two reciprocal comparisons using intact ovarian fragments and follicle wall-enriched tissues, and genes of interest were used in real time quantitative PCR to confirm differential expression. Few differences were detected in intact ovarian fragments, but type IV ice-structuring protein and gephyrin were upregulated later in development and may be involved in lipid and sulfur metabolism, respectively. Candidate gene assays for luteinizing hormone receptor and aromatase also exhibited significant upregulation during vitellogenesis. Many genes were differentially expressed in follicle wall-enriched tissues, including endocrine maturational regulators and smooth muscle genes. Overall, maturational and ovulatory competencies during vitellogenesis in Atlantic cod are associated with up- and downregulation of many genes involved in lipid metabolism, endocrine regulation, and ovulatory preparation.

Characterization and evaluation of sex-specific expression of suppressors of cytokine signaling (SOCS)-1 and -3 in juvenile yellow perch (Perca flavescens) treated with lipopolysaccharide

The suppressor of cytokine signaling (SOCS) proteins are a family of intracellular proteins that are centrally involved with vertebrate growth, development and immunity via their effects as negative feed-back regulators of cytokine (and hormone) signaling. The genes for SOCS-1 & -3 were cloned, sequences analyzed and expression patterns examined in the commercially-important teleost, yellow perch (Perca flavescens). The deduced (mature) proteins for yellow perch (yp)SOCS-1 and (yp)SOCS-3 consist of 211 and 205 amino acids, respectively. Functional domains such as the Src homology-2 (SH2) and SOCS-box were present in ypSOCS-1 and ypSOCS-3 and these domains were well conserved between teleost species. Sequence analysis showed that ypSOCS-1 & -3 share highest homology (among similar teleost sequences), to the stickleback (Gasterosteus aculatus) SOCS-1 & -3 protein homologs. To investigate sex-specific expression of the ypSOCS-1 and ypSOCS-3 mRNAs, juvenile male and female yellow perch were immunologically challenged with a single injection (10 μg/g bw) of lipopolysaccharide (LPS) and tissues (gill, head kidney, kidney, liver and spleen) were sampled over a 48-h time-course. Quantitative real-time PCR analysis showed that ypSOCS-1 & -3 were expressed in all tissues examined and at all sampling time-points. LPS injection significantly induced ypSOCS-1 & -3 mRNA levels in gill, head kidney, liver, kidney and spleen, with maximal induction occurring at 6 h post-injection in each tissue. By 48-h post-injection, expression levels for ypSOCS-1 & -3 mRNAs approached, or reached, control levels in all tissues examined. While there were statistical interactions among variables (treatment, time and sex) for ypSOCS-1, we only found a main effect of sex on SOCS-3 mRNA expression in head kidney with higher copy numbers occurring in males than in females treated with LPS. Sexually-dimorphic expression of SOCS-1 or -3 mRNA has not been examined, or described, in a teleost. Our findings suggest the involvement of the SOCS genes in the yellow perch immune response and that differences among the sexes are evident and should be explored further.

PAMPs, PRRs and the genomics of gram negative bacterial recognition in fish

Understanding the mechanisms that underpin pathogen recognition and subsequent orchestration of the immune response in fish is an area of significant importance for both basic research and management of health in aquaculture. In recent years much attention has been given to the identification of pattern recognition receptors (PRRs) in fish, however, characterisation of interactions with specific pathogen-associated molecular patterns (PAMPs) is still incomplete. Microarray studies have significantly contributed to functional studies and early descriptions of PAMP-PRR driven activation of specific response cassettes in the genome have been obtained although much is left to be done. In this review we will address gram negative (G-negative) bacterial recognition in fish addressing contributing factors such as structure-function relationships between G-negative PAMPs, current knowledge of fish PRRs and the input achieved by microarray-based studies ranging from in vivo infection studies to directed in vitro PAMP-cell studies. Finally we revisit the endotoxic recognition paradigm in fish and suggest a series of future perspectives that could contribute toward the further elucidation of G-negative bacterial recognition across the highly diverse group of vertebrates that encompass the fishes.

RNA-Seq reveals an integrated immune response in nucleated erythrocytes

Background

Throughout the primary literature and within textbooks, the erythrocyte has been tacitly accepted to have maintained a unique physiological role; namely gas transport and exchange. In non-mammalian vertebrates, nucleated erythrocytes are present in circulation throughout the life cycle and a fragmented series of observations in mammals support a potential role in non-respiratory biological processes. We hypothesised that nucleated erythrocytes could actively participate via ligand-induced transcriptional re-programming in the immune response.

Methodology/Principal Findings

Nucleated erythrocytes from both fish and birds express and regulate specific pattern recognition receptor (PRR) mRNAs and, thus, are capable of specific pathogen associated molecular pattern (PAMP) detection that is central to the innate immune response. In vitro challenge with diverse PAMPs led to de novo specific mRNA synthesis of both receptors and response factors including interferon-alpha (IFNα) that exhibit a stimulus-specific polysomal shift supporting active translation. RNA-Seq analysis of the PAMP (Poly (I∶C), polyinosinic∶polycytidylic acid)-erythrocyte response uncovered diverse cohorts of differentially expressed mRNA transcripts related to multiple physiological systems including the endocrine, reproductive and immune. Moreover, erythrocyte-derived conditioned mediums induced a type-1 interferon response in macrophages thus supporting an integrative role for the erythrocytes in the immune response.

