Lower environmental temperature delays and prolongs myogenic regulatory factor expression and muscle differentiation in rainbow trout (Onchrhynchus mykiss) embryos

Cloning, phylogenetic and expression analysis of two MyoDs in yellowtail kingfish (Seriola lalandi)

Yellowtail kingfish (Seriola lalandi) is a pelagic piscivore distributed circumglobally. Owing to its great market value, the growth mechanism of S. lalandi, including muscle development and growth, is a hot research topic. The myoblast determination protein (MyoD) gene has been shown to play an important role in formation of myoblasts and the function of somites in fish. The open reading frame (ORF) sequences of MyoD1 and MyoD2 in S. lalandi encoded 298 and 263 amino acids possessing three common characteristic domains, respectively, containing a myogenic basic domain, a bHLH domain, and a ser-rich region (helix III). S. lalandi MyoDs shared the highest identity with the MyoDs of S. dumerili. MyoDs are highly expressed in white muscle (P < 0.05) in S. lalandi. The expression level of MyoD1 mRNA was higher than that of MyoD2 mRNA during embryonic and early developmental stages, indicating that the two MyoD isoforms may have different roles in muscle formation. Moreover, the mRNA expression of MyoDs in the brain, pituitary, liver and muscle of endocrine growth axis were analyzed in the various sizes and ages stages. The expression levels of MyoDs in the different sizes and ages of S. lalandi showed that expression of both these genes was particularly high in 400-g fish and 2-year-old fish (P < 0.05). Moreover, the increases in the mRNA expression and plasma levels of growth hormone (GH) and insulin-like growth factor (IGF-I) were accompanied by an increase in mRNA expression of MyoDs, indicating the roles of GH and IGF-I in muscle development and growth of S. lalandi. Overall, the expression profiles of genes associated with muscle development are the first step taken towards deciphering fast growth mechanism in this important Seriola fish.

Identifying the Related Genes of Muscle Growth and Exploring the Functions by Compensatory Growth in Mandarin Fish (Siniperca chuatsi)

How organisms display many different biochemical, physiological processes through genes expression and regulatory mechanisms affecting muscle growth is a central issue in growth and development. In Siniperca chuatsi, the growth-related genes and underlying relevant mechanisms are poorly understood, especially for difference of body sizes and compensatory growth performance. Muscle from 3-month old individuals of different sizes was used for transcriptome analysis. Results showed that 8,942 different expression genes (DEGs) were identified after calculating the RPKM. The DEGs involved in GH-IGF pathways, protein synthesis, ribosome synthesis and energy metabolisms, which were expressed significantly higher in small individuals (S) than large fish (L). In repletion feeding and compensatory growth experiments, eight more significant DEGs were used for further research (GHR2, IGFR1, 4ebp, Mhc, Mlc, Myf6, MyoD, troponin). When food was plentiful, eight genes participated in and promoted growth and muscle synthesis, respectively. Starvation can be shown to inhibit the expression of Mhc, Mlc and troponin, and high expression of GHR2, IGFR1, and 4ebp inhibited growth. Fasting promoted the metabolic actions of GHR2, IGFR1, and 4ebp rather than the growth-promoting actions. MyoD can sense and regulate the hunger, which also worked with Mhc and Mlc to accelerate the compensatory growth of S. chuatsi. This study is helpful to understand the regulation mechanisms of muscle growth-related genes. The elected genes will contribute to the selective breeding in future as candidate genes.

Skeletal Muscle and the Effects of Ammonia Toxicity in Fish, Mammalian, and Avian Species: A Comparative Review Based on Molecular Research

Typically, mammalian and avian models have been used to examine the effects of ammonia on skeletal muscle. Hyperammonemia causes sarcopenia or muscle wasting, in mammals and has been linked to sarcopenia in liver disease patients. Avian models of skeletal muscle have responded positively to hyperammonemia, differing from the mammalian response. Fish skeletal muscle has not been examined as extensively as mammalian and avian muscle. Fish skeletal muscle shares similarities with avian and mammalian muscle but has notable differences in growth, fiber distribution, and response to the environment. The wide array of body sizes and locomotion needs of fish also leads to greater diversity in muscle fiber distribution and growth between different fish species. The response of fish muscle to high levels of ammonia is important for aquaculture and quality food production but has not been extensively studied to date. Understanding the differences between fish, mammalian and avian species’ myogenic response to hyperammonemia could lead to new therapies for muscle wasting due to a greater understanding of the mechanisms behind skeletal muscle regulation and how ammonia effects these mechanisms. This paper provides an overview of fish skeletal muscle and ammonia excretion and toxicity in fish, as well as a comparison to avian and mammalian species.

