Core microbiome profiles and their modification by environmental, biological, and rearing factors in aquaculture hatcheries

16S rRNA gene sequencing and bacteria- and genus-specific quantitative PCR was used to profile microbial communities and their associated functions in water, live feed (microalgae, Artemia, and rotifer), and European sea bass and gilthead sea bream larvae from hatcheries in Greece and Italy. The transfer to larvae of genus containing potential pathogens of fish was more likely with Artemia and rotifer than with microalgae or water, irrespective of geographic location. The presence of potentially pathogenic bacteria (Vibrio and Pseudoalteromonas) in the core microbiota of water, live feed, and fish larvae, the enrichment of different bacterial resistance pathways and biofilm formation, and the overall low beneficial bacteria load during larval ontogeny emphasizes the risk for disease outbreaks. The present data characterizing microbiota in commercial aquaculture hatcheries provides a baseline for the design of strategies to manage disease and to model or remediate potential adverse environmental impacts.

Factors Driving Bacterial Microbiota of Eggs from Commercial Hatcheries of European Seabass and Gilthead Seabream

A comprehensive understanding of how bacterial community abundance changes in fishes during their lifecycle and the role of the microbiota on health and production is still lacking. From this perspective, the egg bacterial communities of two commercially farmed species, the European seabass (Dicentrarchus labrax) and the gilthead seabream (Sparus aurata), from different aquaculture sites were compared, and the potential effect of broodstock water microbiota and disinfectants on the egg microbiota was evaluated. Moreover, 16S ribosomal RNA gene sequencing was used to profile the bacterial communities of the eggs and broodstock water from three commercial hatcheries. Proteobacteria were the most common and dominant phyla across the samples (49.7% on average). Vibrio sp. was the most highly represented genus (7.1%), followed by Glaciecola (4.8%), Pseudoalteromonas (4.4%), and Colwellia (4.2%), in eggs and water across the sites. Routinely used iodine-based disinfectants slightly reduced the eggs' bacterial load but did not significantly change their composition. Site, species, and type of sample (eggs or water) drove the microbial community structure and influenced microbiome functional profiles. The egg and seawater microbiome composition differed in abundance but shared similar functional profiles. The strong impact of site and species on egg bacterial communities indicates that disease management needs to be site-specific and highlights the need for species- and site-specific optimization of disinfection protocols.

Climate change impacts on fish reproduction are mediated at multiple levels of the brain-pituitary-gonad axis

Anthropogenic emissions of carbon dioxide in the atmosphere have generated rapid variations in atmospheric composition which drives major climate changes. Climate change related effects include changes in physico-chemical proprieties of sea and freshwater, such as variations in water temperature, salinity, pH/pCO₂ and oxygen content, which can impact fish critical physiological functions including reproduction. In this context, the main aim of the present review is to discuss how climate change related effects (variation in water temperature and salinity, increases in duration and frequency of hypoxia events, water acidification) would impact reproduction by affecting the neuroendocrine axis (brain-pituitary-gonad axis). Variations in temperature and photoperiod regimes are known to strongly affect sex differentiation and the timing and phenology of spawning period in several fish species. Temperature mainly acts at the level of gonad by interfering with steroidogenesis, (notably on gonadal aromatase activity) and gametogenesis. Temperature is also directly involved in the quality of released gametes and embryos development. Changes in salinity or water acidification are especially associated with reduction of sperm quality and reproductive output. Hypoxia events are able to interact with gonad steroidogenesis by acting on the steroids precursor cholesterol availability or directly on aromatase action, with an impact on the quality of gametes and reproductive success. Climate change related effects on water parameters likely influence also the reproductive behavior of fish. Although the precise mechanisms underlying the regulation of these effects are not always understood, in this review we discuss different hypothesis and propose future research perspectives.

LPS Modulates the Expression of Iron-Related Immune Genes in Two Antarctic Notothenoids

The non-specific immunity can induce iron deprivation as a defense mechanism against potential bacterial pathogens, but little information is available as to its role in Antarctic fish. In this study the response of iron metabolism related genes was evaluated in liver and head kidney of the Antarctic notothenoids Notothenia coriiceps and Notothenia rossii 7 days after lipopolysaccharide (LPS) injection. Average plasma Fe²⁺ concentration was unaffected by treatment in any of the species. The gene expression response to LPS varied between tissues and species, being stronger in N. coriiceps and more prominent in the head kidney than liver. The reaction to LPS was marked by increased individual variability in most genes analyzed, even when the change in expression was not statistically significant, suggesting different individual sensitivity and coping responses in these wild fish. We found that iron related genes had an attenuated and homogenous response to LPS but there was no detectable relationship between plasma Fe²⁺ and gene expression. However, overall in both tissues and species LPS exposure set a multilevel response that concur to promote intracellular accumulation of iron, an indication that Antarctic Notothenoids use innate nutritional immunity as a resistance mechanism against pathogens.

Genistein and estradiol have common and specific impacts on the sea bass (Dicentrarchus labrax) skin-scale barrier

Teleost fish scales play important roles in animal protection and homeostasis. They can be targeted by endogenous estrogens and by environmental estrogenic endocrine disruptors. The phytoestrogen genistein is ubiquitous in the environment and in aquaculture feeds and is a disruptor of estrogenic processes in vertebrates. To test genistein disrupting actions in teleost fish we used a minimally invasive approach by analysing scales plucked from the skin of sea bass (Dicentrarchus labrax). Genistein transactivated all three fish nuclear estrogen receptors and was most potent with the Esr2, had the highest efficacy with Esr1, but reached, in all cases, transactivation levels lower than those of estradiol. RNA-seq revealed 254 responsive genes in the sea bass scales transcriptome with an FDR < 0.05 and more than 2-fold change in expression, 1 or 5 days after acute exposure to estradiol or to genistein. 65 genes were specifically responsive to estradiol and 106 by genistein while 83 genes were responsive to both compounds. Estradiol specifically regulated genes of protein/matrix turnover and genistein affected sterol biosynthesis and regeneration, while innate immune responses were affected by both compounds. This comprehensive study revealed the impact on the fish scale transcriptome of estradiol and genistein, providing a solid background to further develop fish scales as a practical screening tool for endocrine disrupting chemicals in teleosts.

Estradiol and genistein effects on the sea bass (Dicentrarchus labrax) scales: Transcriptome dataset

Fish scales are mineralized structures that play important roles in protection and mineral homeostasis. This tissue expresses multiple estrogen receptor subtypes and can be targeted by estrogens or estrogenic endocrine-disrupting compounds, but their effects are poorly explored. The transcriptome data here presented support the findings reported in the research article “Genistein and estradiol have common and specific impacts on the sea bass (Dicentrarchus labrax) skin-scale barrier” [1]. Juvenile sea bass were exposed to estradiol and the phytoestrogen genistein for 1 and 5 days, by intraperitoneal injections, and the effects on scale transcript expression were analysed by RNA-seq using an Illumina Hi-seq 1500. The raw reads of the 30 libraries produced have been deposited in the NCBI-SRA database with the project accession number SRP102504. Mapping of RNA-seq reads against the sea bass reference genome using the Cufflinks/TopHat package identified 371 genes that had significant (FDR<0.05) differential expression with the estradiol or genistein treatments in relation to the control scales at each exposure time, 254 of which presented more than a 2-fold change in expression. The identity of the differentially expressed genes was obtained using both automatic and manual annotations against multiple public sequence databases and they were grouped according to their patterns of expression using hierarchical clustering and heat-maps. The biological processes and KEGG pathways most significantly affected by the estradiol and/or genistein treatments were identified using Cytoscape/ClueGO enrichment analyses.

Genomic analysis of Sparus aurata reveals the evolutionary dynamics of sex-biased genes in a sequential hermaphrodite fish

Sexual dimorphism is a fascinating subject in evolutionary biology and mostly results from sex-biased expression of genes, which have been shown to evolve faster in gonochoristic species. We report here genome and sex-specific transcriptome sequencing of Sparus aurata, a sequential hermaphrodite fish. Evolutionary comparative analysis reveals that sex-biased genes in S. aurata are similar in number and function, but evolved following strikingly divergent patterns compared with gonochoristic species, showing overall slower rates because of stronger functional constraints. Fast evolution is observed only for highly ovary-biased genes due to female-specific patterns of selection that are related to the peculiar reproduction mode of S. aurata, first maturing as male, then as female. To our knowledge, these findings represent the first genome-wide analysis on sex-biased loci in a hermaphrodite vertebrate species, demonstrating how having two sexes in the same individual profoundly affects the fate of a large set of evolutionarily relevant genes.