Conclusions/Significance

We demonstrate that nucleated erythrocytes in non-mammalian vertebrates spanning significant phylogenetic distance participate in the immune response. RNA-Seq studies highlight a mRNA repertoire that suggests a previously unrecognized integrative role for the erythrocytes in other physiological systems.

Disruption of the salmon reproductive endocrine axis through prolonged nutritional stress: changes in circulating hormone levels and transcripts for ovarian genes involved in steroidogenesis and apoptosis

Mechanisms regulating the normal progression of ovarian follicular growth versus onset of atresia in fishes are poorly understood. To gain a better understanding of these processes, we exposed immature female coho salmon (Oncorhynchus kisutch) to prolonged fasting to induce follicular atresia and monitored body growth, development of the ovarian follicles, changes in reproductive hormones, and transcripts for ovarian genes. Prolonged fasting reduced body and ovary weight and increased the appearance of atretic follicles relative to normally fed controls. Endocrine analyses showed that fasting reduced plasma insulin-like growth factor 1 (IGF1), estradiol-17β (E2), and pituitary, but not plasma, levels of follicle-stimulating hormone (FSH). Transcripts for ovarian fsh receptor (fshr) and steroidogenesis-related genes, such as steroidogenic acute regulatory protein (star), 3β-hydroxysteroid dehydrogenase (hsd3b), and P450 aromatase (cyp19a1a) were significantly lower in fasted fish. Ovarian expression of apoptosis-related genes, such as Fas-associated death domain (fadd), caspase 8 (casp8), caspase 3 (casp3), and caspase 9 (casp9) were significantly elevated in fasted fish compared to fed fish, indicating that apoptosis is involved in the process of atresia in this species. Interestingly, some genes such as fadd, casp8, casp3, and hsd3b, were differentially expressed prior to increases in the number of atretic follicles and reductions in hormone levels induced by fasting, and may therefore have potential as early indicators of atresia. Together these results suggest that prolonged nutritional stress may disrupt the reproductive system and induce follicular atresia in part via reductions in ovarian IGF and FSH signaling, and downstream effects on steroidogenesis-related genes and E2 production.

Immunological stimuli change expression of genes and neutrophil function in fathead minnow Pimephales promelas Rafinesque

Fathead minnows Pimephales promelas were exposed to lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid [poly(I:C)] to observe immunological responses during simulated bacterial and viral challenge at the level of gene expression and granulocyte function. Complementary DNA libraries were created from LPS- and poly(I:C)-treated fish and c. 5000 expressed sequence tags (ESTs) were sequenced. The ESTs were subjected to BLASTx analysis and 1500 genes were annotated, grouped by function and 20 immune genes were selected for expression studies by real-time PCR. Lipopolysaccharide treatment significantly downregulated expression of interferon regulatory factor 2 binding protein 1 (nine-fold), Chemokine (C-X-C motif) ligand 12a (three-fold) and TNF-related apoptosis-inducing ligand, TRAIL (two-fold). In poly(I:C)-treated fish, a significant upregulation was observed for IFN-inducible and antiviral proteins belonging to the family of Mx proteins (73-fold) and chemokine CCL-C5a (28-fold). Blood neutrophil count was significantly increased in poly(I:C)-treated fish at 24 and 48 h post-injection. Neutrophil extracellular trap release and respiratory burst of kidney granulocytes were suppressed in poly(I:C)-treated fish, while degranulation of primary granules was not affected significantly by the treatment. The changes in gene expression and neutrophil function in P. promelas exposed to LPS and poly(I:C) support the use of this species as an alternative model for studies of pathogen effects on the innate immune system of fishes.

Cellular and molecular evidence for a role of tumor necrosis factor alpha in the ovulatory mechanism of trout

BACKGROUND

The relevance of immune-endocrine interactions to the regulation of ovarian function in teleosts is virtually unexplored. As part of the innate immune response during infection, a number of cytokines such as tumor necrosis factor alpha (TNF alpha) and other immune factors, are produced and act on the reproductive system. However, TNF alpha is also an important physiological player in the ovulatory process in mammals. In the present study, we have examined for the first time the effects of TNF alpha in vitro in preovulatory ovarian follicles of a teleost fish, the brown trout (Salmo trutta).

METHODS

To determine the in vivo regulation of TNF alpha expression in the ovary, preovulatory brook trout (Salvelinus fontinalis) were injected intraperitoneally with either saline or bacterial lipopolysaccharide (LPS). In control and recombinant trout TNF alpha (rtTNF alpha)-treated brown trout granulosa cells, we examined the percentage of apoptosis by flow cytometry analysis and cell viability by propidium iodide (PI) staining. Furthermore, we determined the in vitro effects of rtTNF alpha on follicle contraction and testosterone production in preovulatory brown trout ovarian follicles. In addition, we analyzed the gene expression profiles of control and rtTNF alpha-treated ovarian tissue by microarray and real-time PCR (qPCR) analyses.

RESULTS

LPS administration in vivo causes a significant induction of the ovarian expression of TNF alpha. Treatment with rtTNF alpha induces granulosa cell apoptosis, decreases granulosa cell viability and stimulates the expression of genes known to be involved in the normal ovulatory process in trout. In addition, rtTNF alpha causes a significant increase in follicle contraction and testosterone production. Also, using a salmonid-specific microarray platform (SFA2.0 immunochip) we observed that rtTNF alpha induces the expression of genes known to be involved in inflammation, proteolysis and tissue remodeling. Furthermore, the expression of kallikrein, TOP-2, serine protease 23 and ADAM 22, genes that have been postulated to be involved in proteolytic and tissue remodeling processes during ovulation in trout, increases in follicles incubated in the presence of rtTNF alpha.

