Identification of a new growth hormone family protein, somatolactin-like protein, in the rainbow trout (Oncorhyncus mykiss) pituitary gland

Distinguishing between ante factum and post factum properties of animal cell lines and demonstrating their use in grouping ray-finned fish cell lines into invitromes

In this review, animal cell lines are considered to have two classes of attributes: "before-the-fact" (ante factum) and "after-the-fact" (post factum) properties. Fish cell lines from Actinopterygii (ray-finned fishes) are used to illustrate this distinction and to demonstrate how these properties can be used in various ways to categorize cell lines into groups or invitromes. Before-the-fact properties are set at initiation and are properties of the sample and species from which the cell line arose and of the scientist(s) who developed the cell line. On the basis of the Actinopterygii sample, invitromes exist for embryos, larvae, juveniles, adults, and spawning fish, and for most solid organs but rarely for biological fluids. For species, invitromes exist for only a small fraction of the Actinopterygii total. As to their development, scientists from around the world have contributed to invitromes. By contrast, after-the-fact properties are limitless and become apparent during development, characterization, use, and storage of the cell line. For ray-finned invitromes, cell lines appear to acquire immortality during development, are characterized poorly for differentiation potential, have numerous uses, and are stored formally only sporadically. As an example of applying these principles to a specific organ, the skeletal muscle invitrome is used. For ante factum properties, the cell lines are mainly from trunk muscle of economically important fish from 11 orders, 15 families, 19 genera, and 21 species of ray-finned fishes. For post factum properties, fibroblast-like and myogenic cell lines have been described but epithelial-like FHM is most widely used and curated. Considering cell lines by their before- and after-the-fact properties should facilitate integration of new cell lines into the literature and help incorporate the discipline of cell biology into other research areas, particularly the natural history of fishes.

Evolution of the growth hormone, prolactin, prolactin 2 and somatolactin family

Growth hormone (GH), prolactin (PRL), prolactin 2 (PRL2) and somatolactin (SL) belong to the same hormone family and have a wide repertoire of effects including development, osmoregulation, metabolism and stimulation of growth. Both the hormone and the receptor family have been proposed to have expanded by gene duplications in early vertebrate evolution. A key question is how hormone-receptor preferences have arisen among the duplicates. The first step to address this is to determine the time window for these duplications. Specifically, we aimed to see if duplications resulted from the two basal vertebrate tetraploidizations (1R and 2R). GH family genes from a broad range of vertebrate genomes were investigated using a combination of sequence-based phylogenetic analyses and comparisons of synteny. We conclude that the PRL and PRL2 genes arose from a common ancestor in 1R/2R, as shown by neighboring gene families. No other gene duplicates were preserved from these tetraploidization events. The ancestral genes that would give rise to GH and PRL/PRL2 arose from an earlier duplication; most likely a local gene duplication as they are syntenic in several species. Likewise, some evidence suggests that SL arose from a local duplication of an ancestral GH/SL gene in the same time window, explaining the lack of similarity in chromosomal neighbors to GH, PRL or PRL2. Thus, the basic triplet of ancestral GH, PRL/PRL2 and SL genes appear to be unexpectedly ancient. Following 1R/2R, only SL was duplicated in the teleost-specific tetraploidization 3R, resulting in SLa and SLb. These time windows contrast with our recent report that the corresponding receptor genes GHR and PRLR arose through a local duplication in jawed vertebrates and that both receptor genes duplicated further in 3R, which reveals a surprising asynchrony in hormone and receptor gene duplications.

Characterization and expression analyses of somatolactin-α and -β genes in rare minnows (Gobiocypris rarus) following waterborne cadmium exposure

