Time-resolved near backscatter imaging system on Laser MegaJoule

The newly operating near-backscattering imaging (NBI) system on the Laser MegaJoule (LMJ) is briefly described with emphasis on the temporally resolved measurements and their synchronization with the LMJ laser pulse through target shots taken as part of the diagnostic commissioning campaign. The NBI measures the stimulated Brillouin and Raman scattered light around two quadruplets (one inner and one outer) of the upper LMJ hemisphere. The temporal resolution is achieved with a unique system: a specifically designed wide-open optical lens images 40 points of a diffuser onto an array of optical fibers with the scattered light recorded on a multiplexed photodiode array.

IASI-Derived Sea Surface Temperature Data Set for Climate Studies

Sea surface temperature (SST) is an essential climate variable, that is directly used in climate monitoring. Although satellite measurements can offer continuous global coverage, obtaining a long-term homogeneous satellite-derived SST data set suitable for climate studies based on a single instrument is still a challenge. In this work, we assess a homogeneous SST data set derived from reprocessed Infrared Atmospheric Sounding Interferometer (IASI) level-1 (L1C) radiance data. The SST is computed using Planck's Law and simple atmospheric corrections. We assess the data set using the ERA5 reanalysis and the EUMETSAT-released IASI level-2 SST product. Over the entire period, the reprocessed IASI SST shows a mean global difference with ERA5 close to zero, a mean absolute bias under 0.5°C, with a SD of difference around 0.3°C and a correlation coefficient over 0.99. In addition, the reprocessed data set shows a stable bias and SD, which is an advantage for climate studies. The interannual variability and trends were compared with other SST data sets: ERA5, Hadley Centre's SST (HadISST), and NOAA's Optimal Interpolation SST Analysis (OISSTv2). We found that the reprocessed SST data set is able to capture the patterns of interannual variability well, showing the same areas of high interannual variability (>1.5°C), including over the tropical Pacific in January corresponding to the El Niño Southern Oscillation. Although the period studied is relatively short, we demonstrate that the IASI data set reproduces the same trend patterns found in the other data sets (i.e., cooling trend in the North Atlantic, warming trend over the Mediterranean).

Adaptive capacities from survival to stress responses of two isogenic lines of rainbow trout fed a plant-based diet

The composition of feed for farmed salmonids has strongly evolved during the last decades due to the substitution of fishery-derived fish oil and fishmeal by ingredients of plant origin. Little information is available regarding the effects of this transition on adaptive capacities in fish. Two rainbow trout isogenic lines, known for their divergent ability to grow on a plant-based diet (PBD), were fed for seven months from first feeding either a fully PBD or a control marine-resources diet and were compared for their growing and survival capacities over time and their behavioral and stress responses at similar sizes but different ages. Although fish displayed similar appetitive behaviour, the two lines were highly affected by the PBD translated in decreased growth and apathetic behaviour, but also stronger stress responses displayed by stronger cortisol increases and more stress-related behaviour when isolated. The two lines were found to be similarly sensitive to a PBD for the assessed stress-related parameters, but one line displayed a lower survival during the early rearing period. Overall, these results suggest that a PBD supplied to fish from the alevin stage has strong effects on physiological and behavioural parameters, with possible impairment of fish welfare, but also genome-dependent survival.

Quantitative trait loci for magnitude of the plasma cortisol response to confinement in rainbow trout

Better understanding of the mechanisms underlying interindividual variation in stress responses and their links with production traits is a key issue for sustainable animal breeding. In this study, we searched for quantitative trait loci (QTL) controlling the magnitude of the plasma cortisol stress response and compared them to body size traits in five F2 full-sib families issued from two rainbow trout lines divergently selected for high or low post-confinement plasma cortisol level. Approximately 1000 F2 individuals were individually tagged and exposed to two successive acute confinement challenges (1 month interval). Post-stress plasma cortisol concentrations were determined for each fish. A medium density genome scan was carried out (268 markers, overall marker spacing less than 10 cM). QTL detection was performed using qtlmap software, based on an interval mapping method (http://www.inra.fr/qtlmap). Overall, QTL of medium individual effects on cortisol responsiveness (<10% of phenotypic variance) were detected on 18 chromosomes, strongly supporting the hypothesis that control of the trait is polygenic. Although a core array of QTL controlled cortisol concentrations at both challenges, several QTL seemed challenge specific, suggesting that responses to the first and to a subsequent exposure to the confinement stressor are distinct traits sharing only part of their genetic control. Chromosomal location of the steroidogenic acute regulatory protein (STAR) makes it a good potential candidate gene for one of the QTL. Finally, comparison of body size traits QTL (weight, length and body conformation) with cortisol-associated QTL did not support evidence for negative genetic relationships between the two types of traits.

Fish welfare and genomics

There is a considerable public and scientific debate concerning welfare of fish in aquaculture. In this review, we will consider fish welfare as an integration of physiological, behavioral, and cognitive/emotional responses, all of which are essentially adaptative responses to stressful situations. An overview of fish welfare in this context suggests that understanding will rely on knowledge of all components of allostatic responses to stress and environmental perturbations. The development of genomic technologies provides new approaches to this task, exemplified by how genome-wide analysis of genetic structures and corresponding expression patterns can lead to the discovery of new aspects of adaptative responses. We will illustrate how the genomic approach may give rise to new biomarkers for fish welfare and also increase our understanding of the interaction between physiological, behavioral, and emotional responses. In a first part, we present data on expression of candidate genes selected a priori. This is a common avenue to develop molecular biomarkers capable of diagnosing a stress condition at its earliest onset, in order to allow quick corrective intervention in an aquaculture setting. However, most of these studies address isolated physiological functions and stress responses that may not be truly indicative of animal welfare, and there is only rudimentary understanding of genes related to possible cognitive and emotional responses in fish. We also present an overview on transcriptomic analysis related to the effect of aquaculture stressors, environmental changes (temperature, salinity, hypoxia), or concerning specific behavioral patterns. These studies illustrate the potential of genomic approaches to characterize the complexity of the molecular mechanisms which underlies not only physiological but also behavioral responses in relation to fish welfare. Thirdly, we address proteomic studies on biological responses to stressors such as salinity change and hypoxia. We will also consider proteomic studies developed in mammals in relation to anxiety and depressive status which may lead to new potential candidates in fish. Finally, in the conclusion, we will suggest new developments to facilitate an integrated view of fish welfare. This includes use of laser microdissection in the transcriptomic/proteomic studies, development of meta-analysis methods for extracting information from genomic data sets, and implementation of technological advances for high-throughput proteomic studies. Development of these new approaches should be as productive for our understanding of the biological processes underlying fish welfare as it has been for the progress of pathophysiological research.

Effect of seawater transfer on CYP1A gene expression in rainbow trout gills

During the transfer of rainbow trout from freshwater to seawater, the gills have to switch from an ion-absorption epithelium to an ion-secretion epithelium in order to maintain equilibrium of their hydromineral balance. After a change to ambient salinity, several gill modifications have already been demonstrated, including ion transporters. In order to identify new branchial mechanisms implicated in seawater acclimation, we carried out an extensive analysis of gene expression in gills using microarray technology. This strategy allowed us to show that CYP1A gene expression was up-regulated in the gills after salinity transfer. This increase was confirmed by real-time reverse transcription PCR. Furthermore, measurements of CYP1A enzyme activity (EROD) showed a significant increase after transfer to seawater. Immunohistochemistry analysis in the gills revealed that cells with a higher expression of CYP1A protein were principally pillar cells and those in the primary lamellae not in contact with the external medium. The results of this study suggest for the first time that CYP1A may be implicated in the seawater acclimation of the gills of rainbow trout.

