Environment and plasticity of myogenesis in teleost fish

Contribution of in vitro myocytes studies to understanding fish muscle physiology

Research on the regulation of fish muscle physiology and growth was addressed originally by classical in vivo approaches; however, systemic interactions resulted in many questions that could be better considered through in vitro myocyte studies. The first paper published by our group in this field was with Tom Moon on brown trout cardiomyocytes, where the insulin and IGF-I receptors were characterized and the down-regulatory effects of an excess of peptides demonstrated. We followed the research on cultured skeletal muscle cells through the collaboration with INRA focused on the characterization of IGF-I receptors and its signaling pathways through in vitro development. Later on, we showed the important metabolic role of IGFs, although these studies were only the first stage of a prolific area of work that has offered a useful tool to advance in our knowledge of the endocrine and nutritional regulation of fish growth and metabolism. Obviously, the findings obtained in vitro serve the purpose to propose the scenario that will need confirmation in vivo, but this technique has made possible many different, easy, fast and better controlled studies. In this review, we have summarized the main advances that the use of cultured muscle cells has permitted, focusing mainly in the role of IGFs regulating fish metabolism and growth. Although many articles have already appeared using this model system in salmonids, gilthead sea bream or zebrafish, it is reasonable to expect new studies with cultured cells using innovative approaches that will help to understand fish physiology and its regulation.

Food Shortage Causes Differential Effects on Body Composition and Tissue-Specific Gene Expression in Salmon Modified for Increased Growth Hormone Production

Growth hormone (GH) transgenic salmon possesses markedly increased metabolic rate, appetite, and feed conversion efficiency, as well as an increased ability to compete for food resources. Thus, the ability of GH-transgenic fish to withstand periods of food deprivation as occurs in nature is potentially different than that of nontransgenic fish. However, the physiological and genetic effects of transgenic GH production over long periods of food deprivation remain largely unknown. Here, GH-transgenic coho salmon (Oncorhynchus kisutch) and nontransgenic, wild-type coho salmon were subjected to a 3-month food deprivation trial, during which time performance characteristics related to growth were measured along with proximate compositions. To examine potential genetic effects of GH-transgenesis on long-term food deprivation, a group of genes related to muscle development and liver metabolism was selected for quantitative PCR analysis. Results showed that GH-transgenic fish lose weight at an increased rate compared to wild-type even though proximate compositions remained relatively similar between the groups. A total of nine genes related to muscle physiology (cathepsin, cee, insulin-like growth factor, myostatin, murf-1, myosin, myogenin, proteasome delta, tumor necrosis factor) and five genes related to liver metabolism (carnitine palmitoyltransferase, fatty acid synthase, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, glucokinase) were shown to be differentially regulated between GH-transgenic and wild-type coho salmon over time. These genetic and physiological responses assist in identifying differences between GH-transgenic and wild-type salmon in relation to fitness effects arising from elevated growth hormone during periods of long-term food shortage.

Variability among individuals is generated at the gene expression level

Selection acts on individuals, specifically on their differences. To understand adaptation and responses to change therefore requires knowledge of how variation is generated and distributed across traits. Variation occurs on different biological scales, from genetic through physiological to morphological, yet it is unclear which of these carries the most variability. For example, if individual variation is mainly generated by differences in gene expression, variability should decrease progressively from coding genes to morphological traits, whereas if post-translational and epigenetic effects increase variation, the opposite should occur. To test these predictions, we compared levels of variation among individuals in various measures of gene expression, physiology (including activity), and morphology in two abundant and geographically widespread Antarctic molluscs, the clam Laternula elliptica and the limpet Nacella concinna. Direct comparisons among traits as diverse as heat shock protein QPCR assays, whole transcription profiles, respiration rates, burying rate, shell length, and ash-free dry mass were made possible through the novel application of an established metric, the Wentworth Scale. In principle, this approach could be extended to analyses of populations, communities, or even entire ecosystems. We found consistently greater variation in gene expression than morphology, with physiological measures falling in between. This suggests that variability is generated at the gene expression level. These findings have important implications for refining current biological models and predictions of how biodiversity may respond to climate change.

Transient up- and down-regulation of expression of myosin light chain 2 and myostatin mRNA mark the changes from stratified hyperplasia to muscle fiber hypertrophy in larvae of gilthead sea bream (Sparus aurata L.)

Hyperplasia and hypertrophy are the two mechanisms by which muscle develops and grows. We study these two mechanisms, during the early development of white muscle in Sparus aurata, by means of histology and the expression of structural and regulatory genes. A clear stage of stratified hyperplasia was identified early in the development of gilthead sea bream but ceased by 35 dph when hypertrophy took over. Mosaic recruitment of new white fibers began as soon as 60 dph. The genes mlc2a and mlc2b were expressed at various levels during the main phases of hyperplasia and hypertrophy. The genes myog and mlc2a were significantly up-regulated during the intensive stratified formation of new fibers and their expression was significantly correlated. Expression of mstn1 and igf1 increased at 35 dph, appeared to regulate the hyperplasia-to-hypertrophy transition, and may have stimulated the expression of mlc2a, mlc2b and col1a1 at the onset of mosaic hyperplasia. The up-regulation of mstn1 at transitional phases in muscle development indicates a dual regulatory role of myostatin in fish larval muscle growth.

Characterisation and expression analysis of cathepsins and ubiquitin-proteasome genes in gilthead sea bream (Sparus aurata) skeletal muscle

Background

The proteolytic enzymes involved in normal protein turnover in fish muscle are also responsible for post-mortem softening of the flesh and are therefore potential determinants of product quality. The main enzyme systems involved are calpains, cathepsins, and the ubiquitin-proteasome (UbP). In this study on Sparus aurata (Sa), the coding sequences of cathepsins (SaCTSB and SaCTSDb) and UbP family members (SaN3 and SaUb) were cloned from fast skeletal muscle, and their expression patterns were examined during ontogeny and in a fasting/re-feeding experiment.

Results

The amino acid sequences identified shared 66-100% overall identity with their orthologues in other vertebrates, with well conserved characteristic functional domains and catalytic residues. SaCTSDb showed phylogenetic, sequence and tissue distribution differences with respect to its paralogue SaCTSDa, previously identified in the ovary. Expression of gilthead sea bream cathepsins (B, L, Da, Db) and UbP members (N3, Ub, MuRF1 and MAFbx) in fast skeletal muscle was determined at three different life-history stages and in response to fasting and re-feeding in juveniles. Most of the proteolytic genes analysed were significantly up-regulated during fasting, and down-regulated with re-feeding and, between the fingerling (15 g) and juvenile/adult stages (~50/500 g), consistent with a decrease in muscle proteolysis in both later contexts. In contrast, SaCTSDa and SaMuRF1 expression was relatively stable with ontogeny and SaUb had higher expression in fingerlings and adults than juveniles.

Conclusions

The data obtained in the present study suggest that cathepsins and UbP genes in gilthead sea bream are co-ordinately regulated during ontogeny to control muscle growth, and indicate that feeding regimes can modulate their expression, providing a potential dietary method of influencing post-mortem fillet tenderisation, and hence, product quality.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1121-0) contains supplementary material, which is available to authorized users.

Characterization of the transcriptome of fast and slow muscle myotomal fibres in the pacu (Piaractus mesopotamicus)

BACKGROUND

The Pacu (Piaractus mesopotamicus) is a member of the Characiform family native to the Prata Basin (South America) and a target for the aquaculture industry. A limitation for the development of a selective breeding program for this species is a lack of available genetic information. The primary objectives of the present study were 1) to increase the genetic resources available for the species, 2) to exploit the anatomical separation of myotomal fibres types to compare the transcriptomes of slow and fast muscle phenotypes and 3) to systematically investigate the expression of Ubiquitin Specific Protease (USP) family members in fast and slow muscle in response to fasting and refeeding.

