Role of the melanocortin system in zebrafish skin physiology.

The agouti-signaling protein (ASIP) acts as both a competitive antagonist and inverse agonist of melanocortin receptors which regulate dorsal-ventral pigmentation patterns in fish. However, the potential role of ASIP in the regulation of additional physiological pathways in the skin is unknown. The skin plays a crucial role in the immune function, acting as a physical limitation against infestation and also as a chemical barrier due to its ability to synthesize and secrete mucus and many immune effector proteins. In this study, the putative role of ASIP in regulating the immune system of skin has been explored using a transgenic zebrafish model overexpressing the asip1 gene (ASIPzf). Initially, the structural changes in skin induced by asip1 overexpression were studied, revealing that the ventral skin of ASIPzf was thinner than that of wild type (WT) animals. A moderate hypertrophy of mucous cells was also found in ASIPzf. Histochemical studies showed that transgenic animals appear to compensate for the lower number of cell layers by modifying the mucus composition and increasing lectin affinity and mucin content in order to maintain or improve protection against microorganism adhesion. ASIPzf also exhibit higher protein concentration under crowding conditions suggesting an increased mucus production under stressful conditions. Exposure to bacterial lipopolysaccharide (LPS) showed that ASIPzf exhibit a faster pro-inflammatory response and increased mucin expression yet severe skin injures and a slight increase in mortality was observed. Electrophysiological measurements show that the ASIP1 genotype exhibits reduced epithelial resistance, an indicator of reduced tissue integrity and barrier function. Overall, not only are ASIP1 animals more prone to infiltration and subsequent infections due to reduced skin epithelial integrity, but also display an increased inflammatory response that can lead to increased skin sensitivity to external infections.

The Bromodomain testis-specific gene (Brdt) characterization and expression in gilthead seabream, Sparus aurata, and European seabass, Dicentrarchus labrax.

Multiple genes and transcription factors are involved in regulation and control of the complex process of sex determination and differentiation of fish species. Also more, several hormonal factors and some environmental conditions can also be adequate spawning strategies and stimuli for inducing reproduction of fish species. Brdt gene belongs to the bromodomain-extraterminal domain (BET) family of transcriptional coregulators. In mammals, Brdt gene is almost exclusively expressed in testis. Furthermore, Brdt protein is involved in elongating spermatids, and is required for proper spermatogenesis and male fertility. However, from our understanding of fish species, the role of this gene as key, during gametogenesis, still remains unknown. In this study, two Brdt mRNA transcripts were isolated from two teleostean fish species, gilthead seabream and European seabass. In both species the shorter form lacked a functional C-terminal domain, which may involve a different function as transcriptional regulator. The pattern of Brdt expression showed that the highest levels occurred in the gonads. Significantly lower levels of expression were detected in brain, pituitary and different organ systems (heart, kidney, gills, among other somatic tissues) from both studied species. In situ hybridization approach evidenced that Brdt mRNA expression was restricted to specific cell-types of the germ line, during both oogenesis and spermatogenesis processes.

Antiviral activity of casein and αs2 casein hydrolysates against the infectious haematopoietic necrosis virus, a rhabdovirus from salmonid fish.

Salmonid fish viruses, such as infectious haematopoietic necrosis virus (IHNV), are responsible for serious losses in the rainbow trout and salmon-farming industries, and they have been the subject of intense research in the field of aquaculture. Thus, the aim of this work is to study the antiviral effect of milk-derived proteins as bovine caseins or casein-derived peptides at different stages during the course of IHNV infection. The results indicate that the 3-h fraction of casein and α(S2) -casein hydrolysates reduced the yield of infectious IHNV in a dose-dependent manner and impaired the production of IHNV-specific antigens. Hydrolysates of total casein and α(S2) -casein target the initial and later stages of viral infection, as demonstrated by the reduction in the infective titre observed throughout multiple stages and cycles. In vivo, more than 50% protection was observed in the casein-treated fish, and the kidney sections exhibited none of the histopathological characteristics of IHNV infection. The active fractions from casein were identified, as well as one of the individual IHNV-inhibiting peptides. Further studies will be required to determine which other peptides possess this activity. These findings provide a basis for future investigations on the efficacy of these compounds in treating other viral diseases in farmed fish and to elucidate the underlying molecular mechanisms of action. However, the present results provide convincing evidence in support of a role for several milk casein fractions as suitable candidates to prevent and treat some fish viral infections.