Multiple corticosteroid receptors in fish: from old ideas to new concepts

The effect of corticosteroid hormones in fish are mediated through intracellular receptors that act as ligand-binding transcription factors. Many studies have been devoted to cortisol binding using radiolabeled ligand in fish and allowed characterization of a single class of high affinity binding sites in various tissues. Molecular characterization of cortisol receptors has only been initiated recently by cloning the different receptor forms: Following a isolation of a first glucocorticoid receptor (GR), a mineralocorticoid receptor (MR) was described and the presence of various GR isoforms was recently reported. Sequence comparison and phylogenetic analysis of these sequences confirm that fish possess both GR and MR and that GR gene is duplicated. The importance of these various corticosteroid receptor forms is also illustrated by analysis of their transcriptional activity. When tested in human cell lines, these receptors showed functionally distinct actions on GR-sensitive promotors, thus suggesting a more complicated corticosteroid signaling system than initially anticipated from binding studies. These results also suggest that, whereas cortisol is certainly the physiological ligand for GR, this may not be the case for MR which showed high sensitivity for deoxycorticosterone (DOC) and aldosterone. As this last hormone is probably absent in fish, these results raise the question as to whether DOC could be a physiological ligand for MR in fish. Information on DOC effect in fish is very scarce and clarification of the differential osmoregulatory roles of cortisol and DOC in fish needs ellucidation. This will require analysis of all actors of the corticosteroid signaling system at pre-receptor, receptor, and post-receptor levels.

11-deoxycorticosterone is a potent agonist of the rainbow trout (Oncorhynchus mykiss) mineralocorticoid receptor

The teleost fish are thought to lack the mineralocorticoid hormone aldosterone but possess mineralocorticoid receptor (MR) homologs. Here we describe the characterization of two rainbow trout (Oncorhynchus mykiss) MRs, called rtMRa and rtMRb. The open reading frame of rtMRa cDNA encoded a protein of 1041 amino acids. The rtMRb predicted protein sequence is similar, differing in only 10 amino acids in the nonconserved A/B domain and lacking a three-amino acid insertion between the two zinc fingers of the C domain. Expression of rtMR mRNA (sum of both forms), measured in juvenile trout by real-time RT-PCR, shows that the transcripts are ubiquitous. Expression was significantly higher in brain than the other tissues studied (eye, trunk kidney, head kidney, gut, gills, liver, spleen, ovary, heart, white muscle, skin). Hormonal stimulation of receptor transactivation activity was studied in COS-7 cells transiently cotransfected with receptor cDNA and a mouse mammary tumor virus-luciferase reporter. The mineralocorticoids 11-deoxycorticosterone and aldosterone were more potent enhancers of rtMRa transcriptional activity (EC50 = 1.6 +/- 0.5 x 10(-10) and 1.1 +/- 0.4 x 10(-10) M, respectively) than the glucocorticoids cortisol and 11-deoxycortisol (EC50 = 1.1 +/- 0.3 x 10(-9) and 3.7 +/- 1.9 x 10(-9) M, respectively). A similar response was observed in transactivation assays with rtMRb. These results are discussed in the view of reported circulating levels of corticosteroids in trout.

Evidence for two distinct functional glucocorticoid receptors in teleost fish

Using RT-PCR with degenerated primers followed by screening of a rainbow trout (Oncorhynchus mykiss) intestinal cDNA library, we have isolated from the rainbow trout a new corticosteroid receptor which shows high sequence homology with other glucocorticoid receptors (GRs), but is clearly different from the previous trout GR (named rtGR1). Phylogenetic analysis of these two sequences and other GRs known in mammals, amphibians and fishes indicate that the GR duplication is probably common to most teleost fish. The open reading frame of this new trout GR (named rtGR2) encodes a protein of 669 amino acids and in vitro translation produces a protein of 80 kDa that appears clearly different from rtGR1 protein (88 kDa). Using rtGR2 cDNA as a probe, a 7.3 kb transcript was observed in various tIssues suggesting that this gene would lead to expression of a steroid receptor. In vitro studies were used to further characterize this new corticosteroid receptor. Binding studies with recombinant rtGR1 and rtGR2 proteins show that the two receptors have a similar affinity for dexamethasone (GR1 K(d)=5.05+/-0.45 nM; GR2 K(d)=3.04+/-0.79 nM). Co-transfection of an rtGR1 or rtGR2 expression vector into CHO-K1 or COS-7 cells, along with a reporter plasmid containing multiple consensus glucocorticoid response elements, shows that both clones are able to induce transcriptional activity in the presence of cortisol and dexamethasone. Moreover, at 10(-)(6 )M 11-deoxycortisol and corticosterone partially induced rtGR2 transactivation activity but were without effect on rtGR1. The other major teleost reproductive hormones, as well as a number of their precursors or breakdown products of these and corticosteroid hormones, were without major effects on either receptor. Interestingly, rtGR2 transactivational activity was induced at far lower concentrations of dexamethasone or cortisol (cortisol EC(50)=0.72+/-0.87 nM) compared with rtGR1 (cortisol EC(50)=46+/-12 nM). Similarly, even though RU486 inhibited transactivation activity in both rtGR1 and rtGR2, rtGR1 was more sensitive to this GR antagonist. Altogether, these results indicate that these two GR sequences encode for two functionally distinct GRs acting as ligand-inducible transcription factors in rainbow trout.

Transfer of tilapia (Oreochromis niloticus) to a hyperosmotic environment is associated with sustained expression of prolactin receptor in intestine, gill, and kidney

Expression of the tilapia prolactin receptor (tiPRL-R) has been characterized in the intestine of Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL binding sites have been further analyzed in this organ, as well as in gill and kidney, during adaptation of tilapia to a hyperosmotic environment. A single high-affinity binding site for tilapia PRL-I (tiPRL-I) was determined in full-length intestine by Scatchard analysis. A heterogeneous distribution of tiPRL-R was detected in this organ, with the posterior part always displaying a higher expression of both tiPRL-R transcript and tiPRL binding sites than the anterior and medial parts. Transfer of tilapia to brackish water (BW) led to an apparent increase in the specific binding of tiPRLs in intestine and gill even for long-term-adapted fish, whereas the high level of kidney tiPRL binding sites measured in control fish reared in fresh water was still detected in BW-adapted tilapia. There was no overall significant modification of tiPRL-R transcript levels in any organ during short-term or long-term adaptation, although a limited decrease occurred in the gill of BW-adapted fish, as shown earlier. Therefore, in O. niloticus adapted to BW, high and sustained levels of tiPRL-R were observed in the three major osmoregulatory organs, gill, kidney, and intestine.