RESULTS

We generated 0.6 Tb of pair-end reads from slow and fast skeletal muscle libraries. Over 665 million reads were assembled into 504,065 contigs with an average length of 1,334 bp and N50 = 2,772 bp. We successfully annotated nearly 47% of the transcriptome and identified around 15,000 unique genes and over 8000 complete coding sequences. 319 KEGG metabolic pathways were also annotated and 380 putative microsatellites were identified. 956 and 604 genes were differentially expressed between slow and fast skeletal muscle, respectively. 442 paralogues pairs arising from the teleost-specific whole genome duplication were identified, with the majority showing different expression patterns between fibres types (301 in slow and 245 in fast skeletal muscle). 45 members of the USP family were identified in the transcriptome. Transcript levels were quantified by qPCR in a separate fasting and refeeding experiment. USP genes in fast muscle showed a similar transient increase in expression with fasting as the better characterized E3 ubiquitin ligases.

CONCLUSION

We have generated a 53-fold coverage transcriptome for fast and slow myotomal muscle in the pacu (Piaractus mesopotamicus) significantly increasing the genetic resources available for this important aquaculture species. We describe significant differences in gene expression between muscle fibre types for fundamental components of general metabolism, the Pi3k/Akt/mTor network and myogenesis, including detailed analysis of paralogue expression. We also provide a comprehensive description of USP family member expression between muscle fibre types and with changing nutritional status.

RNA regulons in Hox 5' UTRs confer ribosome specificity to gene regulation

Emerging evidence suggests that the ribosome has a regulatory function in directing how the genome is translated in time and space. However, how this regulation is encoded in the messenger RNA sequence remains largely unknown. Here we uncover unique RNA regulons embedded in homeobox (Hox) 5' untranslated regions (UTRs) that confer ribosome-mediated control of gene expression. These structured RNA elements, resembling viral internal ribosome entry sites (IRESs), are found in subsets of Hox mRNAs. They facilitate ribosome recruitment and require the ribosomal protein RPL38 for their activity. Despite numerous layers of Hox gene regulation, these IRES elements are essential for converting Hox transcripts into proteins to pattern the mammalian body plan. This specialized mode of IRES-dependent translation is enabled by an additional regulatory element that we term the translation inhibitory element (TIE), which blocks cap-dependent translation of transcripts. Together, these data uncover a new paradigm for ribosome-mediated control of gene expression and organismal development.

Effect of water temperature and prey concentrations on initial development of Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae), a freshwater fish

The aim of this study was to investigate the effects of water temperature and prey concentrations (Artemia nauplii) on the initial development of Lophiosilurus alexandri larvae. The experiment was conducted using a 4 x 2 factorial design, with four water temperatures (23, 26, 29 and 32 °C), two different initial prey concentrations (P700 and P1,300) and three replicates. Feeding was increased during the fifteen-day experiment. At the end of the experiment, the survival and condition factor were affected only by prey concentrations, with elevated numbers of Artemia nauplii leading to higher averages of these variables. The total length (TL) and specific growth rate were separately influenced by temperature and prey concentration, without interaction between them, and weight showed an interaction with these factors. In general, an increase of temperature (23 to 32 °C) improved the growth and nitrogen gain in L alexandri larvae. For TL, the optimal temperatures estimated were 31.4 and 31.0 °C for P700 and P1,300, respectively. Similar mean body weight larvae and nitrogen gain were observed at 23 °C for both levels of prey concentrations. For other temperatures, the P1,300 level provided greater weight gain for L. alexandri. Therefore, it is suggested that temperatures between 29-32 °C combined with a higher level of prey concentration maximise the development and nitrogen gain in L. alexandri larvae. Moreover, this is the first result about nitrogen incorporation in neotropical fish larvae.

Environmental temperature impact on bone and cartilage growth

Environmental temperature can have a surprising impact on extremity growth in homeotherms, but the underlying mechanisms have remained elusive for over a century. Limbs of animals raised at warm ambient temperature are significantly and permanently longer than those of littermates housed at cooler temperature. These remarkably consistent lab results closely resemble the ecogeographical tenet described by Allen's "extremity size rule," that appendage length correlates with temperature and latitude. This phenotypic growth plasticity could have adaptive significance for thermal physiology. Shortened extremities help retain body heat in cold environments by decreasing surface area for potential heat loss. Homeotherms have evolved complex mechanisms to maintain tightly regulated internal temperatures in challenging environments, including "facultative extremity heterothermy" in which limb temperatures can parallel ambient. Environmental modulation of tissue temperature can have direct and immediate consequences on cell proliferation, metabolism, matrix production, and mineralization in cartilage. Temperature can also indirectly influence cartilage growth by modulating circulating levels and delivery routes of essential hormones and paracrine regulators. Using an integrated approach, this article synthesizes classic studies with new data that shed light on the basis and significance of this enigmatic growth phenomenon and its relevance for treating human bone elongation disorders. Discussion centers on the vasculature as a gateway to understanding the complex interconnection between direct (local) and indirect (systemic) mechanisms of temperature-enhanced bone lengthening. Recent advances in imaging modalities that enable the dynamic study of cartilage growth plates in vivo will be key to elucidating fundamental physiological mechanisms of long bone growth regulation.

Critical windows in embryonic development: Shifting incubation temperatures alter heart rate and oxygen consumption of Lake Whitefish (Coregonus clupeaformis) embryos and hatchlings

Critical windows are periods of developmental susceptibility when the phenotype of an embryonic, juvenile or adult animal may be vulnerable to environmental fluctuations. Temperature has pervasive effects on poikilotherm physiology, and embryos are especially vulnerable to temperature shifts. To identify critical windows, we incubated whitefish embryos at control temperatures of 2°C, 5°C, or 8°C, and shifted treatments among temperatures at the end of gastrulation or organogenesis. Heart rate (fH) and oxygen consumption ( [Formula: see text] ) were measured across embryonic development, and [Formula: see text] was measured in 1-day old hatchlings. Thermal shifts, up or down, from initial incubation temperatures caused persistent changes in fH and [Formula: see text] compared to control embryos measured at the same temperature (2°C, 5°C, or 8°C). Most prominently, when embryos were measured at organogenesis, shifting incubation temperature after gastrulation significantly lowered [Formula: see text] or fH. Incubation at 2°C or 5°C through gastrulation significantly lowered [Formula: see text] (42% decrease) and fH (20% decrease) at 8°C, incubation at 2°C significantly lowered [Formula: see text] (40% decrease) and fH (30% decrease) at 5°C, and incubation at 5°C and 8°C significantly lowered [Formula: see text] at 2°C (27% decrease). Through the latter half of development, [Formula: see text] and fH in embryos were not different from control values for thermally shifted treatments. However, in hatchlings measured at 2°C, [Formula: see text] was higher in groups incubated at 5°C or 8°C through organogenesis, compared to 2°C controls (43 or 65% increase, respectively). Collectively, these data suggest that embryonic development through organogenesis represents a critical window of embryonic and hatchling phenotypic plasticity. This study presents an experimental design that identified thermally sensitive periods for fish embryos.