Genetic background and embryonic temperature affect DNA methylation and expression of myogenin and muscle development in Atlantic salmon (Salmo salar)

The development of ectothermic embryos is strongly affected by incubation temperature, and thermal imprinting of body growth and muscle phenotype has been reported in various teleost fishes. The complex epigenetic regulation of muscle development in vertebrates involves DNA methylation of the myogenin promoter. Body growth is a heritable and highly variable trait among fish populations that allows for local adaptations, but also for selective breeding. Here we studied the epigenetic effects of embryonic temperature and genetic background on body growth, muscle cellularity and myogenin expression in farmed Atlantic salmon (Salmo salar). Eggs from salmon families with either high or low estimated breeding values for body growth, referred to as Fast and Slow genotypes, were incubated at 8°C or 4°C until the embryonic 'eyed-stage' followed by rearing at the production temperature of 8°C. Rearing temperature strongly affected the growth rates, and the 8°C fish were about twice as heavy as the 4°C fish in the order Fast8>Slow8>Fast4>Slow4 prior to seawater transfer. Fast8 was the largest fish also at harvest despite strong growth compensation in the low temperature groups. Larval myogenin expression was approximately 4-6 fold higher in the Fast8 group than in the other groups and was associated with relative low DNA methylation levels, but was positively correlated with the expression levels of the DNA methyltransferase genes dnmt1, dnmt3a and dnmt3b. Juvenile Fast8 fish displayed thicker white muscle fibres than Fast4 fish, while Slow 8 and Slow 4 showed no difference in muscle cellularity. The impact of genetic background on the thermal imprinting of body growth and muscle development in Atlantic salmon suggests that epigenetic variation might play a significant role in the local adaptation to fluctuating temperatures over short evolutionary time.

Molecular characterization of Myf5 and comparative expression patterns of myogenic regulatory factors in Siniperca chuatsi

Myogenic regulatory factors (MRFs) are muscle-specific basic helix-loop-helix (bHLH) transcription factor that plays an essential role in regulating skeletal muscle development and growth. To investigate molecular characterization of Myf5 and compare the expressional patterns of the four MRFs, we cloned the Myf5 cDNA sequence and analyzed the MRFs expressional patterns using quantitative real-time polymerase chain reaction in Chinese perch (Siniperca chuatsi). Sequence analysis indicated that Chinese perch Myf5 and other MRFs shared a highly conserved bHLH domain with those of other vertebrates. Sequence alignment and phylogenetic tree showed that Chinese perch MRFs had the highest identity with the MRFs of Epinephelus coioides. Spatio-temporal expressional patterns revealed that the MRFs were primarily expressed in muscle, especially in white muscle. During embryonic development period, Myf5, MyoD and MyoG mRNAs had a steep increase at neurula stage, and their highest expressional level was predominantly observed at hatching period. Whereas the highest expressional level of the MRF4 was observed at the muscular effect stage. The expressional patterns of post-embryonic development showed that the Myf5, MyoD and MyoG mRNAs were highest at 90 days post-hatching (dph). Furthermore, starvation and refeeding results showed that the transcription of the MRFs in the fast skeletal muscle of Chinese perch responded quickly to a single meal after 7 days of fasting. It indicated that the MRFs might contribute to muscle recovery after refeeding in Chinese perch.

In ovo temperature manipulation differentially influences limb musculoskeletal development in two lines of chick embryos selected for divergent growth rates

