Messenger ribonucleic acid expression of the MyoD gene family in muscle tissue at slaughter in relation to selection for porcine growth rate.

Livestock meat production capacity is related to muscle fiber numbers and growth. Muscle fibers develop during early embryonic development from proliferating and differentiating myoblasts. Post-natal muscle growth requires satellite cell proliferation and differentiation. Myoblast and satellite cell proliferation and differentiation is regulated by the genes of the MyoD gene family (myogenin, myf-5, myf-6, and MyoD1). Our aim was to study the mRNA expression of these genes in postnatal muscle tissue in relation to porcine selection for growth rate or leanness. Five boars from a line selected for fast growth (F-line) and five boars from a line selected against backfat thickness (L-line) were slaughtered, and biopsies were taken from 12 muscles. Between-line effects, within-line effects in relation to the performance of the pigs, and muscle-specific effects were studied. Comparing the F-line with the L-line revealed significantly greater myogenin, myf-5, and MyoD1 mRNA expression in some muscles of the F-line. The expression of myf-6 showed a tendency for the opposite effect in some muscles. Muscles were ordered by their muscle-specific growth rate (b-value). Within-line evaluation of the data revealed a systematic muscle effect for the myf-6 expression level in the F-line because higher b-values correlated with increased myf-6 expression level. Backfat thickness was negatively related to myogenin expression in the F-line. A relationship was found between myogenin:MyoD1 mRNA expression ratio and meat color/muscle fiber type composition in the L-line. Furthermore, the myogenin:MyoD1 ratio was greater in muscles from F-line boars than in muscles from L-line boars, which relates to the difference between the lines in muscle fiber type. We conclude that the mRNA levels of the MyoD genes in porcine muscle tissue at slaughter showed different relationships to selection for growth rate when evaluated between selection lines and within selection lines.