IGF-I and amino acids effects through TOR signaling on proliferation and differentiation of gilthead sea bream cultured myocytes

Skeletal muscle growth and development is controlled by nutritional (amino acids, AA) as well as hormonal factors (insulin-like growth factor, IGF-I); however, how its interaction modulates muscle mass in fish is not clearly elucidated. The purpose of this study was to analyze the development of gilthead sea bream cultured myocytes to describe the effects of AA and IGF-I on proliferating cell nuclear antigen (PCNA) and myogenic regulatory factors (MRFs) expression, as well as on the transduction pathways involved in its signaling (TOR/AKT). Our results showed that AA and IGF-I separately increased the number of PCNA-positive cells and, together produced a synergistic effect. Furthermore, AA and IGF-I, combined or separately, increased significantly Myogenin protein expression, whereas MyoD was not affected. These results indicate a role for these factors in myocyte proliferation and differentiation. At the mRNA level, AA significantly enhanced PCNA expression, but no effects were observed on the expression of the MRFs or AKT2 and FOXO3 upon treatment. Nonetheless, we demonstrated for the first time in gilthead sea bream that AA significantly increased the gene expression of TOR and its downstream effectors 4EBP1 and 70S6K, with IGF-I having a supporting role on 4EBP1 up-regulation. Moreover, AA and IGF-I also activated TOR and AKT by phosphorylation, respectively, being this activation decreased by specific inhibitors. In summary, the present study demonstrates the importance of TOR signaling on the stimulatory role of AA and IGF-I in gilthead sea bream myogenesis and contributes to better understand the potential regulation of muscle growth and development in fish.

Ontogeny of redox regulation in Atlantic cod (Gadus morhua) larvae

The reduction potential of a cell is related to its fate. Proliferating cells are more reduced than those that are differentiating, whereas apoptotic cells are generally the most oxidized. Glutathione is considered the most important cellular redox buffer and the average reduction potential (Eh) of a cell or organism can be calculated from the concentrations of glutathione (GSH) and glutathione disulfide (GSSG). In this study, triplicate groups of cod larvae at various stages of development (3 to 63 days post-hatch; dph) were sampled for analyses of GSSG/2GSH concentrations, together with activities of antioxidant enzymes and expression of genes encoding proteins involved in redox metabolism. The concentration of total GSH (GSH+GSSG) increased from 610 ± 100 to 1260 ± 150 μmol/kg between 7 and 14 dph and was then constant until 49 dph, after which it decreased to 810 ± 100 μmol/kg by 63 dph. The 14- to 49-dph period, when total GSH concentrations were stable, coincides with the proposed period of metamorphosis in cod larvae. The concentration of GSSG comprised approximately 1% of the total GSH concentration and was stable throughout the sampling series. This resulted in a decreasing Eh from -239 ± 1 to -262 ± 7 mV between 7 and 14 dph, after which it remained constant until 63 dph. The changes in GSH and Eh were accompanied by changes in the expression of several genes involved in redox balance and signaling, as well as changes in activities of antioxidant enzymes, with the most dynamic responses occurring in the early phase of cod larval development. It is hypothesized that metamorphosis in cod larvae starts with the onset of mosaic hyperplasia in the skeletal muscle at approximately 20 dph (6.8mm standard length (SL)) and ends with differentiation of the stomach and disappearance of the larval finfold at 40 to 50 dph (10-15 mm SL). Thus, metamorphosis in cod larvae seems to coincide with high and stable total concentrations of GSH.

Transcriptional assessment by microarray analysis and large-scale meta-analysis of the metabolic capacity of cardiac and skeletal muscle tissues to cope with reduced nutrient availability in Gilthead Sea Bream (Sparus aurata L.)

The effects of nutrient availability on the transcriptome of cardiac and skeletal muscle tissues were assessed in juvenile gilthead sea bream fed with a standard diet at two feeding levels: (1) full ration size and (2) 70 % satiation followed by a finishing phase at the maintenance ration. Microarray analysis evidenced a characteristic transcriptomic profile for each muscle tissue following changes in oxidative capacity (heart > red skeletal muscle > white skeletal muscle). The transcriptome of heart and secondly that of red skeletal muscle were highly responsive to nutritional changes, whereas that of glycolytic white skeletal muscle showed less ability to respond. The highly expressed and nutritionally regulated genes of heart were mainly related to signal transduction and transcriptional regulation. In contrast, those of white muscle were enriched in gene ontology (GO) terms related to proteolysis and protein ubiquitination. Microarray meta-analysis using the bioinformatic tool Fish and Chips ( http://fishandchips.genouest.org/index.php ) showed the close association of a representative cluster of white skeletal muscle with some of cardiac and red skeletal muscle, and many GO terms related to mitochondrial function appeared to be common links between them. A second round of cluster comparisons revealed that mitochondria-related GOs also linked differentially expressed genes of heart with those of liver from cortisol-treated gilthead sea bream. These results show that mitochondria are among the first responders to environmental and nutritional stress stimuli in gilthead sea bream, and functional phenotyping of this cellular organelle is highly promising to obtain reliable markers of growth performance and well-being in this fish species.

Skeletal muscle plasticity induced by seasonal acclimatization involves IGF1 signaling: implications in ribosomal biogenesis and protein synthesis

One of the most fundamental biological processes in living organisms that are affected by environmental fluctuations is growth. In fish, skeletal muscle accounts for the largest proportion of body mass, and the growth of this tissue is mainly controlled by the insulin-like growth factor (IGF) system. By using the carp (Cyprinus carpio), a fish that inhabits extreme conditions during winter and summer, we assessed the skeletal muscle plasticity induced by seasonal acclimatization and the relation of IGF signaling with protein synthesis and ribosomal biogenesis. The expression of igf1 in muscle decreased during winter in comparison with summer, whereas the expression for both paralogues of igf2 did not change significantly between seasons. The expression of igf1 receptor a (igf1ra), but not of igf1rb, was down-regulated in muscle during the winter as compared to the summer. A decrease in protein contents and protein phosphorylation for IGF signaling molecules in muscle was observed in winter-acclimatized carp. This was related with a decreased expression in muscle for markers of myogenesis (myoblast determination factor (myod), myogenic factor 5 (myf5), and myogenin (myog)); protein synthesis (myosin heavy chain (mhc) and myosin light chain (mlc3 and mlc1b)); and ribosomal biogenesis (pre-rRNA and ribosomal proteins). IGF signaling, and key markers of ribosomal biogenesis, protein synthesis, and myogenesis were affected by seasonal acclimatization, with differential regulation in gene expression and signaling pathway activation observed in muscle between both seasons. This suggests that these molecules are responsible for the muscle plasticity induced by seasonal acclimatization in carp.

MicroRNA in teleost fish

MicroRNAs (miRNAs) are transcriptional and posttranscriptional regulators involved in nearly all known biological processes in distant eukaryotic clades. Their discovery and functional characterization have broadened our understanding of biological regulatory mechanisms in animals and plants. They show both evolutionary conserved and unique features across Metazoa. Here, we present the current status of the knowledge about the role of miRNA in development, growth, and physiology of teleost fishes, in comparison to other vertebrates. Infraclass Teleostei is the most abundant group among vertebrate lineage. Fish are an important component of aquatic ecosystems and human life, being the prolific source of animal proteins worldwide and a vertebrate model for biomedical research. We review miRNA biogenesis, regulation, modifications, and mechanisms of action. Specific sections are devoted to the role of miRNA in teleost development, organogenesis, tissue differentiation, growth, regeneration, reproduction, endocrine system, and responses to environmental stimuli. Each section discusses gaps in the current knowledge and pinpoints the future directions of research on miRNA in teleosts.

