Dietary levels of all-trans retinol affect retinoid nuclear receptor expression and skeletal development in European sea bass larvae

High Levels of Vitamin A in Plant-Based Diets for Gilthead Seabream (Sparus aurata) Juveniles, Effects on Growth, Skeletal Anomalies, Bone Molecular Markers, and Histological Morphology

Substitution of fish-based ingredients may alter the nutritional profile of the feeds, including the vitamin contents, ultimately leading to unbalanced vitamin supply. Vitamin A plays an essential role in epithelium preservation, cell differentiation, reproduction, and vision. It also intervenes in skeletogenesis through chondrocytes development. Therefore, low levels of vitamin A may cause poor growth and abnormal bone development among other symptoms. Besides, in gilthead seabream excess vitamin A altered bone structure and homeostasis, indicating that an upper level for vitamin A in feeds for this species must be defined. For this purpose, a practical plant-based diet (FM 10% and FO 6%) containing five increasing levels of vitamin A (24,000, 26,000, 27,000, 31,000, and 37,000 IU/kg) supplemented as retinyl acetate was formulated to identify the effects of high levels of vitamin A for gilthead seabream juveniles. The trial was conducted with 450 total fish distributed into 15 tanks, where each diet was tested in triplicates for 70 days. At the end of the trial, samples were taken for analyses of vitamin A-relevant markers. At the end of the trial the high levels of vitamin A supplementation did not cause a reduction in growth, whereas no significant effect was observed for the feed efficiency, specific growth rate, and feed convertion ratio. Although not significant, retinol content in liver showed a tendency to increase with the elevation of dietary vitamin A levels. Although minor, the highest level of vitamin A dietary content (37,000 IU/kg) caused a significant increase in caudal vertebrae partial fusion as well as caudal vertebrae malformations. Increasing dietary vitamin A was related to a reduction in the occurrence of microhemorrhages in the liver and a reduction in the presence of eosinophils associated to the pancreas. Overall, the results of the present study suggested that gilthead seabream juveniles fed a plant-based diet are able to tolerate very high levels of vitamin A supplementation when supplemented as retinyl acetate. Nevertheless, further supplementation should be avoided in order to reduce the prevalence of anomalies affecting the caudal vertebrae.

Variability of key-performance-indicators in commercial gilthead seabream hatcheries

Skeletal abnormalities are one of the most important key-performance-indicators (KPIs) in finfish hatcheries. Coping with the problem of skeletal abnormalities relies on the understanding of the link between the variability in the rearing conditions, and the variability in abnormalities incidence. Here, 74 seabream larval populations, from four commercial hatcheries, were examined for the presence of abnormalities and monitored with respect to the applied conditions. The inward folding of gill-cover and pugheadedness were the most frequent abnormalities present, with a mean (± SD) frequency of 11.3 ± 17.9 and 6.0 ± 7.2%, respectively. Other abnormalities were observed at very low mean rates (≤ 1%). A new abnormality type, ray-resorption syndrome, was also found. The recorded rate of normally inflated swimbladder was 92.3 ± 7.4% and mean survival rate was 25.9 ± 21.0%. Classification tree analysis indicated six rearing variables as potentially important predictors for pugheadedness, six variables for caudal-fin abnormalities and 10 variables for survival rate. Complementary genetic analysis, revealed differentiating genetic diversity and significant genetic distances among participating hatcheries, suggestive of the role of company-specific management of genetic resources in KPIs' variability. The results are discussed with respect to their potential use in the control of skeletal abnormalities by commercial hatcheries, as well as for benchmarking among different hatcheries.

Effect of Supplementation of Vitamin A on Growth, Haemato-Biochemical Composition, and Antioxidant Ability in Cyprinus carpio var. communis