Selective breeding has led to diverging phenotypic evolution in layer and broiler chickens through genomic and epigenetic modifications. Here we show that in ovo environmental manipulation differentially influences embryonic limb muscle phenotype in these two breeds. We demonstrate that raising incubation temperature from 37.5 to 38.5°C between embryonic days (ED) 4 and 7 increased motility and body mass in both layer and broiler embryos. In layers, this was accompanied by gastrocnemius muscle hypertrophy, increased fibre and nuclei numbers and a higher nuclei to fibre ratio (ED18), preceded by increased hindlimb Myf5 (ED5–8), Pax7 (ED5–10), BMP4 (ED6–9) and IGF-I (ED9–10, ED18) mRNAs. In broilers, the same temperature treatment led to reduced gastrocnemius cross-sectional area with fewer fibres and nuclei and an unchanged fibre to nuclei ratio (ED18). This was preceded by a delay in the peak of hindlimb Myf5 expression, increased Pax7 (ED5, ED7–10) and BMP4 (ED6–8) but reduced IGF-I (ED8–10) mRNAs. Rather than promoting myogenesis as in layer embryos, the temperature treatment promoted gastrocnemius intramuscular fat deposition in broilers (ED18) preceded by increased hindlimb PPARγ mRNA (ED7–10). The treatment increased tibia/tarsus bone length as well as femur cross-sectional area in both breeds, but femur length and bone to cartilage ratio in the femur and tibia/tarsus were only increased in treated layers (ED18). We conclude that in ovo temperature manipulation differentially affected the molecular regulation of hindlimb myogenic, adipogenic and growth factor expression in broiler and layer embryos, leading to differential changes in muscle phenotype. The underlying interactive mechanisms between genes and the environment need further investigation.

Contemporary temperature-driven divergence in a Nordic freshwater fish under conditions commonly thought to hinder adaptation

Background

Evaluating the limits of adaptation to temperature is important given the IPCC-predicted rise in global temperatures. The rate and scope of evolutionary adaptation can be limited by low genetic diversity, gene flow, and costs associated with adaptive change. Freshwater organisms are physically confined to lakes and rivers, and must therefore deal directly with climate variation and change. In this study, we take advantage of a system characterised by low genetic variation, small population size, gene flow and between-trait trade-offs to study how such conditions affect the ability of a freshwater fish to adapt to climate change. We test for genetically-based differences in developmental traits indicating local adaptation, by conducting a common-garden experiment using embryos and larvae from replicate pairs of sympatric grayling demes that spawn and develop in natural cold and warm water, respectively. These demes have common ancestors from a colonization event 22 generations ago. Consequently, we explore if diversification may occur under severely constraining conditions.

Results

We found evidence for divergence in ontogenetic rates. The divergence pattern followed adaptation predictions as cold-deme individuals displayed higher growth rates and yolk conversion efficiency than warm-deme individuals at the same temperature. The cold-deme embryos had a higher rate of muscle mass development. Most of the growth- and development differences occurred prior to hatch. The divergence was probably not caused by genetic drift as there was a strong degree of parallelism in the divergence pattern and because phenotypic differentiation (Q_ST) was larger than estimated genetic drift levels (microsatellite F_ST) between demes from different temperature groups. We also document that these particular grayling populations cannot develop successfully at temperatures above 12°C, whereas other European populations can, and that increasing the muscle mass development rate comes at the cost of some skeletal trait development rates.

Conclusions

This study shows that genetically based phenotypic divergence can prevail even under conditions of low genetic variation and ongoing gene flow. Furthermore, population-specific maximum development temperatures along with musculoskeletal developmental trade-offs may constrain adaptation.

Characterization and expression of a myosin heavy-chain isoform in juvenile walleye Sander vitreus

In this study, myosin, the major component of myofibrillar protein in the skeletal muscle, was characterized and its expression was monitored during growth in juvenile walleye Sander vitreus. First, the coding region of myosin heavy chain (MyHC) from the fast skeletal muscle of walleye was amplified by long-distance PCR using a full-length cDNA. Phylogenetic analysis was used to determine the evolutionary relationship of this S. vitreus myosin sequence to other vertebrate myosin sequences. Next, it was established that the myosin isoform was most prevalent in the white muscle, compared with the red and cardiac muscle. Myosin expression was monitored over a series of experiments designed to influence growth. Specifically, change in MyHC mRNA was monitored after acute changes in feeding. Fish exposed to a one-week fasting period showed significant decreases in MyHC mRNA levels by the end of the fast. The effect of feeding was also examined more closely over a 24 h period after feeding, but results showed no significant change in myosin expression levels through this time period. Finally, fish with higher growth rates had higher MyHC mRNA and protein expression levels. This study indicates that MyHC mRNA expression is sensitive to the factors that may influence growth in juvenile S. vitreus.

