Molecular Mechanisms Regulating Muscle Plasticity in Fish

Simple Summary Muscle plasticity is defined as the ability of the muscle to respond to changes in environmental conditions. Muscle plasticity is exceptionally dynamic in fish; this is attributed in part to their ectothermic (cold-blooded) nature and ability of indeterminate or continual growth, throughout their lifespans. The molecular mechanisms regulating muscle growth in fish are not completely characterized; however, recent advancements have established that microRNAs and DNA methylation are important mechanisms regulating muscle plasticity. This review examines these mechanisms and describes how they are regulated by genetic and environmental (i.e., nutrition, temperature) factors and they in turn affect muscle growth and plasticity in fish. Growth rates in fish are largely dependent on genetic and environmental factors, of which the latter can be highly variable throughout development. For this reason, muscle growth in fish is particularly dynamic as muscle structure and function can be altered by environmental conditions, a concept referred to as muscle plasticity. Myogenic regulatory factors (MRFs) like Myogenin, MyoD, and Pax7 control the myogenic mechanisms regulating quiescent muscle cell maintenance, proliferation, and differentiation, critical processes central for muscle plasticity. This review focuses on recent advancements in molecular mechanisms involving microRNAs (miRNAs) and DNA methylation that regulate the expression and activity of MRFs in fish. Findings provide overwhelming support that these mechanisms are significant regulators of muscle plasticity, particularly in response to environmental factors like temperature and nutritional challenges. Genetic variation in DNA methylation and miRNA expression also correlate with variation in body weight and growth, suggesting that genetic markers related to these mechanisms may be useful for genomic selection strategies. Collectively, this knowledge improves the understanding of mechanisms regulating muscle plasticity and can contribute to the development of husbandry and breeding strategies that improve growth performance and the ability of the fish to respond to environmental challenges.