In vitro effect of various xenobiotics on trout gill cell volume regulation after hypotonic shock

Their functions and localisation can expose gill cells to volume changes. To maintain their vital functions, these gill cells must regulate their own volume after cellular swelling or shrinkage. Recently, we showed that rainbow trout pavement gill cells in primary culture have the capacity to regulate their own volume after cellular swelling induced by hypotonic shock. This so-called regulatory volume decrease (RVD) is associated with intracellular calcium increase, which occurs as a transient peak followed by a plateau when maintained a hypotonic condition. Return to an isotonic medium restores baseline [Ca2+]i level. In this study, the effect of different xenobiotics on cellular swelling induced RVD and its calcium signal was investigated in trout pavement gill cells in primary culture. These cells were exposed to different pollutants after confluent epithelium was obtained. After 36 h in xenobiotics exposure in vitro, cellular volume and intracellular calcium concentration were measured. Nonylphenol poly- and di-ethoxylate were lethal at concentrations of 10 and 100 microM, respectively. With 10 microM of the diethoxylate form, cells did not die but, unlike non-treated cells, burst during hypotonic shock (2/3rd strength Ringer solution). With 1 microM nonylphenol polyethoxylate (NPnEO), RVD and [Ca2+]i were reduced. Copper (10 and 100 microM) had no significant effect on gill cell volume regulation. However, the heavy metal modified calcium response to hypotonic shock by inhibiting return to baseline level under isotonic conditions. 10 microM prochloraz and 2,4-dichloroaniline had no effect on cell morphology, volume and [Ca2+]i concentration. With 100 microM, however, prochloraz was lethal and dichloroaniline increased baseline [Ca2+]i. These results indicate that the effects observed on gill cells are consistent with the known toxic properties of the molecules tested, thus confirming the validity of primary culture to investigate the toxic effects of xenobiotics on fish gill epithelium.

Evidence of rainbow trout prolactin interaction with its receptor through unstable homodimerisation

This study aims to characterise Prolactin receptor (PRLR) in rainbow trout for which no information is available despite the availability of Salmonid PRL preparations. By screening a freshwater rainbow trout intestine cDNA library with a probe corresponding to the extracellular domain (ECD) of tilapia PRLR, we have cloned a 2.5 kb insert coding for the PRLR. The mature protein of 614 amino acid residues is similar to PRLR isolated in tilapia and also the long form of mammalian PRLR. Analysis of PRLR gene expression in osmoregulatory organs revealed the presence of a unique transcript, thus confirming the involvement of this hormone in the control of osmoregulation in this fish species. By using surface plasmon resonance (SPR) technology, kinetic measurement of interaction between trout PRL and its receptor ECD was studied. This approach allowed us to demonstrate the formation of a transient, unstable homodimeric complex. This unstability could explain the inability to perform binding experiments using homologous PRL. In contrast, heterologous lactogenic ligands were able to interact through a more stable complex. Whether these characteristics of PRL-receptor interaction in rainbow trout are different to what occurs in tilapia where a homologous radioreceptor assay was developed would require further studies.

Molecular cloning and characterization of thyroid hormone receptors in teleost fish

Thyroid hormones are pleiotropic factors important for many developmental and physiological functions in vertebrates. Their effects are mediated by two specific receptors (TRalpha and TRbeta) which are members of the nuclear hormone receptor superfamily. To clarify the function of these receptors, our laboratory has started a comparative study of their role in teleost fish. This type of approach has been hampered by the isolation of specific clones for each fish species studied. In this report, we describe an efficient reverse transcription/PCR procedure that allows the isolation of large fragments corresponding to TRalpha and TRbeta of a wide range of teleost fish. Phylogenetic analysis of these receptors revealed a placement consistent with their origin, sequences from teleost fish being clearly monophyletic for both TRalpha and TRbeta. Interestingly, this approach allowed us to isolate (from tilapia and salmon) several new TRalpha or TRbeta isoforms resulting from alternative splicing. These isoforms correspond to expressed transcripts and thus may have an important physiological function. In addition, we isolated a cDNA encoding TRbeta in the Atlantic salmon (Salmo salar) encoding a functional thyroid hormone receptor which binds specific thyroid hormone response elements and regulates transcription in response to thyroid hormones.

Biological functions of trout pavement-like gill cells in primary culture on solid support: pH(i) regulation, cell volume regulation and xenobiotic biotransformation

This review presents results obtained on rainbow trout gill cells in primary culture on solid support. Ultrastructural analysis showed that cultured gill cells displayed features of pavement cells in situ. Several biological functions have been investigated on these cultured cells. First, it was shown that their intracellular pH at rest and after acidosis is regulated by a Na+/H+ exchanger. Second, gill cells in primary culture can regulate their volume after a cell swelling. Intracellular calcium appears to be involved in this regulation. The effects of different xenobiotics on the capacity of gill cells to regulate their volume are presented. Third, cultured pavement cells contain biotransformation enzymes to metabolize xenobiotics. All these results demonstrate that gill cells in primary culture on solid support represent a promising in vitro model for the study of pavement cells physiology. In conclusion, applications of this culture are discussed and compared with the permeable filter method, together with the limitations and prospects of this in vitro model on solid support.

Molecular characterization of the prolactin receptor in two fish species, tilapia Oreochromis niloticus and rainbow trout, Oncorhynchus mykiss: A comparative approach

We present recent information on the molecular characterization of the prolactin receptor (PRL-R) in two teleost species, tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss), in the perspective of improved understanding of the physiological differences in the control of osmoregulatory function between these two fish species. Although our interest will mainly focus on osmoregulatory organs, we will also discuss evidence of the presence of PRL-R in other tissues such as gonads and hematopoietic organs. The first fish PRL-R was characterized in tilapia. This receptor is similar to that of the long form of mammalian PRL-R, but the most conserved region (extracellular domain) has only 53% identity with mammalian PRL-R. A rainbow trout PRL-R cDNA has been also isolated and appeared very similar in structure to tilapia PRL-R. Expression of the PRL-R gene was studied by Northern blotting for various tissues from tilapia and trout, and a unique transcript size of 3.2-3.4 kb was observed in all tissues studied (including male and female gonads, skin, brain, spleen, head, kidney, and circulating lymphocytes). Osmoregulatory organs (gills, kidney, intestine) were the richest tissues. Using in situ hybridization, PRL-R transcripts were localized in gill chloride cells, both in trout and tilapia. Analysis of PRL-R transcript levels in gills, kidney, and intestine indicated the maintenance of a high level of expression during adaptation to a hyperosmotic environment. These results support PRL being a pleiotropic hormone in fish and suggest the presence of a unique PRL-R form in tilapia and in trout. Finally, characterization of hormone receptor binding has been carried out in both species using a radioreceptor assay (in tilapia) or surface plasmon resonance (SPR) technology (in trout). These studies indicated the presence of a stable hormone-receptor complex in tilapia, while PRL binds to its receptor through an unstable homodimeric complex in trout. Thus, the characteristics of PRL binding on its receptor appear to be significantly different in tilapia and trout. Whether such differences may lead to different signal transduction mechanisms and osmoregulatory actions of PRL in these two euryhaline species merits further investigation.Key words: prolactin receptor, genetic expression, hormone-receptor interaction, surface plasmon resonance, fish osmoregulation.

