Abstract
Pacu (Piaractus mesopotamicus) is a Brazilian fish with a high economic value in pisciculture due to its rusticity and fast growth. Postnatal growth of skeletal muscle in fish occurs by hyperplasia and/or hypertrophy, processes that are dependent on the proliferation and differentiation of myoblasts. A class of small noncoding RNAs, known as microRNAs (miRNAs), represses the expression of target mRNAs, and many studies have demonstrated that miR-1, miR-133, miR-206 and miR-499 regulate different processes in skeletal muscle through the mRNA silencing of hdac4 (histone deacetylase 4), srf (serum response factor), pax7 (paired box 7) and sox6 ((sex determining region Y)-box 6), respectively. The aim of our work was to evaluate the expression of these miRNAs and their putative target mRNAs in fast- and slow-twitch skeletal muscle of pacu during growth. We used pacus in three different development stages: larval (aged 30 days), juvenile (aged 90 days and 150 days) and adult (aged 2 years). To complement our study, we also performed a pacu myoblast cell culture, which allowed us to investigate miRNA expression in the progression from myoblast proliferation to differentiation. Our results revealed an inverse correlation between the expression of the miRNAs and their target mRNAs, and there was evidence that miR-1 and miR-206 may regulate the differentiation of myoblasts, whereas miR-133 may regulate the proliferation of these cells. miR-499 was highly expressed in slow-twitch muscle, which suggests its involvement in the specification of the slow phenotype in muscle fibers. The expression of these miRNAs exhibited variations between different development stages and between distinct muscle twitch phenotypes. This work provides the first identification of miRNA expression profiles in pacu skeletal muscle and suggests an important role of these molecules in muscle growth and in the maintenance of the muscle phenotype.
Highlights
Piaractus mesopotamicus, popularly known as pacu, is a fish whose distribution is more concentrated in the wetland areas of the Brazilian Midwest region, and it is one of the most studied fish in this country [1]
The expression of miR-1 in the fast-twitch muscle was upregulated 10-fold in 2-year-old pacus (p
The expression patterns of miR-1, miR-133a, miR-133b, miR-206 and miR-499 indicate a possible role in the regulation of skeletal muscle in pacu, controlling factors involved in the myoblast proliferation and differentiation, and in the specification and maintenance of the twitch phenotypes in muscle fibers (Fig 9)
Summary
Popularly known as pacu, is a fish whose distribution is more concentrated in the wetland areas of the Brazilian Midwest region, and it is one of the most studied fish in this country [1] This species is characterized by rusticity, fast growth, adaptation to artificial feeding and tasty meat [2], and has a high market value to Brazilian fishery and pisciculture. Postnatal muscle growth in fish involves cells localized at the periphery of muscle fibers, known as satellite cells These cells give rise to myoblasts, the proliferation and differentiation of which are the mechanisms that promote hyperplasia (an increase in muscle fiber number) and hypertrophy (an increase in muscle fiber size) [5,6]. MRFs include MyoD, which regulates the specification and proliferation of myoblasts, and Myogenin, which is involved in the differentiation and fusion of these cells [7]
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