Transmission of lymphocystis disease virus to cultured gilthead seabream, Sparus aurata L., larvae.

The transmission of lymphocystis disease virus (LCDV) to gilthead seabream, Sparus aurata L., larvae was investigated using fertilized eggs from a farm with previous reports of lymphocystis disease. LCDV genome was detected by PCR-hybridization in blood samples from 17.5% of the asymptomatic gilthead seabream broodstock analysed. Using the same methodology, eggs spawned from these animals were LCDV positive, as well as larvae hatched from them. The presence of infective viral particles was confirmed by cytopathic effects development on SAF-1 cells. Whole-mount in situ hybridization (ISH) and immunohistochemistry (IHC) showed the presence of LCDV in the epidermis of larvae hatched from LCDV-positive eggs. When fertilized eggs were disinfected with iodine, no viral DNA was detected either in eggs (analysed by PCR-hybridization) or in larvae (PCR-hybridization and ISH). These results suggest the vertical transmission of LCDV, the virus being transmitted on the egg surface. Larvae hatched from disinfected eggs remain LCDV negative during the endotrophic phase, as showed by PCR-hybridization, ISH and IHC. After feeding on LCDV-positive rotifers, viral antigens were observed in the digestive tract, which suggests that viral entry could be achieved via the alimentary canal, and that rotifers can act as a vector in LCDV transmission to gilthead seabream larvae.

Brain CYP1A in seabream, Sparus aurata exposed to benzo(a)pyrene.

This study compares basal and induced expression of cytochrome P4501A-CYP1A in the brain of gilthead seabream, Sparus aurata. Larval or adult seabream were exposed to benzo(a)pyrene -B(a)P- and the CYP1A response was assessed by analyzing CYP1A mRNA (RT-PCR), CYP1A protein (expression levels: ELISA, western blotting; cellular localization: immunohistochemistry), and CYP1A catalytic activity (7-ethoxyresorufin-O-deethylase-EROD). In the brain of adult S. aurata, CYP1A immunostaining was generally detected in the vasculature. It was present in the neuronal fibers and glial cells of the olfactory bulbs and the ventral telencephalon. ELISA and RT-PCR analyses confirmed CYP1A expression in the brains of non-exposed seabream. B(a)P exposure led to increased CYP1A staining mainly in neuronal fibers and glial cells of the olfactory bulbs, but also in the vascular endothelia. EROD activity, however, could not be detected in the brain of adult seabream, neither in control nor in exposed fish. In the developing brain of S. aurata larvae, immunohistochemical staining detected CYP1A protein exclusively in endothelia of the olfactory placode and in retina. Staining intensity of CYP1A slightly increases with larval development, especially in vascular brain endothelia. Exposing the larvae to 0.3 or 0.5 microg B(a)P/L from hatching until 15 days post hatching (dph) did not result in enhanced CYP1A immunostaining in the brain. In samples of whole seabream larvae, both from controls and BaP treatments, neither CYP1A mRNA, protein nor catalytic activity were detectable. The results demonstrate that CYP1A is expressed already and inducible in the larval brain, but that the regional and cellular expression differs partly between larval and adult brain. This may have implications for the toxicity of CYP1A-inducing xenobiotics on early and mature life stages of seabream.

Comparative gene expression of gonadotropins (FSH and LH) and peptide levels of gonadotropin-releasing hormones (GnRHs) in the pituitary of wild and cultured Senegalese sole (Solea senegalensis) broodstocks.