CONCLUSIONS

In view of these results, we propose that TNF alpha could have an important role in the biomechanics of follicle weakening, ovarian rupture and oocyte expulsion during ovulation in trout, primarily through its stimulation of follicular cell apoptosis and the expression of genes involved in follicle wall proteolysis and contraction.

Peptidoglycan, not endotoxin, is the key mediator of cytokine gene expression induced in rainbow trout macrophages by crude LPS

In rainbow trout macrophages, phenol-extracted lipopolysaccharide (LPS) preparations stimulate proinflammatory cytokine gene expression but ultrapure preparations of LPS are inactive. Crude LPS preparations could potentially have a number of contaminants including peptidoglycans (PGNs), nucleic acids and lipoproteins. Thus, in the current study we individually tested potentially contaminating pathogen associated molecular patterns (PAMPs) on rainbow trout (Oncorhynchus mykiss) macrophages to determine which ones could induce proinflammatory cytokine expression. We found that PGNs derived from Gram-negative bacteria (Escherichia coli 0111:B4 and K12), are potent inducers of IL-1beta and IL-6 gene expression and were equal to, or more potent than, crude LPS. On the other hand, PGNs of Gram-positive bacteria, DNA, RNA and lipoteichoic acid were weak stimulators, and lipid A, lipoprotein (Pam3CSK4) and ultrapure LPS were nonstimulatory. More importantly, crude LPS treated with lysozyme to degrade PGNs, exhibited greatly reduced activity in stimulating IL-1beta and IL-6 gene expression, indicating that PGNs in the crude LPS are responsible for a significant amount of the proinflammatory activity. Finally, we showed that PGN treatment induces expression of COX-2 and the subsequent synthesis and release of prostaglandin E(2) (PGE(2)), an important mediator of inflammatory processes. The strong stimulatory effect of E. coli PGNs by themselves on trout macrophages suggests that the recognition of Gram-negative bacteria in trout is through PGNs in the bacterial wall, and indicates that the systems responsible for bacterial recognition in invertebrates (e.g., Drosophila) may also be conserved in some vertebrates.

Endotoxin recognition in fish results in inflammatory cytokine secretion not gene expression

Macrophages are phagocytes that have a central role in the organization of the immune system after an infection. These cells can recognize specific molecular components of micro-organisms (pathogen-associated molecular patterns, PAMPs) via specific receptors (PRRs) and elicit specific cellular responses. In the past, the expression of immune genes in response to different PAMPs has been characterized in different fish species. However, little is known about actual cytokine release. We characterized the secretion of tumour necrosis factor (TNF)-α in primary macrophage cultures of rainbow trout (Oncorhynchus mykiss) in response to several PAMPs by Western blot and compared this to the induction of TNF-α gene expression as well as other pro-inflammatory cytokines such as interleukin (IL)-1β and IL-6 and anti-viral molecules such as INF-α and Mx protein (Mx). We show that lipopolysaccharide (LPS) and zymosan are major inducers of TNF-α secretion, which is not initially linked to the induction of TNF-α mRNA expression. The secretion of TNF-α, but intriguingly not the expression, is also stimulated by ultrapure LPS meaning that, in fish, contaminants of commercial LPS preparations are better inducers of the inflammatory response. Moreover, we have characterized the signaling pathways that are activated by different PAMPs and the link between those pathways and the final step of TNF-α secretion: TNF-α shedding by TNF-α converting enzyme (TACE/ ADAM17). For the first time, we show that, in fish macrophages, TNF-α is processed by TACE-like activity and this cleavage is dependent upon the activation of ERK, p38MAPK and JNK signaling pathways by LPS.

Stimulation of growth and changes in the hepatic transcriptome by 17β-estradiol in the yellow perch (Perca flavescens)

The effects of dietary 17β-estradiol (E2) on growth and liver transcriptomics were investigated in the yellow perch ( Perca flavescens). After a 3-mo treatment, E2 significantly stimulated an increase in length and weight of juvenile male and female perch relative to control animals. The increase was significantly greater in females compared with males. Separate, unnormalized cDNA libraries were constructed from equal quantities of RNA from 6 male and 6 female livers of E2-treated and control perch, and 3,546 and 3,719 expressed sequence tags (ESTs) were obtained, respectively. To characterize E2-regulated transcripts, EST frequencies between libraries were calculated within contiguous sequences that were assembled from the combined ESTs of both libraries. Frequencies were also determined in EST transcript groupings produced by aligning all of the ESTs from both libraries at the nucleotide level. From these analyses, there were 28 annotated transcripts that were regulated by 75% between libraries and for which there were at least 5 ESTs of the same transcript between libraries. Regulation of a subset ( 14 ) of these transcripts was confirmed by quantitative reverse transcription-polymerase chain reaction (QPCR). Transcripts that were upregulated by E2 included reproduction-related proteins, binding proteins, and proteases and protease inhibitors. While not part of the transcript frequency analysis, QPCR showed significant upregulation of estrogen receptor esr1 and of insulin-like growth factor I (IGF-I) in E2 livers. E2-downregulated transcripts represented a variety of functional categories including components of the respiratory chain, lipid transport and metabolism, glycolysis, amino acid and nitrogen metabolism, binding proteins, a hydrolytic enzyme, and a transcriptional regulator. In perch it appears that exogenous estrogen drastically shifts liver metabolism toward the production of lipoproteins and carbohydrate binding proteins, and that the growth-promoting action may involve an increase in hepatic IGF-I production.