Using reverse transcription-polymerase chain reaction (RT-PCR) and RACE (rapid amplification of cDNA ends), somatolactin-α (rmSLα) and -β (rmSLβ) were identified from the pituitary gland of rare minnows (Gobiocypris rarus). The full-length cDNAs of these two genes were 1288 and 801 bp, encoding prepeptides of 250 and 228 amino acids residues, respectively. rmSLβ can be detected in the brain (including the pituitary), ovary, testis, and gill, while rmSLα was mainly expressed in the brain. On the other hand, rmSLα was expressed in all the fetal developmental stages; however, rmSLβ can just be detected in the stages since from 14 h post-fertilization (hpf). After exposure to acute waterborne cadmium (Cd), rmSLα was distinctly upregulated in juvenile rare minnows at all detected time points, from 24 to 96 h and 10 days, while rmSLβ was significantly altered only in 96 h or 10-day treatment groups. As for adults, acute Cd exposure caused alterations of both rmSLα and rmSLβ in the brain (containing the pituitary) at the 24 h; subchronic waterborne Cd treatment led to upregulation of rmSLα, while decrease of mSLβ in the brain. Alteration of rmSL transcripts following waterborne Cd exposure further confirmed the endocrine disruption of this heavy metal. Besides, exposure to as low as 5 μg/L Cd caused alteration of rmSLα, which suggested that rmSLα might be a potential biomarker for risk assessment of aquatic Cd.

Molecular pathways associated with the nutritional programming of plant-based diet acceptance in rainbow trout following an early feeding exposure

Background

The achievement of sustainable feeding practices in aquaculture by reducing the reliance on wild-captured fish, via replacement of fish-based feed with plant-based feed, is impeded by the poor growth response seen in fish fed high levels of plant ingredients. Our recent strategy to nutritionally program rainbow trout by early short-term exposure to a plant-based (V) diet versus a control fish-based (M) diet at the first-feeding fry stage when the trout fry start to consume exogenous feed, resulted in remarkable improvements in feed intake, growth and feed utilization when the same fish were challenged with the diet V (V-challenge) at the juvenile stage, several months following initial exposure. We employed microarray expression analysis at the first-feeding and juvenile stages to deduce the mechanisms associated with the nutritional programming of plant-based feed acceptance in trout.

Results

Transcriptomic analysis was performed on rainbow trout whole fry after 3 weeks exposure to either diet V or diet M at the first feeding stage (3-week), and in the whole brain and liver of juvenile trout after a 25 day V-challenge, using a rainbow trout custom oligonucleotide microarray. Overall, 1787 (3-week + Brain) and 924 (3-week + Liver) mRNA probes were affected by the early-feeding exposure. Gene ontology and pathway analysis of the corresponding genes revealed that nutritional programming affects pathways of sensory perception, synaptic transmission, cognitive processes and neuroendocrine peptides in the brain; whereas in the liver, pathways mediating intermediary metabolism, xenobiotic metabolism, proteolysis, and cytoskeletal regulation of cell cycle are affected. These results suggest that the nutritionally programmed enhanced acceptance of a plant-based feed in rainbow trout is driven by probable acquisition of flavour and feed preferences, and reduced sensitivity to changes in hepatic metabolic and stress pathways.

Conclusions

This study outlines the molecular mechanisms in trout brain and liver that accompany the nutritional programming of plant-based diet acceptance in trout, reinforces the notion of the first-feeding stage in oviparous fish as a critical window for nutritional programming, and provides support for utilizing this strategy to achieve improvements in sustainability of feeding practices in aquaculture.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2804-1) contains supplementary material, which is available to authorized users.

Evolutionary origin and divergence of the growth hormone receptor family: insight from studies on sea lamprey

Sea lamprey, one of the oldest extant lineages of vertebrates, Agnatha, was used to clarify the evolutionary origin and divergence of the growth hormone receptor (GHR) family. A single full-length cDNA encoding a protein that shares amino acid identity with GHRs and prolactin receptors (PRLRs) previously characterized from teleost fish was identified. Expression of the GHR/PRLR-like transcript was widespread among tissues, including brain, pituitary, heart, liver, and skeletal muscle, which is consistent with the broad physiological roles of GH-family peptides. Phylogenetic analysis suggests that the lamprey possess an ancestral gene encoding a common GHR/PRLR that diverged to give rise to distinct GHRs and PRLRs later in the course of vertebrate evolution. After the divergence of the Actinopterygian and Sarcopterygian lineages, the GHR gene was duplicated in the Actinopterygian lineage during the fish-specific genome duplication event giving rise to two GHRs in teleosts, type 1 GHR and type 2 GHR. A single GHR gene orthologous to the teleost type 1 GHR persisted in the Sarcopterygian lineage, including the common ancestor of tetrapods. Within the teleosts, several subsequent independent duplication events occurred that led to several GHR subtypes. A revised nomenclature for vertebrate GHRs is proposed that represents the evolutionary history of the receptor family. Structural features of the receptor influence ligand binding, receptor dimerization, linkage to signal effector pathways, and, ultimately, hormone function.