Vitamin A requirement in fingerling common carp, Cyprinus carpio var. communis (1.64 ± 0.02 g; ABW ± SD), was evaluated by conducting a 10 week growth experiment. Casein-gelatin-based test diets representing six graded levels of vitamin A (0, 0.03, 0.07, 0.11, 0.15, and 0.19 g/kg, dry diet) were designed and fed to the triplicate group of fish at 08:00 and 16:00 hrs at the rate of 4% body weight per day. Growth parameters like live weight gain (LWG %), feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR), and body protein deposition (BPD) improved significantly (P < 0.05) with each elevated dietary vitamin A level and found maximum growth rate along with the best- FCR at 0.11 g/kg diet. Dietary vitamin A levels also significantly (P < 0.05) affected haematological parameters of the fish. Highest haemoglobin (Hb), erythrocyte count (RBC), haematocrit content (Hct %), and lowest leucocyte count (WBC) were observed at 0.11 g/kg vitamin A fed diet compared to all the diets. Highest protein and lowest fat content were observed in the group of fingerlings fed with 0.11 g/kg vitamin A containing diet. Blood and serum profile also showed some significant (P < 0.05) differences with elevating concentration of dietary vitamin A levels. Serum parameters like aspartate aminotransferase (AST), alanine aminotransferase (ALT), and cholesterol values decreased significantly (P < 0.05) at 0.11 g/kg vitamin A fed diet compared to control diet. However, except albumin the other electrolytes improved significantly (P < 0.05) and maximal values of these parameters were also evident at 0.11 g/kg of vitamin A fed diet. Better value of TBARS was found in the group that fed 0.11 g/kg vitamin A diet. Hepatosomatic index and condition factor improved significantly (P < 0.05) with fish fed at optimal dose 0.11 g/kg of vitamin A diet. Based on quadratic regression analysis of LWG%, FCR, BPD, Hb, and calcium values of C. carpio var. communis against the varying levels of dietary vitamin A, an optimum growth, best FCR, higher BPD, Hb, and Ca values lie in the range of 0.10 to 0.12 g/kg diet, respectively. The data generated during this study would be important in developing vitamin A balanced feed for successful intensive culture of C. carpio var. communis.

Dietary vitamin A deficiency reduces growth performance, immune function of intestine, and alters tight junction proteins of intestine for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

This study was carried out to investigate the effects of dietary vitamin A (VA) on growth performance, antioxidant capacity, digestion, intestinal immune response, and mRNA expression of intestinal tight junction proteins for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Six isonitrogenous and isolipidic experimental diets were formulated to obtain VA levels (317, 1136, 2038, 4142, 7715, 15204 IU/kg diet, respectively). The triplicate groups of fish (average weight of 9.01 ± 0.27 g) were fed twice daily (8:00 and 16:00) for 7 weeks. Based on the broken-line analysis model of WG and LYZ activity, the dietary VA requirement of hybrid grouper were estimated to be 2688.58 and 4096.36 IU/kg diet. The results showed that VA deficiency or excess could reduce Weight gain, specific growth rate, and protein efficiency ratio, and increase feed conversion ratio and hepatosomatic index (P < 0.05). In addition, VA deficiency could reduce the serum activities of acid phosphatase (ACP), superoxide dismutase, and total antioxidant capacity and increase the malondialdehyde content (P < 0.05). VA deficiency also could reduce intestinal activities of ACP, alkaline phosphatase, lysozyme, complement 3, complement 4 contents, and activities of alpha-amylase, lipase, and trypsin (P < 0.05). Meanwhile, VA deficiency could reduce villus height in proximal intestine (PI) and mid intestine (MI), as well as muscle thickness in PI and distal intestine (DI) (P < 0.05). Moreover, VA deficiency could down-regulated antimicrobial peptides (β-defensin, Hepcidin [not in MI and DI], Epinecidin), anti-inflammatory cytokines (interleukin 10 and transforming growth factor β1 [not in DI]), tight junction proteins (occluding and claudin3) mRNA levels in the PI, MI and DI, and up-regulated pro-inflammatory cytokines (tumor necrosis factor α [not in MI] and interleukin 1β [not in MI]), signaling molecules c-Rel and p65 (P < 0.05). Collectively, VA deficiency could reduce growth performance because of a negative effect on intestinal health by depressing digestive abilities, intestinal morphology, immunity and tight junction function in the intestine.

Skeletal anomalies in cultured golden pompano Trachinotus ovatus at early stages of development

Golden pompano Trachinotus ovatus (Linnaeus, 1758) is an important mariculture fish species with high commercial value in China. The present study thoroughly assessed the types and frequencies of skeletal deformities at the early developmental stages of golden pompano in an intensive aquaculture production system. Golden pompano (n = 500) were sampled 30 d posthatch (dph). The specimens were stained with Alcian blue and Alizarin red for the detection of deformities. The results of the study revealed that 77.2% of the specimens showed at least 1 spinal anomaly; most anomalies occurred in the prehemal region, and the most common deformity observed was vertebral fusion (37.4% incidence of deformities). The results of this study provide useful information for the early detection of skeletal deformities and for the optimization of fish fry breeding technologies.