Thermal plasticity of the miRNA transcriptome during Senegalese sole development

Background

Several miRNAs are known to control myogenesis in vertebrates. Some of them are specifically expressed in muscle while others have a broader tissue expression but are still involved in establishing the muscle phenotype. In teleosts, water temperature markedly affects embryonic development and larval growth. It has been previously shown that higher embryonic temperatures promoted faster development and increased size of Senegalese sole (Solea senegalensis) larvae relatively to a lower temperature. The role of miRNAs in thermal-plasticity of growth is hitherto unknown. Hence, we have used high-throughput SOLiD sequencing to determine potential changes in the miRNA transcriptome in Senegalese sole embryos that were incubated at 15°C or 21°C until hatching and then reared at a common temperature of 21°C.

Results

We have identified 320 conserved miRNAs in Senegalese sole, of which 48 had not been previously described in teleosts. mir-17a-5p, mir-26a, mir-130c, mir-206-3p, mir-181a-5p, mir-181a-3p and mir-199a-5p expression levels were further validated by RT- qPCR. The majority of miRNAs were dynamically expressed during early development, with peaks of expression at pre-metamorphosis or metamorphosis. Also, a higher incubation temperature (21°C) was associated with expression of some miRNAs positively related with growth (e.g., miR-17a, miR-181-5p and miR-206) during segmentation and at hatching. Target prediction revealed that these miRNAs may regulate myogenesis through MAPK and mTOR pathways. Expression of miRNAs involved in lipid metabolism and energy production (e.g., miR-122) also differed between temperatures. A miRNA that can potentially target calpain (miR-181-3p), and therefore negatively regulate myogenesis, was preferentially expressed during segmentation at 15°C compared to 21°C.

Conclusions

Temperature has a strong influence on expression of miRNAs during embryonic and larval development in fish. Higher expression levels of miR-17a, miR-181-5p and miR-206-3p and down-regulation of miR-181a-3p at 21°C may promote myogenesis and are in agreement with previous studies in Senegalese sole, which reported enhanced growth at higher embryonic temperatures compared to 15°C. Moreover, miRNAs involved in lipid metabolism and energy production may also contribute to increased larval growth at 21°C compared to 15°C. Taken together, our data indicate that miRNAs may play a role in temperature-induced phenotypic plasticity of growth in teleosts.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-525) contains supplementary material, which is available to authorized users.

Salinity and temperature variations reflecting on cellular PCNA, IGF-I and II expressions, body growth and muscle cellularity of a freshwater fish larvae

The present study assessed the influence of salinity and temperature on body growth and on muscle cellularity of Lophiosilurus alexaxdri vitelinic larvae. Slightly salted environments negatively influenced body growth of freshwater fish larvae and we observed that those conditions notably act as an environmental influencer on muscle growth and on local expression of hypertrophia and hypeplasia markers (IGFs and PCNA). Furthermore, we could see that salinity tolerance for NaCl 4gl(-)(1) diminishes with increasing temperature, evidenced by variation in body and muscle growth, and by irregular morphology of the lateral skeletal muscle of larvae. We saw that an increase of both PCNA and autocrine IGF-II are correlated to an increase in fibre numbers and fibre diameter as the temperature increases and salinity diminishes. On the other hand, autocrine IGF-I follows the opposite way to the other biological parameters assessed, increasing as salinity increases and temperature diminishes, showing that this protein did not participate in muscle cellularity, but participating in molecular/cellular repair. Therefore, slightly salted environments may provide adverse conditions that cause some obstacles to somatic growth of this species, suggesting some osmotic expenditure with a salinity increment.

Influence of in ovo thermal manipulation on lipid metabolism in embryonic duck liver

The growth and development of poultry embryos are easily affected by environmental factors, such as the incubation temperature and humidity. Metabolism, including lipid metabolism, during the embryonic stage is also important for the growth and development of poultry. Our study aimed to investigate the effects of incubation temperature on embryonic lipid metabolism in the liver of ducks. To fully evaluate the effects, thermal treatment was given between embryonic ages 11 and 24 days with a 1 °C higher incubation temperature than the control group, and lipid metabolism parameters in the liver and blood serum were analyzed both at embryonic stage day 20 and 2 weeks post-hatching. Our results showed no significant changes in the embryonic stage in total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) in the blood serum (P>0.05). Additionally, the mRNA expression levels and enzyme activities of fatty acid synthase (FAS), acetyl CoA carboxylase (ACC), and elongase of very long chain fatty acids (ELOVL) did not show significant changes either in the embryonic stage or at hatching day 20 (P>0.05). However, there were significant changes in the gene expression and enzyme activities of TC, LDL-C and FAS at post-hatching stages (P≤0.05). These results may indicate that the thermal treatment has less influence on lipid metabolism in the embryonic stage but has a much stronger effect in the post-hatching stage.

Thermal stress alters expression of genes involved in one carbon and DNA methylation pathways in Atlantic cod embryos

One-carbon (1-C) metabolism is essential for normal embryonic development through its regulation of DNA methylation and cell proliferation. With consideration to the potential future anthropogenic oceanic warming, we studied the effects of both acute thermal stress and continuous thermal stress (10°C) during Atlantic cod embryo development on the expression levels of genes associated with the 1-C metabolism, including DNA methyltransferases. We conducted a phylogenetic analysis of vertebrate DNA methyltransferases to determine the number and similarity of DNMT found in Atlantic cod. This analysis revealed that Atlantic cod have one maintenance dnmt (dnmt1) and five de novo DNMTs (dnmt4, dnmt3, dnmt3b, dnmt3aa, dnmt3ab). Stage specific changes in expression levels occurred for all genes analyzed. The effect of acute thermal stress was evaluated during early development. Compared to controls these experiments showed significant alterations in expression levels of several genes, that in some instances were reversed at later stages of development. A significant effect of continuous thermal stress was found in gastrula embryos where lower mRNA expression levels of 1-C metabolism, de novo DNMTs and cell proliferation genes were detected. One exception was the maintenance DNMT, which was only sensitive to acute and not continuous thermal stress. DNA methylation status indicated that blastula embryos were hypomethylated compared to spermatozoa and late gastrula stages. In post-gastrula stage, however, continuous thermal stress resulted in a higher degree of DNA methylation compared to controls. These data reveal that the regulation of epigenetically important transcripts in the 1-C metabolism of Atlantic cod embryos is sensitive to thermal stress.

Satellite cell activation and populations on single muscle-fiber cultures from adult zebrafish (Danio rerio)

Satellite cells (SCs), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SCs are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27 and 21°C. SCs were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1 mmol l(-1)) or HGF (10 ng ml(-1)) to maximum activation at lower concentrations of both than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 h at 4 cycles per minute) increased activation and was blocked by nitric oxide synthase inhibition and reduced by culture at 21°C. The number of c-met+ SCs per fiber increased rapidly (by 3 h) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch, gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests the use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species.

Rearing temperature induces changes in muscle growth and gene expression in juvenile pacu (Piaractus mesopotamicus)

Pacu (Piaractus mesopotamicus) is a fast-growing fish that is extensively used in Brazilian aquaculture programs and shows a wide range of thermal tolerance. Because temperature is an environmental factor that influences the growth rate of fish and is directly related to muscle plasticity and growth, we hypothesized that different rearing temperatures in juvenile pacu, which exhibits intense muscle growth by hyperplasia, can potentially alter the muscle growth patterns of this species. The aim of this study was to analyze the muscle growth characteristics together with the expression of the myogenic regulatory factors MyoD and myogenin and the growth factor myostatin in juvenile pacu that were submitted to different rearing temperatures. Juvenile fish (1.5 g weight) were distributed in tanks containing water and maintained at 24°C (G24), 28 °C (G28) and 32 °C (G32) (three replicates for each group) for 60 days. At days 30 and 60, the fish were anesthetized and euthanized, and muscle samples (n=12) were collected for morphological, morphometric and gene expression analyses. At day 30, the body weight and standard length were lower for G24 than for G28 and G32. Muscle fiber frequency in the <25 μm class was significantly higher in G24, and the >50 μm class was lower in G24. MyoD gene expression was higher in G24 compared with that in G28 and G32, and myogenin and myostatin mRNA levels were higher in G24 than G28. At day 60, the body weight and the standard length were higher in G32 but lower in G24. The frequency distribution of the <25 μm diameter muscle fibers was higher in G24, and that of the >50 μm class was lower in G24. MyoD mRNA levels were higher in G24 and G32, and myogenin mRNA levels were similar between G24 and G28 and between G24 and G32 but were higher in G28 compared to G32. The myostatin mRNA levels were similar between the studied temperatures. In light of our results, we conclude that low rearing temperature altered the expression of muscle growth-related genes and induced a delay in muscle growth in juvenile pacu (P. mesopotamicus). Our study provides a clear example of thermally induced phenotypic plasticity in pacu fish and shows that changing the rearing temperature during the juvenile stage can have a considerable effect on gene expression and muscle growth in this species.