cDNA cloning and isolation of somatolactin in Mozambique tilapia and effects of seawater acclimation, confinement stress, and fasting on its pituitary expression

Somatolactin (SL) is a member of the growth hormone (GH)/prolactin (PRL) family of pituitary hormones, and is found in a variety of teleost species. Somatolactin is thought to be involved in a wide range of physiological actions, including reproduction, stress response, the regulation of Ca(2+) and acid-base balance, growth, metabolism, and immune response. We report here on the cDNA structure of SL from the pituitary of Mozambique tilapia, Oreochromis mossambicus, and its gene expression in response to seawater acclimation, stress, and fasting. Tilapia SL cDNA (1573bp long) encoded a prehormone of 230 amino acids. Sequence analysis of purified SL revealed that the prehormone is composed of a signal peptide of 23 amino acids and a mature protein of 207 amino acids, which has a possible N-glycosylation site at position 121 and seven Cys residues. Tilapia SL shows over 80% amino acid identity with SLalpha of advanced teleosts such as medaka and flounder, and around 50% identity with SLbeta of carp and goldfish. Acclimation to seawater had no effect on pituitary expression of SL or on hepatic expression of the putative tilapia SL receptor (GHR1). By contrast, seawater acclimation resulted in significant increases in pituitary GH expression and in hepatic expression of tilapia GH receptor (GHR2). Confinement stress had no effect on pituitary expression of either SL or GH, or on hepatic expression of GHR1, whereas a significant increase was seen in GHR2 expression in the liver. Fasting for 4 weeks resulted in significant reductions in SL transcripts both in fresh water and seawater. It is highly likely that SL is involved in metabolic processes in tilapia along with the GH/IGF-I axis.

Cloning of somatolactin alpha, beta forms and the somatolactin receptor in Atlantic salmon: seasonal expression profile in pituitary and ovary of maturing female broodstock

BACKGROUND

Somatolactin (Sl) is a fish specific adenohypophyseal peptide hormone related to growth hormone (Gh). Some species, including salmonids, possess two forms: Sl alpha and Sl beta. The somatolactin receptor (slr) is closely related to the growth hormone receptor (ghr). Sl has been ascribed many physiological functions, including a role in sexual maturation. In order to clarify the role of Sl in the sexual maturation of female Atlantic salmon (Salmo salar), the full length cDNAs of slr, Sl alpha and Sl beta were cloned and their expression was studied throughout a seasonal reproductive cycle using real-time quantitative PCR (RTqPCR).

METHODS

Atlantic salmon Sl alpha, Sl beta and slr cDNAs were cloned using a PCR approach. Gene expression of Sl alpha, SL beta and slr was studied using RTqPCR over a 17 month period encompassing pre-vitellogenesis, vitellogenesis, ovulation and post ovulation in salmon females. Histological examination of ovarian samples allowed for the classification according to the degree of follicle maturation into oil drop, primary, secondary or tertiary yolk stage.

RESULTS

The mature peptide sequences of Sl alpha, Sl beta and slr are highly similar to previously cloned salmonid forms and contained the typical motifs. Phylogenetic analysis of Atlantic salmon Sl alpha and Sl beta shows that these peptides group into the two Sl clades present in some fish species. The Atlantic salmon slr grouped with salmonid slr amongst so-called type I ghr. An increase in pituitary Sl alpha and Sl beta transcripts before and during spawning, with a decrease post-ovulation, and a constant expression level of ovarian slr were observed. There was also a transient increase in Sl alpha and Sl beta in May prior to transfer from seawater to fresh water and ensuing fasting.