The Senegalese sole (Solea senegalensis) is a valuable flatfish for aquaculture, but it presents important reproductive problems in captivity. Spawning is achieved by wild-caught breeders but cultured broodstocks fail to spawn spontaneously and, when they do, eggs are unfertilized. To gain knowledge on the physiological basis underlying this reproductive dysfunction, this study aimed at analyzing comparative hormone levels between wild and cultured broodstocks at the spawning season. The Senegalese sole gonadotropin (GTH) subunits, FSHbeta, LHbeta and GPalpha, were cloned and qualitative (in situ hybridization) and quantitative (real-time PCR) assays developed to analyze pituitary GTH gene expression. In females, FSHbeta and GPalpha mRNA levels were higher in wild than in cultured broodstocks, whereas in males all three subunits were highest in cultured. By ELISA, three GnRH forms were detected in the pituitary, displaying a relative abundance of GnRH2>GnRH1>GnRH3. All GnRHs were slightly more abundant in wild than cultured females, whereas no differences were observed in males. Plasma levels of vitellogenin and sex steroids were also analyzed. Results showed endocrine differences between wild and cultured broodstocks at the spawning period, which could be related to the endocrine failure of the reproductive axis in cultured breeders.

Nutritional cellular biomarkers in early life stages of fish.

Histological (tissular and cellular) indices have a tradition of determining the nutritional condition of fish both in the laboratory and in the wild. The assessment of condition by means of microscopical methods is probably the mos accurate indicator of nutritional status during the early life stages of fish. This success is partly attributable large amount of information that can be derived from their study and because they are thought to be the only true starvation indices. The technique usually consists of the examination of cells and organs and the establishment of a grading system based on the presence/absence of standardised biomarkers. Each organ is examined, and the cellular aspect or tissular cohesion is evaluated qualitatively and even quantitatively in order to obtain a measure of the general condition of a larva. The literature indicates that there are certain tissular and cellular responses to food availability and quality, particularly in the digestive and muscular tissues, which are common to most teleost fish larvae. These responses, which are independent of water temperature, can be used for assessing fish larvae nutritional condition. In this regard, the microscopical organization of the liver hepatocytes, the intestinal mucosa, the exocrine pancreas and the muscular fibers, which are generally used as target tissues and organs to assess the nutritional condition of fish larvae, is deeply reviewed. The advantages and disadvantages of the use of different cellular biomarkers of effect are discussed considering different conditions.

Effects of sediment sorbed linear alkylbenzene sulphonate on juveniles of the Senegal sole, Solea senegalensis: toxicity and histological indicators.

Many synthetic organic substances, including surfactants, tend to be sorbed on suspended solids and to accumulate finally on bottom sediments, where benthic communities may be exposed to them. Concentrations of Linear Alkylbenzene Sulphonates (LAS) have been detected in estuarine and coastal sediments, presenting wide concentration ranges depending on the presence of treatment facilities, hydrodynamic conditions, organic matter content etc. Senegal sole, Solea senegalensis, larvae (40 days posthatching; dph) were exposed to increasing concentrations of LAS spiked sediments, comprised between 0.37 and 880.78 mg LAS x kg(-1) during 30 days. The obtained results showed that survival of exposed larvae was not significantly affected at environmentally relevant concentrations, the LC50 value being obtained after 30 days 876.46 mg x kg(-1). However, the histological and histopathological analyses carried out in target organs revealed, that first alterations from the normal pattern were observed at concentrations of 222.66 mg x kg(-1), presenting effects such as blood extravasation and hyperplasy of the lamellar epithelium in gills, increase of inter-myotomal spaces of the skeletal musculature and edematous separation of the skin from epidermis. At the highest exposure concentrations (755.27 and 880.78 mg LAS x kg(-1)), shrinkage of hepatocytes, nuclear pycnosis and blood stagnation are observed in the liver, degeneration of pancreatic cells, reduction of hemocytopoietic tissue in the kidney and vacuolisation of intestinal enterocytes was observed at histological level, as well as severe separation of the epidermis from the underlying tissues. Simultaneously, a significant increase of the wet weight with exposure concentration was observed in the test organisms.