Zygoparity and sex steroid hormone profiles in bluemouth Helicolenus dactylopterus

Two hundred and seven individuals (103 females and 104 males) of bluemouth Helicolenus dactylopterus (Scorpaeniformes, Sebastidae), a commercially important deep-water species with an unusual reproductive strategy, from the eastern Atlantic Ocean ranging from 13·9 to 37·5 cm total length (L_T ) were analysed from September 2011 to October 2012. The analysis included gonad maturity phases and blood-plasma levels of oestradiol-17β (E₂ ), 11-ketotestosterone (11-KT) and 17,20β-dihydroxypregn-4-en-3-one (17,20β-P). Results confirmed the existence of an annual reproductive cycle with asynchrony between females and males and a spawning season from January to May. A pronounced peak in 17,20β-P in October for both sexes was associated with possible mating behaviour and recent copula. Levels of E₂ increased preceding the elevation of the gonado-somatic index during ovarian growth and were lower during regression and regeneration. The frequency distribution of oocyte-embryonic stages and variation of hormone levels suggest the existence of daily rhythms. Fertilization was detected between 2000-0000 and 0800-1200 h and spawning took place throughout the day peaking between 2000 and 0000 h. The cyclic pattern of sex steroids and ovarian recruitment provides a new insight into the reproductive strategy of this species.

Pth4, an ancient parathyroid hormone lost in eutherian mammals, reveals a new brain-to-bone signaling pathway

Regulation of bone development, growth, and remodeling traditionally has been thought to depend on endocrine and autocrine/paracrine modulators. Recently, however, brain-derived signals have emerged as key regulators of bone metabolism, although their mechanisms of action have been poorly understood. We reveal the existence of an ancient parathyroid hormone (Pth)4 in zebrafish that was secondarily lost in the eutherian mammals' lineage, including humans, and that is specifically expressed in neurons of the hypothalamus and appears to be a central neural regulator of bone development and mineral homeostasis. Transgenic fish lines enabled mapping of axonal projections leading from the hypothalamus to the brainstem and spinal cord. Targeted laser ablation demonstrated an essential role for of pth4-expressing neurons in larval bone mineralization. Moreover, we show that Runx2 is a direct regulator of pth4 expression and that Pth4 can activate cAMP signaling mediated by Pth receptors. Finally, gain-of-function experiments show that Pth4 can alter calcium/phosphorus levels and affect expression of genes involved in phosphate homeostasis. Based on our discovery and characterization of Pth4, we propose a model for evolution of bone homeostasis in the context of the vertebrate transition from an aquatic to a terrestrial lifestyle.-Suarez-Bregua, P., Torres-Nuñez, E., Saxena, A., Guerreiro, P., Braasch, I., Prober, D. A., Moran, P., Cerda-Reverter, J. M., Du, S. J., Adrio, F., Power, D. M., Canario, A. V. M., Postlethwait, J. H., Bronner, M E., Cañestro, C., Rotllant, J. Pth4, an ancient parathyroid hormone lost in eutherian mammals, reveals a new brain-to-bone signaling pathway.

Steroidogenesis by testis and accessory glands of the Lusitanian toadfish, Halobatrachus didactylus, during reproductive season

In teleost fish sex steroids are essential for gonadal function and have marked effects in reproductive and agonistic behavior and in the expression of secondary sexual characteristics. The Lusitanian toadfish, Halobatrachus didactylus, has two male morphotypes: type I males are territorial nest-holders and have large accessory glands while type II males are smaller, have a relatively large testis and small accessory glands. In the present study, the steroidogenic activity of the testis and accessory testicular glands of the Lusitanian toadfish were examined in vitro as well as their presence in urine. The testis of type I males produced 11-ketotestosterone (11KT) and 11β-hydroxy-4-androstene-3,17-dione (11βA) from tritiated 17-hydroxyprogesterone, while those of type II males produced testosterone (T) and 11β,17β-dihydroxy-4-andosten-3-one (11βT), but not 11KT. Additionally, the testis and accessory glands of both morphs produced mostly 5β,3α-reduced and 17,20α-hydroxylated metabolites. Type I, but not of type II, males synthesised 5β-reduced androgens in their accessory glands. The presence of 11βA exclusively in the urine of type I males during reproductive season suggests an association with maintenance of secondary sexual characteristics and behavior in this morph. The urine of both types of males contained two 5α-androstane and 5β-pregnane glucuronides. Among the latter steroids, those that are 17,21-dihydroxylated are potentially metabolites from cortisol and were found only in type I males during the spawning season. The diversity of metabolites produced by the testis and accessory glands and the presence of some in urine is suggestive of a potential role in chemical communication and reproductive behavior.

Stanniocalcin 1 effects on the renal gluconeogenesis pathway in rat and fish

The mammalian kidney contributes significantly to glucose homeostasis through gluconeogenesis. Considering that stanniocalcin 1 (STC1) regulates ATP production, is synthesized and acts in different cell types of the nephron, the present study hypothesized that STC1 may be implicated in the regulation of gluconeogenesis in the vertebrate kidney. Human STC1 strongly reduced gluconeogenesis from (14)C-glutamine in rat renal medulla (MD) slices but not in renal cortex (CX), nor from (14)C-lactic acid. Total PEPCK activity was markedly reduced by hSTC1 in MD but not in CX. Pck2 (mitochondrial PEPCK isoform) was down-regulated by hSTC1 in MD but not in CX. In fish (Dicentrarchus labrax) kidney slices, both STC1-A and -B isoforms decreased gluconeogenesis from (14)C-acid lactic, while STC1-A increased gluconeogenesis from (14)C-glutamine. Overall, our results demonstrate a role for STC1 in the control of glucose synthesis via renal gluconeogenesis in mammals and suggest that it may have a similar role in teleost fishes.

How integrated are behavioral and endocrine stress response traits? A repeated measures approach to testing the stress-coping style model

It is widely expected that physiological and behavioral stress responses will be integrated within divergent stress-coping styles (SCS) and that these may represent opposite ends of a continuously varying reactive–proactive axis. If such a model is valid, then stress response traits should be repeatable and physiological and behavioral responses should also change in an integrated manner along a major axis of among-individual variation. While there is some evidence of association between endocrine and behavioral stress response traits, few studies incorporate repeated observations of both. To test this model, we use a multivariate, repeated measures approach in a captive-bred population of Xiphophorus birchmanni. We quantify among-individual variation in behavioral stress response to an open field trial (OFT) with simulated predator attack (SPA) and measure waterborne steroid hormone levels (cortisol, 11-ketotestosterone) before and after exposure. Under the mild stress stimulus (OFT), (multivariate) behavioral variation among individuals was consistent with a strong axis of personality (shy–bold) or coping style (reactive–proactive) variation. However, behavioral responses to a moderate stressor (SPA) were less repeatable, and robust statistical support for repeatable endocrine state over the full sampling period was limited to 11-ketotestosterone. Although post hoc analysis suggested cortisol expression was repeatable over short time periods, qualitative relationships between behavior and glucocorticoid levels were counter to our a priori expectations. Thus, while our results clearly show among-individual differences in behavioral and endocrine traits associated with stress response, the correlation structure between these is not consistent with a simple proactive–reactive axis of integrated stress-coping style. Additionally, the low repeatability of cortisol suggests caution is warranted if single observations (or indeed repeat measures over short sampling periods) of glucocorticoid traits are used in ecological or evolutionary studies focussed at the individual level.

European sea bass genome and its variation provide insights into adaptation to euryhalinity and speciation

The European sea bass (Dicentrarchus labrax) is a temperate-zone euryhaline teleost of prime importance for aquaculture and fisheries. This species is subdivided into two naturally hybridizing lineages, one inhabiting the north-eastern Atlantic Ocean and the other the Mediterranean and Black seas. Here we provide a high-quality chromosome-scale assembly of its genome that shows a high degree of synteny with the more highly derived teleosts. We find expansions of gene families specifically associated with ion and water regulation, highlighting adaptation to variation in salinity. We further generate a genome-wide variation map through RAD-sequencing of Atlantic and Mediterranean populations. We show that variation in local recombination rates strongly influences the genomic landscape of diversity within and differentiation between lineages. Comparing predictions of alternative demographic models to the joint allele-frequency spectrum indicates that genomic islands of differentiation between sea bass lineages were generated by varying rates of introgression across the genome following a period of geographical isolation.