Characterisation and expression of myogenesis regulatory factors during in vitro myoblast development and in vivo fasting in the gilthead sea bream (Sparus aurata)

The aim of this study was to characterise a primary cell culture isolated from fast skeletal muscle of the gilthead sea bream. Gene expression profiles during culture maturation were compared with those obtained from a fasting-refeeding model which is widely used to modulate myogenesis in vivo. Myogenesis is controlled by numerous extracellular signals together with intracellular transcriptional factors whose coordinated expression is critical for the appropriate development of muscle fibres. Full-length cDNAs for the transcription factors Myf5, Mrf4, Pax7 and Sox8 were cloned and sequenced for gilthead sea bream. Pax7, sox8, myod2 and myf5 levels were up-regulated during the proliferating phase of the myogenic cultures coincident with the highest expression of proliferating cell nuclear antigen (PCNA). In contrast, myogenin and mrf4 transcript abundance was highest during the differentiation phase of the culture when myotubes were present, and was correlated with increased myosin heavy chain (mhc) and desmin expression. In vivo, 30days of fasting resulted in muscle fibre atrophy, a reduction in myod2, myf5 and igf1 expression, lower number of Myod-positive cells, and decreased PCNA protein expression, whereas myogenin expression was not significantly affected. Myostatin1 (mstn1) and pax7 expression were up-regulated in fasted relative to well-fed individuals, consistent with a role for Pax7 in the reduction of myogenic cell activity with fasting. The primary cell cultures and fasting-feeding experiments described provide a foundation for the future investigations on the regulation of muscle growth in gilthead sea bream.

Regulation of skeletal muscle growth in fish by the growth hormone--insulin-like growth factor system

The growth hormone (GH)-insulin-like growth factor (IGF) system is the key promoter of growth in vertebrates; however, how this system modulates muscle mass in fish is just recently becoming elucidated. In fish, the GH induces muscle growth by modulating the expression of several genes belonging to the myostatin (MSTN), atrophy, GH, and IGF systems as well as myogenic regulatory factors (MRFs). The GH controls the expression of igf1 via Janus kinase 2 (JAK2)/signal transducers and activators of the transcription 5 (STAT5) signaling pathway, but it seems that it is not the major regulator. These mild effects of the GH on igf1 expression in fish muscle seem to be related with the presence of higher contents of truncated GH receptor1 (tGHR1) than full length GHR (flGHR1). IGFs in fish stimulate myogenic cell proliferation, differentiation, and protein synthesis through the MAPK/ERK and PI3K/AKT/TOR signaling pathways, concomitant with abolishing protein degradation and atrophy via the PI3K/AKT/FOXO signaling pathway. Besides these signaling pathways control the expression of several genes belonging to the atrophy and IGF systems. Particularly, IGFs and amino acid control the expression of igf1, thus, suggesting other of alternative signaling pathways regulating the transcription of this growth factor. The possible role of IGF binding proteins (IGFBPs) and the contribution of muscle-derived versus hepatic-produced IGF1 on fish muscle growth is also addressed. Thus, a comprehensive overview on the GH-IGF system regulating fish skeletal muscle growth is presented, as well as perspectives for future research in this field.

Growth response and expression of muscle growth-related candidate genes in adult zebrafish fed plant and fishmeal protein-based diets

The main objective of this study was to examine the effects of a plant protein- vs. fishmeal-based diet on growth response in a population of 24 families, as well as expression of growth-related genes in the muscle of adult zebrafish (Danio rerio). Each family was split to create two fish populations with similar genetic backgrounds, and the fish were fed either fishmeal (FM diet) or plant protein (PP diet) as the unique protein source in their diets from 35 to 98 days postfertilization (dpf). To understand the effect of the PP diet on gene expression, individuals from three families, representative of the mean weight in both populations, were selected. To understand the effect of familiar variation on gene expression, the same families were evaluated separately. At 98 dpf, growth-related genes Igf1a, Igf2a, mTOR, Pld1a, Mrf4, Myod, Myogenin, and Myostatin1b were evaluated. In males, Myogenin, Mrf4, and Igf2a showed changes attributable to the PP diet. In females, the effect of the PP diet did not modulate the expression in any of the eight genes studied. The effect of familiar variation on gene expression was observed among families. This study shows that PP diet and family variation have effects on gene expression in fish muscle.

Insulin-like growth factors effects on the expression of myogenic regulatory factors in gilthead sea bream muscle cells

Gilthead sea bream (Sparus aurata) is a widely cultured fish; however, muscle development regulation is poorly known. Myogenesis can be activated by the myogenic regulatory factors (MRFs: MyoD, Myf5, myogenin and MRF4) and by endocrine signals from the growth hormone (GH)/insulin-like growth factors (IGFs) axis. We cultured gilthead sea bream myocytes to better understand the role of IGFs in muscle growth and differentiation through the regulation of MRFs expression. First, we studied the expression pattern during culture development of IGFs and IGF-I splice variants. The expression of igf-II was highest at the beginning of the culture and decreased when the cells started to differentiate, similarly to that observed for total igf-I. Igf-Ib showed a paralleled expression pattern as that of total igf-I, whereas igf-Ic was more stable during culture progression. Next, we analyzed the expression of IGFs and MRFs after incubation of cells at day 4 with GH, IGF-I, IGF-II and combinations of them at 3, 6 and 18 h. IGF-II increased myod2 and myf5 expression, genes involved in early muscle cell proliferation. Moreover, IGF-I caused an increase on mrf4 and myogenin expression, both involved in the later stages of development corresponding to differentiation. Regarding the regulation of IGFs expression, igf-I was stimulated by GH and IGF-II alone and combined, whereas igf-II expression was increased in response to IGF-I, suggesting a nice model of crossed regulation. Overall, the present model could be very useful to understand the different regulatory roles of these endocrine and transcription factors on fish myogenesis.

Exploring the larval transcriptome of the common sole (Solea solea L.)

BACKGROUND

The common sole (Solea solea) is a promising candidate for European aquaculture; however, the limited knowledge of the physiological mechanisms underlying larval development in this species has hampered the establishment of successful flatfish aquaculture. Although the fact that genomic tools and resources are available for some flatfish species, common sole genomics remains a mostly unexplored field. Here, we report, for the first time, the sequencing and characterisation of the transcriptome of S. solea and its application for the study of molecular mechanisms underlying physiological and morphological changes during larval-to-juvenile transition.

