In vivo regulation of the beta-myosin heavy chain gene in soleus muscle of suspended and weight-bearing rats.
In the weight-bearing hindlimb soleus muscle of the rat, approximately 90% of muscle fibers express the beta-myosin heavy chain (beta-MHC) isoform protein. Hindlimb suspension (HS) causes the MHC isoform population to shift from beta toward the fast MHC isoforms. Our aim was to establish a model to test the hypothesis that this shift in expression is transcriptionally regulated through specific cis elements of the beta-MHC promoter. With the use of a direct gene transfer approach, we determined the activity of different length beta-MHC promoter fragments, linked to a firefly luciferase reporter gene, in soleus muscle of control and HS rats. In weight-bearing rats, the relative luciferase activity of the longest beta-promoter fragment (-3500 bp) was threefold higher than the shorter promoter constructs, which suggests that an enhancer sequence is present in the upstream promoter region. After 1 wk of HS, the reporter activities of the -3500-, -914-, and -408-bp promoter constructs were significantly reduced ( approximately 40%), compared with the control muscles. However, using the -215-bp construct, no differences in promoter activity were observed between HS and control muscles, which indicates that the response to HS in the rodent appears to be regulated within the -408 and -215 bp of the promoter.
Giger
J M
JM
Department of Physiology and Biophysics, University of California, Irvine 92697, USA.
Haddad
F
F
Qin
A X
AX
Baldwin
K M
KM
D000818:Animals; D002467:Cell Nucleus / Q000502:physiology; D001517:Coleoptera; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D017930:Genes, Reporter; D019417:Hindlimb Suspension / Q000502:physiology*; D008156:Luciferases / Q000235:genetics; D018482:Muscle, Skeletal / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D014162:Transfection; D016474:Weight-Bearing / Q000502:physiology*
D008156:Luciferases; D018995:Myosin Heavy Chains