Characterization and expression of NADPH oxidase in LPS-, poly(I:C)- and zymosan-stimulated trout (Oncorhynchus mykiss W.) macrophages

In vertebrates, the generation of superoxide reactive oxygen species (ROS) via activation of the Nox/Duox family of NADPH oxidases is a prototypical feature of the pathogen-induced defensive responses of activated professional phagocytes. To understand the role of the rainbow trout (Oncorhynchus mykiss) Phox oxidase from a phylogenetic and functional perspective we describe the cloning, sequencing and expression analysis of multiple NADPH components in cultured macrophages. Phylogenetic analyses support the notion of the emergence of Phox-related components before the diversification of basal euteleosts and add to the limited collection of teleost NADPH oxidases. Expression studies using lipopolysaccharide, polyinosine-polycytidylic acid and zymosan to mimic the onset of inflammatory responses in trout macrophages suggest differences in regulation of the NADPH complex throughout the maturation/differentiation period of culture and between different treatments.

Stress-induced regulation of steroidogenic acute regulatory protein expression in head kidney of Gilthead seabream (Sparus aurata)

Steroidogenic acute regulatory protein (StAR) transfers cholesterol over the inner mitochondrial membrane. In mammals, StAR controls this rate-limiting step of steroidogenesis, but its expression and regulation has not been well explored in fish. The present work investigates StAR mRNA expression in the head kidney of the gilthead seabream (Sparus aurata) under different stressors. We have cloned the StAR cDNA (1461 bp) in seabream (accession number EF640987), which has an open reading frame of 861 nucleotides encoding a polypeptide of 286 aa, and displays high sequence identity with StAR of other fish and mammalian counterparts. Seabream StAR transcripts were found to be expressed exclusively in head kidneys and gonads. In fish under acute stress (chased with a net), plasma cortisol levels peaked within 1 h, were still high after 6 h, and decreased after 16 h, although no increases in head kidney StAR expression were observed at any time post-stressor. Fish under chronic high-density stress showed cortisol levels 90-fold higher than controls and StAR mRNA levels increased threefold. Lipopolysaccharide (LPS) injection increased head kidney StAR mRNA levels after 6 h, reached a maximum at 12 h, and decreased until 72 h. When the head kidney cells were incubated in vitro and treated with ACTH or LPS, ACTH induced an increase in StAR expression as expected, but LPS induced a reduction in StAR expression. In conclusion, StAR expression in seabream head kidneys is highly regulated by different stressors.

Identification of differentially expressed ovarian genes during primary and early secondary oocyte growth in coho salmon, Oncorhynchus kisutch

BACKGROUND

The aim of this study was to identify differentially expressed ovarian genes during primary and early secondary oocyte growth in coho salmon, a semelparous teleost that exhibits synchronous follicle development.

METHODS

Reciprocal suppression subtractive hybridization (SSH) libraries were generated from ovaries with perinucleolus (P) or cortical alveolus (CA) stage follicles and selected genes were assessed with quantitative PCR (qPCR). An assessment of changes in RNA composition during oocyte growth and its relationship to transcript levels was also conducted.

RESULTS

SSH revealed several differentially expressed genes during early oogenesis, some which will not likely be utilized until 1-3 years later in salmon. Zona pellucida glycoprotein (zp) genes, vitellogenin receptor (vldlr) isoforms, cathepsin B (ctsba), cyclin E (ccne), a DnaJ transcript (dnaja2), and a ferritin subunit (fth3) were significantly elevated at the P stage, while a C-type lectin, retinol dehydrogenase (rdh1), and a coatomer protein subunit (cope) were upregulated at the CA stage. Putative follicle cell transcripts such as anti-Müllerian hormone (amh), lipoprotein lipase (lpl), apolipoprotein E (apoe), gonadal soma-derived growth factor (gsdf) and follicle-stimulating hormone receptor (fshr) also increased significantly at the CA stage. The analysis of RNA composition during oocyte growth showed that the total RNA yield and proportion of messenger RNA relative to non-polyadenylated RNAs declined as oogenesis progressed. This influenced apparent transcript levels depending on the type of RNA template used and normalization method.

CONCLUSION

In coho salmon, which exhibit a dramatic change in oocyte size and RNA composition during oogenesis, use of messenger RNA as template and normalization of qPCR data to a housekeeping gene, ef1a, yielded results that best reflected transcript abundance within the ovarian follicle. Synthesis of zp transcripts and proteins involved in yolk incorporation and processing occurred during primary growth, while increased expression of a CA component and genes related to lipid incorporation occurred concomitant with the appearance of CA, but prior to lipid accumulation. Significant increases in transcripts for fshr, gsdf, and amh at the CA stage suggest a role of FSH and TGFbeta peptides in previtellogenic oocyte growth and puberty onset in female salmon.

Characterization and expression of the transcription factor PU.1 during LPS-induced inflammation in the rainbow trout (Oncorhynchus mykiss)

The transcription factor PU.1 plays a key role in hematopoietic lineage development and therefore in determining immune cell fate. A full length cDNA transcript of 1237 nucleotides encoding a highly conserved putative protein of 293 amino acids was identified by EST analysis in lipopolysaccharide (LPS) activated trout macrophages. Phylogenetic analyses highlight the significant level of structural conservation of the PU.1 transcription factor reinforcing the importance of this molecule in animal immunity. In trout, the PU.1 mRNA shows a tissue-specific expression pattern and is induced in vivo by LPS in muscle, liver, intestine and brain. Furthermore PU.1 is highly expressed in trout macrophages in primary culture. In situ expression analysis in the head kidney describes a large number of PU.1+ve cells distributed through the tissue in both LPS-treated and control animals. Cellular proliferation examined by BrdU immunohistochemistry (IHC) shows that LPS regulates hematopoietic processes in adult fish by stimulating cellular proliferation 3 days after treatment. These studies provide initial insights into hematopoietic/cellular processes in the head kidney of rainbow trout after in vivo LPS challenge.