Molecular characterization of the prolactin receptor in two fish species, tilapia Oreochromis niloticus and rainbow trout, Oncorhynchus mykiss: a comparative approach

We present recent information on the molecular characterization of the prolactin receptor (PRL-R) in two teleost species, tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss), in the perspective of improved understanding of the physiological differences in the control of osmoregulatory function between these two fish species. Although our interest will mainly focus on osmoregulatory organs, we will also discuss evidence of the presence of PRL-R in other tissues such as gonads and hematopoietic organs. The first fish PRL-R was characterized in tilapia. This receptor is similar to that of the long form of mammalian PRL-R, but the most conserved region (extracellular domain) has only 53% identity with mammalian PRL-R. A rainbow trout PRL-R cDNA has been also isolated and appeared very similar in structure to tilapia PRL-R. Expression of the PRL-R gene was studied by Northern blotting for various tissues from tilapia and trout, and a unique transcript size of 3.2-3.4 kb was observed in all tissues studied (including male and female gonads, skin, brain, spleen, head, kidney, and circulating lymphocytes). Osmoregulatory organs (gills, kidney, intestine) were the richest tissues. Using in situ hybridization, PRL-R transcripts were localized in gill chloride cells, both in trout and tilapia. Analysis of PRL-R transcript levels in gills, kidney, and intestine indicated the maintenance of a high level of expression during adaptation to a hyperosmotic environment. These results support PRL being a pleiotropic hormone in fish and suggest the presence of a unique PRL-R form in tilapia and in trout. Finally, characterization of hormone receptor binding has been carried out in both species using a radioreceptor assay (in tilapia) or surface plasmon resonance (SPR) technology (in trout). These studies indicated the presence of a stable hormone-receptor complex in tilapia, while PRL binds to its receptor through an unstable homodimeric complex in trout. Thus, the characteristics of PRL binding on its receptor appear to be significantly different in tilapia and trout. Whether such differences may lead to different signal transduction mechanisms and osmoregulatory actions of PRL in these two euryhaline species merits further investigation.

Transgenic rainbow trout expressed sGnRH-antisense RNA under the control of sGnRH promoter of Atlantic salmon

A recombinant vector containing antisense DNA complementary to Atlantic salmon (Salmo salar) sGnRH cDNA driven by specific promoter Pab derived from a corresponding sGnRH gene was introduced into rainbow trout (Oncorhynchus mykiss) eggs. This resulted in transgenic animals that had integrated one copy of the transgene into their genome and transmitted it through the germline. Antisense-sGnRH mRNA (AS) was expressed mainly in the brain of transgenic AS(+) fish. Levels of sGnRH endogenous mRNA in the brain were lower in 11-month-old AS(+) fish compared with nontransgenic AS(-) individuals from the same F2 progeny. sGnRH levels significantly decreased in the pituitary of transgenic males and females around the maturation period and in the brain of AS(+) immature females compared with controls. No reliable statistical difference was found in the levels of FSH and LH between AS(+) and AS(-) groups either in immature or mature fish. The majority of transgenic fish reached maturity at the same time as did nontransgenic individuals, although the maturation of AS(+) animals seemed to be more asynchronous. For the first time, the influence of antisense messengers on endogenous mRNA in transgenic fish and the corresponding protein is described.

Chronology of the appearance of beta, A, and alpha mitochondria-rich cells in the gill epithelium during ontogenesis of the brown trout (Salmo trutta)

Three types of mitochondria-rich (MR) cells, the alpha, beta, and accessory cells, are observed in the gill epithelium of juvenile and adult freshwater teleosts. In addition to numerous mitochondria, their cytoplasm contains a network of membranous tubules, the tubular system, connected to the laterobasal plasma membrane. Because they are believed to play a role in ionic regulation, it is of interest to examine the order of appearance and the ultrastructural characteristics of such cells during the embryogenesis and larval life of the brown trout. Gills of embryos and fry maintained in freshwater were thus removed at different stages and prepared for transmission and scanning electron microscopic examination. One week before hatching, cells resembling the beta cells of juvenile and adult teleosts appeared first among the epithelial cells located at the base of the filaments in the gills of the brown trout larva. In addition to their tubular system, they contained numerous and large apical structures seemingly originating from the Golgi apparatus. At approximately hatching time, small pear-shaped cells were seen to be closely apposed to the lateral side of the beta cells; they were usually devoid of apical structures and were considered to be accessory cells. After yolk sac resorption, additional cells, the alpha cells, were present along the lamellae. In contrast to the beta cells, they only exhibited poorly developed apical structures. The possible role of these three types of MR cells in osmoregulation during fish development is discussed.

Cloning and expression analysis of an inducible HSP70 gene from tilapia fish

We isolated and characterized the tilapia (Oreochromis mossambicus) HSP70 gene, highly homologous to other HSP70 genes. A dramatic increase of tilapia HSP70 mRNA levels was observed after heat shock of whole animals in all organs tested. Reporter constructs were tested for transient expression in carp cells and in microinjected zebrafish embryos. The entire isolated regulatory region (-851/+157) was able to mediate heat shock inducible expression of the reporter gene, with no preference for a particular tissue. Our studies represent the first transcriptional analysis of a HSP70 promoter from fish, revealing a powerful tool to direct controlled, tissue-independent gene expression in fish.

Recombinant prolactin receptor extracellular domain of rainbow trout (Oncorhynchus mykiss): subcloning, preparation, and characterization

The cDNA of the extracellular domain of rainbow trout (Oncorhynchus mykiss) prolactin receptor (trPRLR-ECD) was cloned in the prokaryotic expression vector pMON to enable its expression in Escherichia coli after induction with nalidixic acid. The bacterially expressed trPRLR-ECD protein, contained within the refractile body pellet, was solubilized in 4.5 M urea, refolded, and purified on a Q-Sepharose column, pH 8, by stepwise elution with NaCl. The bioactive monomeric 26-kDa fraction was eluted in 0.2 M NaCl, yielding 20 mg/2.5 L of induced culture. The purified protein was over 98% homogeneous, as shown by SDS-PAGE in the presence or absence of reducing agent and by chromatography on a Superdex column. Binding experiments using [125I]ovine placental lactogen (oPL) as a ligand revealed that human growth hormone (hGH), oPL, and ovine prolactin (oPRL) were the most effective competitors, with respective IC50 values of 1.32, 2.27, and 2.70 nM. Chicken (ch) PRL did not compete at all, and homologous trPRL was much less effective, with a corresponding IC50 value of 1826 nM. Gel-filtration was used to determine the stoichiometry of trPRLR-ECD's interaction with oPL, hGH, and oPRL. Only oPL yielded a 2:1 complex, whereas hGH and oPRL formed only 1:1 complexes, with excess trPRLR-ECD being seen at the initial 2:1 trPRLR-ECD:hGH or trPRLR-ECD:oPRL ratios. No studies were performed with chPRL because of its inability to compete with [125I]oPL or with trPRL because of its low affinity toward trPRLR-ECD. The present results agree with previous findings indicating, as in mammals, that homologous PRL interacts transiently with its receptor and suggest that transient homologous PRL-induced homodimerization of the receptor is sufficient to initiate a biological signal, despite the fact that, in classical binding experiments, only low specific binding can be detected.

Expression of the prolactin receptor (tiPRL-R) gene in tilapia Oreochromis niloticus: tissue distribution and cellular localization in osmoregulatory organs

The expression of the prolactin receptor (PRL-R) gene has been investigated in various tissues of tilapia (Oreochromis niloticus) reared in fresh or brackish water. Using a cDNA probe spanning the extracellular domain of the tilapia PRL-R and Northern blot analysis, the presence of tilapia PRL-R mRNA has been confirmed in the osmoregulatory organs and has been detected in other tissues, including the skin, the brain, the reproductive organs, and the two major hematopoietic organs (spleen and head kidney), as well as circulating lymphocytes. These findings suggest a conservation of the physiological processes regulated by prolactin throughout the vertebrates, including immunity and central nervous activity. A non-radioactive in situ hybridization procedure has allowed us to detect the expression of the tilapia PRL-R in the branchial chloride cells and the intestinal mucosal layer of fresh water animals, confirming the direct control exerted by prolactin on the water and ionic exchanges in tilapia. In all the tissues examined one unique PRL-R transcript has been detected with a similar size (3.2 kb) whatever the salinity conditions. Thus, the transcriptional expression of the tilapia PRL-R strongly differs from the complex RNA pattern reported for the higher vertebrates PRL-R and provides an additional argument for the existence of a single PRL-R for both prolactin isoforms in this fish species.