The European sea bass is an economically important fish species, which is subject to intense selective breeding. Here, the authors sequence the genome of the European sea bass and highlight gene family expansions underlying adaptation to salinity change, as well as the genomic architecture of speciation between two divergent sea bass lineages.

Identity of a tilapia pheromone released by dominant males that primes females for reproduction

Knowledge of the chemical identity and role of urinary pheromones in fish is scarce, yet it is necessary in order to understand the integration of multiple senses in adaptive responses and the evolution of chemical communication [1]. In nature, Mozambique tilapia (Oreochromis mossambicus) males form hierarchies, and females mate preferentially with dominant territorial males, which they visit in aggregations or leks [2]. Dominant males have thicker urinary bladder muscular walls than subordinates or females and store large volumes of urine, which they release at increased frequency in the presence of subordinate males or preovulatory, but not postspawned, females [3-5]. Females exposed to dominant-male urine augment their release of the oocyte maturation-inducing steroid 17α,20β-dihydroxypregn-4-en-3-one (17,20β-P) [6]. Here we isolate and identify a male Mozambique tilapia urinary sex pheromone as two epimeric (20α- and 20β-) pregnanetriol 3-glucuronates. We show that both males and females have high olfactory sensitivity to the two steroids, which cross-adapt upon stimulation. Females exposed to both steroids show a rapid, 10-fold increase in production of 17,20β-P. Thus, the identified urinary steroids prime the female endocrine system to accelerate oocyte maturation and possibly promote spawning synchrony. Tilapia are globally important as a food source but are also invasive species, with devastating impact on local freshwater ecosystems [7, 8]. Identifying the chemical cues that mediate reproduction may lead to the development of tools for population control [9-11].

Prolactin regulates luminal bicarbonate secretion in the intestine of the sea bream (Sparus aurata L.)

The pituitary hormone prolactin is a pleiotropic endocrine factor that plays a major role in the regulation of ion balance in fish, with demonstrated actions mainly in the gills and kidney. The role of prolactin in intestinal ion transport remains little studied. In marine fish, which have high drinking rates, epithelial bicarbonate secretion in the intestine produces luminal carbonate aggregates believed to play a key role in water and ion homeostasis. The present study was designed to establish the putative role of prolactin in the regulation of intestinal bicarbonate secretion in a marine fish. Basolateral addition of prolactin to the anterior intestine of sea bream mounted in Ussing chambers caused a rapid (<20 min) decrease of bicarbonate secretion measured by pH-stat. A clear inhibitory dose-response curve was obtained, with a maximal inhibition of 60-65% of basal bicarbonate secretion. The threshold concentration of prolactin for a significant effect on bicarbonate secretion was 10 ng ml(-1), which is comparable with putative plasma levels in seawater fish. The effect of prolactin on apical bicarbonate secretion was independent of the generation route for bicarbonate, as shown in a preparation devoid of basolateral HCO(3)(-)/CO(2) buffer. Specific inhibitors of JAK2 (AG-490, 50 μmol l(-1)), PI3K (LY-294002, 75 μmol l(-1)) or MEK (U-012610, 10 μmol l(-1)) caused a 50-70% reduction in the effect of prolactin on bicarbonate secretion, and demonstrated the involvement of prolactin receptors. In addition to rapid effects, prolactin has actions at the genomic level. Incubation of intestinal explants of anterior intestine of the sea bream in vitro for 3 h demonstrated a specific effect of prolactin on the expression of the Slc4a4A Na(+)-HCO(3)(-) co-transporter, but not on the Slc26a6A or Slc26a3B Cl(-)/HCO(3)(-) exchanger. We propose a new role for prolactin in the regulation of bicarbonate secretion, an essential function for ion/water homeostasis in the intestine of marine fish.

Reference genes to quantify gene expression during oogenesis in a teleost fish

Understanding the molecular events involved in the acquisition of competence during oogenesis is a key step to determine the secret of 'high quality' eggs for aquaculture. Quantitative real time polymerase chain reaction (qPCR) is the technique of election to determine changes in transcript abundance in such studies, but choosing reference genes for normalization, in particular during oogenesis, remains a challenge. In the present study, transcription of 6 functionally distinct genes, β actin (ACTB), cathepsin D (CTSD), cathepsin Z (CTSZ), elongation factor 1 α (EEF1A), TATA binding protein (TBP) and tubulin A (TUBA1A) was assessed as normalizers of bone morphogenetic protein (BMP) and activin membrane-bound inhibitor (BAMBI) gene expression in mRNA from Mozambique tilapia oocytes during oogenesis. Reverse transcription was equally efficient and varies little in all samples. Most of the genes considered for reference were stable during early stages of oogenesis but variations were observed during vitellogenesis. A single gene and up to 3 genes were shown to be insufficient for reliable normalization throughout the whole oogenesis. The combination of the genes ACTB, CTSD, EEF1A and CTSZ as reference was found to minimize variation and has the most stable expression pattern between maturation stages.

Heritability of cortisol response to confinement stress in European sea bass dicentrarchus labrax

BACKGROUND

In fish, the most studied production traits in terms of heritability are body weight or growth, stress or disease resistance, while heritability of cortisol levels, widely used as a measure of response to stress, is less studied. In this study, we have estimated heritabilities of two growth traits (body weight and length) and of cortisol response to confinement stress in the European sea bass.

FINDINGS

The F1 progeny analysed (n = 922) belonged to a small effective breeding population with contributions from an unbalanced family structure of just 10 males and 2 females. Heritability values ranged from 0.54 (± 0.21) for body weight to 0.65 (± 0.22) for standard body length and were low for cortisol response i.e. 0.08 (± 0.06). Genetic correlations were positive (0.94) between standard body length and body weight and negative between cortisol and body weight and between cortisol and standard body length (-0.60 and -0.55, respectively).

CONCLUSION

This study confirms that in European sea bass, heritability of growth-related traits is high and that selection on such traits has potential. However, heritability of cortisol response to stress is low in European sea bass and since it is known to vary greatly among species, further studies are necessary to understand the reasons for these differences.

Skin healing and scale regeneration in fed and unfed sea bream, Sparus auratus

Background

Fish scales are an important reservoir of calcium and phosphorus and together with the skin function as an integrated barrier against environmental changes and external aggressors. Histological studies have revealed that the skin and scales regenerate rapidly in fish when they are lost or damaged. In the present manuscript the histological and molecular changes underlying skin and scale regeneration in fed and fasted sea bream (Sparus auratus) were studied using a microarray 3 and 7 days after scale removal to provide a comprehensive molecular understanding of the early stages of these processes.

Results

Histological analysis of skin/scales revealed 3 days after scale removal re-epithelisation and formation of the scale pocket had occurred and 53 and 109 genes showed significant up or down-regulation, respectively. Genes significantly up-regulated were involved in cell cycle regulation, cell proliferation and adhesion, immune response and antioxidant activities. 7 days after scale removal a thin regenerated scale was visible and only minor changes in gene expression occurred. In animals that were fasted to deplete mineral availability the expression profiles centred on maintaining energy homeostasis. The utilisation of fasting as a treatment emphasised the competing whole animal physiological requirements with regard to barrier repair, infection control and energy homeostasis.

Conclusions

The identification of numerous genes involved in the mitotic checkpoint and cell proliferation indicate that the experimental procedure may be useful for understanding cell proliferation and control in vertebrates within the context of the whole animal physiology. In response to skin damage genes of immune surveillance were up-regulated along with others involved in tissue regeneration required to rapidly re-establish barrier function. Additionally, candidate fish genes were identified that may be involved in cytoskeletal re-modelling, mineralization and stem cells, which are of potential use in aquaculture and fish husbandry, as they may impact on the ability of the fish to produce structural proteins, such as muscle, efficiently.

Divergence of duplicate POMC genes in gilthead sea bream Sparus auratus

Proopiomelanocorticotrophin (POMC) in vertebrates is produced in the pituitary gland and undergoes post-translational processing to give rise to a range of biologically active peptides. Teleosts possess 2-3 different POMC transcripts which have been proposed to have originated from a whole or partial genome duplication. In the present study 2 transcripts of gilthead sea bream POMC (sbPOMC-α1 and α2) were cloned and characterised. sbPOMC-α1 is expressed principally in the melanotroph cells of the pars intermedia (PI) and sbPOMC-α2 is expressed in the corticotroph cells of the rostral pars distalis and probably also in the PI. The 2 sbPOMC transcripts have a differential tissue distribution in extra-pituitary sites. An appraisal of POMC evolution indicates sbPOMCs belong to one of the two main clades that exist in teleosts and that overall a non conservative process of gene loss occurred in this infraclass.