Fatty acids from fish or vegetable oils promote the adipogenic fate of mesenchymal stem cells derived from gilthead sea bream bone potentially through different pathways

Fish are rich in n-3 long-chain polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, thus they have a great nutritional value for human health. In this study, the adipogenic potential of fatty acids commonly found in fish oil (EPA and DHA) and vegetable oils (linoleic (LA) and alpha-linolenic (ALA) acids), was evaluated in bone-derived mesenchymal stem cells (MSCs) from gilthead sea bream. At a morphological level, cells adopted a round shape upon all treatments, losing their fibroblastic form and increasing lipid accumulation, especially in the presence of the n-6 PUFA, LA. The mRNA levels of the key transcription factor of osteogenesis, runx2 significantly diminished and those of relevant osteogenic genes remained stable after incubation with all fatty acids, suggesting that the osteogenic process might be compromised. On the other hand, transcript levels of the main adipogenesis-inducer factor, pparg increased in response to EPA. Nevertheless, the specific PPARγ antagonist T0070907 appeared to suppress the effects being caused by EPA over adipogenesis. Moreover, LA, ALA and their combinations, significantly up-regulated the fatty acid transporter and binding protein, fatp1 and fabp11, supporting the elevated lipid content found in the cells treated with those fatty acids. Overall, this study has demonstrated that fatty acids favor lipid storage in gilthead sea bream bone-derived MSCs inducing their fate into the adipogenic versus the osteogenic lineage. This process seems to be promoted via different pathways depending on the fatty acid source, being vegetable oils-derived fatty acids more prone to induce unhealthier metabolic phenotypes.

Water temperature induces jaw deformity and bone morphogenetic proteins (BMPs) gene expression in golden pompano Trachinotus ovatus larvae

Golden pompano Trachinotus ovatus larvae were kept at 26, 29 and 33 °C for 15 days from 3-day post hatching (DPH) to 18 DPH to test temperature-dependent growth and jaw malformation. The growth, survival, jaw deformity and the gene expressions of bone morphogenetic proteins (BMPs) were used as criteria to examine the fish response to temperature manipulation. The growth rate of fish at 29 or 33 °C was significantly faster than fish at 26 °C, while fish survival at 29 °C was significantly higher than fish at 33 °C. Jaw deformity was significantly affected by water temperature. The highest jaw deformity occurred on fish at 33 °C, and the lowest jaw deformity was at 26 °C. The expressions of all BMP genes except BMP10 were significantly affected by water temperature. The highest gene expression of BMP2 was on fish at 29 °C, and the lowest expression was at 33 °C. For the BMP4 gene, the highest and lowest expressions were found on fish at 33 and 26 °C, respectively. The present study indicates that jaw deformity of golden pompano larvae increases with increasing temperature, and the gene expression of BMP4 proteins coincides with high jaw deformity and water temperature elevation.

Transcriptional regulation of genes involved in retinoic acid metabolism in Senegalese sole larvae

The aim of this study was the characterization of transcriptional regulatory pathways mediated by retinoic acid (RA) in Senegalese sole larvae. For this purpose, pre-metamorphic larvae were treated with a low concentration of DEAB, an inhibitor of RALDH enzyme, until the end of metamorphosis. No differences in growth, eye migration or survival were observed. Nevertheless, gene expression analysis revealed a total of 20 transcripts differentially expressed during larval development and only six related with DEAB treatments directly involved in RA metabolism and actions (rdh10a, aldh1a2, crbp1, igf2r, rarg and cyp26a1) to adapt to a low-RA environment. In a second experiment, post-metamorphic larvae were exposed to the all-trans RA (atRA) observing an opposite regulation for those genes involved in RA synthesis and degradation (rdh10a, aldh1a2, crbp1 and cyp26a1) as well as other related with thyroid- (dio2) and IGF-axes (igfbp1, igf2r and igfbp5) to balance RA levels. In a third experiment, DEAB-pretreated post-metamorphic larvae were exposed to atRA and TTNPB (a specific RAR agonist). Both drugs down-regulated rdh10a and aldh1a2 and up-regulated cyp26a1 expression demonstrating their important role in RA homeostasis. Moreover, five retinoic receptors that mediate RA actions, the thyroid receptor thrb, and five IGF binding proteins changed differentially their expression. Overall, this study demonstrates that exogenous RA modulates the expression of some genes involved in the RA synthesis, degradation and cellular transport through RAR-mediated regulatory pathways establishing a negative feedback regulatory mechanism necessary to balance endogenous RA levels and gradients.