CD83 expression in sea bream macrophages is a marker for the LPS-induced inflammatory response

CD83, a cell surface membrane glycoprotein member of the Ig superfamily which is commonly used as standard surface marker for dendritic cells, was cloned from gilthead sea bream macrophages using degenerate primers against conserved motifs of known CD83 sequences. The obtained cDNA contains an open reading frame of 669 nucleotides that translate into a 222 amino acid putative peptide. The deduced protein sequence shows conservation of features shared by vertebrate CD83 and multiple alignment with fish CD83 sequences reveals high homology. In cultured sea bream macrophages CD83 mRNA expression was significantly enhanced in a dose- and time-dependent fashion after stimulation with Escherichia coli LPS. These results indicate that in fish, macrophages express high levels of CD83 mRNA after LPS exposure and CD83 is therefore a good marker for activated mature myeloid cells in fish.

Zebrafish and giant danio as models for muscle growth: determinate vs. indeterminate growth as determined by morphometric analysis

The zebrafish has become an important genetic model, but their small size makes them impractical for traditional physiological studies. In contrast, the closely related giant danio is larger and can be utilized for physiological studies that can also make use of the extensive zebrafish genomic resources. In addition, the giant danio and zebrafish appear to exhibit different growth types, indicating the potential for developing a comparative muscle growth model system. Therefore, the present study was conducted to compare and characterize the muscle growth pattern of zebrafish and giant danio. Morphometric analyses demonstrated that giant danio exhibit an increased growth rate compared with zebrafish, starting as early as 2 wk posthatch. Total myotome area, mean fiber area, and total fiber number all exhibited positive correlations with larvae length in giant danio but not in zebrafish. Morphometric analysis of giant danio and zebrafish larvae demonstrated faster, more efficient growth in giant danio larvae. Similar to larger teleosts, adult giant danio exhibited increased growth rates in response to growth hormone, suggesting that giant danio exhibit indeterminate growth. In contrast, adult zebrafish do not exhibit mosaic hyperplasia, nor do they respond to growth hormone, suggesting they exhibit determinate growth like mammals. These results demonstrate that giant danio and zebrafish can be utilized as a direct comparative model system for muscle growth studies, with zebrafish serving as a model organism for determinate growth and giant danio for indeterminate growth.

Cloning and expression analysis of an IL-6 homolog in rainbow trout (Oncorhynchus mykiss)

A partial cDNA with significant similarity to IL-6 was identified in rainbow trout. Rapid amplification of cDNA ends was used to obtain the full sequence of the trout IL-6 homolog which contains 1180 nucleotides. The transcript encodes a predicted protein of 219 amino acids and eight instability motifs in the 3'UTR. While the complete sequence of the trout IL-6 is poorly conserved, the protein contains a distinct IL-6/G-CSF/MGF family consensus pattern and predicted characteristic alpha-helical tertiary structure. However, like in fugu, trout IL-6 lacks a pair of cysteine residues, which in mammals are involved in formation of a disulphide bond. The expression of the IL-6 homolog in trout mononuclear phagocytes was highly up-regulated by LPS but not poly(I:C) as demonstrated by Northern analysis. Using RT-PCR the IL-6 expression was detected in trout spleen, gill, gastrointestinal tract, ovary and brain. The highest transcript levels were detected in the ovary suggesting that IL-6 may perform specific functions within this organ.

Bacterial lipopolysaccharide induces apoptosis in the trout ovary

BACKGROUND

In mammals it is well known that infections can lead to alterations in reproductive function. As part of the innate immune response, a number of cytokines and other immune factors is produced during bacterial infection or after treatment with lipopolysaccharide (LPS) and acts on the reproductive system. In fish, LPS can also induce an innate immune response but little is known about the activation of the immune system by LPS on reproduction in fish. Therefore, we conducted studies to examine the in vivo and in vitro effects of lipopolysaccharide (LPS) on the reproductive function of sexually mature female trout.

METHODS

In saline- and LPS -injected brook trout, we measured the concentration of plasma steroids as well as the in vitro steroidogenic response (testosterone and 17alpha-hydroxyprogesterone) of ovarian follicles to luteinizing hormone (LH), the ability of 17alpha,20beta-dihydroxy-4-pregnen-3-one to induce germinal vesicle breakdown (GVBD) in vitro, and that of epinephrine to stimulate follicular contraction in vitro. We also examined the direct effects of LPS in vitro on steroid production, GVBD and contraction in brook trout ovarian follicles. The incidence of apoptosis was evaluated by TUNEL analysis. Furthermore, we examined the gene expression pattern in the ovary of saline- and LPS-injected rainbow trout by microarray analysis.

RESULTS

LPS treatment in vivo did not affect plasma testosterone concentration or the basal in vitro production of steroids, although a small but significant potentiation of the effects of LH on testosterone production in vitro was observed in ovarian follicles from LPS-treated fish. In addition, LPS increased the plasma concentration of cortisol. LPS treatment in vitro did not affect the basal or LH-stimulated steroid production in brook trout ovarian follicles. In addition, we did not observe any effects of LPS in vivo or in vitro on GVBD or follicular contraction. Therefore, LPS did not appear to impair ovarian steroid production, oocyte final maturation or follicular contraction under the present experimental conditions. Interestingly, LPS administration in vivo induced apoptosis in follicular cells, an observation that correlated with changes in the expression of genes involved in apoptosis, as evidenced by microarray analysis.

