Skeletal muscle in fish comprises 40-60% of total body and the growth occurs by fibers hypertrophy and/or hyperplasia, mechanisms that vary among the species, stage of development and nutritional status. The growth, development and muscle phenotype are controlled by pathways responsible for muscle-specific genes activation or inhibition, events that can regulate muscle catabolic and anabolic state. Based on this information, studies involving the molecular mechanisms controlling the muscle mass are fundamental to better understand the changes in anabolic and catabolic homeostasis that can occur during fasting and refeeding conditions. In this study we will evaluate the skeletal muscle of pacu (300g) during periods of fasting (10 days) and refeeding (05 days) in the following parameters: (a) muscle fibers morphology and morphometry, (b) gene expression of the components of the pathways related to catabolism (Foxo - MuRF - MAFbx) and anabolism (IGF - PI3K - AKT - mTOR) and the MyoD family of transcription factors (MyoD , Myf5 , myogenin and MRF4), (c) the expression profile of muscle specific microRNAs (miR - 1, miR - 133a, miR - 133b, miR - 206 and miR -499) and yours target genes highly expressed in vivo and (d) the differentially expressed microRNAs and target genes after silencing in primary culture of myoblasts. The fish will be rearing in tanks of water (0.5m³) with distinct recirculation systems. Samples of red and white muscle (n = 10) will be removed every 2 days of fasting and every 6 hours of refeeding periods. In the experiments in vivo and in vitro, the gene expression and microRNAs will be detected by quantitative real-time polymerase Chain Reaction (RT-qPCR).The silencing of microRNAs more expressed in vivo in red and white muscles during fasting will be realized, in vitro, using oligonucleotide antisense inhibitors.The data will be submitted to appropriate statistical analysis after normality and homoscedasticity tests.
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