Estrogen-responsive genes in macrophages of the bony fish gilthead seabream: a transcriptomic approach

The role of sex steroids in the modulation of fish immune responses has received little attention. Previous studies have demonstrated that 17β-estradiol (E(2)) is able to alter the response of gilthead seabream leukocytes to infectious agents. We have used suppression subtractive hybridization to identify genes upregulated by E(2) (50 ng/ml) in macrophage cultures from gilthead seabream. We isolated 393 up-regulated cDNA fragments that led to the identification of 162 candidate estrogen-responsive genes. Functional analyses revealed the presence of several enriched immune processes and molecular pathways. The E(2) up-regulation of some immune-relevant genes was further confirmed by real time RT-PCR. Bioinformatics analysis revealed the ability of E(2) to orchestrate profound alterations in the macrophage expression profile, especially immune-related processes and pathways. This is the first report on E(2)-dependent modifications of fish macrophage transcriptome and lends weight to a suggested role for estrogen in the immune system, the possible significance of which is discussed.

In silico mining and characterization of simple sequence repeats from gilthead sea bream (Sparus aurata) expressed sequence tags (EST-SSRs); PCR amplification, polymorphism evaluation and multiplexing and cross-species assays

We screened for simple sequence repeats (SSRs) found in ESTs derived from an EST-database development project ('Marine Genomics Europe' Network of Excellence). Different motifs of di-, tri-, tetra-, penta- and hexanucleotide SSRs were evaluated for variation in length and position in the expressed sequences, relative abundance and distribution in gilthead sea bream (Sparus aurata). We found 899 ESTs that harbor 997 SSRs (4.94%). On average, one SSR was found per 2.95 kb of EST sequence and the dinucleotide SSRs are the most abundant accounting for 47.6% of the total number. EST-SSRs were used as template for primer design. 664 primer pairs could be successfully identified and a subset of 206 pairs of primers was synthesized, PCR-tested and visualized on ethidium bromide stained agarose gels. The main objective was to further assess the potential of EST-SSRs as informative markers and investigate their cross-species amplification in sixteen teleost fish species: seven sparid species and nine other species from different families. Approximately 78% of the primer pairs gave PCR products of expected size in gilthead sea bream, and as expected, the rate of successful amplification of sea bream EST-SSRs was higher in sparids, lower in other perciforms and even lower in species of the Clupeiform and Gadiform orders. We finally determined the polymorphism and the heterozygosity of 63 markers in a wild gilthead sea bream population; fifty-eight loci were found to be polymorphic with the expected heterozygosity and the number of alleles ranging from 0.089 to 0.946 and from 2 to 27, respectively. These tools and markers are expected to enhance the available genetic linkage map in gilthead sea bream, to assist comparative mapping and genome analyses for this species and further with other model fish species and finally to help advance genetic analysis for cultivated and wild populations and accelerate breeding programs.

Development of an oligo DNA microarray for the European sea bass and its application to expression profiling of jaw deformity

Background

The European sea bass (Dicentrarchus labrax) is a marine fish of great importance for fisheries and aquaculture. Functional genomics offers the possibility to discover the molecular mechanisms underlying productive traits in farmed fish, and a step towards the application of marker assisted selection methods in this species. To this end, we report here on the development of an oligo DNA microarray for D. labrax.

Results

A database consisting of 19,048 unique transcripts was constructed, of which 12,008 (63%) could be annotated by similarity and 4,692 received a GO functional annotation. Two non-overlapping 60mer probes were designed for each unique transcript and in-situ synthesized on glass slides using Agilent SurePrint™ technology. Probe design was positively completed for 19,035 target clusters; the oligo microarray was then applied to profile gene expression in mandibles and whole-heads of fish affected by prognathism, a skeletal malformation that strongly affects sea bass production. Statistical analysis identified 242 transcripts that are significantly down-regulated in deformed individuals compared to normal fish, with a significant enrichment in genes related to nervous system development and functioning. A set of genes spanning a wide dynamic range in gene expression level were selected for quantitative RT-PCR validation. Fold change correlation between microarray and qPCR data was always significant.

Conclusions

The microarray platform developed for the European sea bass has a high level of flexibility, reliability, and reproducibility. Despite the well known limitations in achieving a proper functional annotation in non-model species, sufficient information was obtained to identify biological processes that are significantly enriched among differentially expressed genes. New insights were obtained on putative mechanisms involved on mandibular prognathism, suggesting that bone/nervous system development might play a role in this phenomenon.

Piscine PTHrP regulation of calcium and phosphate transport in winter flounder renal proximal tubule primary cultures

Multiple factors control calcium (Ca(2+)) and inorganic phosphate (P(i)) transport in the fish nephron, and the recently discovered members of the piscine parathyroid hormone-like protein family are likely participants in such regulatory mechanisms. The effects of an NH(2)-terminal peptide (amino acids 1-34) of Takifugu rubripes parathyroid hormone-related protein, (1-34)PTHrP, on Ca(2+) and P(i) transport were investigated in winter flounder (Pseudopleuronectes americanus) proximal tubule cells in primary culture (fPTCs). RT-PCR performed on RNA extracted from fPTCs and from intact kidney tissue indicated that expression of PTHrP and types 1 and 3 PTH/PTHrP receptors occurred both in vivo and in vitro and that circulating levels of PTHrP measured by specific radioimmunoassay averaged 2.5 +/- 0.13 ng/ml. fPTC monolayers were mounted in Ussing chambers, and under neutral electrochemical conditions, addition of 10 nM (1-34)PTHrP to the basolateral side induced a slight increase in Ca(2+) transport rate from luminal to peritubular side, significantly stimulating net Ca(2+) reabsorption. (1-34)PTHrP also significantly increased the P(i) secretory flux, and slightly reduced P(i) reabsorption, evoking a significant increase in P(i) net secretion. This stimulatory effect was partially inhibited by bisindolylmaleimide, an inhibitor of protein kinase C. Incubation of ex vivo flounder renal tubules with (1-34)PTHrP resulted in apparent reduction of Na(+)-P(i) cotransporter type II (NaP(i)-II) protein in tubule membranes. PTHrP seems therefore to participate in the modulation of Ca(2+) and P(i) homeostasis by fish kidney.

CRTAC1 homolog proteins are conserved from cyanobacteria to man and secreted by the teleost fish pituitary gland

Cartilage acidic protein 1 (CRTAC1) gene expression is used as a marker for chondrocyte differentiation in stem cell-based tissue engineering. It is also transcribed outside the skeleton where at least two different transcripts are expressed in lung and brain. In the pituitary gland of the teleost fish sea bream Sparus auratus, we have found a transcript with a high degree of sequence identity to CRTAC1 family members but lacking the EGF-like calcium-binding domain encoding sequence of CRTAC1 and designated it as CRTAC2. Database searches revealed many previously unidentified members of the CRTAC1 and CRTAC2 in phylogenetically distant organisms, such as cyanobacteria, bryophyta, lancelets, and diverse representatives of vertebrates. Phylogenetic analyses showed that the genes encoding CRTAC1 and CRTAC2 proteins coexist in teleost fish genomes. Structural prediction analysis identified the N-terminal region of the CRTAC1/CRTAC2 family members as a potential seven-bladed beta-propeller structure, closely related to those of integrin alpha chains and glycosylphosphatidylinositol-specific phospholipase D1 protein families. This relationship is confirmed by phylogenetic analysis with the N-terminal domain of sea bream CRTAC2 as the most divergent sequence. Because teleost fishes are the only phylogenetic group where both CRTAC1 and CRTAC2 genes are present, they occupy a pivotal position in studies of the mechanisms governing the specific expression patterns of each gene/protein subfamily. This will be essential to elucidate their respective biological roles.

The European sea bass Dicentrarchus labrax genome puzzle: comparative BAC-mapping and low coverage shotgun sequencing

Background

Food supply from the ocean is constrained by the shortage of domesticated and selected fish. Development of genomic models of economically important fishes should assist with the removal of this bottleneck. European sea bass Dicentrarchus labrax L. (Moronidae, Perciformes, Teleostei) is one of the most important fishes in European marine aquaculture; growing genomic resources put it on its way to serve as an economic model.