Xenobiotic and steroid biotransformation activities in rainbow trout gill epithelial cells in culture

The biotransformation of xenobiotics and steroids was investigated in cultured respiratory epithelial cells from rainbow trout (Oncorhynchus mykiss) gills. As a first approach, ethoxyresorufin-O-deethylase (EROD), chosen as a marker of CYP1A activity, was measured in monolayers of adherent cells. The induction of this enzyme was studied in cells exposed to beta-naphthoflavone (BNF) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in concentrations ranging from 10(-6) to 10(-12) M. After 24 h, TCDD showed a maximal induction at a concentration of 10(-9) M while BNF showed a maximal induction at a concentration of 10(-7) M. Concurrently, a variety of substrates involved in cytochrome P450-dependent metabolism as well as phase II reactions, namely ethoxycoumarin, aniline and testosterone were incubated with cultured gill cells for 2 or 8 h and with freshly isolated hepatocytes for comparison. Our results revealed a significant cytochrome P450-dependent activity in gill cells with ethoxycoumarin and aniline, but no hydroxylation was observed with testosterone as substrate. No trace of sulfate conjugate was detected. With 2.5 µM aniline as substrate, 2-hydroxyaniline accounted for 32.1% of the radioactivity after 2 h incubation whereas acetanilide amounted to 6.4%. Significant differences were found between gill cells and isolated hepatocytes in the capacity of these systems to conduct oxidative and conjugating metabolic pathways. Qualitatively, the main difference was observed for testosterone which is hydroxylated in position 6beta and 16beta and conjugated to glucuronic acid in liver cells, whereas reductive biotransformation giving rise to dihydrotestosterone and androstanediol and traces of androstenedione were observed in gill cells. Quantitatively, the biotransformation activity in gill epithelial cells, expressed as pmol/h per mg protein, was between 1.5 and 14% of the activity level observed in isolated hepatocytes, depending on the substrate.

Effect of egg deprivation on sex steroids, gonadotropin, prolactin, and growth hormone profiles during the reproductive cycle of the mouthbrooding cichlid fish Oreochromis niloticus

Various hormones were analyzed during the course of a reproductive cycle in the cichlid fish Oreochromis niloticus: plasma levels of the gonadal steroids 17beta-estradiol (E2), testosterone (T), 17, 20beta-OH progesterone (17,20beta-P), gonadotropin (taGtH), and plasma and pituitary concentrations of prolactin (tiPRL(I) and tiPRL(II)) and growth hormone (tiGH). Two categories of fish were sampled and sacrificed on days 1 and 3 postspawning and at 3-day intervals thereafter: typical incubating females (INC), and nonincubating females (NI), deprived of their eggs just after spawning. Such deprivation is known to suppress maternal behavior and to accelerate ovarian development and especially vitellogenesis, thus shortening the mean interspawning interval. In both groups, variations of the plasma concentrations of E2 and T appeared to depend on ovarian stages, and differences between groups appeared to reflect underlying differences in the kinetics of ovarian development. The observation of noticeable levels of 17,20beta-P in plasma before spawning, when high values of taGtH could also be detected in NI females, suggests the implication of this progestin in the control of final maturation events, as in some other teleosts. Moreover, 17,20beta-P, which was still detected a few days after spawning, but at low concentrations and only in the plasma of INC females, might play a role at the beginning of the reproductive cycle in incubating females (maternal behavior and/or slowing down of ovarian growth). The pituitary and plasma profiles of both tiPRLs isoforms appeared to depend mainly on the kinetics of ovarian development in each group of fish, suggesting a role during the beginning of vitellogenesis. However, the variance of plasma tiPRL(II), which was significantly enhanced during maternal behavior in INC females, also suggests an implication of this hormone in the control of that behavior. Concerning tiGH, comparison of the plasma profiles in INC and NI fish also suggest an influence on the control of maternal behavior, but a main effect of starvation of INC during mouthbrooding cannot be excluded.

Synthesis of gill Na(+)-K(+)-ATPase in Atlantic salmon smolts: differences in alpha-mRNA and alpha-protein levels

Several parameters were analyzed to determine the mechanisms responsible for the enhancement of the gill Na(+)-K(+)-ATPase activity of Atlantic salmon smolts. A major alpha-subunit transcript of 3.7 kb was revealed by Northern blot in both parr and smolt gills when hybridized with two distinct cDNA probes. The alpha-mRNA abundance demonstrated an increase to maximal levels in smolts at an early stage of the parr-smolt transformation. This was followed by a gradual rise in alpha-protein levels, revealed by Western blots with specific antibodies and by an increase in gill Na(+)-K(+)-ATPase hydrolytic activity, both only reaching maximum levels a month later, at the peak of the transformation process. Parr fish experienced a decrease in alpha-mRNA abundance and had basal levels of alpha-protein and enzyme activity. Measurement of the binding of [(3)H]ouabain to Na(+)-K(+)-ATPase was characterized in smolts and parr gill membranes showing more than a twofold elevation in smolts and was of high affinity in both groups (dissociation constant = 20-23 nM). Modulation of the enzyme due to increased salinity was also observed in seawater-transferred smolts, as demonstrated by an increase in alpha-mRNA levels after 24 h with a rise in Na(+)-K(+)-ATPase activity occurring only after 11 days. No qualitative change in alpha-expression was revealed at either the mRNA or protein level. Immunological identification of the alpha-protein was performed with polyclonal antibodies directed against the rat alpha-specific isoforms, revealing that parr, freshwater, and seawater smolts have an alpha(3)-like isoform. This study shows that the increase in Na(+)-K(+)-ATPase activity in smolt gills depends first on an increase in the alpha-mRNA expression and is followed by a slower rise in alpha-protein abundance that eventually leads to a higher synthesis of Na(+)-K(+) pumps.

Activation of gene transcription by tilapia prolactin variants tiPRL188 and tiPRL177

In the tilapia species Oreochromis niloticus, the pituitary releases two forms of prolactins (tiPRL188 and tiPRL177). The binding parameters and the activation of tiPRL-induced JAK2/Stat5 signalling pathway were analysed using a mammalian cell line transiently transfected with the tiPRL receptor (tiPRLR). Our data indicate that the tiPRLR is able to mediate transcriptional activation of the PRL responsive element. At nanomolar concentrations, tiPRL188 activates gene transcription whereas at micromolar concentrations it inhibits luciferase transcription from the lactogenic responsive element. This is consistent with a model of receptor dimerisation. In contrast, the activation by tiPRL177 was only reached at high (microM) concentrations. The transcriptional activities induced by tiPRL177 and tiPRL188 are discussed in the context of the physiology of these hormones.

Isolation and functional analysis of the histone H3 promoter from atlantic salmon (Salmo salar L.)