CONCLUSION

The up-regulation of Sl alpha and Sl beta during vitellogenesis and spawning, with a subsequent decrease post-ovulation, supports a role for Sl during gonadal growth and spawning. Sl could also be involved in calcium/phosphate mobilization associated with vitellogenesis or have a role in energy homeostasis associated with lipolysis during fasting. The up-regulation of both Sl alpha and Sl beta prior to fasting and freshwater transfer, suggests a role for Sl linked to reproduction that may be independent of the maturation induced fasting.

Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-alpha and -beta gene expression via activation of pituitary PAC-I receptors

Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. At present, SL can be identified only in fish but not in tetrapods and its regulation at the pituitary level has not been fully characterized. Using grass carp as a model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL secretion and synthesis at the pituitary cell level. As a first step, the structural identity of grass carp SL, SLalpha and SLbeta, was established by 5'/3'-rapid amplification of cDNA ends. These two SL isoforms are single-copy genes and are expressed in two separate populations of pituitary cells located in the pars intermedia. In the carp pituitary, PACAP nerve fibers were detected in the nerve tracts of the neurohypophysis and extended into the vicinity of pituitary cells forming the pars intermedia. In primary cultures of grass carp pituitary cells, PACAP was effective in stimulating SL release, cellular SL content, and total SL production. The increase in SL production also occurred with parallel rises in SLalpha and SLbeta mRNA levels. With the use of a combination of molecular and pharmacological approaches, PACAP-induced SL release and SL gene expression were shown to be mediated by pituitary PAC-I receptors. These findings, as a whole, suggest that PACAP may serve as a hypophysiotropic factor in fish stimulating SL secretion and synthesis at the pituitary level. Apparently, PACAP-induced SL production is mediated by upregulation of SLalpha and SLbeta gene expression through activation of PAC-I receptors.

Molecular characterization and sex-specific tissue expression of prolactin, somatolactin and insulin-like growth factor-I in yellow perch (Perca flavescens)

The cDNA sequences encoding prolactin (PRL), somatolactin (SL) and insulin-like growth factor-I (IGF-I) genes of the yellow perch were obtained. Brain, pituitary, gill, heart, liver, stomach, kidney, spleen, muscle and gonad tissues were analyzed from both male and female adult yellow perch for sex-specific tissue expression. The full length cDNA of yellow perch PRL consists of 2306 bp and PRL expression was highest in the yellow perch pituitary with low to moderate expression in other tissues including brain, gill and post-vitellogenic oocytes. The full length cDNA of yellow perch SL consists of 1589 bp and SL expression was highest in the yellow perch pituitary with low to moderate expression in other tissues including brain, gill, liver, stomach, spleen and kidney. The full length cDNA of yellow perch IGF-Ib consists of 814 bp and tissue expression analysis of yellow perch IGF-I revealed a second yellow perch transcript (IGF-Ia) that is 81 nucleotides smaller. Both IGF-Ib and IGF-Ia had the greatest expression in liver tissue with moderate expression in brain, spleen and kidney tissues of both sexes. These sequences are valuable molecular tools which can be used in future studies investigating the basis for sexually dimorphic growth in yellow perch.

The dawn and evolution of hormones in the adenohypophysis

The adenohypophysial hormones have been believed to have evolved from several ancestral genes by duplication followed by evolutionary divergence. To understand the origin and evolution of the endocrine systems in vertebrates, we have characterized adenohypophysial hormones in an agnathan, the sea lamprey Petromyzon marinus. In gnathostomes, adrenocorticotropin (ACTH) and melanotropin (MSH) together with beta-endorphins (beta-END) are encoded in a single gene, designated as proopiomelanocortin (POMC), however in sea lamprey, ACTH and MSH are encoded in two distinct genes, proopoicortin (POC) gene and proopiomelanotropin (POM) gene, respectively. The POC and POM genes are expressed specifically in the rostral pars distalis (RPD) and the pars intermedia (PI), respectively. Consequently, the final products from both tissues are the same in all vertebrates, i.e., ACTH from the PD and MSH from the PI. The POMC gene might have been established in the early stages of invertebrate evolution by internal gene duplication of the MSH domains. The ancestral gene might be then inherited in lobe-finned fish and tetrapods, while internal duplication and deletion of MSH domains as well as duplication of whole POMC gene took place in lamprey and gnathostome fish. Sea lamprey growth hormone (GH) is expressed in the cells of the dorsal half of the proximal pars distalis (PPD) and stimulates the expression of an insulin-like growth factor (IGF) gene in the liver as in other vertebrates. Its gene consists of 5 exons and 4 introns spanning 13.6 kb, which is the largest gene among known GH genes. GH appears to be the only member of the GH family in the sea lamprey, which suggests that GH is the ancestral hormone of the GH family that originated first in the molecular evolution of the GH family in vertebrates and later, probably during the early evolution of gnathostomes. The other member of the gene family, PRL and SL, appeared by gene duplication. A beta-chain cDNA belonging to the gonadotropin (GTH) and thyrotropin (TSH) family was cloned. It is expressed in cells of the ventral half of PPD. Since the expression of this gene is stimulated by lamprey gonadotropin-releasing hormone, it was assigned to be a GTHbeta. This GTHbeta is far removed from beta-subunits of LH, FSH, and TSH in an unrooted tree derived from phylogenetic analysis, and takes a position as an out group, suggesting that lampreys have a single GTH gene, which duplicated after the agnathans and prior to the evolution of gnathostomes to give rise to LH and FSH.