CONCLUSION

These results indicate that female trout are particularly resistant to an acute administration of LPS in terms of ovarian hormone responsiveness. However, LPS caused a marked increase in apoptosis in follicular cells, suggesting that the trout ovary could be sensitive to the pro-apoptotic effects of LPS-induced inflammatory cytokines.

Transcriptional analysis of LPS-stimulated activation of trout (Oncorhynchus mykiss) monocyte/macrophage cells in primary culture treated with cortisol

Primary immune responses to pathogen invasion are mediated by the innate immune system in which tissue macrophages play a key role. During infectious processes glucocorticoids generally may function to dampen inflammatory responses. In this study, the ability of cortisol to directly modulate the transcriptional response of rainbow trout macrophages to the cellular activator lipopolysaccharide (LPS) was investigated. The results indicate that cortisol significantly inhibits the well-described LPS-dependent induction of the expression of TNF-alpha2, a pro-inflammatory cytokine. In order to further characterize the molecular effects of LPS and the immunomodulatory role of cortisol, the in vitro macrophage response to LPS in the absence or presence of 12-h cortisol exposure was analyzed utilizing a salmonid-specific microarray platform. Genes that were stimulated or inhibited with LPS plus cortisol fell into several major functional groups. The first, a general "response" group comprising genes within ontology classes including the response to external stimuli, stress, humoral immunity and apoptosis, exhibited a significant increase after LPS stimulation, whereas suppression of this response was observed in the presence of cortisol. LPS stimulated other genes in a second group involved in cell signalling and also genes in a third group involved in the activation of transcription. Categories activated with cortisol were mainly related to various aspects of metabolism (including protein biosynthesis, binding and transport of ions) and structural proteins (mainly cytoskeleton and microtubules). The immunomodulatory action of cortisol on LPS-stimulated macrophages therefore appears more complex than simply the antagonism of LPS-induced transcriptional responses.

Endotoxin recognition: in fish or not in fish?

The interaction between pathogens and their multicellular hosts is initiated by activation of pathogen recognition receptors (PRRs). These receptors, that include most notably members of the toll-like receptor (TLR) family, recognize specific pathogen-associated molecular patterns (PAMPs). TLR4 is a central part of the receptor complex that is involved in the activation of the immune system by lipopolysaccharide (LPS) through the specific recognition of its endotoxic moiety (Lipid A). This is a critical event that is essential for the immune response to Gram-negative bacteria as well as the etiology of endotoxic shock. Interestingly, compared to mammals, fish are resistant to endotoxic shock. This in vivo resistance concurs with in vitro studies demonstrating significantly lowered sensitivity of fish leukocytes to LPS activation. Further, our in vitro analyses demonstrate that in trout mononuclear phagocytes, LPS fails to induce antiviral genes, an event that occurs downstream of TLR4 and is required for the development of endotoxic shock. Finally, an in silico approach that includes mining of different piscine genomic and EST databases, reveals the presence in fish of all of the major TLR signaling elements except for the molecules specifically involved in TLR4-mediated endotoxin recognition and signaling in mammals. Collectively, our analysis questions the existence of TLR4-mediated cellular responses to LPS in fish. We further speculate that other receptors, in particular beta-2 integrins, may play a primary role in the activation of piscine leukocytes by LPS.

The isolation, characterization, and expression of a novel GDF11 gene and a second myostatin form in zebrafish, Danio rerio

In the current study, the first non-mammalian growth/differentiation factor (GDF) 11-like homolog was cloned from zebrafish. At the nucleotide level, zebrafish GDF11 is most similar to human GDF11 (79%), while the peptide is most similar to mouse GDF11 (78%). Phylogenetic analysis showed that the zebrafish GDF11 clusters with mammalian GDF11s. This study also cloned a second MSTN form in zebrafish most similar to Salmonid MSTN2 forms. Based on real time PCR, GDF11 is expressed in multiple adult tissues, with levels highest in whole heads and gonads, and expression is less ubiquitous when compared to MSTN expression. During embryonic development, real time PCR demonstrated increasing GDF11 mRNA levels 10 h post-fertilization (hpf), while MSTN mRNA levels remain low until 48 hpf. This is the first report of a transforming growth factor (TGF)-beta superfamily member in a non-mammalian species that is more closely related to GDF11 than MSTN, and also a second form of MSTN in zebrafish; suggesting that a more complex TGF-beta superfamily array exists in primitive vertebrates than previously thought.

Characterization of the cod (Gadus morhua) steroidogenic acute regulatory protein (StAR) sheds light on StAR gene structure in fish

The full-length cDNA for the cod (Gadus morhua) StAR was cloned by RT-PCR and library screening using ovarian RNA. From the library screening, 2 size classes of cDNA were obtained; a 1577 bp cDNA (cStAR1) and a 2851 bp cDNA (cStAR2). The cStAR1 cDNA presumably encodes a protein of 286 amino acids. The cStAR2 cDNA was composed of 6 separated sequences that contained all of the coding regions of cStAR1 when added together, but also contained 5 noncoding regions not observed in cStAR1. Polymerase chain reactions of cod genomic DNA produced products slightly larger than cStAR2. The sequence of these products were the same as cStAR2 but revealed one additional noncoding region (intron). Thus, the fish StAR gene contains the same number of exons (7) and introns (6) as observed in mammals, but is approximately half the size of the mammalian gene. Using Northern analysis and RT-PCR, cStAR1 expression was observed only in testes, ovaries and head kidneys. Polymerase chain reaction products were also observed using cDNA from steroidogenic tissues and primers designed to regions specific for cStAR2, indicating that cStAR2 is expressed in tissues and may account for the presence of larger transcripts observed on Northern blots.