RESULTS

The S. solea transcriptome was generated from whole larvae and adult tissues using the Roche 454 platform. The assembly process produced a set of 22,223 Isotigs with an average size of 726 nt, 29 contigs and a total of 203,692 singletons. Of the assembled sequences, 75.2% were annotated with at least one known transcript/protein; these transcripts were then used to develop a custom oligo-DNA microarray. A total of 14,674 oligonucleotide probes (60 nt), representing 12,836 transcripts, were in situ synthesised onto the array using Agilent non-contact ink-jet technology. The microarray platform was used to investigate the gene expression profiles of sole larvae from hatching to the juvenile form. Genes involved in the ontogenesis of the visual system are up-regulated during the early stages of larval development, while muscle development and anaerobic energy pathways increase in expression over time. The gene expression profiles of key transcripts of the thyroid hormones (TH) cascade and the temporal regulation of the GH/IGF1 (growth hormone/insulin-like growth factor I) system suggest a pivotal role of these pathways in fish growth and initiation of metamorphosis. Pre-metamorphic larvae display a distinctive transcriptomic landscape compared to previous and later stages. Our findings highlighted the up-regulation of gene pathways involved in the development of the gastrointestinal system as well as biological processes related to folic acid and retinol metabolism. Additional evidence led to the formation of the hypothesis that molecular mechanisms of cell motility and ECM adhesion may play a role in tissue rearrangement during common sole metamorphosis.

CONCLUSIONS

Next-generation sequencing provided a good representation of the sole transcriptome, and the combination of different approaches led to the annotation of a high number of transcripts. The construction of a microarray platform for the characterisation of the larval sole transcriptome permitted the definition of the main processes involved in organogenesis and larval growth.

Hypoxia tolerance of common sole juveniles depends on dietary regime and temperature at the larval stage: evidence for environmental conditioning

An individual's environmental history may have delayed effects on its physiology and life history at later stages in life because of irreversible plastic responses of early ontogenesis to environmental conditions. We chose a marine fish, the common sole, as a model species to study these effects, because it inhabits shallow marine areas highly exposed to environmental changes. We tested whether temperature and trophic conditions experienced during the larval stage had delayed effects on life-history traits and resistance to hypoxia at the juvenile stage. We thus examined the combined effect of global warming and hypoxia in coastal waters, which are potential stressors to many estuarine and coastal marine fishes. Elevated temperature and better trophic conditions had a positive effect on larval growth and developmental rates; warmer larval temperature had a delayed positive effect on body mass and resistance to hypoxia at the juvenile stage. The latter suggests a lower oxygen demand of individuals that had experienced elevated temperatures during larval stages. We hypothesize that an irreversible plastic response to temperature occurred during early ontogeny that allowed adaptive regulation of metabolic rates and/or oxygen demand with long-lasting effects. These results could deeply affect predictions about impacts of global warming and eutrophication on marine organisms.

Redox regulation in Atlantic cod (Gadus morhua) embryos developing under normal and heat-stressed conditions

With regard to predicted oceanic warming, we studied the effects of heat stress on the redox system during embryonic development of Atlantic cod (Gadus morhua), with emphasis on the glutathione balance, activities of key antioxidant enzymes, and their mRNA levels. The embryos were incubated at optimal temperature for development (6 °C) or slightly above the threshold temperature (10 °C). The regulation of all the redox-related parameters measured at optimum development was highly dynamic and complex, indicating the importance of both maternal and zygotic contributions to maintaining redox equilibrium. Development at 10 °C caused a significantly higher mortality at the blastula and early gastrula stages, indicating severe stress. Measures of the glutathione redox couple showed a significantly more reduced state in embryos at 10 °C compared to 6 °C at the post-gastrula stages. Mean normalized expression of nrf2, trxred, g6pd, gclc, nox1, CuZnsod, and mt in embryos kept at 10 °C revealed stage-specific significantly reduced mRNA levels. Activities of antioxidant enzymes changed both during ontogenesis and in response to temperature, but did not correlate with mRNA levels. As the embryos need a tightly regulated redox environment to coordinate between growth and differentiation, these findings suggest that the altered redox balance might participate in inducing phenotypic changes caused by elevated temperature.

Temperature affects methylation of the myogenin putative promoter, its expression and muscle cellularity in Senegalese sole larvae

Myogenin (myog) encodes a highly conserved myogenic regulatory factor that is involved in terminal muscle differentiation. It has been shown in mammals that methylation of cytosines within the myog promoter plays a major role in regulating its transcription. In the present study, the Senegalese sole (Solea senegalensis) myog putative proximal promoter was identified and found to be highly conserved among teleosts. Therefore, it is plausible that it plays a similar role in controlling myog expression. Cytosine methylation of the myog promoter in skeletal muscle of Senegalese sole larvae undergoing metamorphosis was influenced by rearing temperature. A lower temperature (15°C) significantly increased myog promoter methylation in skeletal muscle, particularly at specific CpG sites, relatively to higher rearing temperatures (18 and 21°C). Myog transcription was downregulated at 15°C, whereas expression of dnmt1 and dnmt3b was upregulated, consistently with the higher myog methylation observed at this temperature. Rearing temperature also affected growth and fast muscle cellularity, producing larger fibers at 21°C. Taken together, our data provide the first evidence of an epigenetic mechanism that may be underlying the temperature-induced phenotypic plasticity of muscle growth in teleosts.

Temperature during embryonic development has persistent effects on metabolic enzymes in the muscle of zebrafish

Global warming is intensifying interest in the physiological consequences of temperature change in ectotherms, but we still have a relatively poor understanding of the effects of temperature on early life stages. This study determined how embryonic temperature (TE) affects development and the activity of metabolic enzymes in the swimming muscle of zebrafish. Embryos developed successfully to hatching (survival ≥ 88%) from 22°C to 32°C, but suffered sharp increases in mortality outside of this range. Embryos that were incubated until hatching at a control TE (27°C) or near the extremes for successful development (22°C or 32°C) were next raised to adulthood under control conditions at 27°C. Growth trajectories after hatching were altered in the 22°C and 32°C TE groups compared to 27°C TE controls, but growth slowed after 3 months of age in all groups. Maximal enzyme activities of cytochrome c oxidase (COX), citrate synthase (CS), hydroxyacyl-coA dehydrogenase (HOAD), pyruvate kinase (PK), and lactate dehydrogenase (LDH) were measured across a range of assay temperatures (22°C, 27°C, 32°C, 36°C) in adults from each TE group that were acclimated to 27°C or 32°C. Substrate affinities (Km) were also determined for COX and LDH. In adult fish acclimated to 27°C, COX and PK activities were higher in 22°C and 32°C TE groups than in 27°C TE controls, and the temperature optimum for COX activity was higher in the 32°C TE group than in the 22°C TE group. Warm acclimation reduced COX, CS, and/or PK activities in the 22°C and 32°C TE groups, possibly to compensate for thermal effects on molecular activity. This response did not occur in the 27°C TE controls, which instead increased LDH and HOAD activities. Warm acclimation also increased thermal sensitivity (Q10) of HOAD to cool temperatures across all TE groups. We conclude that the temperature experienced during early development can have a persistent impact on energy metabolism pathways and acclimation capacity in later life.

