Project description:Background A unique feature of fish is that new muscle fibres continue to be produced throughout much of the life cycle; a process termed muscle hyperplasia. In trout, this process begins in the late embryo stage and occurs in both a discrete, continuous layer at the surface of the primary myotome (stratified hyperplasia) and between existing muscle fibres throughout the myotome (mosaic hyperplasia). In post-larval stages, muscle hyperplasia is only of the mosaic type and persists until 40% of the maximum body length is reached. To characterise the genetic basis of myotube neoformation in trout, we combined laser capture microdissection and microarray analysis to compare the gene expression profile of hyperplastic areas of the late embryo myotome with that of adult myotomal muscle which displays only limited muscle hyperplasia. Results. Gene expression was analysed using Agilent trout oligo microarrays. Our analysis identified more than 6800 transcripts that were significantly up-regulated in the superficial hyperplastic zones of the late embryonic myotome compared to adult myotomal muscle. In addition to Pax3, Pax7 and the fundamental myogenic basic helix-loop-helix regulators, we identified a large set of up-regulated transcriptional factors, including Myc paralogs, members of Hes family and many homeobox-containing transcriptional regulators. Other cell-autonomous regulators overexpressed in hyperplastic zones included a large set of cell surface proteins belonging to the Ig superfamily. Among the secreted molecules found to be overexpressed in hyperplastic area, we noted growth factors as well as signalling molecules. A novel finding in our study is that many genes that regulate planar cell polarity (PCP) were overexpressed in superficial hyperplastic zones, suggesting that the PCP pathway is involved in the oriented elongation of the neofibres. Our microarray results were validated by in situ hybridisation of transcripts overexpressed in laser captured growth zones. Conclusion. The results obtained in this study provide a valuable resource for further analysis of novel genes potentially involved in hyperplastic muscle growth in fish. Ultimately, this study could yield insights into particular genes, pathways or cellular processes that may potentially regulate muscle regeneration in other vertebrates. To characterise the genetic basis of myotube neoformation in trout, we combined laser capture microdissection and microarray analysis to compare the gene expression profile of hyperplastic areas of the late embryo myotome (peripheral and deep domains) with that of adult myotomal muscle which displays only limited muscle hyperplasia.

Project description:Methods for studying mitochondrial adaptations in skeletal muscle have mostly used whole-muscle samples, where results may be confounded by the presence of a mixture of type I and II skeletal muscle fibres. In this project, we utilised the latest Mass spectrometry (MS) techniques to provide new insights into mitochondrial adaptations in type I and II fibres in response to two different types of training – moderate-intensity-continuous training (MICT) and sprint-interval training (SIT). An 8-week training intervention was undertaken by 23 men who performed either MICT or SIT. Single muscle fibres from skeletal muscle biopsies were collected at rest, before and after the 8 weeks of training, and pooled for subsequent MS analysis. A proteomic workflow was applied that permitted a three-tiered comparison and quantification of mitochondrial proteins in different fibre types. Our protocol includes tandem mass tag labelling for increased identification of low-abundant proteins. We quantified more than 45% of known mitochondrial proteins in skeletal muscle. When comparing type I to type II fibres,24 mitochondrial proteins were differentially expressed following MICT and 10 following SIT. These altered proteins were associated with known cellular pathways within the mitochondria, including oxidative phosphorylation, the TCA cycle and fatty acid oxidation. There were distinct trends for fibre-type-specific protein responses to different types of exercise training. Following MICT proteins mostly increased in abundance in type I fibres, without analogous changes observed following SIT. This greater upregulation of mitochondrial proteins observed following MICT, suggests exercise volume is a powerful stimulus for mitochondrial adaptations. This upregulation mostly seen in type I fibres is consistent with the predominate recruitment of this fibre type with MICT. When normalised to mitochondrial content further evidence to fibre-specific non-stoichiometrically induced increases in the expression of fatty acid mitochondrial proteins is presented, highlighting mitochondria as a pivotal subcellular site in facilitating substrate utilisation to increase ATP production in type I fibres. Conversely, the research suggests very high-intensity exercise training altered the systematic biogenesis of oxidative phosphorylation (OXPHOS) components, in particular complex IV subunits of the OXPHOS pathway. These results question the existing knowledge of fibre-type-specific changes to mitochondrial proteins in response to exercise training and provide a valuable contribution to understanding the mechanisms by which exercise helps to improve health and prevent disease.