Tissue-specific induction of EROD activity and CYP1A protein in Sparus aurata exposed to B(a)P and TCDD.

The purpose of this study was to compare xenobiotic CYP1A induction in liver, gills, and excretory kidney of gilthead seabream, Sparus aurata. Fishes were exposed via water for 20 days to different concentrations of benzo(a)pyrene (B(a)P) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). CYP1A was measured at the enzyme activity level as 7-ethoxyresorufin-O-deethylase (EROD) activity, and at the protein level by means of ELISA. The liver displayed the highest absolute levels of EROD activity, both under non-exposed and exposed conditions. Organ- or inducer-related differences in the time course of CYP1A induction were moderate; however, the magnitude of the induction response varied between the organs and between B(a)P and TCDD. In the case of TCDD, liver, and kidney yielded a comparable induction response, whereas in the case of B(a)P, the kidney showed a substantially higher maximum induction factor than the liver. In the gills, the two xenobiotics resulted in similar maximum induction factors. In B(a)P-exposed seabream, EROD activities and CYP1A protein levels showed a good correlation in all three organs, whereas with TCDD as inducer the correlation was poor, what was mainly due to a decrease of EROD activities at the higher concentrations of TCDD, while CYP1A protein levels showed no concomitant decline. Overall, the study revealed both similarities and differences in the time-, concentration-, and inducer-dependent CYP1A responses of the three target organs, liver, kidney, and gills. Although, the findings of this study principally confirm the notion of the liver as the major metabolic organ in fish, they also provide evidence for substantial metabolic potential in gills and particularly in the kidney.

Larval organogenesis of Pagrus pagrus L., 1758 with special attention to the digestive system development.

Organogenesis of the red porgy (Pagrus pagrus L., 1758) was examined from hatching until 63 days post-hatching (dph) using histological and histochemical techniques. At hatching, the heart appeared as a tubular structure which progressively developed into four differentiated regions at 2 dph: bulbus arteriosus, atrium, ventricle and sinus venosus. First ventricle and atrium trabeculae were appreciated at 6 and 26 dph, respectively. Primordial gill arches were evident at 2 dph. Primordial filaments and first lamellae were observed at 6 and 15 dph, respectively. At mouth opening (3dph), larvae exhausted their yolk-sac reserves. The pancreatic zymogen granules appeared at 6 dph. Glycogen granules, proteins and neutral lipids (vacuoles in paraffin sections) were detected in the cytoplasm of the hepatocytes from 4-6 dph. Hepatic sinusoids could be observed from 9 dph. Pharyngeal and buccal teeth were observed at 9 and 15 dph, respectively. Oesophageal goblet cells appeared around 6 dph, containing neutral and acid mucosubstances. An incipient stomach could be distinguished at 2 dph. The first signs of gastric gland development were detected at 26 dph, increasing in number and size by 35-40 dph. Gastric glands were concentrated in the cardiac stomach region and presented a high content of protein rich in tyrosine, arginine and tryptophan. The intestinal mucous cells appeared at 15 dph and contained neutral and acid glycoconjugates, the carboxylated mucins being more abundant than the sulphated ones. Acidophilic supranuclear inclusions in the intestinal cells of the posterior intestine, related to pynocitosis of proteins, were observed at 4-6 dph.

Histopathological alterations, EROD activity, CYP1A protein and biliary metabolites in gilthead seabream Sparus aurata exposed to benzo(a)pyrene.