Development temperature has persistent effects on muscle growth responses in gilthead sea bream

Initially we characterised growth responses to altered nutritional input at the transcriptional and tissue levels in the fast skeletal muscle of juvenile gilthead sea bream. Fish reared at 21-22°C (range) were fed a commercial diet at 3% body mass d(-1) (non-satiation feeding, NSF) for 4 weeks, fasted for 4d (F) and then fed to satiation (SF) for 21d. 13 out of 34 genes investigated showed consistent patterns of regulation between nutritional states. Fasting was associated with a 20-fold increase in MAFbx, and a 5-fold increase in Six1 and WASp expression, which returned to NSF levels within 16h of SF. Refeeding to satiation was associated with a rapid (<24 h) 12 to 17-fold increase in UNC45, Hsp70 and Hsp90α transcripts coding for molecular chaperones associated with unfolded protein response pathways. The growth factors FGF6 and IGF1 increased 6.0 and 4.5-fold within 16 h and 24 h of refeeding respectively. The average growth in diameter of fast muscle fibres was checked with fasting and significant fibre hypertrophy was only observed after 13d and 21d SF. To investigate developmental plasticity in growth responses we used the same experimental protocol with fish reared at either 17.5-18.5°C (range) (LT) or 21-22°C (range) (HT) to metamorphosis and then transferred to 21-22°C. There were persistent effects of development temperature on muscle growth patterns with 20% more fibres of lower average diameter in LT than HT group of similar body size. Altering the nutritional input to the muscle to stimulate growth revealed cryptic changes in the expression of UNC45 and Hsp90α with higher transcript abundance in the LT than HT groups, whereas there were no differences in the expression of MAFbx and Six1. It was concluded that myogenesis and gene expression patterns during growth are not fixed, but can be modified by temperature during the early stages of the life cycle.

Transcriptomic characterization of the larval stage in gilthead seabream (Sparus aurata) by 454 pyrosequencing

Gilthead seabream (Sparus aurata) is a teleost belonging to the family Sparidae with a high economical relevance in the Mediterranean countries. Although genomic tools have been developed in this species in order to investigate its physiology at the molecular level and consequently its culture, genomic information on post-embryonic development is still scarce. In this study, we have investigated the transcriptome of a marine teleost during the larval stage (from hatching to 60 days after hatching) by the use of 454 pyrosequencing technology. We obtained a total of 68,289 assembled contigs, representing putative transcripts, belonging to 54,606 different clusters. Comparison against all S. aurata expressed sequenced tags (ESTs) from the NCBI database revealed that up to 34,722 contigs, belonging to about 61% of gene clusters, are sequences previously not described. Contigs were annotated through an iterative Blast pipeline by comparison against databases such as NCBI RefSeq from Danio rerio, SwissProt or NCBI teleost ESTs. Our results indicate that we have enriched the number of annotated sequences for this species by more than 50% compared with previously existing databases for the gilthead seabream. Gene Ontology analysis of these novel sequences revealed that there is a statistically significant number of transcripts with key roles in larval development, differentiation, morphology, and growth. Finally, all information has been made available online through user-friendly interfaces such as GBrowse and a Blast server with a graphical frontend.

Fast skeletal muscle transcriptome of the gilthead sea bream (Sparus aurata) determined by next generation sequencing

Background

The gilthead sea bream (Sparus aurata L.) occurs around the Mediterranean and along Eastern Atlantic coasts from Great Britain to Senegal. It is tolerant of a wide range of temperatures and salinities and is often found in brackish coastal lagoons and estuarine areas, particularly early in its life cycle. Gilthead sea bream are extensively cultivated in the Mediterranean with an annual production of 125,000 metric tonnes. Here we present a de novo assembly of the fast skeletal muscle transcriptome of gilthead sea bream using 454 reads and identify gene paralogues, splice variants and microsatellite repeats. An annotated transcriptome of the skeletal muscle will facilitate understanding of the genetic and molecular basis of traits linked to production in this economically important species.

Results

Around 2.7 million reads of mRNA sequence data were generated from the fast myotomal of adult fish (~2 kg) and juvenile fish (~0.09 kg) that had been either fed to satiation, fasted for 3-5d or transferred to low (11°C) or high (33°C) temperatures for 3-5d. Newbler v2.5 assembly resulted in 43,461 isotigs >100 bp. The number of sequences annotated by searching protein and gene ontology databases was 10,465. The average coverage of the annotated isotigs was x40 containing 5655 unique gene IDs and 785 full-length cDNAs coding for proteins containing 58–1536 amino acids. The v2.5 assembly was found to be of good quality based on validation using 200 full-length cDNAs from GenBank. Annotated isotigs from the reference transcriptome were attributable to 344 KEGG pathway maps. We identified 26 gene paralogues (20 of them teleost-specific) and 43 splice variants, of which 12 had functional domains missing that were likely to affect their biological function. Many key transcription factors, signaling molecules and structural proteins necessary for myogenesis and muscle growth have been identified. Physiological status affected the number of reads that mapped to isotigs, reflecting changes in gene expression between treatments.

Conclusions

We have produced a comprehensive fast skeletal muscle transcriptome for the gilthead sea bream, which will provide a resource for SNP discovery in genes with a large effect on production traits of commercial interest and for expression studies of growth and adaptation.

Parental identity influences progeny responses to incubation thermal stress in sockeye salmon Onchorhynchus nerka

The influence of individual parentage on progeny responses to early developmental temperature stress was examined in a cross-fertilization experiment using sockeye salmon Oncorhynchus nerka. Differences in survival, hatch timing and size were examined among five paternally linked and five maternally linked offspring families (Weaver Creek population, British Columbia, Canada) incubated at 12, 14 and 16° C from just after fertilization to hatch. Mean embryonic survival was significantly lower at 14 and 16° C; however, offspring families had substantially different survival responses across the thermal gradient (crossing reaction norms). Within temperature treatments, substantial variation in embryonic survival, alevin mass, time-to-hatch and hatch duration were attributable to family identity; however, most traits were governed by significant temperature-family interactions. For embryonic survival, large differences between families at 16° C were due to both female and male spawner influence, whereas inter-family differences were obscured at 14° C (high intra-family variation), and minimal at 12° C (only maternal influence detected). Despite post-hatch rearing under a common cool thermal regime, persistent effects of both temperature and parentage were detected in alevin and 3 week-old fry. Collectively, these findings highlight the crucial role that parental influences on offspring may have in shaping future selection within salmonid populations exposed to elevated thermal regimes. An increased understanding of parental and temperature influences and their persistence in early development will be essential to developing a more comprehensive view of population spawning success and determining the adaptive capacity of O. nerka populations in the face of environmental change.

Detection of growth-related QTL in turbot (Scophthalmus maximus)

Background

The turbot (Scophthalmus maximus) is a highly appreciated European aquaculture species. Growth related traits constitute the main goal of the ongoing genetic breeding programs of this species. The recent construction of a consensus linkage map in this species has allowed the selection of a panel of 100 homogeneously distributed markers covering the 26 linkage groups (LG) suitable for QTL search. In this study we addressed the detection of QTL with effect on body weight, length and Fulton's condition factor.

Results

Eight families from two genetic breeding programs comprising 814 individuals were used to search for growth related QTL using the panel of microsatellites available for QTL screening. Two different approaches, maximum likelihood and regression interval mapping, were used in order to search for QTL. Up to eleven significant QTL were detected with both methods in at least one family: four for weight on LGs 5, 14, 15 and 16; five for length on LGs 5, 6, 12, 14 and 15; and two for Fulton's condition factor on LGs 3 and 16. In these LGs an association analysis was performed to ascertain the microsatellite marker with the highest apparent effect on the trait, in order to test the possibility of using them for marker assisted selection.

Conclusions

The use of regression interval mapping and maximum likelihood methods for QTL detection provided consistent results in many cases, although the high variation observed for traits mean among families made it difficult to evaluate QTL effects. Finer mapping of detected QTL, looking for tightly linked markers to the causative mutation, and comparative genomics are suggested to deepen in the analysis of QTL in turbot so they can be applied in marker assisted selection programs.