Results

End sequencing of a sea bass genomic BAC-library enabled the comparative mapping of the sea bass genome using the three-spined stickleback Gasterosteus aculeatus genome as a reference. BAC-end sequences (102,690) were aligned to the stickleback genome. The number of mappable BACs was improved using a two-fold coverage WGS dataset of sea bass resulting in a comparative BAC-map covering 87% of stickleback chromosomes with 588 BAC-contigs. The minimum size of 83 contigs covering 50% of the reference was 1.2 Mbp; the largest BAC-contig comprised 8.86 Mbp. More than 22,000 BAC-clones aligned with both ends to the reference genome. Intra-chromosomal rearrangements between sea bass and stickleback were identified. Size distributions of mapped BACs were used to calculate that the genome of sea bass may be only 1.3 fold larger than the 460 Mbp stickleback genome.

Conclusions

The BAC map is used for sequencing single BACs or BAC-pools covering defined genomic entities by second generation sequencing technologies. Together with the WGS dataset it initiates a sea bass genome sequencing project. This will allow the quantification of polymorphisms through resequencing, which is important for selecting highly performing domesticated fish.

Effect of acute copper sulfate exposure on olfactory responses to amino acids and pheromones in goldfish (Carassius auratus)

Exposure of olfactory epithelium to environmentally relevant concentrations of copper disrupts olfaction in fish. To examine the dynamics of recovery at both functional and morphological levels after acute copper exposure, unilateral exposure of goldfish olfactory epithelia to 100 microM CuSO(4) (10 min) was followed by electro-olfactogram (EOG) recording and scanning electron microscopy. Sensitivity to amino acids (l-arginine and l-serine), generally considered food-related odorants, recovered most rapidly (three days), followed by that to catecholamines (3-O-methoxytyramine), bile acids (taurolithocholic acid) and the steroid pheromone, 17,20beta-dihydroxy-4-pregnen-3-one 20-sulfate, which took 28 days to reach full recovery. Sensitivity to the postovulatory pheromone prostaglandin F(2alpha) had not fully recovered even at 28 days. These changes in sensitivity were correlated with changes in the recovery of ciliated and microvillous receptor cell types. Microvillous cells appeared largely unaffected by CuSO(4) treatment. Cilia in ciliated receptor neurones, however, appeared damaged one day post-treatment and were virtually absent after three days but had begun to recover after 14 days. Together, these results support the hypothesis that microvillous receptor neurones detect amino acids whereas ciliated receptor neurones were not functional and are responsible for detection of social stimuli (bile acids and pheromones). Furthermore, differences in sensitivity to copper may be due to different transduction pathways in the different cell types.

A yeast assay based on the gilthead sea bream (teleost fish) estrogen receptor beta for monitoring estrogen mimics

A yeast (Saccharomyces cerevisiae)-based assay was developed and tested with steroids and chemicals (mostly pesticides). The induction of beta-galactosidase activity was strictly dependent on the presence of seabream (Sparus aurata) betaa estrogen receptor (sbERbetaa) and substances known to have estrogenic activity. 17beta-Estradiol (E(2)) and diethylstilbestrol (DES), both agonists, were most active and the antagonist tamoxifen (TAM) was 14-fold less active than E(2). Among the chemicals tested bisphenol-A was most active, followed by pentachlorophenol and naphthalene. Ligand-binding assays with recombinant sbERbetaa and sbERalpha revealed that sbERbetaa binds E(2) with 6.5-fold higher affinity than sbERalpha, confirming the selection of a high sensitive receptor for the yeast assay. DES, ICI 182,780, estrone and TAM had higher relative binding affinity to E2 in sbERalpha than sbERbetaa, although there was no difference in IC50 for these steroids between the two receptors. These results reveal the usefulness of using the yeast-based receptor assay for detecting chemical interaction with steroid receptors from contaminated samples.

Ca(2+)-Calmodulin regulation of testicular androgen production in Mozambique tilapia (Oreochromis mossambicus)

The Ca(2+)-Calmodulin (CaM) signaling pathway has previously been shown to be involved in the regulation of teleost fish ovarian steroidogenesis. However, a putative role of CaM in testicular steroidogenesis and potential targets has not been examined. To examine whether basal steroidogenesis is modulated by Ca(2+) and CaM levels in the testis of Mozambique tilapia (Oreochromis mossambicus) we have incubated testicular fragments in vitro under different conditions and analyzed steroid output. Calcium-free medium with or without EGTA did not affect testicular basal 11-ketotestosterone (11-KT) and testosterone (T) secretion. However, addition of 80microM the CaM inhibitor W7 significantly reduced basal 11-KT, T and androstenedione secretion. Interestingly, the decreased androgen production by 80microM of W7 was accompanied by increased 11-desoxicortisol output and by the activation of cortisol synthesis in the testis, the latter undetected in untreated tissues. However, production of 17,20alpha-dihydroxy-4-pregnen-3-one was unaltered by W7. This suggests that C17,20 desmolase, 21-hydroxylase and possibly 11beta-hydroxysteroid dehydrogenase are targets for CaM. In addition, androgen production was also found to be regulated by the level of cAMP since incubations with forskolin (FK) significantly increased 11-KT and T output. A cross-talk between the cAMP and Ca(2+)-CaM signaling pathways was detected since W7 administration also decreased FK stimulated androgen production. Altogether, these data show that both basal and cAMP stimulated androgen levels were modulated by intracellular Ca(2+)-dependent CaM and that possibly Ca(2+)-CaM determines the shift in steroidogenesis from C21 steroids to androgens.

Development and validation of a gene expression oligo microarray for the gilthead sea bream (Sparus aurata)

Background

Aquaculture represents the most sustainable alternative of seafood supply to substitute for the declining marine fisheries, but severe production bottlenecks remain to be solved. The application of genomic technologies offers much promise to rapidly increase our knowledge on biological processes in farmed species and overcome such bottlenecks. Here we present an integrated platform for mRNA expression profiling in the gilthead sea bream (Sparus aurata), a marine teleost of great importance for aquaculture.

Results

A public data base was constructed, consisting of 19,734 unique clusters (3,563 contigs and 16,171 singletons). Functional annotation was obtained for 8,021 clusters. Over 4,000 sequences were also associated with a GO entry. Two 60mer probes were designed for each gene and in-situ synthesized on glass slides using Agilent SurePrint™ technology. Platform reproducibility and accuracy were assessed on two early stages of sea bream development (one-day and four days old larvae). Correlation between technical replicates was always > 0.99, with strong positive correlation between paired probes. A two class SAM test identified 1,050 differentially expressed genes between the two developmental stages. Functional analysis suggested that down-regulated transcripts (407) in older larvae are mostly essential/housekeeping genes, whereas tissue-specific genes are up-regulated in parallel with the formation of key organs (eye, digestive system). Cross-validation of microarray data was carried out using quantitative qRT-PCR on 11 target genes, selected to reflect the whole range of fold-change and both up-regulated and down-regulated genes. A statistically significant positive correlation was obtained comparing expression levels for each target gene across all biological replicates. Good concordance between qRT-PCR and microarray data was observed between 2- and 7-fold change, while fold-change compression in the microarray was present for differences greater than 10-fold in the qRT-PCR.

Conclusion

A highly reliable oligo-microarray platform was developed and validated for the gilthead sea bream despite the presently limited knowledge of the species transcriptome. Because of the flexible design this array will be able to accommodate additional probes as soon as novel unique transcripts are available.

CYP27A1 expression in gilthead sea bream (Sparus auratus, L.): effects of calcitriol and parathyroid hormone-related protein

Little is known about vitamin D metabolism in fishes. Several reports have shown hydroxylase activities in various organs to produce vitamin D metabolites, but the enzymes involved have not been isolated or characterized. We isolated and characterized a renal mitochondrial hydroxylase, CYP27A1, that governs vitamin D metabolism in gilthead sea bream, Sparus auratus. The enzyme is highly expressed in kidney and to a far lesser extent in liver. When treated with 25-hydroxy vitamin D or calcitriol, the kidney responded differentially and time dependently with CYP27A1 mRNA expression levels. This response substantiates a role for CYP27A1 in fish vitamin D metabolism. This notion is strengthened by upregulation of CYP27A1 in sea bream treated with parathyroid hormone-related protein (PTHrP), and suggests an original role for PTHrP in calcitriol-regulated processes n fish similar to the role of PTH in mammalian vitamin D-dependent processes.