This study compared for seabream, Sparus aurata exposed to benzo(a)pyrene-B(a)P-, the response of molecular cytochrome P450 1A (CYP1A) and cellular histopathology biomarkers. Male gilthead seabream, Sparus aurata specimens were exposed for 20 days via water to a series of high B(a)P concentrations. CYP1A was assessed by measuring enzymatic activity (EROD) and CYP1A protein content, and cellular responses were evaluated by routine histopathological methods. In addition, biliary metabolites were measured in order to verify that B(a)P was absorbed and metabolised. Histological lesions, both in liver and gills, increased in parallel to B(a)P concentrations, with the majority of changes representing rather non-specific alterations. Hepatic EROD and CYP1A proteins data showed a concentration-dependent induction, while in the gills, EROD activity but not CYP1A proteins showed a non-monotonous dose response, with a maximum induction level at 200 microg B(a)P.L-1 and decreasing levels thereafter. The findings provide evidence that short-term, high dose exposure of fish can result in significant uptake and metabolism of the lipophilic B(a)P, and in pronounced pathological damage of absorptive epithelia and internal organs.

Osteocalcin and matrix Gla protein in zebrafish (Danio rerio) and Senegal sole (Solea senegalensis): comparative gene and protein expression during larval development through adulthood.

Bone Gla protein (Bgp or osteocalcin) and matrix Gla protein (Mgp) are important in calcium metabolism and skeletal development, but their precise roles at the molecular level remain poorly understood. Here, we compare the tissue distribution and accumulation of Bgp and Mgp during larval development and in adult tissues of zebrafish (Danio rerio) and throughout metamorphosis in Senegal sole (Solea senegalensis), two fish species with contrasting environmental calcium levels and degrees of skeletal reorganization at metamorphosis. Mineral deposition was investigated in parallel using a modified Alizarin red/Alcian blue protocol allowing sensitive simultaneous detection of bone and cartilage. In zebrafish, bgp and mgp mRNAs were localized in all mineralized tissues during and after calcification including bone and calcified cartilage of branchial arches. Through immunohistochemistry we demonstrated that these proteins accumulate mainly in the matrix of skeletal structures already calcified or under calcification, confirming in situ hybridization results. Interestingly, some accumulation of Bgp was also observed in kidney, possibly due to the presence of a related protein, nephrocalcin. Chromosomal localization of bgp and mgp using a zebrafish radiation hybrid panel indicated that both genes are located on the same chromosome, in contrast to mammals where they map to different chromosomes, albeit in regions showing synteny with the zebrafish location. Results in Senegal sole further indicate that, during metamorphosis, there is an increase in expression of both bgp and mgp, paralleling calcification of axial skeleton structures. In contrast with results obtained for previously studied marine fishes, in zebrafish and Senegal sole Mgp accumulates in both calcified tissues and non-mieralized vessel walls of the vascular system. These results suggest different patterns of Mgp accumulation between fish and mammals.

Cloning of matrix Gla protein in a marine cartilaginous fish, Prionace glauca: preferential protein accumulation in skeletal and vascular systems.

Matrix Gla protein (MGP) belongs to the family of vitamin K dependent, Gla containing proteins and, in mammals, birds and Xenopus, its mRNA has been previously detected in bone, cartilage and soft tissue extracts, while the accumulation of the protein was found mainly in calcified tissues. More recently, the MGP gene expression was also studied in marine teleost fish where it was found to be associated with chondrocytes, smooth muscle and endothelial cells. To date no information is available on the sites of MGP expression or accumulation in cartilaginous fishes that diverged from osteichthyans, a group that includes mammals, over 400 million years ago. The main objectives of this work were to study the sites of MGP gene expression and protein accumulation by means of in situ hybridization and immunohistochemistry. MGP mRNA and protein were localized as expected not only in cartilage from branchial arches and vertebra but also in the endothelia of the vascular system as well as in the tubular renal endothelium. The accumulation of MGP in non mineralized soft tissues was unexpected and suggests differences in localization or regulation of this protein in shark soft tissues compared to tetrapods and teleosts. Our results also corroborate the hypothesis that in Prionace glauca, as previously shown in mammals, the MGP protein probably also acts as a calcification inhibitor, protecting soft tissues from abnormal and ectopic calcification.

Cellular distribution and induction of CYP1A following exposure of gilthead seabream, Sparus aurata, to waterborne and dietary benzo(a)pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin: an immunohistochemical approach.