Activation of rainbow trout (Oncorhynchus mykiss) mononuclear phagocytes by different pathogen associated molecular pattern (PAMP) bearing agents

Rainbow trout (Oncorhynchus mykiss) cells of a monocyte-macrophage lineage (rtMOCs) were used to characterize the ability of the trout innate immune system to recognize and respond to different pathogen associated molecular pattern (PAMP) bearing substances. Compared to what has been reported for mammalian macrophages, rtMOCs responded with lower sensitivity to lipopolysaccharide (LPS) from Escherichia coli (EC-LPS) and Pseudomonas aeruginosa (PA-LPS). The sensitivity of rtMOCs to LPS was not influenced by the presence of serum which suggests that the resistance to endotoxic shock in fish may be due to the lack of serum-borne factors that confer sensitivity to LPS in mammals. The time course of the response to PAMPs could be separated into two patterns. EC-LPS induced stable cytokine expression whereas PA-LPS, zymosan and muramyl dipeptide induced transient TNF2 expression. By analogy to the type of stimulation observed in mammals it can be hypothesized that different signaling pathways, possibly initiated by different receptors, may be involved in the recognition of these PAMPs by rtMOCs.

Transgenic salmon overexpressing growth hormone exhibit decreased myostatin transcript and protein expression

To characterize the role of myostatin (MSTN) in fast growing animals and to examine the relationship between MSTN and growth hormone (GH), MSTN transcript and protein expression were measured in coho salmon overexpressing GH and in wild-type coho salmon. Quantitative real-time RT-PCR and western analysis were used to measure RNA expression of the two salmonid MSTN genes (1 and 2) and levels of MSTN immunoreactive protein (MIP) in developing embryos and adult coho salmon tissues. In transgenic and control coho embryos, MSTN1 and MSTN2 RNA expression were initially observed at about the time of eying, and a 42 kDa MIP was just detected prior to hatching. Expression of the MSTN1 transcript in transgenic salmon was not different from that in wild-type adult coho salmon muscle and brain tissue. However, expression of the MSTN2 transcript was less in white muscle, and greater in red muscle, from transgenic fish compared to wild-type salmon of the same size. Northern analysis revealed that expression of the MSTN2 transcript was less in white muscle from wild-type, age-matched salmon than in transgenic fish. In addition, there was less presumed bioactive MIP in muscle taken from adult transgenic fish compared to controls and evidence of differential protein processing. Decreased MSTN expression in faster growing fish suggests that MSTN does act as a negative regulator of muscle growth in fish, as it does in mammals. The results of this study also suggest that the anabolic effects of GH could be mediated through MSTN.

Analysis of genes isolated from lipopolysaccharide-stimulated rainbow trout (Oncorhynchus mykiss) macrophages

A primary cell culture system was used to obtain differentiated rainbow trout (Oncorhynchus mykiss) macrophages that were stimulated with Escherichia coli lipopolysaccharide (LPS-10 microg/ml) for 12 h in vitro. Messenger RNA from the LPS-stimulated cells was used to create two cDNA libraries from which a total of 1048 sequences were analyzed. A large number of cDNAs were obtained that could be related to immune function including structural proteins, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors, lectins and immunoglobulins, cytokines and chemokines, cell surface antigens, signal transduction proteins, antimicrobial peptides, and enzymes involved in eicosanoid synthesis. Selected genes that were analyzed by RT-PCR and real time PCR and found to be upregulated by LPS, included vascular cell adhesion molecule, the CCAAT/enhancer binding protein beta, the inhibitor of NF-kB alpha, CD209, a major histocompatibility class II-invariant chain protein, cyclin L1, acute phase serum amyloid A, and prostaglandin endoperoxide synthase 2.

Characterization of a myostatin-like gene from the bay scallop, Argopecten irradians

A complete cDNA was cloned from the bay scallop (Argopecten irradians) that codes for a 382-amino-acid myostatin-like protein (sMSTN). The sMSTN sequence is most similar to mammalian myostatin (MSTN), containing a conserved proteolytic cleavage site (RXXR) and conserved cysteine residues in the C-terminus. Based on quantitative RT-PCR, the sMSTN gene is predominantly expressed in the adductor muscle, with limited expression in other tissues. Using the sMSTN sequence, a Ciona MSTN-like gene was also identified from the Ciona intestinalis genome. These findings indicate that the MSTN gene has been conserved throughout evolution and suggests that MSTN could play a major role in muscle growth and development in invertebrates, as it does in mammals.

Characterization of a highly inducible novel CC chemokine from differentiated rainbow trout (Oncorhynchus mykiss) macrophages

A full-length cDNA clone encoding a novel trout CC chemokine was identified in expressed sequence tags generated from lipopolysaccharide (LPS)-stimulated in vitro differentiated macrophages isolated from the head kidney of the rainbow trout (Oncorhynchus mykiss). The putative 101-amino-acid protein is 38% similar to Macaca mulatta CCL4 (macrophage inflammatory protein 1beta) but is also similar to several other related mammalian CC chemokines, including human Act-2. Real-time PCR and conventional RT-PCR revealed significant up-regulation of transcript levels of the trout CCL4-like mRNA in LPS-stimulated in vitro differentiated macrophages. In unstimulated trout, CCL4-like mRNA expression was detected at different levels in all tissues tested, whereas in LPS-challenged animals (6 mg/kg), CCL4-like mRNA increased in intestine, ovary and spleen at both 24 h and 72 h post-injection. In gills, CCL4-like mRNA expression was inhibited after LPS administration. Based on the highly regulated expression pattern exhibited by the trout CCL4-like mRNA, it is likely that this chemokine plays an important regulatory role in the immune response of trout.