Thermally induced phenotypic plasticity of swimming performance in European sea bass Dicentrarchus labrax juveniles

The vulnerability of embryonic and larval stages of European sea bass Dicentrarchus labrax to environmental temperature and the longer-term consequences for the early juveniles was demonstrated. This phenotypic plasticity was highlighted by subjecting D. labrax at 15.2 +/- 0.3 or 20.0 +/- 0.4 degrees C (mean +/-s.d.) up to metamorphosis and then at the same temperature (18.5 +/- 0.7 degrees C). After 4-6 weeks at the same temperature, the measurement of critical swimming speed at four exercise temperatures (15, 20, 25 and 28 degrees C) showed a significantly higher swimming capacity in the fish initially reared at 15 degrees C than for fish initially reared at 20 degrees C. This performance was correlated with significant differences in the phenotype of red muscle. Thermally induced phenotypic plasticity was clearly demonstrated as an important mechanism controlling swimming performance in early juveniles of D. labrax.

Myogenesis and muscle metabolism in juvenile Atlantic salmon (Salmo salar) made transgenic for growth hormone

Atlantic salmon (Salmo salar) made transgenic for growth hormone(GH) and non-transgenic salmon were sampled at 4 and 7 months of age to estimate myogenic factors, satellite cell proliferation and metabolic enzyme activities. The growth rate of 4 month old transgenic salmon was higher than that of non-transgenic salmon. Myosatellite cell (MC) proliferation rates were higher in cells isolated from GH-transgenic salmon compared with cells from non-transgenic salmon of the same mass. Moreover, MCs extracted from non-transgenic salmon demonstrated a higher proliferation capacity when exposed in vitro to salmon GH. White muscle MyoD I mRNA content was higher in transgenic and non-transgenic salmon at 7 months compared with that at 4 months, indicating an effect of age on MyoD I mRNA expression. White muscle myogenin mRNA content varied with fish age and presence of the transgene, and was higher in transgenic fish at 7 months, suggesting a higher differentiation capacity. MyoD I, MyoD II and myogenin mRNA content was higher in red muscle of GH-transgenic fish at 7 months compared with non-transgenic salmon at 7 months. However, red muscle myogenic factor expression was not different between transgenic and non-transgenic fish of the same weight. Enzyme activities in white muscle and liver were highly affected by the presence of the transgene, although this effect was generally dependent on the age of the fish. Glycolytic and oxidative enzyme activities were increased in transgenic salmon liver, indicating a higher metabolic rate in transgenics. This study demonstrates that (1) the higher growth rate of transgenic salmon particularly at 4 months of age could be explained at least in part by higher numbers and proliferation rates of MCs, (2) GH can directly stimulate the proliferation of myosatellite cells extracted from salmon, indicating that GH is one possible factor involved in the higher myosatellite cell proliferation rates in transgenic salmon, (3) MyoD and myogenin mRNA expression are affected by fish age, and (4) metabolic enzyme activities are affected by the age of the fish at least in liver and white muscle, and any transgene effect is dependent upon the age of the fish.

Temperature influences the coordinated expression of myogenic regulatory factors during embryonic myogenesis in Atlantic salmon (Salmo salarL.)

Potential molecular mechanisms regulating developmental plasticity to temperature were investigated in Atlantic salmon embryos (Salmo salarL.). Six orthologues of the four myogenic regulatory factors (MRFs:individually: smyf5, smyoD1a/1b/1c, smyoG and sMRF4), the master transcription factors regulating vertebrate myogenesis, were characterised at the mRNA/genomic level. In situ hybridisation was performed with specific cRNA probes to determine the expression patterns of each gene during embryonic myogenesis. To place the MRF data in the context of known muscle fibre differentiation events, the expression of slow myosin light chain-1 and Pax7 were also investigated. Adaxial myoblasts expressed smyoD1a prior to and during somitogenesis followed by smyoD1c (20-somite stage, ss),and sMRF4 (25–30 ss), before spreading laterally across the myotome, followed closely by the adaxial cells. Smyf5 was detected prior to somitogenesis, but not in the adaxial cells in contrast to other teleosts studied. The expression domains of smyf5, smyoD1band smyoG were not confined to the s-smlc1 expression field,indicating a role in fast muscle myogenesis. From the end of segmentation,each MRF was expressed to a greater or lesser extent in zones of new muscle fibre production, the precursor cells for which probably originated from the Pax7 expressing cell layer external to the single layer of s-smlc1+ fibres. SmyoD1a and smyoGshowed similar expression patterns with respect to somite stage at three different temperatures investigated (2°C, 5°C and 8°C) in spite of different rates of somite formation (one somite added each 5 h, 8 h and 15 h at 8°C, 5°C and 2°C, respectively). In contrast, the expression of smyf5, sMRF4 and s-smlc1 was retarded with respect to somite stage at 2°C compared to 8°C, potentially resulting in heterochronies in downstream pathways influencing later muscle phenotype.