The histone H3 (sH3) promoter of Atlantic salmon (Salmo salar) was cloned via polymerase chain reaction using primers designed from the rainbow trout (Oncorhynchus mykiss) promoter sequence. A comparison of the nucleotide sequence with the equivalent sequences from rainbow trout and sockeye salmon (Oncorhynchus nerka) revealed a high degree of conservation. In vivo expression analysis of the sH3 promoter was carried out in both rainbow trout and zebrafish (Danio rerio) embryos. A direct comparison of the sH3 promoter with the viral RSV promoter in rainbow trout resulted in stronger expression of the sH3 promoter. Furthermore, lacZ expression directed by the sH3 promoter was ubiquitous in several different cell types in developing zebrafish embryos. These results suggest that the sH3 promoter will be useful in transgenic studies in Atlantic salmon.

Effect of confinement stress on circulating levels of growth hormone and two prolactins in freshwater-adapted tilapia (Oreochromis niloticus)

The aim of the present study was to assess a potential link between confinement stress and prolactin (PRL), the hormone responsible for adaptation to a hypoosmotic environment in freshwater-adapted tilapia (Oreochromis niloticus). The effect of stress on plasma levels of the two tilapia PRL forms, tiPRLI (or tiPRL188) and tiPRLII (or tiPRL177), was examined along with the effects on plasma levels of cortisol and growth hormone (GH). In a preliminary study, various sampling protocols (immediate sampling; sampling one by one; anesthesia at 0.5, 1, 2 ml/liter phenoxyethanol) were tested for their ability to modify basal plasma PRL and cortisol. In fish sampled within 1 min of capture (immediate sampling), no changes in the plasma levels of these hormones were observed, whereas when fish were sampled one at a time, PRL levels did not change but cortisol levels were modified. The immediate sampling protocol was used to study the effects of 1 hr confinement stress, which induced a large increase in plasma cortisol levels as well as increases tiPRLI and tiPRLII levels with kinetics similar to those of cortisol. In contrast, plasma tiGH levels significantly decreased after 1 hr confinement. When this stress situation was removed, plasma cortisol and tiPRL levels decreased and plasma GH levels increased. Two and one-half hours later, values were not significantly different from those measured in control fish. In tilapia exposed to 24 hr confinement stress, similar changes in hormone levels were observed. However, after 24 hr confinement, only cortisol levels were significantly different from those measured in control fish. None of these stress conditions significantly changed plasma chloride levels. Together, these results indicate that both PRL and GH have important roles in the adaptive response of freshwater-adapted tilapia to confinement stress.

Plasma prolactin, cortisol, and thyroid responses of the brown trout (Salmo trutta) exposed to lethal and sublethal aluminium in acidic soft waters

Brown trout, with indwelling dorsal aortic cannulae, were exposed to various concentrations of aluminium (Al; 50 micrograms liter-1, 100% mortality over 48 hr; 25 micrograms liter-1, 50% mortality over 120 hr; 12.5 micrograms liter-1, 0% mortality over 120 hr) in acidic (pH 5.0) soft water. The plasma concentrations of prolactin (PRL), cortisol, thyroxine (T4), and triiodothyronine (T3) were monitored. Plasma PRL concentrations were transiently depressed (to less than 20% of resting concentrations) after 12 hr in trout in the two highest water Al concentrations, but were unchanged in the trout exposed to 12.5 micrograms liter-1 Al. Plasma cortisol concentrations were elevated in response to all water Al levels and remained elevated in trout in the lethal conditions. The sublethally exposed trout showed a recovery in plasma cortisol concentrations by 120 hr. Plasma T4 concentrations were significantly elevated in trout exposed to both the lethal and the sublethal Al concentrations (from mean resting concentrations of 1-2 ng ml-1 to peaks of 8.9 and 9.0 ng ml-1 in the 50 and 12.5 micrograms liter-1 Al groups, respectively), although a recovery in plasma concentrations was evident in the sublethally exposed trout from 72 hr onwards. Plasma T3 concentrations were relatively stable in the trout exposed to the two highest doses of Al, whereas the trout under the lowest, sublethal, Al conditions exhibited a sustained (12-72 hr) elevation in plasma T3 concentrations (from a mean resting concentration of 0.9 ng ml-1 to a peak of 4.2 ng ml-1 at 48 hr). No clear relationship was apparent between the plasma PRL concentrations and the previously reported ionoregulatory status of the trout.

Comparison between parr and smolt Atlantic salmon (Salmo salar) α subunit gene expression of Na(+)/K (+) ATPase in gill tissue

Increases in branchial Na(+)/K(+) ATPase activity during seawater adaptation of euryhaline fish species, have been well documented. During the parr-smolt transformation of salmonids this activity increases two to five fold and is used as an indicator of the transformation. In order to improve the understanding of differences in enzyme activity found between Atlantic salmonSalmo salar parr and smolt fish, we investigated the gene expression of the Na(+)/K(+) ATPase α-subunit(s) in gill tissue. Gill mRNAs were analyzed and quantified at distinct time points using Northern and Dot blot techniques. We amplified by PCR, a conserved region of the cDNA encoding the Na(+)/K(+) ATPase α-subunit of the rainbow troutOncorhynchus mykiss. The PCR products (670 bp) were cloned and all independent clones showed a sequence corresponding to the α subunit of the Na(+)/K(+) ATPase. The fragments obtained appeared as a heterogenous population of three sequences showing, when compared between each other, 86 to 93% identity. This suggests that different allelic forms of the α-subunit are expressed in gill tissue. Hybridization studies performed with these PCR probes revealed two mRNA species, a major 3.7 kb transcript and a minor transcript of 1.8 kb. Enhanced 3.7 kb transcript levels are concurrent with elevated enzyme activity in smolts during the March and April parrsmolt transformation of Atlantic salmon. Interestingly, our study disclosed that smolt fish only displayed a two-fold increase in transcript levels when compared to parr whereas enzyme activity showed a 4 to 5 fold increase. This suggests that the increase in the 3.7 kb mRNA content of gill tissue is probably not the only mediator leading to the rise in enzyme activity during parr-smolt transformation.

Influence of growth hormone on the hepatic mixed function oxidase and transferase systems of rainbow trout

The effect of GH treatment on hepatic cytochrome P450 content, aryl hydrocarbon hydroxylase (AHH), aminopyrine-N-demethylase (AND), testosterone hydroxylase, testosterone 5α- and 5β-reductase, UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) activities in immature rainbow trout were investigated. Hepatic cytochrome P450 content, AHH and GST activities were measured in both GH implanted and GH injected animals whereas other activities were assayed in GH implanted trout only.GH implants significantly decreased cytochrome P450 content at 15 days compared to the control but no significant effect was observed at 15 or 30 d when GH was injected biweekly. In both cases, AHH activity was significantly decreased by GH treatment compared to the control whereas GST remained unchanged. Compared to the control, GH implanted fish exhibited a pronounced inhibition of AND, a decreased 6β and 16β-testosterone hydroxylation, an inhibition of UDPGT with testosterone as substrate and an enhanced 17β-testosterone oxidation.