Molecular cloning and expression analysis of the retinoid X receptor (RXR) gene in golden pompano Trachinotus ovatus fed Artemia nauplii with different enrichments

The retinoid X receptors (RXRs) are involved in the skeletal development and other biological process such as blood vessel formation and metabolism. Partial sequences of RXRα and β genes were obtained, and their expressions were quantified on golden pompano Trachinotus ovatus at 28 days post hatching (DPH) to explore the molecular response to nutritional manipulation in fish larvae. As live food, Artemia nauplii were separately enriched with Nannochloropsis and Algamac 3080 and non-enriched Artemia nauplii (control) for fish feeding. The expressions of RXRs were detected in the embryos and fish larvae at early stages, suggesting that the skeletal development in golden pompano initiated before yolk re-sorption completion. Fish fed non-enriched Artemia nauplii ended up with higher jaw malformation. The highest specific growth rate was obtained when fish were fed with the Artemia nauplii enriched with Algamac 3080, and the lowest growth rate was observed when fish were fed with unenriched Artemia nauplii. The highest survival was obtained when fish were fed with non-enriched or Nannochloropsis-enriched Artemia nauplii. This study indicates that the use of enriched formula for Artemia nauplii can significantly affect the expression levels of RXRs and jaw malformation of golden pompano larvae, but there is no clear correlation between RXRs expressions and malformation rates when fish are subjected to nutrient challenge.

Vitamin A and arachidonic acid altered the skeletal mineralization in Atlantic cod (Gadus morhua) larvae without any interactions on the transcriptional level

The main object of this study was to evaluate the impact of different levels of vitamin A (VA) and arachidonic acid (ARA) in relation to eicosapentaenoic acid (EPA) on mineralization and gene expression in Atlantic cod larvae (Gadus morhua). First-feeding larvae were fed enriched rotifers from start-feeding until 29 days post hatch (dph). Larvae in four tanks were fed one of the following diets: control (EPA/ARA ratio: 15.8, 0.9μg VA g(-1)), control+VA (EPA/ARA ratio: 15.8, 7.8μg VA g(-1)), High ARA (EPA/ARA ratio: 0.9, 1.5μg VA g(-1)) or High ARA+VA (EPA/ARA ratio: 0.9, 12.0μg VA g(-1)). Larvae fed High ARA+VA were shorter at 29dph compared to the other groups and had significantly less mineralized bones when comparing larvae of similar size, showing interaction effects between VA and ARA. Although transcriptomic analysis did not reveal any interaction effects, a higher number of genes were differentially expressed in the high ARA fed larvae compared to control+VA fed larvae. Furthermore, bglap1, bglap2 and col10a1 were all down-regulated in larvae fed High ARA-diets and to a greater extent than larvae fed VA supplemented diet, indicating an additive effect on mineralization. In conclusion, this study showed that the dietary increase in ARA and VA altered the skeletal metabolism during larval development, most likely through signaling pathways specific for each nutrient rather than an interaction. The present study also demonstrates that VA could affect the larval response to ARA, even within the accepted non-toxic/non-deficient range.

Quantitative analysis of orofacial development and median clefts in Xenopus laevis

Xenopus has become a useful tool to study the molecular mechanisms underlying orofacial development. However, few quantitative analyses exist to describe the anatomy of this region. In this study we combine traditional facial measurements with geometric morphometrics to describe anatomical changes in the orofacial region during normal and abnormal development. Facial measurements and principal component (PC) analysis indicate that during early tadpole development the face expands primarily in the midface region accounting for the development of the upper jaw and primary palate. The mouth opening correspondingly becomes flatter and wider as it incorporates the jaw elements. A canonical variate analysis of orofacial and mouth opening shape emphasized that changes in the orofacial shape occur gradually. Orofacial anatomy was quantified after altered levels of retinoic acid using all-trans retinoic acid or an inhibitor of retinoic acid receptors or by injecting antisense oligos targeting RALDH2. Such perturbations resulted in major decreases in the width of the midface and the mouth opening illustrated in facial measurements and a PC analysis. The mouth opening shape also had a gap in the primary palate resulting in a median cleft in the mouth opening that was only illustrated quantitatively in the morphometric analysis. Finally, canonical and discriminant function analysis statistically distinguished the orofacial and mouth opening shape changes among the different modes used to alter retinoic acid signaling levels. By combining quantitative analyses with molecular studies of orofacial development we will be better equipped to understand the complex morphogenetic processes involved in palate development and clefting.