MyoD and Myogenin expression during myogenic phases in brown trout: a precocious onset of mosaic hyperplasia is a prerequisite for fast somatic growth

Muscle cell recruitment (hyperplasia) during myogenesis in the vertebrate embryo is known to occur in three consecutive phases. In teleost fish (including zebrafish), however, information on myogenic precursor cell activation is largely fragmentary, and comprehensive characterization of the myogenic phases has only been fully undertaken in a single slow-growing cyprinid species by examination of MEF2D expression. Here, we use molecular techniques to provide a comprehensive characterization of MyoD and Myogenin expression during myogenic cell activation in embryos and larvae of brown trout, a fast-growing salmonid with exceptionally large embryos. Results confirm the three-phase pattern, but also demonstrate that the second and third phases begin simultaneously and progress vigorously, which is different from the previously described consecutive activation of these phases. Furthermore, we suggest that Pax7 is expressed in myogenic progenitor cells that account for second- and third-phase myogenesis. These findings are discussed in relation to teleost myotome development and to teleost growth strategies.

Larval programming of post-hatch muscle growth and activity in Atlantic salmon (Salmo salar)

Larval muscle development in Atlantic salmon is known to be affected by temperature; however, the long term effects and possible mechanisms involved are less well understood. Therefore, the aim of this study was to evaluate the influence of egg incubation temperature on post-hatch muscle growth and fish activity.

Salmon eggs were incubated at either 10°C or 5°C from fertilization until hatching, then subsequently both groups were reared at 5°C. Fish from both groups were sampled at the eyed stage, 6 and 21 weeks after first feeding, for muscle cellularity analysis and immunocytochemistry. In addition,to try to establish a mechanism for altered growth, the activity of the fish was measured at 3, 6 and 21 weeks after first feeding.

Our results demonstrate that whereas fish incubated at 10°C grow faster, the fish incubated at 5°C show a more sustained period of muscle growth and by 21 weeks are significantly longer, heavier and have more muscle fibres than those fish incubated at a higher temperature. We also demonstrate that fish raised at 5°C show increased food seeking activity throughout development and that this may explain their sustained growth and muscle development.

These results taken together, demonstrate that egg incubation temperature up to hatching in salmon is critical for longer term muscle growth, twinned with increased activity. This is of interest to the aquaculture industry in term of the production of good quality fish protein.

Cloning and expression analysis of myogenin from flounder (Paralichthys olivaceus) and promoter analysis of muscle-specific expression

Myogenin is a bHLH transcription factor of the MyoD family. It plays a crucial role in myoblast differentiation and maturation. We report here the isolation of flounder myogenin gene and the characterization of its expression patterns. Sequence analysis indicated that flounder myogenin shared a similar structure and the conserved bHLH domain with other vertebrate myogenin genes. Flounder myogenin gene contains 3 exons and 2 introns. Sequence alignment and phylogenetic showed that flounder myogenin was more homologous with halibut (Hippoglossus hippoglossus) myogenin and striped bass (Morone saxatilis) myogenin. Whole-mount embryo in situ hybridization revealed that flounder myogenin was first detected in the medial region of somites that give rise to slow muscles, and expanded later to the lateral region of the somite that become fast muscles. The levels of myogenin transcripts dropped significantly in matured somites at the trunk region. Its expression could only be detected in the caudal somites, which was consistent with the timing of somite maturation. Transient expression analysis showed that the 546 bp flounder myogenin promoter was sufficient to direct muscle-specific GFP expression in zebrafish embryos.

Phases of myogenic cell activation and possible role of dermomyotome cells in teleost muscle formation

Present knowledge indicates that fibre recruitment (hyperplasia) in developing teleost fish occurs in three distinct phases. However, the origin and relationship of the myogenic precursors activated during the different phases remains unclear. Here, we address this issue using molecular techniques on embryos and larvae of pearlfish, a large cyprinid species. Results provide comprehensive molecular characterisation of cell recruitment over the three phases of myogenesis, identifying muscle types as they arise. Specifically, we show that the myogenic cells arising during 2nd phase myogenesis are clearly different from the myogenic cells arising during the 3rd phase and that the dermomyotome is a major source of myogenic cells driving 2nd phase hyperplasia. These findings are discussed in relation to their implications for the generality of vertebrate developmental patterns.