Expression cloning of a cDNA encoding a fish prolactin receptor

By using an expression cloning strategy, we isolated a single positive clone encoding a tilapia prolactin (PRL) receptor. Tilapia PRL188 was used to screen a freshwater tilapia kidney expression library transfected in COS cells. The tilapia PRL receptor is a mature protein of 606 amino acids. The extracellular domain is devoid of the tandem repeat units present in birds and has two pairs of cysteine residues, a Trp-Ser-Xaa-Trp-Ser motif, and two potential N-glycosylation sites. The cytoplasmic domain contains 372 amino acids, including box 1, a sequence previously shown to be important for signal transduction in mammalian species. Thus, the general structure is similar to the long form of mammalian PRL receptors; however, amino acid comparisons reveal a rather low identity (approximately 37%). Northern blot analysis shows the existence of a single transcript in osmoregulatory tissues and reproductive organs. This localization is in agreement with known functions of PRL in teleosts.

Regulation of gill prolactin receptors in tilapia (Oreochromis niloticus) after a change in salinity or hypophysectomy

Prolactin (PRL) receptors in gill tissue have been analyzed in tilapia (Oreochromis niloticus) after transfer from fresh water (FW) to brackish water (BW). This study has indicated the presence of only one class of tilapia PRL (tiPRL) receptor whatever the salinity. After transfer, however, the percentage of specific binding of the two forms of tiPRL (tiPRLI and tiPRLII) increased significantly. Scatchard analysis of tiPRLI binding indicated an increase in receptor affinity, an effect which was not accompanied by any change in receptor specificity. Transfer to BW also caused the number of tiPRL receptors to increase rapidly, remaining high in fish adapted to BW for 28 days. Based on the sharp reduction in plasma tiPRLI and tiPRLII levels after transfer to BW, one possible explanation may be that tiPRL itself is an important factor regulating the number of free receptors. This hypothesis finds support in the fact that the number of tiPRL receptors also increased in hypophysectomized fish reared in FW. However, the absence of change in receptor affinity after hypophysectomy suggested that yet other factors are involved in tiPRL receptor regulation during the transfer from FW to BW. The paradoxically high numbers of tiPRL receptors in the gills of BW-adapted tilapia, even though PRL is known to be a FW-adapting hormone, is discussed with regard to the environment in which tilapia live.

Apical structures of "mitochondria-rich" alpha and beta cells in euryhaline fish gill: their behaviour in various living conditions

BACKGROUND

One of the characteristic features of the two types (alpha and beta) of "mitochondria-rich" (chloride) cells in the gill epithelium of freshwater fishes is the presence in their apical region of tubulovesicular structures. A further analysis of the ultrastructural features of these apical elements as well as that of their modifications under various living conditions should help to understand better the respective rôle of both alpha and beta cells in these conditions.

METHODS

Atlantic salmon (Salmo salar) maintained in fresh water as well as tilapia (Oreochromis niloticus) maintained either in fresh water or in deionized water or in 20% saltwater were examined. Measurements of surface areas of apical structures in the various living conditions were also performed.

RESULTS

In the alpha cells of freshwater fishes, the apical structures consisted of isolated vesicles containing a filamentous material resembling that coating the apical surface. They were closely related to the apical plasma membrane and did not penetrate the region containing the tubular system. When fishes were transferred to deionized water, the number of the apical membrane folds increased significantly, as did the number and size of apical structures which became elongated. In saltwater-adapted fishes, the apical structures showed a tendency to collapse and took the appearance of flattened and slightly curved elements. These observations tended to indicate that in alpha cells the apical structures were extensions of the apical plasma membrane and thereby might be implicated in sodium uptake when fishes are placed in fresh or deionized water and in chloride excretion when they are transferred to salt water. In beta cells, the apical structures were usually separated from the apical plasma membrane by a zone rich in cytoskeleton elements. They penetrated deeply into the supranuclear region, where they intermingled with the elements of the tubular system. They consisted mainly of tubular elements that contained a material resembling that present in the trans tubular Golgi network from which they might originate. The apical structures remained unaltered in beta cells whatever the medium (fresh or deionized water) in which the fish was placed.

CONCLUSIONS

The alpha cells which are usually thought to be mainly involved in chloride excretion when fishes are transferred into seawater might also be implicated in sodium uptake in freshwater living conditions. The rôle of beta cells, in contrast, still remains to be established.

Absence of a tiGH effect on adaptability to brackish water in tilapia (Oreochromis niloticus)

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this process. Plasma levels of growth hormone do not change upon transfer to brackish water. Treatment of intact tilapia in fresh water with growth hormone prior to transfer did not enable the fish to preadapt to brackish water: the duration of the hydromineral imbalance after transfer was the same in treated animals and controls. The major osmoregulatory role of prolactin in fresh water led us to test the hypothesis that prolactin might antagonize the effect of growth hormone on adaptation to brackish water. Growth-hormone-treated hypophysectomized animals, however, exhibited no increased osmoregulatory capacity as compared to hypophysectomized controls, confirming the absence of a growth-hormone-related osmoregulatory effect. When prolactin and growth hormone were coinjected, growth hormone also proved unable to oppose the Na+ retaining effect of prolactin, in both brackish and fresh water. Surprisingly, hypophysectomized animals adapt better to brackish water than do sham-operated animals. This result is discussed in light of the effects of prolactin and cortisol on osmoregulation in brackish water and we suggest that an important event which allows O. niloticus to adapt to hyperosmotic environment is the reduction of plasma PRL upon transfer to brackish water.

Characterization of a single prolactin (PRL) receptor in tilapia (Oreochromis niloticus) which binds both PRLI and PRLII

In tilapia, there are two forms of prolactin (PRL) whose effects on sodium and chloride movements differ and depend on the living environment of the fish. To see whether different receptors or the same receptor mediates these different effects, we have characterized the specific binding of both forms of tilapia (ti)PRL in two osmoregulatory organs, the gill and kidney. Two recombinant tiPRLs were used for this analysis. The recombinant hormones had the same properties as the native hormones in a tilapia gill radioreceptor assay. Specific binding to gill and kidney membranes was increased by optimizing the quality of the tissue preparations (physiological state of fish, membrane preparation) and the incubation conditions (pH, salt concentrations, temperature, time). Under these optimized conditions, we detected only one class of high affinity PRL receptor in gill and kidney. Its binding affinity was higher for tiPRLI than for tiPRLII in both gill and kidney (for tiPRLI the respective affinity values were 2.9 and 2.3 x 10(10) per M, for tiPRLII they were 1.9 and 0.5 x 10(10) per M). In competition studies, tiPRLI was more potent, followed by tiPRLII and ovine (o)PRL. tiGH and oGH did not significantly displace either tiPRL. The receptor we have characterized thus recognizes quite specifically both tiPRLs.

Effects of growth hormone on gill chloride cells in juvenile Atlantic salmon (Salmo salar)

Experiments were performed to investigate the effects of ovine growth hormone (oGH) on both the ultrastructural features of chloride cells and the ability of gills to extrude Na+ after transfer into seawater. February presmolts and June parrs of the Atlantic salmon (Salmo salar) were implanted with oGH. In such animals, spontaneously showing a poor ability to adapt themselves to seawater life, GH significantly increased gill Na(+)-K(+)-adenosinetriphosphatase activity as well as gill sodium efflux into seawater. When examined by electron microscope, two types of chloride cells (alpha- and beta-types) were identified in control parrs and presmolts. GH treatment induced an increase in size and number of alpha-cells that displayed an extensive tubular system, while the beta-cells, thought to be specific to freshwater life, decreased in number. There was, concomitantly, an increase in number of accessory cells associated with the apical portion of the alpha-cells and, as a result, the formation of extensive shallow junctions between these cell types. Such functional and ultrastructural modifications that mimicked those naturally occurring during the last steps of the smoltification strongly suggest that GH stimulates the differentiation of freshwater chloride cells toward a seawater type.