A PTH/PTHrP receptor antagonist blocks the hypercalcemic response to estradiol-17β

Estradiol (E2) increases circulating calcium and phosphate levels in fish, thus acting as a hypercalcemic and hyperphosphatemic factor during periods of high calcium requirements, such as during vitellogenesis. Since parathyroid hormone (PTH)-related protein (PTHrP) has been shown to be calciotropic in fish, we hypothesized that the two hormones could be mediating the same process. Sea bream ( Sparus auratus) juveniles receiving a single intraperitoneal injection of piscine PTHrP(1-34) showed an elevation in calcium plasma levels within 24 h. In contrast, injections of the PTH/PTHrP receptor antagonist PTHrP(7-34) decreased circulating levels of calcium in the same period. Intraperitoneal implants of estradiol-17β (E2; 10 μg/g) evoked significant increases of circulating plasma levels of calcium and phosphorus and a sustained increases of circulating plasma levels of PTHrP. However, a combined treatment of E2 and PTHrP(7-34) evoked a markedly lower calcium response compared with E2 alone. We conclude that PTHrP or a related peptide that binds the PTH/PTHrP receptor mediates, at least in part, the hypercalcemic effect of E2 in calcium and phosphate balance in fish.

Parathyroid hormone-related protein and calcium regulation in vitamin D-deficient sea bream (Sparus auratus)

Gilthead sea bream (Sparus auratus L.) were fed a vitamin D-deficient diet for 22 weeks. Growth rate, whole body mineral pools and calcium balance were determined. Plasma parathyroid hormone-related protein (PTHrP) and calcitriol levels were assessed. Expression of mRNA for pthrp and pth1r was quantified in gills and hypophysis. Fish on vitamin D-deficient diet (D- fish) showed reduced growth and lower calcium turnover (calcium influx, efflux and accumulation rates decreased) and unaltered plasma calcium levels. Plasma calcitriol levels became undetectable, PTHrP levels decreased in the D- fish. In controls, a significant increase in plasma PTHrP level over time was seen, i.e. it increased with body mass. Relationships were found between plasma PTHrP and the whole body pools of calcium, phosphorus and magnesium, indicative of a role for PTHrP in bone development. Expression of pthrp and pth1r mRNA was down-regulated in the hypophysis of D-fish, whereas in gill tissue, pthrp and pth1r mRNA were up-regulated. We conclude that lower pthrp mRNA expression and plasma values in D- fish reflect lower turnover of PTHrP under conditions of hampered growth; up-regulation of pthrp mRNA in gills indicate compensatory paracrine activity of PTHrP during calcitriol deficiency to guarantee well-regulated branchial calcium uptake. This is the first report to document a relation between PTHrP and calcitriol in fish.

Ovarian development and plasma sex steroid levels in cultured female Senegalese sole Solea senegalensis

Ovarian development was studied in cultured female Senegalese sole Solea senegalensis. Females with regressed ovaries, mainly occupied by perinucleolar oocytes, predominated throughout summer exhibiting low condition factor (K), gonadosomatic index (I(G)), and plasma 17beta-estradiol and testosterone levels. Throughout autumn and winter (ovaries at early and intermediate maturation), oocytes progressed to cortical alveoli and vitellogenic stages accompanied by increasing K, I(G), and plasma 17beta-estradiol and testosterone levels. At late winter/early spring, ovarian development reached its maximum with the predominance of females at intermediate and final maturation (the latter occupied by late vitellogenic oocytes and few early maturation oocytes) and peak values of K, I(G), and 17beta-estradiol and testosterone concentrations. Steroid levels were lower (especially testosterone) than those for naturally-spawning females, which might cause extensive atresia without final oocyte maturation (no spawning was observed). This degenerative process reduced de size of the ovary (initial and intermediate phases of regression) in association with declining K, I(G), and plasma 17beta-estradiol and testosterone levels and increasing proportions of perinucleolar oocytes. The circulating 17,20beta-dihydroxy-4-pregnen-3-one levels, the proposed maturation-inducing steroid, remained relatively constant throughout the experimental period, suggesting that oocytes were unable to respond adequately to its stimulation. We propose the inadequate seasonal thermal regime as the main cause of such dysfunction.

A cDNA for European sea bass (Dicentrachus labrax) 11beta-hydroxylase: gene expression during the thermosensitive period and gonadogenesis

Steroid P450 11beta-hydroxylase, encoded by the CYP11B gene, is a key mitochondrial enzyme for the production of 11-oxygenated androgens, which have been shown to be potent masculinising steroids in several fish species. In this study we have isolated a CYP11B cDNA of 1903 base pairs from the testis of European sea bass (Dicentrarchus labrax) encoding a predicted protein of 552 amino acids. The amino acid identities to other vertebrate 11beta-hydroxylase proteins ranged from 66% to 72% to other fish; 45% to amphibian and 35-39% to mammalian. Southern blot indicated that a single CYP11B gene is present. Northern blot analysis detected two transcripts in testis and head kidney, one of the same size of the isolated clone and the other of 3.9 kb. Reverse transcriptase-polymerase chain reaction showed abundant mRNA expression only in testis and head kidney, being residual in a range of other tissues. Expression of CYP11B and CYP19A (which encodes for ovarian aromatase) was detected from at least 4 days post-hatching and did not appear to be affected by rearing temperature (15 and 20 degrees C) during the first 60 days, a period in which high temperatures promote masculinisation in European sea bass. Throughout, gonadogenesis (60-300 dph), a highly dimorphic pattern of CYP11B expression was consistent with a role of this gene in testicular development.

PTHrP regulation and calcium balance in sea bream (Sparus auratus L.) under calcium constraint

Juvenile gilthead sea bream were exposed to diluted seawater (2.5 per thousand salinity; DSW) for 3 h or, in a second experiment, acclimated to DSW and fed a control or calcium-deficient diet for 30 days. Branchial Ca2+ influx, drinking rate and plasma calcium levels were assessed. Sea bream plasma parathyroid hormone related protein (sPTHrP) was measured, and mRNAs of pthrp, its main receptor, pth1r, and the calcium-sensing receptor (casr) were quantified in osmoregulatory tissues and the pituitary gland. When calcium is limited in water or diet, sea bream maintain calcium balance; however, both plasma Ca2+ and plasma sPTHrP concentrations were lower when calcium was restricted in both water and diet. Positive correlations between plasma sPTHrP and plasma Ca2+ (R2 = 0.30, N = 39, P < 0.05), and plasma sPTHrP and body mass of the fish (R2 = 0.37, N = 148, P < 0.001) were found. Immunoreactive sPTHrP was demonstrated in pituitary gland pars intermedia cells that border the pars nervosa and co-localises with somatolactin. In the pituitary gland, pthrp, pth1r and casr mRNAs were downregulated after both short- and long-term exposure to DSW. A correlation between pituitary gland pthrp mRNA expression and plasma Ca2+ (R2 = 0.71, N = 7, P < 0.01) was observed. In gill tissue, pthrp and pth1r mRNAs were significantly upregulated after 30 days exposure to DSW, whereas no effect was found for casr mRNA expression. We conclude that in water of low salinity, declining pituitary gland pthrp mRNA expression accompanied by constant plasma sPTHrP levels points to a reduced sPTHrP turnover and that sPTHrP, through paracrine interaction, is involved in the regulation of branchial calcium handling, independently of endocrine pituitary gland sPTHrP.

PTHrP potentiating estradiol-induced vitellogenesis in sea bream (Sparus auratus, L.)

In fish, vitellogenin is an important nutritional precursor protein produced solely in the liver and released into the blood where it binds calcium. In the gilthead sea bream (Sparus auratus) 17beta-Estradiol (E2) plays an important role in the synthesis of vitellogenin, but also the pituitary hormones prolactin (PRL) and growth hormone (GH) can stimulate vitellogenin induction in fish. Considering the emerging involvement of PTHrP in fish calcium metabolism and the importance of calcium regulation in reproduction, we investigated the possible role of PTHrP in vitellogenesis. E2-naïve and E2-primed sea bream hepatocytes were used in an in vitro primary hepatocyte culture and stimulated with a recombinant sea bream PTHrP (sbPTHrP) to establish the contribution of sbPTHrP alone or in combination with E2 to the regulation of hepatic vitellogenin synthesis. Hepatocytes stimulated solely with sbPTHrP were not affected in their vitellogenesis. However, in hepatocytes stimulated with E2 in combination with sbPTHrP a higher vitellogenin production was seen than with E2 alone. It is concluded that sbPTHrP has a potentiating effect on estradiol stimulation of vitellogenin production by sea bream hepatocytes. The sea bream provides a unique model where vitellogenesis regulation can be studied on E2-naïve liver cells, both in vivo and in vitro.