Involvement of somatolactin in background adaptation of the cichlid fish Cichlasoma dimerus

Somatolactin (SL) is a pituitary hormone present exclusively in fish that is involved in different physiological processes. The role of SL was evaluated in Cichlasoma dimerus (Teleostei, Perciformes) exposed for 10 days to a black and white background (BB and WB). Changes in alpha-melanophore stimulating hormone (alphaMSH) and melanin concentrating hormone (MCH) cells were also analyzed for comparison with SL. A melanin dispersing effect was observed in fish exposed to a BB, while a concentrating one was observed in those exposed to a WB. By Western blot, three SL-immunoreactive (ir) bands (32, 28 and 23.5 kD) were evidenced. Pituitary SL-ir levels were 2.66- and 2.67-fold greater in the 32 Kd and 28 kD bands, respectively, in BB fish compared with those of WB fish. The SL-ir 23.5 Kd band was not included in the analysis because of its unknown identity. In addition, SL-ir cell number and area were significantly higher in the BB condition (BB 22.73+/-1.46, WB 7.37+/-0.54 and BB 27.39+/-1.00 microm2; WB: 16.61+/-0.65 microm2). No significant differences were observed in the number of the hypothalamic MCH-ir neurons. However, a significant difference was observed in their nuclear area (BB 11.61+/-0.42 microm2, WB 17.80+/-0.84 microm2). alphaMSH-ir cells showed a marked increased in number (BB 35.96+/-1.22, WB 24.36+/-1.04), but no significant differences were observed in the cell area. In conclusion, this study presented clear evidence towards a possible involvement of SL in the adaptation to background colors in teleost together with alphaMSH and MCH.

Effects of endocrine disrupters on the expression of growth hormone and prolactin mRNA in the rainbow trout pituitary

It is now widely accepted that chemical pollutants in the environment can interfere with the endocrine system of animals, thus affecting development and reproduction. Some of these endocrine disrupters (EDs) can have estrogenic or antiestrogenic effects. Most studies to date have focused on the effects of EDs on the reproductive system and sex hormones and only limited information exists on how EDs may affect pituitary gland function. A rainbow trout (Oncorhynchus mykiss) pituitary gland culture system was used for studying the effects of EDs on growth hormone (GH) and prolactin (PRL) mRNA expression. We determined that the pituitary glands actively synthesized and secreted GH and PRL over the experimental time-course. In addition, we found that treatment with 17beta-estradiol (positive control) increased levels of GH and PRL mRNA, in a concentration-dependent manner. Treatment of pituitary glands with 500 and 1000 nM of a xenoestrogen, o,p'-DDT (o,p'-dichlorodiphenyltrichloroethane), resulted in a significant induction of GH and PRL mRNA, with a 20-fold increase for PRL and 3-fold increase for GH following treatment with 1000 nM o,p'-DDT. Co-incubation of pituitary glands with ICI 182 780 (a selective estrogen receptor antagonist) and o,p'-DDT resulted in inhibition of PRL mRNA levels; however, the stimulatory effect of DDT on GH mRNA was not seen in this experiment, nor was the inhibitory effect of ICI 182 780 observed with GH mRNA. To the contrary, ICI 182 780 (2.5 nM) had a stimulatory effect on GH mRNA levels. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which is known to exert antiestrogenic effects, had an estrogenic-like effect that resulted in a concentration-dependent increase in the levels of GH and PRL mRNA. Co-incubation of pituitaries with TCDD and alpha-napthoflavone (ANF), which is an inhibitor of the aryl hydrocarbon receptor (AhR), caused an inhibition of TCDD-induced PRL mRNA at the higher and lower concentrations, but these effects were less consistent on GH mRNA levels. However, the responses of PRL and GH mRNA to co-incubation with TCDD and ANF, at the various concentrations, were bi-phasic wherein stimulation was seen at the low concentrations and inhibition at the high concentrations. Combined, these results suggest that o,p'-DDT and TCDD are xenoestrogens and that their effects on the expression of GH and PRL genes in the rainbow trout pituitary are modulated, in part, through the ER and AhR, respectively.

