Quantitative expression of myogenic regulatory factors MyoD and myogenin in pacu (Piaractus mesopotamicus) skeletal muscle during growth

UNESP, Institute of Biosciences, Department of Morphology, 18618-000, Botucatu, São Paulo, Brazil.
Micron (Impact Factor: 1.99). 12/2010; 41(8):997-1004. DOI: 10.1016/j.micron.2010.06.012
Source: PubMed


Skeletal muscle growth is regulated by differential expression of myogenic regulatory factors (MRFs). We evaluated hyperplasia, hypertrophy and quantitative expression of MRFs MyoD and myogenin in 45, 90, 180, and 400 days post-hatching (dph) and adult pacu (Piaractus mesopotamicus) skeletal muscle. Transverse sections of white dorsal muscles were obtained to evaluate hypertrophy and hyperplasia. MyoD and myogenin gene expression was determined by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR). Pacu skeletal muscle had similar morphology at all stages. The highest and the lowest frequencies of fiber diameters <20 μm were found at the 45 dph and adult stages, respectively. Their frequency was similar in the 90, 180, and 400 dph stages. The highest percentage of >50 μm diameter fibers were found in 180 and 400 dph, and adult fish. Hyperplasia was the main mechanism observed in pacu skeletal muscle growth at 45dph; this declined through 90, 180, and 400 dph and remained low in adult fish; the latter presented hypertrophy as the main mechanism responsible for skeletal muscle growth. The high frequencies of 20-50 μm diameter fibers at 90, 180, and 400 dph can be related to intense hypertrophy. The mRNA levels for MyoD and myogenin were similar in 45, 90, and 400 dph and adult fish, peaking at 180 dph. The high MyoD expression at 180 dph can be related to intense myoblast proliferation and hyperplasia, while high myogenin expression can be related to intense myoblast differentiation and fusion during hypertrophy. MyoD and myogenin expression patterns in adults can respectively be associated with myoblast proliferation and differentiation, which both contribute to hypertrophy. Differential MyoD and myogenin expression in pacu white muscle probably is associated with differences in growth patterns during the stages analyzed. In this study, the 180 dph pacu could represent an interesting phase to investigate suitable strategies in commercial fish production focusing on skeletal muscle growth improvement to raise healthy, fast-growing fish.

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Available from: Robson Carvalho, Jul 07, 2015
    • "MyoD and myf-5 control myogenic lineage determination and myoblast activation and proliferation, whereas myogenin and mrf4 control the differentiation and fusion of myoblasts to form myofibers (for review see Johnston, 2006). Hyperplasia is the main skeletal muscle growth mechanism in pacu at 45 dph (TL of 22 mm) (Fig. 1E), decreasing over the course of development and remaining low in adult fish (Almeida et al., 2010). In pacu larvae and juveniles, hyperplasia predominance in muscle growth is associated with high levels of MyoD expression (Almeida et al., 2008; Leitão et al., 2011). "
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    • "The basic helix-loop-helix myogenic regulatory factors, including MyoD, Myf-5, and myogenin, play seminal functions that trigger the expression of myofibrillar proteins and permit the assembly of functional muscle fibers [25]. Muscle fiber hyperplasia occurs with high expression of MyoD and Myf-5 proteins [26]. Myogenin is required for committed cells to terminally differentiate into myocytes and mature into muscle fibers, thus associated with muscle fiber hyperplasia and hypertrophy [27]. "
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