Environment and plasticity of myogenesis in teleost fish

Embryonic development in teleosts is profoundly affected by environmental conditions, particularly temperature and dissolved oxygen concentrations. The environment determines the rate of myogenesis, the composition of sub-cellular organelles, patterns of gene expression, and the number and size distribution of muscle fibres. During the embryonic and larval stages, muscle plasticity to the environment is usually irreversible due to the rapid pace of ontogenetic change. In the early life stages, muscle can affect locomotory performance and behaviour, with potential consequences for larval survival. Postembryonic growth involves myogenic progenitor cells (MPCs) that originate in the embryo. The embryonic temperature regime can have long-term consequences for the growth of skeletal muscle in some species, including the duration and intensity of myotube formation in adult stages. In juvenile and adult fish, abiotic (temperature, day-length, water flow characteristics, hypoxia) and biotic factors (food availability, parasitic infection) have complex effects on the signalling pathways regulating the proliferation and differentiation of MPCs, protein synthesis and degradation, and patterns of gene expression. The phenotypic responses observed to the environment frequently vary during ontogeny and are integrated with endogenous physiological rhythms, particularly sexual maturation. Studies with model teleosts provide opportunities for investigating the underlying genetic mechanisms of muscle plasticity that can subsequently be applied to non-model species of more ecological or commercial interest.

Somite formation and expression ofMyoD,myogeninandmyosinin Atlantic halibut (Hippoglossus hippoglossusL.)embryos incubated at different temperatures: transient asymmetric expression ofMyoD

Genes encoding the myogenic regulating factors MyoD and myogenin and the structural muscle proteins myosin light chain 2 (MyLC2) and myosin heavy chain(MyHC) were isolated from juvenile Atlantic halibut (Hippoglossus hippoglossus L.). The impact of temperature on their temporal and spatial expression during somitogenesis were examined by incubating halibut embryos at 4, 6 and 8°C, and regularly sampling for whole-mount in situhybridisation and reverse transcription (RT)–PCR.

There were no significant effects of temperature on the onset of somitogenesis or number of somites at hatching. The rate of somite formation increased with increasing temperature, and the expression of MyoD, myogenin and MyHC followed the cranial-to-caudal somite formation. Hence, no significant effect of temperature on the spatial and temporal expression of the genes studied was found in relation to somite stage. MyoD, which has subsequently been shown to encode the MyoD2 isoform, displayed a novel bilaterally asymmetric expression pattern only in white muscle precursor cells during early halibut somitogenesis. The expression of myogenin resembled that previously described for other fish species, and preceded the MyHC expression by approximately five somites. Two MyLC2 cDNA sequences were for the first time described for a flatfish, probably representing embryonic (MyLC2a) and larval/juvenile(MyLC2b) isoforms.

Factors regulating muscle determination, differentiation and development have so far mostly been studied in vertebrates with external bilateral symmetry. The findings of the present study suggest that more such investigations of flatfish species could provide valuable information on how muscle-regulating mechanisms work in species with different anatomical,physiological and ecological traits.

Alterations in expression of genes associated with muscle metabolism and growth during nutritional restriction and refeeding in rainbow trout

Rainbow trout, as well as many other species of fish, demonstrate the ability to survive starvation for long periods of time. During starvation, growth rate is decreased and muscle exhibits signs of wasting. However, upon resumption of feeding, accelerated growth is often observed. Alterations in muscle metabolism occur during feed restriction and refeeding, although the ways in which these alterations affect the molecular pathways that control muscle growth have not been fully determined. To analyze changes in muscle metabolism and growth during starvation and refeeding, real-time PCR was used to test the expression of six metabolic-related genes and eight muscle-specific genes in rainbow trout white muscle prior to and after 30 days of starvation, and after 4 and 14 days of refeeding. The six metabolic-related genes chosen are indicative of specific metabolic pathways: glycolysis, glycogenesis, gluconeogenesis, the pentose phosphate pathway, and fatty acid formation. The eight muscle specific genes chosen are key components in muscle growth and structural integrity, i.e., MRFs, MEFs, myostatins, and myosin. Alterations in expression of the tested metabolic-related genes and muscle-specific genes suggest that during both starvation and refeeding, changes in specific metabolic pathways initiate shifts in muscle that result mainly in the modification of myotube hypertrophy. The expression levels of many of the metabolic-related genes were altered during the refeeding period compared to those observed before the starvation period began. However, the accelerated growth often observed during refeeding is likely driven by changes in normal muscle metabolism, and the altered expression observed here may be a demonstration of those changes.

