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

Abstract

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.

• Authors: P E Mozdziak, M L Greaser, E Schultz
• Journal: Aviation, space, and environmental medicine (Aviat Space Environ Med) Vol. 70 Issue 5 Pg. 511-6 (May 1999) ISSN: 0095-6562 [Print] United States
• PMID: 10332949 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

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

Topics

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