Consequences of metal exposure on retinoid metabolism in vertebrates: a review

What we generally refer to as 'vitamin A' is a group of naturally-occurring molecules structurally similar to retinol that are capable of exerting biological activity. These retinoids are essential to diverse physiological functions including vision, immune response, bone mineralization, reproduction, cell differentiation, and growth. As well, some retinoids have antioxidant properties. Independent studies published over the last few decades have revealed that many fish and wildlife populations living in highly polluted environments have altered retinoid status possibly associated with retinoid metabolic or homeostatic mechanisms. Substantial evidence links organic contaminant exposure with changes in retinoid status in animal populations, but only a few detailed studies have been published implicating inorganic contaminants such as metals. This mini-review selectively deals with field and laboratory studies reporting associations between environmental contaminants, especially trace metals, and alterations in retinoid status. Both essential and non-essential trace metals have been reported to affect retinoid status. This review focuses on metabolic imbalances of retinoids in relation to metal contamination and illustrates possible modes of action. The role of retinoids as antioxidants and their potential as biomarkers of metal contamination are discussed.

Retinoic acid induces two osteocalcin isoforms and inhibits markers of osteoclast activity in Atlantic cod (Gadus morhua) ex vivo cultured craniofacial tissues

Nutritional status including vitamin A could explain some of the developmental deformities observed in cultivated teleosts, including Atlantic cod (Gadus morhua). In the present study we aimed to investigate the transcriptional effect of retinoic acid (RA) on bone related genes using Atlantic cod craniofacial explants tissue cultures. Two different osteoblast specific osteocalcin/bone gla protein isoforms were discovered in cod. Transcription of both isoforms was up-regulated following RA treatment of 65 dph cod lower jaw explants. In contrast, transcripts coding for genes related to bone resorption and osteoclast activity, matrix metalloproteinase 9 and cathepsin K were down-regulated following RA treatment. This could be linked to the decreased transcriptional ratio between receptor activator of nuclear factor kappa-B ligand rankl and osteoprotegerin observed in the same tissue samples. RA treatment of juvenile explants had no effect on runt-related transcription factor 2 and osterix mRNA levels. However, osterix was significantly down-regulated in 25 dph cod head explants following RA treatment. In situ hybridizations revealed differential spatial distribution of the two isoforms and the predominant expression of cathepsin K in bone surrounding tissues. The present study indicates that RA causes a shift in the balance between osteoclast activity and osteoblast activity in favor of the latter.

Imbalanced dietary ascorbic acid alters molecular pathways involved in skeletogenesis of developing European sea bass (Dicentrarchus labrax)

The influence of dietary ascorbic acid (AA) on growth and morphogenesis during the larval development of European sea bass (Dicentrarchus labrax) was evaluated until 45days post hatching. Diets incorporated 0, 5, 15, 30, 50 or 400mg AA per kg diet to give AA-0, AA-5, AA-15, AA-30, AA-50 and AA-400 dietary treatments, respectively. Dietary AA levels lower than 15mg/kg reduced larval growth and survival was affected in specimens fed diets devoid of AA. Globally, disruption of the expression of genes involved in AA and calcium absorption in the intestine (SVCT-1, TRPV-6), skeletogenesis (BMP-4, IGF-1, RARγ) and bone mineralization (VDRβ, osteocalcin) were observed in groups fed doses lower and higher than 50mg AA/kg diet. Such disturbances detected at molecular level were associated with disruptions of the ossification process and the appearance of skeletal abnormalities.