The present study aimed to investigate cellular expression of cytochrome P4501A (CYP1A) protein in the seabream, Sparus aurata, exposed to one of two CYP1A-inducing contaminants, benzo(a)pyrene (B(a)P) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Male adult fish were exposed to several concentrations of TCDD or B(a)P either via water or via food. Fish were sampled after 0, 5, 10, 15 or 20 days of treatment and the time- and concentration-dependent induction of CYP1A protein in cells and tissues was studied using immunohistochemistry. A general site of CYP1A induction was the vascular endothelium. Aqueous exposures resulted in elevation of CYP1A immunoreactivity in gill pillar cells, heart endothelium, renal tubular epithelium, hepatocytes, and gut mucosal epithelium. In contrast, dietary exposure resulted in strong CYP1A immunostaining in gut epithelium but in only mild to moderate staining elsewhere. Both B(a)P and TCDD induced CYP1A in similar cellular response patterns in most organs examined, although TCDD generally led to higher staining intensity and frequency (i.e. the number of CYP1A-positive cells within an organ), an effect that is likely to be related to compound-specific differences in induction potency, metabolism and penetration. Contaminant-specific staining patterns were observed in the gills, where TCDD exposure evoked CYP1A immunostaining in the endothelial pillar cells, while B(a)P induced CYP1A staining in the branchial epithelial cells. This work points to the importance of immunohistochemical identification of cell-specific CYP1A responses in assessing the toxicology of CYP1A-inducing xenobiotics.

Osteocalcin and matrix GLA protein in developing teleost teeth: identification of sites of mRNA and protein accumulation at single cell resolution.

In this study, the tissue distribution and accumulation of osteocalcin or bone Gla protein (BGP) and matrix Gla protein (MGP) were determined during tooth development in a teleost fish, Argyrosomus regius. In this species, the presence of BGP and MGP mRNA in teeth was revealed by in situ hybridization. mRNA for BGP was detected in the odontoblasts as well as in its cytoplasmic processes emerging through dentinal tubules, while mRNA for MGP was expressed in the enamel portion within the apical portion of the elongated cell bodies of enameloblasts, adjacent to the root of the teeth as well as in cells within the pulpal space. Immunolocalization of BGP and MGP demonstrated that these proteins accumulate mainly in the mineralized dentin or in enameloblastic processes, confirming in situ hybridization results. In this study, we examined for the first time the localization of both BGP and MGP gene expression and protein accumulation within the different regions of the vertebrate tooth. We clearly demonstrated that although the overall pattern of BGP and MGP gene expression and protein accumulation in A. regius teeth was in general agreement to what is known for other vertebrates such as rats or rodents, our study provided novel information and highlighted some species-differences between fish and higher vertebrates.

Sublethal effects of linear alkylbenzene sulphonate on larvae of the seabream (Sparus aurata): histological approach.

Neonate (< 24 h) larvae of the seabream, Sparus aurata, were exposed to sublethal concentrations (0.1-1.0 mg x L(-1)) of the anionic surfactant Linear Alkyl-benzene Sulphonate (LAS) for 72 h under laboratory conditions. The first histopathological changes, such as peri-yolk sac edema, were observed at concentrations of 0.2 mg x L(-1). Higher exposure concentrations provoked disorganisation of the nervous system, trunk musculature and trophoblastic sincitium as well as in the digestive epithelium. Immunohystochemical CYP1A analysis, however, was not shown to be an adequate indicator of sublethal effects produced by exposure to this type of anionic surfactant

Toxicity, histopathological alterations and immunohistochemical CYP1A induction in the early life stages of the seabream, Sparus aurata, following waterborne exposure to B(a)P and TCDD.

