title: Quantitative expression of myogenic regulatory factors MyoD and myogenin in pacu (Piaractus mesopotamicus) skeletal muscle during growth.
abstract: 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.
authors.affiliation: UNESP, Institute of Biosciences, Department of Morphology, 18618-000, Botucatu, São Paulo, Brazil. fernandalosi@gmail.com
authors.forename: Fernanda Losi Alves
authors.initials: FL
authors.lastname: de Almeida
authors.forename: Nabila Scabine
authors.initials: NS
authors.lastname: Pessotti
authors.forename: Danillo
authors.initials: D
authors.lastname: Pinhal
authors.forename: Carlos Roberto
authors.initials: CR
authors.lastname: Padovani
authors.forename: Natália de Jesus
authors.initials: Nde J
authors.lastname: Leitão
authors.forename: Robson Francisco
authors.initials: RF
authors.lastname: Carvalho
authors.forename: Cesar
authors.initials: C
authors.lastname: Martins
authors.forename: Maria Célia
authors.initials: MC
authors.lastname: Portella
authors.forename: Maeli
authors.initials: M
authors.lastname: Dal Pai-Silva
mesh_terms: D000818:Animals; D005399:Fishes / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006984:Hypertrophy; D018482:Muscle, Skeletal / Q000254:growth & development / Q000502:physiology*; D017570:MyoD Protein / Q000096:biosynthesis* / Q000235:genetics; D018008:Myogenin / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017570:MyoD Protein; D018008:Myogenin