The parathyroid hormone family of peptides: structure, tissue distribution, regulation, and potential functional roles in calcium and phosphate balance in fish

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are two factors that share amino acid sequence homology and act via a common receptor. In tetrapods, PTH is the main endocrine factor acting in bone and kidney to regulate calcium and phosphate. PTHrP is an essential paracrine developmental factor present in many tissues and is involved in the regulation of ossification, mammary gland development, muscle relaxation, and other functions. Fish apparently lack an equivalent of the parathyroid gland and were long thought to be devoid of PTH. Only in recent years has the existence of PTH-like peptides and their receptors in fish been firmly established. Two forms of PTH, two of PTHrP, and a protein with intermediate characteristics designated PTH-L are encoded by separate genes in teleost fish. Three receptors encoded by separate genes in fish mediate PTH/PTHrP actions, whereas only two receptors have so far been found in terrestrial vertebrates. PTHrP has been more intensively studied than PTH, from lampreys to advanced teleosts. It is expressed in many tissues and is present in high concentration in fish blood. Administration of this peptide alters calcium metabolism and has marked effects on associated gene expression and enzyme activity in vivo and in vitro. This review provides a comprehensive overview of the physiological roles, distribution, and molecular relationships of the piscine PTH-like peptides.

Cortisol and parathyroid hormone-related peptide are reciprocally modulated by negative feedback

In previous in vitro studies, we have shown that the N-terminal region of parathyroid hormone-related protein (PTHrP) can stimulate cortisol production in sea bream, Sparus auratus, interrenal tissue, possibly through a paracrine action. In the current study, the systemic interaction between cortisol and PTHrP was studied in vivo. Sustained elevated blood cortisol levels, induced either by cortisol injection or confinement stress, suppressed circulating PTHrP 6 and 24-fold, respectively, by comparison to control fish. Dexamethasone treatment reduced cortisol levels, prevented the decrease of plasma PTHrP observed in confined fish and raised plasma PTHrP levels in non-confined fish. In contrast, a single injection of (1-34) PTHrP caused a short-term (within 30 min and up to 2.5 h) decrease in plasma cortisol. The antagonistic effects between PTHrP and cortisol were substantiated by an overall (data pooled from all experiments) highly significant negative correlation (r0=-0.745, p<0.001, n=115) between the plasma levels of the two hormones. Although the underlying mechanism of the interaction still has to be determined, the high levels of PTHrP in circulation and the existence of systemic regulation favour the hypothesis that in fish PTHrP may act as an endocrine factor, although the gland that produces it still remains to be identified.

Testicular development and plasma sex steroid levels in cultured male Senegalese sole Solea senegalensis Kaup

Testicular development and plasma levels of sex steroids (11-ketotestosterone (11-KT), testosterone (T) and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P)) were investigated for the first time in cultured male Senegalese sole Solea senegalensis. The germ cell dynamics and gonadosomatic index (IG) were monitored. Based on the relative abundance of the different types of germ cells present, the spermatogenetic cycle was divided into five stages: early (I; spermatogonia (SPG)), mid (II; SPG, spermatocytes (SPC) and spermatids (SPD)), and late spermatogenesis (III; SPC, SPD, and spermatozoa (SPZ)), functional maturation (IV; SPD and SPZ), and recovery (V; SPD, SPZ, and SPG). During summer, fish had stage I and V testes and the lowest values in plasma levels of sex steroids and IG. Testicular recrudescence seemed to begin in autumn, as denoted by the first increase in IG and in the levels of 11-KT and T, and the appearance of testes at stage II and III. During winter, the levels of 11-KT and T peaked and soon began to decrease, the IG slightly declined and the proportion of running males (RM) gradually increased. In spring, levels of 11-KT and T continued to decline, the IG slightly increased and the proportion of RM peaked concomitantly with the occurrence of stage IV testes. Plasma levels of 17,20beta-P did not change significantly throughout testicular development. Transformation of SPD into SPZ followed a group-synchronous fashion, a phenomenon which parallels asynchronous oocyte development reported in females. This mechanism would be consistent with the observed small quantity of sperm that can be manually stripped at any one time and other aspects of S. senegalensis reproductive biology.

Intra-adrenal interactions in fish: Catecholamine stimulated cortisol release in sea bass (Dicentrarchus labrax L.)

The effect of the catecholamines, adrenaline and noradrenaline, on sea bass (Dicentrarchus labrax) and sea bream (Sparus auratus) interrenal cortisol production was studied in vitro using a dynamic superfusion system technique. Increasing concentrations of catecholamines (10(-6), 10(-8) and 10(-10) M) stimulated cortisol production in a dose-dependent manner, in sea bass only. The increase in cortisol production stimulated by adrenaline (10(-6) M) and noradrenaline (10(-6) M) was inhibited by sotalol (2 x 10(-5) M), but not by prazosin suggesting that catecholamines stimulate cortisol release through the beta-receptor subtype. To evaluate catecholamine-induced signal transduction in head kidney cells, measurements of cAMP production and [H3]myo-inositol incorporation were determined in head kidney cell suspensions. Adrenaline and noradrenaline (10(-6) M) increased cAMP production, but had no effect on total inositol phosphate accumulation. These results indicate that catecholamines released from the chromaffin cells within the interrenal tissue may act as a paracrine factor to stimulate interrenal steroidogenesis in the sea bass.

Novel bioactive parathyroid hormone and related peptides in teleost fish

We report the identification, gene expression and biological activity of two parathyroid hormones (PTH; PTHA and PTHB), two PTH-related peptides (PTHrP; PTHrPA and PTHrPB) and a PTH-like ligand (PTH-L) with hybrid characteristics in puffer fishes (Takifugu rubripes and Tetraodon fluviatilis). Experimental data are consistent with PTH-L and PTHrPA having calciotropic activities equivalent, respectively, to tetrapod PTH and PTHrP. We hypothesise on the basis of phylogenetic and functional analysis that PTH-L could be a fish relic of an ancestral PTH/PTHrP gene.

Ligand binding and signalling pathways of PTH receptors in sea bream (Sparus auratus) enterocytes

Whole animal studies have indicated that Ca(2+) uptake by the gastrointestinal tract is regulated by the action of parathyroid hormone-related peptide (PTHrP) in teleost fish. We have characterised PTH receptors (PTHR) in piscine enterocytes and established, by using amino-terminal PTHrP peptides, the amino acid residues important for receptor activation and for stabilising the ligand/receptor complex. Ligand binding of (125)I-(1-35(tyr)) PTHrP to the membrane fraction of isolated sea bream enterocytes revealed the existence of a single saturable high-affinity receptor (K (D)=2.59 nM; B (max)=71 fmol/mg protein). Reverse transcription/polymerase chain reaction with specific primers for sea bream PTH1R and PTH3R confirmed the mRNA expression of only the later receptor. Fugu (1-34)PTHrP increased cAMP levels in enterocytes but had no effect on total inositol phosphate accumulation. The amino-terminal peptides (2-34)PTHrP, (3-34)PTHrP and (7-34)PTHrP bound efficiently to the receptor but were severely defective in stimulating cAMP in enterocyte cells indicating that the first six residues of piscine (1-34)PTHrP, although not important for receptor binding, are essential for activation of the adenylate cyclase/phosphokinase A (AC-PKA)-receptor-coupled intracellular signalling pathway. Therefore, PTHrP in teleosts acts on the gastrointestinal tract through PTH3R and the AC-PKA intracellular signalling pathway and might regulate Ca(2+) uptake at this site. Ligand-receptor binding and activity throughout the vertebrates appears to be allocated to the same amino acid residues of the amino-terminal domain of the PTHrP molecule.