Myogenin in model pufferfish species: Comparative genomic analysis and thermal plasticity of expression during early development

Myogenin (Myog) is a muscle-specific basic helix-loop-helix transcription factor that plays an essential role in the specification and differentiation of myoblasts. The myogenin genes from the tiger pufferfish, Takifugu rubripes, and green-spotted pufferfish, Tetraodon nigroviridis, were cloned and a comparative genomic analysis performed. The gene encoding myogenin is composed of three exons and has a relatively similar genomic structure in T. rubripes, T. nigroviridis and human. Introns 1 and 2 were approximately 2-fold and 8-fold longer respectively in human than pufferfish. Myogenin is located in a 100 kb region of conserved synteny between these organisms, corresponding to chromosome 1 in human, chromosome 11 in T. nigroviridis and scaffold 208 in T. rubripes. Pufferfish myogenin contained a serine-rich region at the carboxyl terminus that is highly conserved amongst teleosts. During embryonic development of T. rubripes, myogenin was expressed in a rostral-caudal gradient in the developing somites and subsequently during the pharyngula period in the pectoral fin bud primordia, jaw muscles and extraocular muscle precursors. In T. rubripes, the time required to form a somite pair during the linear phase of somitogenesis ( identical withsomite-interval) was 122 min, 97 min and 50 min in embryos incubated at 15, 18 and 21 degrees C, respectively. Myogenin mRNA transcripts were quantified using qPCR and normalised to the highest level of expression. Peak myogenin expression occurred later with respect to developmental stage (standardised using somite-intervals) and was over 2-fold higher at 21 degrees C than at either 18 or 15 degrees C. Changes in the relative timing and intensity of myogenin expression are a potential mechanism for explaining thermal plasticity of muscle phenotype in larvae via effects on the differentiation programme.

Temperature and the expression of myogenic regulatory factors (MRFs) and myosin heavy chain isoforms during embryogenesis in the common carp Cyprinus carpio L

Embryos of the common carp, Cyprinus carpio L., were reared from fertilization of the eggs to inflation of the swim bladder in the larval stage at 18 and 25 degrees C. cRNA probes were used to detect transcripts of the myogenic regulatory factors MyoD, Myf-5 and myogenin, and five myosin heavy chain (MyHC) isoforms during development. The genes encoding Myf-5 and MyoD were switched on first in the unsegmented mesoderm, followed by myogenin as the somites developed. Myf-5 and MyoD transcripts were initially limited to the adaxial cells, but Myf-5 expression spread laterally into the presomitic mesoderm before somite formation. Two distinct bands of staining could be seen corresponding to the cellular fields of the forming somites, but as each furrow delineated, Myf-5 mRNA levels declined. Upon somite formation, MyoD expression spread laterally to encompass the full somite width. Expression of the myogenin gene was also switched on during somite formation, and expression of both transcripts persisted until the somites became chevron-shaped. Expression of MyoD was then downregulated shortly before myogenin. The expression patterns of the carp myogenic regulatory factor (MRF) genes most-closely resembled that seen in the zebrafish rather than the rainbow trout (where expression of MyoD remains restricted to the adaxial domain of the somite for a prolonged period) or the herring (where expression of MyoD persists longer than that of myogenin). Expression of two embryonic forms of MyHC began simultaneously at the 25-30 somite stage and continued until approximately two weeks post-hatch. However, the three adult isoforms of fast muscle MyHC were not detected in any stage examined, emphasizing a developmental gap that must be filled by other, as yet uncharacterised, MyHC isoform(s). No differences in the timing of expression of any mRNA transcripts were seen between temperature groups. A phylogenetic analysis of the MRFs was conducted using all available full-length amino acid sequences. A neighbour-joining tree indicated that all four members evolved from a common ancestral gene, which first duplicated into two lineages, each of which underwent a further duplication to produce Myf-5 and MyoD, and myogenin and MRF4. Parologous copies of MyoD from trout and Xenopus clustered closely together within clades, indicating recent duplications. By contrast, MyoD paralogues from gilthead seabream were more divergent, indicating a more-ancient duplication.

