title: Time course of changes in markers of myogenesis in overloaded rat skeletal muscles.
abstract: During the process of compensatory muscle hypertrophy, satellite cells are thought to proliferate, differentiate, and then fuse with existing myofibers. We hypothesized that early in this process changes occur in the expression of cellular markers indicative of the onset of myogenic processes. The plantaris muscles of rats were overloaded via the unilateral ablation of synergists. Groups of rats were killed at time points from 6 h to 12 days. Changes in muscle gene expression (mRNA) of cyclin D1, p21, myogenin, MyoD, and insulin-like growth factor I (IGF-I, mRNA and peptide) were measured. Cyclin D1 (a cell cycle marker) was increased after 24 h of overloading and corresponded with changes in muscle DNA content. In contrast, p21 and myogenin, markers of cellular differentiation, were increased after just 12 h. Muscle IGF-I peptide levels were also increased at early time points. The results of this study indicate that myogenic processes are activated in response to increased loading at very early time points (e.g., 12 h) and that IGF-I may be modulating this response. Furthermore, these findings suggest that some cells may have been differentiating very early in the adaptation process before events leading to cellular proliferation have been initiated.
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: Adams
authors.forename: F
authors.initials: F
authors.lastname: Haddad
authors.forename: K M
authors.initials: KM
authors.lastname: Baldwin
mesh_terms: D000818:Animals; D015415:Biomarkers; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D019938:Cyclin D1 / Q000096:biosynthesis / Q000235:genetics; D004247:DNA / Q000032:analysis / Q000096:biosynthesis; D005260:Female; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000235:genetics; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development* / Q000502:physiology*; D017570:MyoD Protein / Q000096:biosynthesis / Q000235:genetics; D018008:Myogenin / Q000096:biosynthesis / Q000235:genetics; D015689:Oncogene Protein p21(ras) / Q000096:biosynthesis / Q000235:genetics; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D015415:Biomarkers; D017570:MyoD Protein; C503803:Myog protein, rat; D018008:Myogenin; D012333:RNA, Messenger; D019938:Cyclin D1; D007334:Insulin-Like Growth Factor I; D004247:DNA; D015689:Oncogene Protein p21(ras)