Coordinated gene expression during gilthead sea bream skeletogenesis and its disruption by nutritional hypervitaminosis A

BACKGROUND

Vitamin A (VA) has a key role in vertebrate morphogenesis, determining body patterning and growth through the control of cell proliferation and differentiation processes. VA regulates primary molecular pathways of those processes by the binding of its active metabolite (retinoic acid) to two types of specific nuclear receptors: retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which promote transcription of downstream target genes. This process is well known in most of higher vertebrates; however, scarce information is available regarding fishes. Therefore, in order to gain further knowledge of fish larval development and its disruption by nutritional VA imbalance, the relative expression of some RARs and RXRs, as well as several genes involved in morpho- and skeletogenesis such as peroxisome proliferator-activated receptors (PPARA, PPARB and PPARG); retinol-binding protein (RBP); insulin-like growth factors I and II (IGF1 and IGF2, respectively); bone morphogenetic protein 2 (Bmp2); transforming growth factor β-1 (TGFB1); and genes encoding different extracellular matrix (ECM) proteins such as matrix Gla protein (mgp), osteocalcin (bglap), osteopontin (SPP1), secreted protein acidic and rich in cysteine (SPARC) and type I collagen α1 chain (COL1A1) have been studied in gilthead sea bream.

RESULTS

During gilthead sea bream larval development, specific expression profiles for each gene were tightly regulated during fish morphogenesis and correlated with specific morphogenetic events and tissue development. Dietary hypervitaminosis A during early larval development disrupted the normal gene expression profile for genes involved in RA signalling (RARA), VA homeostasis (RBP) and several genes encoding ECM proteins that are linked to skeletogenesis, such as bglap and mgp.

CONCLUSIONS

Present data reflects the specific gene expression patterns of several genes involved in larval fish RA signalling and skeletogenesis; and how specific gene disruption induced by a nutritional VA imbalance underlie the skeletal deformities. Our results are of basic interest for fish VA signalling and point out some of the potential molecular players involved in fish skeletogenesis. Increased incidences of skeletal deformities in gilthead sea bream fed with hypervitaminosis A were the likely ultimate consequence of specific gene expression disruption at critical development stages.

Novel methodologies in marine fish larval nutrition

Major gaps in knowledge on fish larval nutritional requirements still remain. Small larval size, and difficulties in acceptance of inert microdiets, makes progress slow and cumbersome. This lack of knowledge in fish larval nutritional requirements is one of the causes of high mortalities and quality problems commonly observed in marine larviculture. In recent years, several novel methodologies have contributed to significant progress in fish larval nutrition. Others are emerging and are likely to bring further insight into larval nutritional physiology and requirements. This paper reviews a range of new tools and some examples of their present use, as well as potential future applications in the study of fish larvae nutrition. Tube-feeding and incorporation into Artemia of (14)C-amino acids and lipids allowed studying Artemia intake, digestion and absorption and utilisation of these nutrients. Diet selection by fish larvae has been studied with diets containing different natural stable isotope signatures or diets where different rare metal oxides were added. Mechanistic modelling has been used as a tool to integrate existing knowledge and reveal gaps, and also to better understand results obtained in tracer studies. Population genomics may assist in assessing genotype effects on nutritional requirements, by using progeny testing in fish reared in the same tanks, and also in identifying QTLs for larval stages. Functional genomics and proteomics enable the study of gene and protein expression under various dietary conditions, and thereby identify the metabolic pathways which are affected by a given nutrient. Promising results were obtained using the metabolic programming concept in early life to facilitate utilisation of certain nutrients at later stages. All together, these methodologies have made decisive contributions, and are expected to do even more in the near future, to build a knowledge basis for development of optimised diets and feeding regimes for different species of larval fish.

Retinoic acid is a negative regulator of matrix Gla protein gene expression in teleost fish Sparus aurata

Matrix Gla protein (MGP) is an extracellular mineral-binding protein expressed in several tissues while accumulated only in bone and cartilage under physiological conditions. Although the precise molecular mechanism of action of MGP remains unknown, all available evidence indicates that it acts as a physiological inhibitor of mineralization. This work presents the cloning of gilthead seabream MGP gene (SaMGP) and the functional analysis of its promoter. SaMGP gene was found to be organized in five exons and to be under control of a distal and a proximal promoter, both, capable of activating SaMGP transcription in transient transfections. Furthermore, we present strong evidence that retinoic acid down-regulates SaMGP gene transcription by interacting, through binding of its receptor, with a specific region within distal promoter. Interestingly, the presence of repetitive motifs in the proximity of SaMGP gene regulatory regions suggests that they may modulate promoter accessibility to transcription machinery, as already seen for other genes. This work provides additional evidence of the usefulness of non-mammalian model systems to elucidate the complex regulation of MGP gene transcription.

