Myogenin, MyoD, and myosin heavy chain isoform expression following hindlimb suspension

Aviat Space Environ Med. 1999 May;70(5):511-6.


Background: Myogenin expression is associated with a slow myofiber phenotype, and MyoD expression is associated with a fast myofiber phenotype. Hindlimb suspension (HS) will induce muscular atrophy, and a transition from a slow to fast myofiber phenotype in the rat soleus.

Hypothesis: Hindlimb suspension will induce myofiber atrophy, and a slow to fast myofiber type transition with corresponding changes in myogenin and MyoD expression.

Methods: Myofiber phenotype was evaluated by electrophoretically separating the myosin heavy chain isoforms. Myogenin expression was evaluated by Northern analysis, while MyoD expression was evaluated by Northern analysis and semiquantitative RT-PCR.

Result: After 28 d of hindlimb suspension, there was significantly (p < 0.05) less myosin heavy chain Type IIA, and more (p < 0.05) myosin heavy chain Type IIX in the soleus muscles of hindlimb suspended rats compared with soleus muscles from weight-bearing (WB) rats. Although there was a shift to a faster myosin heavy chain phenotype in soleus muscles from hindlimb suspended rats, there was no change in myogenin expression, and MyoD expression was undetectable by Northern analysis. Semi-quantitative RT-PCR revealed an up-regulation of MyoD expression following 14 d of hindlimb suspension.

Conclusions: Myogenin expression levels do not change during the slow to fast myofiber phenotypic transition that occurs during hindlimb suspension; MyoD expression appears to increase at the same time as the phenotypic transition. Thus, MyoD expression or the Myogenin: MyoD mRNA ratio may be important in the phenotypic transition. Neither myogenin nor MyoD appear to play a critical role in the muscular atrophy that occurs during weightlessness.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Blotting, Northern
  • Disease Models, Animal
  • Female
  • Gene Expression Regulation / genetics*
  • Hindlimb Suspension / adverse effects*
  • Hindlimb Suspension / physiology*
  • Muscle Fibers, Fast-Twitch / chemistry*
  • Muscle Fibers, Slow-Twitch / chemistry*
  • Muscle, Skeletal / chemistry*
  • Muscular Atrophy / etiology*
  • Muscular Atrophy / metabolism*
  • MyoD Protein / analysis*
  • MyoD Protein / genetics*
  • Myogenin / analysis*
  • Myogenin / genetics*
  • Myosin Heavy Chains / analysis*
  • Myosin Heavy Chains / genetics*
  • Phenotype
  • Rats
  • Rats, Inbred Strains
  • Reverse Transcriptase Polymerase Chain Reaction
  • Space Flight
  • Time Factors
  • Weight-Bearing / physiology


  • MyoD Protein
  • Myog protein, rat
  • Myogenin
  • Myosin Heavy Chains