Temperature-dependent modification of muscle precursor cell behaviour is an underlying reason for lasting effects on muscle cellularity and body growth of teleost fish

Temperature is an important factor influencing teleost muscle growth, including a lasting ('imprinted') influence of embryonic thermal experience throughout all further life. However, little is known about the cellular processes behind this phenomenon. The study reported here used digital morphometry and immunolabelling for Pax7, myogenin and H3P to quantitatively examine the effects of thermal history on muscle precursor cell (MPC) behaviour and muscle growth in pearlfish (Rutilus meidingeri) until the adult stage. Fish were reared at three different temperatures (8.5, 13 and 16°C) until hatching and subsequently kept under the same (ambient) thermal conditions. Cellularity data were combined with a quantitative analysis of Pax7+ MPCs including those that were mitotically active (Pax7+/H3P+) or had entered differentiation (Pax7+/myogenin+). The results demonstrate that at hatching, body lengths, fast and slow muscle cross-sectional areas and fast fibre numbers are lower in fish reared at 8.5 and 13°C than at 16°C. During the larval period, this situation changes in the 13°C-fish, so that these fish are finally the largest. The observed effects can be related to divergent cellular mechanisms at the MPC level that are initiated in the embryo during the imprinting period. Embryos of 16°C-fish have reduced MPC proliferation but increased differentiation, and thus give rise to larger hatchlings. However, their limited MPC reserves finally lead to smaller adults. By contrast, embryos of 13°C-fish and, to a lesser extent, 8.5°-fish, show enhanced MPC proliferation but reduced differentiation, thus leading to smaller hatchlings but allowing for a larger MPC pool that can be used for enhanced post-hatching growth, finally resulting in larger adults.

Growth patterns and nuclear distribution in white muscle fibers from black sea bass, Centropristis striata: evidence for the influence of diffusion

This study investigated the influence of fiber size on the distribution of nuclei and fiber growth patterns in white muscle of black sea bass, Centropristis striata, ranging in body mass from 0.45 to 4840 g. Nuclei were counted in 1 μm optical sections using confocal microscopy of DAPIand Acridine-Orange-stained muscle fibers. Mean fiber diameter increased from 36±0.87 μm in the 0.45 g fish to 280±5.47 μm in the 1885 g fish. Growth beyond 2000 g triggered the recruitment of smaller fibers, thus significantly reducing mean fiber diameter. Nuclei in the smaller fibers were exclusively subsarcolemmal (SS), whereas in larger fibers nuclei were more numerous and included intermyofibrillar (IM) nuclei. There was a significant effect of body mass on nuclear domain size (F=118.71, d.f.=3, P<0.0001), which increased to a maximum in fish of medium size (282-1885 g) and then decreased in large fish (>2000 g). Although an increase in the number of nuclei during fiber growth can help preserve the myonuclear domain, the appearance of IM nuclei during hypertrophic growth seems to be aimed at maintaining short effective diffusion distances for nuclear substrates and products. If only SS nuclei were present throughout growth, the diffusion distance would increase in proportion to the radius of the fibers. These observations are consistent with the hypothesis that changes in nuclear distribution and fiber growth patterns are mechanisms for avoiding diffusion limitation during animal growth.

Transcriptomics for understanding marine fish larval development1This review is part of a virtual symposium on current topics in aquaculture of marine fish and shellfish

The larval phase is a crucial period in the life of marine fish. During this phase, the organism will acquire the phenotype of an adult fish through the development of tissues and organs and the maturation of some of the principal physiological functions. Many biological processes (differentiation, cellular proliferation, growth, etc.) are regulated during this period. These regulations take place at different biological levels and particularly concern the expression of genes involved in larval ontogenesis processes. The development of bioinformatic resources (DNA or cDNA sequences) and molecular tools enabling high throughput gene expression analysis (microarrays) have allowed the transcriptome of marine fish species to be studied. In the present review, we summarize the main findings from transcriptomic investigations of development of marine fish larvae. Special attention is paid to investigations of transcriptomic patterns during postembryonic development and to the impact of environmental or nutritional factors on the transcriptome of marine fish larvae. Transcriptomic approaches will be especially useful in the future for investigating the effect of temperature and water acidification (or pH) on the development of different fish species in the context of global climate change.

An opinion paper: emphasis on white muscle development and growth to improve farmed fish flesh quality

Due to rapid depletion of wild stocks, the necessity to cultivate fish is eminent. Current fish farming practices seek to improve flesh quality. The notion that white muscles are the main target of the fishing industry is emphasized. A novel approach is suggested based on the development of white muscles in wild fish from eggs to adults. A compilation of facts about white muscle structure, function and ontogeny is followed by an account of the changes in swimming behaviour and performance related to the use of white muscle during growth from larva to adult. Ecological data narrate early swimming performance with white muscle development and growth, unveiling some of the important natural selection factors eliminating weak swimmers and poor growers from the breeding stock. A comparison between fish culture practise and natural conditions reveals fundamental differences. New approaches following wild breeding processes promise several important advantages regarding the quality of white muscle.

Differential effects on proliferation of GH and IGFs in sea bream (Sparus aurata) cultured myocytes

Primary culture of gilthead sea bream skeletal muscle cells was used to examine the effects of growth hormone (GH) and insulin-like growth factors (IGFs) in fish muscle proliferation and growth. Proliferation was measured as the percentage of positive cells expressing the proliferating cell nuclear antigen (PCNA) analyzed by immunocytochemistry. First, the effects of GH from two different origins (mammals and fish) were tested. GH from human (hGH) did not stimulate proliferation except at 3h at the dose of 1 nM. On the other hand, sea bream GH (sbGH) significantly stimulated proliferation, without differences between the three incubation times studied (3, 6, and 18 h), at the dose of 10nM, demonstrating that the homologous hormone has a more potent effect. In addition, the results with the IGFs indicated that both peptides, IGF-I and IGF-II significantly stimulated proliferation of sea bream myocytes, but IGF-II showed higher effects than IGF-I, and even than those of sbGH. Finally, the combinations of peptide treatments (GHs with IGFs) indicated that IGF-I has higher effects on proliferation when it is combined with GHs compared with IGF-I alone, while IGF-II has similar effects alone or combined with either GH. These results indicate that IGF-II may have an important role on muscle proliferation that appears to be independent of GH. On the contrary, IGF-I seems to play a synergistic action with GH stimulating myocyte proliferation.

Expression of the myosin light chains 1, 2 and 3 in the muscle of blackspot seabream (Pagellus bogaraveo, Brunnich), during development

Previous studies on the histochemistry and immunoreactivity of fibres in lateral muscle of blackspot seabream indicated that there is a developmental transition in the composition of myofibrillar proteins, which presumably reflects changes in contractile function as the fish grows. We hypothesize that the phenomenon underscores age and spatial differences in the expression of myosin light chains (MLC), not studied yet in this species. In this study, we examined selected stages in the post-hatching development of the muscle of blackspot seabream: hatching (0 days), mouth opening (5 days), weaning (40 days) and juveniles (70 days). The spatial expression of embryonic MLC 1 (MLC1), 2 (MLC2) and 3 (MLC3) was studied by in situ hybridization. Overall, MLC expression patterns were overlapping and restricted to the fast muscle. At hatching and mouth opening, all MLC types were highly expressed throughout the musculature in fast muscle. The expression levels in fast muscle remained high until weaning when germinal zones appeared on the dorsal and ventral areas. The germinal zones were characterized by small-diameter fast fibres with high levels of MLC expression. This pattern persisted up to day 70, when the germinal zones disappeared and expression of MLCs was observed only in the smaller cells of the fast muscle mosaic. These results support our hypothesis and, together with previous imuno- and histochemistry results, allow a better understanding of the mechanism of muscle differentiation and growth in fish beyond larval stages, and form- the basis for further comparative and experimental studies with this economically relevant species.