Dietary vitamin mix levels influence the ossification process in European sea bass (Dicentrarchus labrax) larvae

The influence of dietary vitamins on growth, survival, and morphogenesis was evaluated until day 38 of posthatching life in European sea bass larvae (Dicentrarchus labrax). A standard vitamin mix (VM), at double the concentration of the U.S. National Research Council's recommendations, was incorporated into larval feeds at 0.5%, 1.5%, 2.5%, 4.0%, and 8.0% to give treatments VM 0.5, VM 1.5, VM 2.5, VM 4.0, and VM 8.0, respectively. The group fed the VM 0.5 diet all died before day 30. At day 38, the larvae group fed VM 1.5 had 33% survival, while the other groups, with higher vitamin levels, showed at least 50% survival. The higher the percentage VM in the diet, the lower the percentage of column deformities. High dietary vitamin levels positively influenced the formation of mineralized bone in larvae: the higher the dietary vitamin level, the higher the ossification status. In the larvae group fed at the highest vitamin levels, we observed a temporal sequence of coordinated growth factor expression, in which the expression of bone morphometric protein (BMP-4) preceded the expression of IGF-1, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). In groups fed lower proportions of vitamins, elevated proliferator peroxisome-activated receptors (PPAR-gamma) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-gamma transcripts in larvae-fed diets with a low VM content converted some osteoblasts into adipocytes during the first two weeks of life. This loss of osteoblasts is likely to have caused skeletal deformities.

Intake of high levels of vitamin A and polyunsaturated fatty acids during different developmental periods modifies the expression of morphogenesis genes in European sea bass (Dicentrarchus labrax)

The effect of the feeding period on larval development was investigated in European sea bass larvae by considering the expression level of some genes involved in morphogenesis. Larvae were fed a control diet except during three different periods (period A: from 8 to 13 d post-hatching (dph); period B: from 13 to 18 dph; period C: from 18 to 23 dph) with two compound diets containing high levels of vitamin A or PUFA. European sea bass morphogenesis was affected by these two dietary nutrients during the early stages of development. The genes involved in morphogenesis could be modulated between 8 and 13 dph, and our results indicated that retinoids and fatty acids influenced two different molecular pathways that in turn implicated two different gene cascades, resulting in two different kinds of malformation. Hypervitaminosis A delayed development, reducing the number of vertebral segments and disturbing bone formation in the cephalic region. These malformations were correlated to an upregulation of retinoic acid receptor gamma, retinoid X receptor (RXR) alpha and bone morphogenetic protein (BMP)4. An excess of PUFA accelerated the osteoblast differentiation process through the upregulation of RXRalpha and BMP4, leading to a supernumerary vertebra. These results suggest that the composition of diets devoted to marine fish larvae has a particularly determining effect before 13 dph on the subsequent development of larvae and juvenile fish.

Effect of nature of dietary lipids on European sea bass morphogenesis: implication of retinoid receptors

The effect of the nature and form of supply of dietary lipids on larval development was investigated in European sea bass larvae, by considering the expression of several genes involved in morphogenesis. Fish were fed from 7 to 37 d post-hatch with five isoproteic and isolipidic compound diets incorporating different levels of EPA and DHA provided by phospholipid or neutral lipid. Phospholipid fraction containing 1.1 % (PL1 diet) to 2.3 % (PL3 diet) of EPA and DHA sustained good larval growth and survival, with low vertebral and cephalic deformities. Similar levels of EPA and DHA provided by the neutral lipid fraction were teratogenic and lethal. Nevertheless, dietary phospholipids containing high levels of DHA and EPA (PL5 diet) induced cephalic (8.5 %) and vertebral column deformities (35.3 %) adversely affecting fish growth and survival; moreover, a down-regulation of retinoid X receptor alpha (RXRalpha), retinoic acid receptor alpha, retinoic acid receptor gamma and bone morphogenetic protein-4 genes was also noted in PL5 dietary group at day 16. High levels of dietary PUFA in neutral lipid (NL3 diet) first up-regulated the expression of RXRalpha at day 16 and then down-regulated most of the studied genes at day 23, leading to skeletal abnormalities and death of the larvae. A moderate level of PUFA in neutral lipids up-regulated genes only at day 16, inducing a lesser negative effect on growth, survival and malformation rate than the NL3 group. These results showed that retinoid pathways can be influenced by dietary lipids leading to skeletal malformation during sea bass larvae development.