In this paper, the toxicity (percentage of hatching and LC50) and histopathological alterations induced by benzo(a)pyrene (B(a)P; 0.032, 0.056, 0.1, 0.32, 0.56 and 0.1 microg l(-1)) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 0.025, 0.05, 0.1, 1.5 and 5 pg l(-1)) have been studied in the early life stages of the seabream, Sparus aurata, from 0 to 15 days post-hatching (dph). Toxicity assays showed that the percentage of hatching decreased with increasing the contaminant concentration. Moreover, the number of hatched larvae was lower for TCDD-exposed eggs in comparison with the B(a)P exposed ones. The sensitivity of the larvae, in terms of LC50, towards B(a)P and TCDD increased with age of the larvae. The LC50 were 0.81 microg l(-1) for B(a)P and 4.37 pg l(-1) for TCDD in neonate larvae and 0.11 microg l(-1) for B(a)P and 1.45 pg l(-1) for TCDD in 5 dph larvae. For histopathological examination, samples from LC50 experiments were taken at different concentrations of B(a)P (between 0.032 and 0.1 microg l(-1)) and TCDD (between 0.025 and 5 pg l(-1)). In both, B(a)P- and TCDD-exposed larvae, a concentration-dependency of the histopathological alterations was detected. In contrast, an age-dependency was not clearly detected, possibly due to the lack of development of mostly the organs in the early life stages. Cytoplasmic vacuolization of hepatocytes, as well as subcutaneous edema and necrosis of the trunk musculature, were the most common histopathological disorders detected in both B(a)P- and TCDD-exposed larvae. On the other hand, there were differences in histopathology on exposure to B(a)P and TCDD. Epithelial desquamation in gills, lack of inflation of the swim bladder, as well as lesions in the nervous system were specific for TCDD, while hepatic, vascular and muscular alterations were common for both toxicants. In parallel to the histopathological examinations, immunohistochemical analyses on cytochrome P450-1A isoenzyme (CYP1A) expression were performed on the same samples. The basal/constitutive distribution of CYP1A and its induction was also analysed in similar stages of larval development of the seabream under control conditions and after sublethal exposure to B(a)P (between 0.032 and 0.1 microg l(-1)) and TCDD (between 0.025 and 5 pg l(-1)). During the endogenous nutrition period (from hatching until 4 dph), constitutive CYP1A immunoreactivity was observed in the syncytium and in the matrix of the yolk sac. On the other hand, during exogenous feeding (between 4 and 10 dph), basal CYP1A immunoreactivity was detected in vascular hepatic system, whereas exocrine pancreas showed no reactivity. In gut, basal CYP1A immunoreactivity was restricted to the intestinal brush border and the apical cytoplasm of some enterocytes. Induced CYP1A immunoreactivity in B(a)P-exposed larvae was detected within cytoplasm of hepatocytes, intestinal enterocytes and endothelial cells of the heart. Finally, in TCDD-exposed larvae, CYP1A induction was also detected in pancreatic acinar cells, as well as in renal epithelial cells. The results of this study provided preliminary evidence that constitutive and inducible CYP1A organ distribution in S. aurata larvae was similar to that existing in adult fish. Moreover, exposure to TCDD was more toxic for the larvae and induced more CYP1A that exposure to B(a)P.

Organogenesis of the digestive tract in the white seabream, Diplodus sargus. Histological and histochemical approaches.

The ontogeny of the digestive tract of the white seabream, Diplodus sargus during the larval development up to day 45 post-hatching (dph) has been studied using histological and histochemical techniques. The oesophageal goblet cells appeared around 6 dph and contained neutral and acid mucosubstances (PAS/diastase-PAS and Alcian Blue pH 2.5 positive reactions). An incipient stomach can be distinguished from 2 dph but the first sign of gastric gland development was detected around 13-15 dph, increasing in number and size by 22-23 dph. Gastric glands were concentrated in the cardiac stomach region and they had a high content of protein rich in tyrosine, arginine and tryptophan. Acidophilic supranuclear inclusions related to pynocitosis of proteins, were already observed in the intestinal cells of the posterior intestine around 4-6 dph (exogenous feeding) and they were present until 25 dph. The intestinal mucous cells appeared between 15-18 dph and contained a mixture of neutral and acid mucosubstances/glycoconjugates, carboxylated ones being more abundant than the sulphated ones. The stomach and gastric glands were fully developed by the first month of life marking the beginning of digestive features characteristic of the juvenile stage. Around 4-6 dph, glycogen, proteins and neutral lipids were observed in the granular cytoplasm of hepatocytes. Strongly acidophilic zymogen granules were also present, at this time, in the basophilic cytoplasm of the exocrine pancreatic acinar cells and contained abundant proteins, especially rich in arginine, tyrosine and tryptophan.