Project description:Compensatory growth is a phase of rapid growth, greater than the growth rate of control animals, that occurs after a period of growth-stunting conditions. Fish show a capacity for compensatory growth after alleviation of dietary restriction, but the underlying cellular mechanisms are unknown. To learn more about the contribution of genes regulating hypertrophy (an increase in muscle fibre size) and hyperplasia (the generation of new muscle fibres) in the compensatory muscle growth response in fish, we used high-density microarray analysis to investigate the global gene expression in muscle of trout during a fasting-refeeding schedule and in muscle of control-fed trout displaying normal growth.The compensatory muscle growth signature, as defined by genes up-regulated in muscles of refed trout compared with control-fed trout, showed enrichment in functional categories related to protein biosynthesis and maturation, such as RNA processing, ribonucleoprotein complex biogenesis, ribosome biogenesis, translation and protein folding. This signature was also enriched in chromatin-remodelling factors of the protein arginine N-methyl transferase family. Unexpectedly, functional categories related to cell division and DNA replication were not inferred from the molecular signature of compensatory muscle growth, and this signature contained virtually none of the genes previously reported to be up-regulated in hyperplastic growth zones of the late trout embryo myotome and to potentially be involved in production of new myofibres, notably genes encoding myogenic regulatory factors, transmembrane receptors essential for myoblast fusion or myofibrillar proteins predominant in nascent myofibres.Genes promoting myofibre growth, but not myofibre formation, were up-regulated in muscles of refed trout compared with continually fed trout. This suggests that a compensatory muscle growth response, resulting from the stimulation of hypertrophy but not the stimulation of hyperplasia, occurs in trout after refeeding. The generation of a large set of genes up-regulated in muscle of refed trout may yield insights into the molecular and cellular mechanisms controlling skeletal muscle mass in teleost and serve as a useful list of potential molecular markers of muscle growth in fish.

Project description:The dramatic increase in myotomal muscle mass in fish is related to their ability to lastingly produce new muscle fibres, a process termed hyperplasia. The molecular and cellular mechanisms underlying fish muscle hyperplasia largely remain unknown. In this study, we aimed to characterize intrinsic properties of myogenic cells originating from fish hyperplasic muscle. For this purpose, we compared in situ proliferation, in vitro cell behavior and transcriptomic profile of myogenic precursors originating from hyperplasic muscle of juvenile trout (JT) and from non-hyperplasic muscle of fasted juvenile trout (FJT) and adult trout (AT). For the first time, we showed that myogenic precursors proliferate in hyperplasic muscle from JTas shown by in vivo BrdU labeling. This proliferative rate was very low in AT and FJT muscle. Transcriptiomic analysis revealed that myogenic cells from FJT and AT displayed close expression profiles with only 64 differentially expressed genes (BH corrected p-val < 0.001). In contrast, 2623 differentially expressed genes were found between myogenic cells from JT and from both FJT and AT. Functional categories related to translation, mitochondrial activity, cell cycle, and myogenic differentiation were inferred from genes up regulated in JT compared to AT and FJT myogenic cells. Conversely, Notch signaling pathway, that signs cell quiescence, was inferred from genes down regulated in JT compared to FJT and AT. In line with our transcriptomic data JT myogenic precursors displayed higher proliferation and differentiation capacities than FJT and AT myogenic precursors. The transcriptomic analysis and examination of cell behavior converge to support the view that myogenic cells extracted from hyperplastic muscle of juvenile trout are intrinsically more potent to form myofibres than myogenic cells extracted from non-hyperplasic muscle. The generation of gene expression profiles in myogenic cell extracted from muscle of juvenile trout may yield insights into the molecular and cellular mechanisms controlling hyperplasia and provides a useful list of potential molecular markers of hyperplasia.

Project description:Background A unique feature of fish is that new muscle fibres continue to be produced throughout much of the life cycle; a process termed muscle hyperplasia. In trout, this process begins in the late embryo stage and occurs in both a discrete, continuous layer at the surface of the primary myotome (stratified hyperplasia) and between existing muscle fibres throughout the myotome (mosaic hyperplasia). In post-larval stages, muscle hyperplasia is only of the mosaic type and persists until 40% of the maximum body length is reached. To characterise the genetic basis of myotube neoformation in trout, we combined laser capture microdissection and microarray analysis to compare the gene expression profile of hyperplastic areas of the late embryo myotome with that of adult myotomal muscle which displays only limited muscle hyperplasia. Results. Gene expression was analysed using Agilent trout oligo microarrays. Our analysis identified more than 6800 transcripts that were significantly up-regulated in the superficial hyperplastic zones of the late embryonic myotome compared to adult myotomal muscle. In addition to Pax3, Pax7 and the fundamental myogenic basic helix-loop-helix regulators, we identified a large set of up-regulated transcriptional factors, including Myc paralogs, members of Hes family and many homeobox-containing transcriptional regulators. Other cell-autonomous regulators overexpressed in hyperplastic zones included a large set of cell surface proteins belonging to the Ig superfamily. Among the secreted molecules found to be overexpressed in hyperplastic area, we noted growth factors as well as signalling molecules. A novel finding in our study is that many genes that regulate planar cell polarity (PCP) were overexpressed in superficial hyperplastic zones, suggesting that the PCP pathway is involved in the oriented elongation of the neofibres. Our microarray results were validated by in situ hybridisation of transcripts overexpressed in laser captured growth zones. Conclusion. The results obtained in this study provide a valuable resource for further analysis of novel genes potentially involved in hyperplastic muscle growth in fish. Ultimately, this study could yield insights into particular genes, pathways or cellular processes that may potentially regulate muscle regeneration in other vertebrates.

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Global gene expression in muscle from fasted/refed trout reveals up-regulation of genes promoting myofibre hypertrophy but not myofibre production

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