Evidence that two tilapia (Oreochromis niloticus) prolactins have different osmoregulatory functions during adaptation to a hyperosmotic environment

Two forms of prolactin (tiPRLI and tiPRLII), with only 69% sequence identity, have been previously described in the cichlid fish tilapia (Oreochromis species). In the present study we have attempted to investigate the biological activity of these two prolactin forms during adaptation to a hyperosmotic environment. For this purpose, we have developed two highly sensitive (sensitivity: 0.05 ng/ml) and specific (cross-reactivity < 0.04%) radioimmunoassays for tiPRLI and tiPRLII, using recombinant hormones. When fish were directly transferred from fresh to brackish water, the measured levels of plasma tiPRLI and tiPRLII dropped abruptly until 12 h after transfer. Thereafter, plasma tiPRLII remained stable (around 0.5 ng/ml) until the end of the experiment, whereas plasma tiPRLI continued to decrease to undetectable levels. These different patterns of change are reflected in the calculated ratio of plasma tiPRLII to tiPRLI, which increased from 2-3 in fresh water-adapted fish to over 10 in fish which had spent 3 days or more in brackish water. The pituitary contents of tiPRLI and tiPRLII varied in a qualitatively similar fashion after transfer to brackish water. The tiPRLI content dropped continuously after 12 h, reaching one-twelfth of its initial level after 2 weeks. The pituitary tiPRLII content, on the other hand, did not decrease significantly until day 7, and after a 2-week exposure to brackish water it had only decreased by 50%. When injected into tilapia adapted to brackish water, both ovine prolactin and recombinant tiPRLI induced a clear dose-dependent ion-retaining effect. In contrast, the effect induced by tiPRLII treatment was markedly smaller and not dose-dependent. Northern blot analysis of tiPRL mRNAs using either a tiPRLI or a tiPRLII cDNA probe indicated the presence of two mRNAs differing in size: a 1.7 kb mRNA coding for tiPRLI and a 1.3 kb mRNA coding for tiPRLII. After transfer to brackish water, levels of the two mRNAs decreased similarly. The present study indicates that, in O. niloticus, the two forms of prolactin have different osmoregulatory roles during adaptation to brackish water. Accordingly, their synthesis are differentially regulated after transfer to a hyperosmotic environment, presumably at a post-transcriptional level.

GABA-ergic control of prolactin release in rainbow trout (Oncorhynchus mykiss) pituitaries in vitro

The involvement of γ-aminobutyric acid (GABA) in the control of prolactin (PRL) release was investigated in rainbow trout using both perifused pituitary fragments and pituitary cells in primary culture. In our perifusion system, infusion of GABA (10(-6) to 10(-4) M) caused an inhibition of PRL release (between 20 and 40%). Administration on perifused pituitary fragments of 3APS, a GABAa agonist, mimicked this inhibitory effect. Moreover, bicuculline, a specific antagonist of GABAa receptors, totally abolished GABA effect. When tested on cultured pituitary cells during 40h exposure, GABA (10(-5) M) caused a significant decrease in PRL release (24.5%). Baclofen, a specific agonist for GABAb receptor tested at 10(-6) and 10(-5) M, also inhibited PRL released from cultured pituitary cells. These results demonstrate that GABA inhibits PRL release by acting directly on pituitary cells and that probably both types of GABA receptor (a and b) are involved in this regulation.

Effects of prolactin on alpha and beta chloride cells in the gill epithelium of the saltwater adapted tilapia "Oreochromis niloticus"

Tilapia (Oreochromis niloticus), 21 g average body weight, were divided into two groups. A group was maintained in fresh water, whereas another group was adapted for 2 weeks to 20% salt water. Among the latter, fishes were injected every 2 days for a week with tilapia prolactin (ti-PRL I). Gills were prepared for electron microscopy in order to determine the types and surface areas of chloride cells in each experimental condition. Two types of chloride cells, the alpha and beta cells were easily distinguished on the basis of their location and ultrastructural features in the gills of freshwater fishes, while only one type of cell, the saltwater alpha cells presumably derived from the transformation of the freshwater alpha cells, were encountered in saltwater adapted animals. After PRL injection of saltwater adapted fishes, small chloride cells, which displayed ultrastructural features similar to those of beta cells in freshwater tilapia, reappeared in interlamellar regions of the gills. In the same experimental conditions, the voluminous saltwater alpha cells showed a tendency to resume ultrastructural features more characteristic of the freshwater alpha cells from which they were derived. These observations tend to indicate that prolactin behaves as a "freshwater adapting hormone" and that beta cells are specifically involved in fish adaptation to freshwater living conditions.

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss)

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of confinement stress on circulating prolactin levels in rainbow trout (Oncorhynchus mykiss) in fresh water

Rainbow trout were confined for 48 hr, during which time water quality either was allowed to deteriorate (resulting in elevated NH3, elevated free CO2, and reduced dissolved O2) or was maintained at preconfinement levels. Fish were removed and blood samples taken at 0, 2, 4, 8, 24, and 48 hr after the onset of confinement from both stressed (confined) and unstressed (unconfined) fish. Plasma cortisol and plasma prolactin (PRL) levels were determined using specific RIAs. Chronic confinement of rainbow trout, accompanied by a decline in water quality, resulted in significant elevation of plasma cortisol, maintained for the period of confinement. Plasma PRL levels were significantly lower in stressed fish, by up to 60% relative to control fish, during the first 24 hr of confinement. The stress of confinement alone, in the absence of deterioration in water quality, produced similar results, with the change in prolactin levels being less rapid but more prolonged under these conditions.

Effect of somatostatin on prolactin in rainbow trout (Oncorhynchus mykiss) pituitary cells in primary culture

To study the control of prolactin secretion in fish, an in-vitro technique using a monolayer cell culture system of rainbow trout pituitary glands was developed. Such secretion was characterized by measurement of both prolactin release and prolactin mRNA content using a trout prolactin cDNA as a probe. This cell culture technique, already used to study the regulation of gonadotrophin secretion in rainbow trout, was further validated by measuring total DNA and protein content. Both parameters appeared to be stable after 2 days of culture. Studying the effect of somatostatin (SRIF) on prolactin cells indicated that a maximal inhibitory effect (62%) was observed after 24 h of treatment. Significant inhibition of prolactin release was obtained for SRIF doses ranging from 50 nM to 1 microM. However, in the same experiment, SRIF was much more potent as an inhibitor of growth hormone release. Short-term (< 12 h) incubation with SRIF did not induce a significant change in prolactin release, whereas growth hormone release was reduced at as early as 1 h after SRIF exposure. SRIF did not have a significant effect on total prolactin content or prolactin mRNA levels, suggesting the absence of an effect on prolactin synthesis. No increase in the magnitude of the inhibitory effect of SRIF was observed when using pituitary cells from immature, mature male or mature female trout. When comparing effects on primary cultures containing cells from the whole pituitary with a prolactin cell-enriched population, SRIF appeared to have the same inhibitory effect on prolactin release, supporting a direct action of SRIF on prolactin cells. These results provide further support for SRIF being a prolactin-inhibiting factor in rainbow trout and acting as a modulator of a dominant stimulatory control of prolactin release.