Medaka receptors for somatolactin and growth hormone: phylogenetic paradox among fish growth hormone receptors

Somatolactin (SL) in fish belongs to the growth hormone/prolactin family. Its ortholog in tetrapods has not been identified and its function(s) remains largely unknown. The SL-deficient mutant of medaka (color interfere, ci) and an SL receptor (SLR) recently identified in salmon provide a fascinating field for investigating SL's function(s) in vivo. Here we isolated a medaka ortholog of the salmon SLR. The mRNA is transcribed in variable organs. Triglycerides and cholesterol contents in the ci are significantly higher than those in the wild type, providing the first evidence of SL's function in suppressing lipid accumulation to organs. Interestingly, phylogenetic comparisons between the medaka SLR and growth hormone receptor (GHR), which is also isolated in this study, in relation to GHRs of other fish, suggested that all GHRs reported from nonsalmonid species are, at least phylogenetically, SLRs. An extra intron inserted in medaka and pufferfish SLRs and flounder and sea bream GHRs also supports their orthologous relationship, but not with tetrapod GHRs. These results may indicate lineage-specific diversification of SLR and GHR functions among fish or just an inappropriate naming of these receptors. Further functional and comparative reassessments are necessary to address this question.

Nutritional assessment of somatolactin function in gilthead sea bream (Sparus aurata): concurrent changes in somatotropic axis and pancreatic hormones

The role of somatolactin (SL) in the regulation of energy homeostasis in gilthead sea bream (Sparus aurata) has been analysed. First, a down-regulation of plasma SL levels in response to gross shifts in dietary amino acid profile and the graded replacement of fish meal by plant protein sources (50%, 75% and 100%) has been observed. Thus, the impaired growth performance with changes in dietary amino acid profile and dietary protein source was accompanied by a decrease in plasma SL levels, which also decreased over the course of the post-prandial period irrespective of dietary nitrogen source. Secondly, we examined the effect of SL and growth hormone (GH) administration on voluntary feed intake. A single intraperitoneal injection of recombinant gilthead sea bream SL (0.1 microg/g fish) evoked a short-term inhibition of feed intake, whereas the same dose of GH exerted a marked enhancement of feed intake that still persisted 1 week later. Further, we addressed the effect of arginine (Arg) injection upon SL and related metabolic hormones (GH, insulin-like growth factor-I (IGF-I), insulin and glucagon) in fish fed diets with different nitrogen sources. A consistent effect of Arg injection (6.6 micromol/g fish) on plasma GH and IGF-I levels was not found regardless of dietary treatment. In contrast, the insulinotropic effect of Arg was found irrespective of dietary treatment, although the up-regulation of plasma glucagon and glucose levels was more persistent in fish fed a fish meal based diet (diet FM) than in those fed a plant protein diet with a 75% replacement (diet PP75). In the same way, a persistent and two-fold increase in plasma SL levels was observed in fish fed diet FM, whereas no effect was found in fish fed diet PP75. Taken together, these findings provide additional evidence for a role of SL as a marker of energy status, which may be perceived by fish as a daily and seasonal signal of abundant energy at a precise calendar time.