In ovo temperature manipulation influences post-hatch muscle growth in the turkey

1. The effect of manipulating egg incubation temperature for short periods on turkey muscle development was determined using the M. semitendinosus, a thigh muscle, as the model. 2. Experiment 1. Eggs were incubated at a control temperature of 37.5 degrees C. For a 4-d period of 0 to 4, 5 to 8, 9 to 12, 13 to 16, 17 to 20 or 21 to 24 embryonic days (ED) eggs were transferred to either 38.5 or 35.5 degrees C. A regime of 38.5 degrees C at 5 to 8 and 9 to 12 ED caused an increased myonuclei number and muscle fibre number, respectively. 3. Experiment 2. Eggs were incubated at a control temperature of 37.5 degrees C. At 5 to 8 ED eggs were transferred to 38.5 or 35.5 degrees C. Temperature-manipulated embryos showed a delay in differentiation (myogenin expression) of the semitendinosus muscle compared to controls. 4. Manipulating the incubation temperature for 4 d in early incubation alters muscle development in the turkey with no observation of deformities or reduction in hatchability. We speculate that this increase in temperature may result in an improved muscle growth in the post-hatch bird.

Temperature and the expression of seven muscle-specific protein genes during embryogenesis in the Atlantic cod Gadus morhua L

Seven cDNA clones coding for different muscle-specific proteins (MSPs) were isolated from the fast muscle tissue of Atlantic cod Gadus morhua L. In situ hybridization using cRNA probes was used to characterize the temporal and spatial patterns of gene expression with respect to somite stage in embryos incubated at 4 degrees C, 7 degrees C and 10 degrees C. MyoD transcripts were first observed in the presomitic mesoderm prior to somite formation, and in the lateral compartment of the forming somites. MyoD expression was not observed in the adaxial cells that give rise to the slow muscle layer, and expression was undetectable by in situ hybridization in the lateral somitic mesoderm after the 35-somite stage, during development of the final approximately 15 somites. RT-PCR analysis, however, confirmed the presence of low levels of the transcript during these later stages. A phylogenetic comparison of the deduced aminoacid sequences of the full-length MyoD cDNA clone and those from other teleosts, and inference from the in situ expression pattern suggested homology with a second paralogue (MyoD2) recently isolated from the gilthead seabream Sparus aurata. Following MyoD expression, alpha-actin was the first structural gene to be switched on at the 16-somite stage, followed by myosin heavy chain, troponin T, troponin I and muscle creatine kinase. The final mRNA in the series to be expressed was troponin C. All genes were switched on prior to myofibril assembly. The troponin C sequence was unusual in that it showed the greatest sequence identity with the rainbow trout Oncorhynchus mykiss cardiac/slow form, but was expressed in the fast myotomal muscle and not in the heart. In addition, the third TnC calcium binding site showed a lower level of sequence conservation than the rest of the sequence. No differences were seen in the timing of appearance or rate of posterior progression (relative to somite stage) of any MSP transcripts between embryos raised at the different temperatures. It was concluded that myofibrillar genes are activated asynchronously in a distinct temporal order prior to myofibrillar assembly and that this process was highly canalized over the temperature range studied.

Expression, purification and DNA-binding activity of tilapia muscle-specific transcription factor, MyoD, produced in Escherichia coli

MyoD is one of several helix-loop-helix proteins regulating muscle-specific gene expression. Using a reverse transcription-polymerase chain reaction, 5'-rapid cDNA end amplification, and plaque hybridization, MyoD cDNA was cloned from the mRNA of tilapia dorsal skeletal muscle. The 1015 bp MyoD cDNA product contained an 846 bp open reading frame with flanking regions of 115 and 64 bp at the 5'- and 3'-ends, respectively. Results showed that the tilapia MyoD sequence, which includes one polypeptide of 281 amino acids, shared sequence identities of 64.3, 64.1, 62.6 and 62.4% with those of zebrafish, carp, and two rainbow trout, respectively. Results from a molecular phylogenic tree assay showed that the tilapia MyoD was more closely related to those of other fishes than of higher vertebrates. Using Escherichia coli, a pET expression system, and an Ni(2+)-NTA column, we purified approximately 35 kDa recombinant tilapia MyoD. Results from an electrophoretic mobility shift assay demonstrated that the purified E. coli-produced tilapia MyoD was capable of binding to the DNA fragment sequence CA(C/T)(C/A)TG.