Growth hormone differentially regulates muscle myostatin1 and -2 and increases circulating cortisol in rainbow trout (Oncorhynchus mykiss)

Myostatin (MSTN) negatively regulates muscle growth in vertebrates. Salmonids produce two myostatin transcripts from separate genes. Surprisingly, quantitative analyses indicate different regulatory mechanisms for the two myostatin genes in rainbow trout. MSTN1 mRNA levels were elevated 26% following recombinant bovine growth hormone (rbGH) treatment, while MSTN2 mRNA levels were reduced 74% compared to controls. MSTN precursor protein (42kDa) levels were elevated in rbGH treated fish compared to controls. In addition, circulating cortisol levels were elevated 71% following rbGH treatment compared to controls. In treated and control fish, cortisol levels were elevated 245% at day 0 compared to subsequent days. Treated fish exhibited cortisol levels 207% higher than controls at 0.5 day, and remained at least 50% higher for 7 days following treatment. This pattern of change was positively correlated to MSTN1 mRNA levels. This is the first time a direct relationship has been reported between GH, cortisol, and myostatin. In addition, following rbGH administration, myosin protein concentrations in skeletal muscle samples increased, suggesting that GH regulates expression of the most abundant muscle protein. These results indicate the two myostatin genes are differentially regulated and may possess different functions in rainbow trout muscle, and suggests a possible interaction between GH, cortisol, and muscle growth.

Acute neurosteroid modulation and subunit isolation of the gamma-aminobutyric acidA receptor in the bullfrog, Rana catesbeiana

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) has multiple receptors. In mammals, the GABA(A) receptor subtype is modulated by neurosteroids. However, whether steroid interaction with the GABA(A) receptor is unique to mammals or a conserved feature in vertebrates is unknown. Thus, neurosteroid modulation of the GABA(A) receptor was investigated in the brain of the bullfrog (Rana catesbeiana) using the mammalian GABA(A) receptor agonist [(3)H]muscimol. Two neurosteroids, allopregnanolone and pregnenolone sulfate, affected [(3)H]muscimol specific binding in bullfrog brain membrane preparations. Allopregnanolone significantly increased [(3)H]muscimol specific binding in a dose- and time-dependent manner. The pattern of allopregnanolone modulation supports the hypothesis that the bullfrog brain possesses both high-affinity and low-affinity [(3)H]muscimol binding sites. Unlike allopregnanolone, pregnenolone sulfate showed biphasic modulation with increased [(3)H]muscimol specific binding at low nanomolar concentrations and decreased specific binding at micromolar concentrations. Additionally, three cDNA fragments with significant homology to mammalian GABA(A) receptor subunits were isolated from the bullfrog brain. These fragments belong to the alpha1, beta1, and gamma2 subunit families. In mammals, GABA(A) receptors composed of these specific subunit isoforms are effectively modulated by neurosteroids, including allopregnanolone. Neurosteroid modulation of the amphibian brain GABA(A) receptor is therefore supported by both [(3)H]muscimol binding studies and subunit sequences. Allopregnanolone and pregnenolone sulfate modulation of this receptor may thus represent a significant mechanism for steroid influence on amphibian brain and behavior.

Tumor necrosis factors

Since the discovery of tumor necrosis factor (TNF) and lymphotoxin, many structurally related factors have been elucidated in mammals that are grouped together in the TNF Ligand Superfamily. These factors have profound pleiotropic roles involving inflammation, apoptosis, cell proliferation and stimulation of the immune system. TNF has only been isolated from mammals and fish. While two TNFs (alpha and beta) are present in mammals, it appears that only one form of TNF is found in fish that is more similar in structure and genomic organization to mammalian TNFalpha. TNF transcripts are expressed in both mammals and fish with similar kinetics, and the involvement of NF-kappaB in TNF expression in fish suggests that transcriptional regulation may be similar within vertebrates. Mammalian TNFalpha stimulates macrophage activity in fish and birds, and in both groups of vertebrates, macrophage-derived supernatants have been shown to contain TNF-like activities, suggesting the presence of bioactive native TNFalpha.

Myostatin protein and RNA transcript levels in adult and developing brook trout

Quantitative real-time RT-PCR and Western analysis were used to measure RNA expression of the two brook trout myostatin (MSTN) genes ("ovarian", ov and "brain/muscle", b/m), and levels of MSTN immunoreactive protein (MIP) in developing embryos and muscle of brook trout adults. In developing brook trout embryos, ov and b/m MSTN RNAs and MIP significantly increased 45 days post-fertilization. In adult brook trout, the b/m MSTN form was expressed at higher levels in red versus white muscle regardless of gender or time of year. While few changes were observed in MSTN transcripts in fish sampled throughout the year, a significant increase in the processed 14 kDa MIP was observed at spawning in a tissue specific manner, and differences were observed between males and females. These data, along with promoter sequence analysis of the of b/m and ov genes, support a role for MSTN in muscle growth and development in fish.