Production and characterization of recombinantly derived peptides and antibodies for accurate determinations of somatolactin, growth hormone and insulin-like growth factor-I in European sea bass (Dicentrarchus labrax)

A specific radioimmunoassay (RIA) for European sea bass (Dicentrarchus labrax) growth hormone (GH) was developed and validated. For this purpose, a stable source of GH was produced by means of recombinant DNA technology in a bacteria system. The identity of the purified protein (ion exchange chromatography) was demonstrated by Western blot and a specific GH antiserum was raised in rabbit. In Western blot and RIA system, this antiserum recognized specifically native and recombinant GH, and it did not cross-react with fish prolactin (PRL) and somatolactin (SL). In a similar way, a specific polyclonal antiserum against the now available recombinant European sea bass SL was raised and used in the RIA system to a sensitivity of 0.3 ng/ml (90% of binding of tracer). Further, European sea bass insulin-like growth factor-I (IGF-I) was cloned and sequenced, and its high degree of identity with IGF-I peptides of barramundi, tuna, and sparid fish allowed the use of a commercial IGF-I RIA based on barramundi IGF-I antiserum. These assay tools assisted for the first time accurate determinations of SL and GH-IGF-I axis activity in a fish species of the Moronidae family. Data values were compared to those found with gilthead sea bream (Sparus aurata), which is currently used as a Mediterranean fish model for growth endocrinology studies. As a characteristic feature, the average concentration year round of circulating GH in growing mature males of European sea bass was higher than in gilthead sea bream. By contrast, the average concentration of circulating SL was lower. Concerning to circulating concentration of IGF-I, the measured plasma values for a given growth rate were also lower in European sea bass. These findings are discussed on the basis of a different energy status that might allowed a reduced but more continuous growth in European sea bass.

Somatolactin selectively regulates proliferation and morphogenesis of neural-crest derived pigment cells in medaka

Species-specific colors and patterns on animal body surfaces are determined primarily by neural-crest-derived pigment cells in the skin (chromatophores). However, even closely related species display widely differing patterns. These contrasting aspects of chromatophores (i.e., the fixed developmental control within species and extreme diversity among species) seem to be a curious and suitable subject for understanding evolution and diversity of organisms. Here we identify a gene responsible for medaka "color interfere" mutants by positional cloning. These mutants do not show any obvious morphological and physiological defects other than defects in chromatophore proliferation and morphogenesis. The mutation has been identified as an 11-base deletion in somatolactin, which causes truncation 91 aa upstream of the C terminus of the protein's 230 aa. Somatolactin transcription changed dramatically during morphological body color adaptation to different backgrounds. This genetic evidence explains somatolactin function. Studying this mutant will provide further insights into the development and regulation of chromatophores and clues for reassessing other functions of somatolactin suggested in other fish.

Growth differences and growth hormone expression in male and female European eels [Anguilla anguilla (L.)]

In this study, we examined the growth differences of males and females following a sex reversion, and the growth hormone (GH) expression variation between sexes of European eels [Anguilla anguilla (L.)]. A high percentage of females (88%) was found in the group fed with estradiol 17beta compared to the control group (comprised of only 6% female eels), which was defined as the male population. Significant differences between growth rate and size were found following 480 days of growth, whereby the males reached 60+/-4.3 g (means+/-SE) in size and the females 73.4+/-5.9 (g+/-SE); after 600 days, the males reached 114.1+/-4.3 and the females 171+/-11.7 (g+/-SE). A cDNA coding for the complete growth hormone of the European eel A. anguilla (eeGH) was cloned by RACE PCR using several sets of degenerate oligonucleotides. The eeGH cDNA coding region is 627 bp long. A sequence comparison of eeGH with Anguilla japonica GH (jeGH) cDNA showed a 98% identical base. Comparison of the deduced amino acid sequence revealed 99% identical residues, meaning that a difference exists in only two of the 209 residues. In both cases, the differing residues in the eeGH amino acid sequence are lysine. We measured the mRNA levels of growth hormone in the pituitaries of male and female eels growing at different rates. A significantly higher expression of eeGH was found in the female eels in comparison to the males. These results show that different levels of GH transcription eeGH can explain the growth rate differences between male and female European eels.