Calcium mobilization from fish scales is mediated by parathyroid hormone related protein via the parathyroid hormone type 1 receptor

The scales of bony fish represent a significant reservoir of calcium but little is known about their contribution, as well as of bone, to calcium balance and how calcium deposition and mobilization are regulated in calcified tissues. In the present study we report the action of parathyroid hormone-related protein (PTHrP) on calcium mobilization from sea bream (Sparus auratus) scales in an in vitro bioassay. Ligand binding studies of piscine 125I-(1-35(tyr))PTHrP to the membrane fraction of isolated sea bream scales revealed the existence of a single PTH receptor (PTHR) type. RT-PCR of fish scale cDNA using specific primers for two receptor types found in teleosts, PTH1R, and PTH3R, showed expression only of PTH1R. The signalling mechanisms mediating binding of the N-terminal amino acid region of PTHrP were investigated. A synthetic peptide (10(-8) M) based on the N-terminal 1-34 amino acid residues of Fugu rubripes PTHrP strongly stimulated cAMP synthesis and [3H]myo-inositol incorporation in sea bream scales. However, peptides (10(-8) M) with N-terminal deletions, such as (2-34), (3-34) and (7-34)PTHrP, were defective in stimulating cAMP production but stimulated [3H]myo-inositol incorporation. (1-34)PTHrP induced significant osteoclastic activity in scale tissue as indicated by its stimulation of tartrate-resistant acid phosphatase. In contrast, (7-34)PTHrP failed to stimulate the activity of this enzyme. This activity could also be abolished by the adenylyl cyclase inhibitor SQ-22536, but not by the phospholipase C inhibitor U-73122. The results of the study indicate that one mechanism through which N-terminal (1-34)PTHrP stimulates osteoclastic activity of sea bream scales, is through PTH1R and via the cAMP/AC intracellular signalling pathway. It appears, therefore, that fish scales can act as calcium stores and that (1-34)PTHrP regulates calcium mobilization from them; it remains to be established if this mechanism contributes to calcium homeostasis in vivo.

Branchial osmoregulatory response to salinity in the gilthead sea bream, Sparus auratus

The branchial osmoregulatory response of gilthead sea bream (Sparus auratus L.) to short-term (2-192 hr) and long-term (2 weeks) exposure to different environmental salinities (5 per thousand, 15 per thousand, 25 per thousand, 38 per thousand and 60 per thousand) was investigated. A "U-shaped" relationship was observed between environmental salinity and gill Na+,K+ -ATPase activity in both long- and short-term exposure to altered salinity, with the increase in activity occurring between 24 and 96 hr after the onset of exposure. Plasma osmolality and plasma ions (sodium, chloride, calcium and potassium) showed a tendency to increase in parallel with salinity. These variables only differed significantly (P<0.05) in fish adapted to 60 per thousand salinity with respect to fish adapted to full-strength sea-water (SW). Plasma glucose remained unchanged whereas plasma lactate was elevated at 5 per thousand and 60 per thousand. Muscle water content (MWC) was significantly lower in fish adapted to 60 per thousand. Chloride cells (CC) were only present on the surface of the gill filaments and absent from the secondary lamellae. CC distribution was not altered by external salinity. However, the number and size of CC were significantly increased at salinity extremes (5 per thousand and 60 per thousand), whereas fish exposed to intermediate salinities (15 per thousand and 25 per thousand) had fewer and smaller cells. Furthermore, the CC of fish exposed to diluted SW became rounder whereas they were more elongated in fish in full-strength and hypersaline SW. This is consistent with previous reports indicating the existence of two CC types in euryhaline fish. At likely environmental salinities, gilthead sea bream show minor changes in plasma variables and the effective regulation of gill Na+,K+ -ATPase. However, at very low salinities both haemodilution and up-regulation of gill Na+,K+ -ATPase predict a poor adaptation most likely related to deficiency or absence of specific components of the CC important for ion xuptake.

Brain aromatase from pejerrey fish (Odontesthes bonariensis): cDNA cloning, tissue expression, and immunohistochemical localization

The brain-type aromatase (CYP19A2) cDNA from pejerrey Odontesthes bonariensis was characterized. Its sequence differs from the ovarian-derived aromatase (CYP19A1) previously reported for the same species. The cDNA is 2305bp in length and the deduced protein comprises 501 amino-acids. The percentage of identity was higher when compared to other brain-derived aromatase proteins (85-63%) and lower with ovarian-derived aromatases (64-57%). Pejerrey aromatases share 61% of identity. The tissue expression analysis showed that CYP19A2 was expressed in the kidney, brain, and pituitary gland of both sexes and also in the ovary, but not in the eye, spleen, liver, gill, and testis. Semi-quantitative RT-PCR analysis of different brain areas revealed that CYP19A2 was expressed significantly higher in anterior male brain areas than in the corresponding female areas, and also when compared to posterior brain areas from both sexes. An immunological analysis using a polyclonal anti-teleost aromatase showed immunoreactive aromatase cells bordering the telencephalic ventricle and a strong signal in the ependymal cells of the preoptic area and the hypothalamus. In the optic tectum immunoreactive aromatase cells were labeled in the ventral wall and in the ependymal layer of the third and fourth ventricle with lateral projections. In the pituitary gland immunoreactive aromatase cells could be found in the rostral and proximal pars distalis. In this gland, aromatase fibers were also detected in different areas; many of them concentrated around blood vessels.

Production and characterisation of gilthead sea bream (Sparus auratus) recombinant parathyroid hormone related protein

The production and purification of gilthead sea bream recombinant parathyroid hormone related protein [sbPTHrP(1-125)] using an Escherichia coli system and one step purification process with continuous elution gel electrophoresis is reported. The cDNA encoding sbPTHrP(1-125) was cloned into a prokaryotic expression vector pET-11a. The recombinant plasmid was used to transfect E. coli BL21(DE3) pLysS and sbPTHrP(1-125) synthesis was induced by addition of 1mM isopropyl-beta-d-thiogalactopyranoside. The rapid one step isolation method gave pure sbPTHrP(1-125) as judged by SDS-PAGE and yielded up to 40mg/L of culture medium (3.3mg protein/g of bacteria). The bioactivity of recombinant sbPTHrP(1-125) assessed using an in vitro scale bioassay was found to be equipotent to PTHrP(1-34) in stimulating cAMP accumulation. Assessment of the immunological reactivity of the isolated protein by Western blot revealed it cross-reacts with antisera specific for the N-terminal and C-terminal region of PTHrP. In a radioimmunoassay specific for piscine N-terminal (1-34aa) PTHrP, the recombinant sbPTHrP(1-125) was equipotent with PTHrP(1-34) in displacing labelled (125)I-PTHrP(1-36) PTHrP from the antisera. The availability of recombinant sbPTHrP will allow the development of region specific assays and studies aimed at defining post-secretory processing of this protein and its biological activity in fish.

Ontogeny of osteonectin expression in embryos and larvae of sea bream (Sparus auratus)

Osteonectin (OSN) is a glycoprotein which is implicated in development, bone formation and mineralisation, tumorigenesis, angiogenesis, and wound healing. Regulation of its expression by hormones may be one of the mechanisms by which the endocrine system affects bone metabolism. As a first step to understanding OSN function in fish, the gene expression of the recently cloned cDNA for sea bream, Sparus auratus, osteonectin (sbOSN) was characterised during embryonic and larval development. sbOSN mRNA was first detected by semi-quantitative reverse transcription-polymerase chain reaction in embryos at early gastrula and its expression increased continuously until hatch, after which it decreased until 15 days post-hatch (dph), increased transiently until 24 dph and decreased thereafter. In situ hybridisation showed it had a differential tissue distribution which was age dependent. In general, sbOSN mRNA was identified in cartilaginous and calcified structures of both dermal and endochondral origin but its expression was not restricted to the skeleton. sbOSN transcripts were also detected in the skin, perichordal sheath, nerve cord, and kidney tubules.

Calcium handling in Sparus auratus: effects of water and dietary calcium levels on mineral composition, cortisol and PTHrP levels

Juvenile gilthead sea bream (Sparus auratus L.; 10-40 g body mass) were acclimatized in the laboratory to full strength (34 per thousand) or dilute (2.5 per thousand) seawater and fed normal, calcium-sufficient or calcium-deficient diet for nine weeks. Mean growth rate, whole-body calcium and phosphorus content and accumulation rates were determined, as well as plasma levels of ionic and total calcium, cortisol and parathyroid hormone related protein (PTHrP; a hypercalcemic hormone in fish). When confronted with limited calcium access (low salinity and calcium-deficient diet), sea bream show growth arrest. Both plasma cortisol and PTHrP increase when calcium is limited in water or diet, and a positive relationship was found between plasma PTHrP and plasma ionic calcium (R(2)=0.29, N=18, P<0.05). Furthermore, a strong correlation was found between net calcium and phosphorus accumulation (R(2)=0.92, N=16, P<0.01) and between body mass and whole-body calcium (R(2)=0.84, N=25, P<0.01) and phosphorus (R(2)=0.88, N=24, P<0.01) content. Phosphorus accumulation is strongly calcium dependent, as phosphorus accumulation decreases in parallel to calcium accumulation when the diet is calcium deficient but phosphorus sufficient. We conclude that PTHrP and cortisol are involved in the regulation of the hydromineral balance of these fish, with growth-related calcium accumulation as an important target.