Purification of matrix Gla protein from a marine teleost fish, Argyrosomus regius: calcified cartilage and not bone as the primary site of MGP accumulation in fish.

Matrix Gla protein (MGP) belongs to the family of vitamin K-dependent, Gla-containing proteins, and in mammals, birds, and Xenopus, its mRNA was previously detected in extracts of bone, cartilage, and soft tissues (mainly heart and kidney), whereas the protein was found to accumulate mainly in bone. However, at that time, it was not evaluated if this accumulation originated from protein synthesized in cartilage or in bone cells because both coexist in skeletal structures of higher vertebrates and Xenopus. Later reports showed that MGP also accumulated in costal calcified cartilage as well as at sites of heart valves and arterial calcification. Interestingly, MGP was also found to accumulate in vertebra of shark, a cartilaginous fish. However, to date, no information is available on sites of MGP expression or accumulation in teleost fishes, the ancestors of terrestrial vertebrates, who have in their skeleton mineralized structures with both bone and calcified cartilage. To analyze MGP structure and function in bony fish, MGP was acid-extracted from the mineralized matrix of either bone tissue (vertebra) or calcified cartilage (branchial arches) from the bony fish, Argyrosomus regius, separated from the mineral phase by dialysis, and purified by Sephacryl S-100 chromatography. No MGP was recovered from bone tissue, whereas a protein peak corresponding to the MGP position in this type of gel filtration was obtained from an extract of branchial arches, rich in calcified cartilage. MGP was identified by N-terminal amino acid sequence analysis, and the resulting protein sequence was used to design specific oligonucleotides suitable to amplify the corresponding DNA by a mixture of reverse transcription-polymerase chain reaction (RT-PCR) and 5'rapid amplification of cDNA (RACE)-PCR. In parallel, ArBGP (bone Gla protein, osteocalcin) was also identified in the same fish, and its complementary DNA cloned by an identical procedure. Tissue distribution/accumulation was analyzed by Northern blot, in situ hybridization, and immunohistochemistry. In mineralized tissues, the MGP gene was predominantly expressed in cartilage from branchial arches, with no expression detected in the different types of bone analyzed, whereas BGP mRNA was located in bone tissue as expected. Accordingly, the MGP protein was found to accumulate, by immunohistochemical analysis, mainly in the extracellular matrix of calcified cartilage. In soft tissues, MGP mRNA was mainly expressed in heart but in situ hybridization, indicated that cells expressing the MGP gene were located in the bulbus arteriosus and aortic wall, rich in smooth muscle and endothelial cells, whereas no expression was detected in the striated muscle myocardial fibers of the ventricle. These results show that in marine teleost fish, as in mammals, the MGP gene is expressed in cartilage, heart, and kidney tissues, but in contrast with results obtained in Xenopus and higher vertebrates, the protein does not accumulate in vertebra of non-osteocytic teleost fish, but only in calcified cartilage. In addition, our results also indicate that the presence of MGP mRNA in heart tissue is due, at least in fish, to the expression of the MGP gene in only two specific cell types, smooth muscle and endothelial cells, whereas no expression was found in the striated muscle fibers of the ventricle. In light of these results and recent information on expression of MGP gene in these same cell types in mammalian aorta, it is likely that the levels of MGP mRNA previously detected in Xenopus, birds, and mammalian heart tissue may be restricted to regions rich in smooth muscle and endothelial cells. Our results also emphasize the need to re-evaluate which cell types are involved in MGP gene expression in other soft tissues and bring further evidence that fish are a valuable model system to study MGP gene expression and regulation.