Time-dependent changes in myosin heavy chain mRNA and protein isoforms in unloaded soleus muscle of rat.
Time-dependent changes in myosin heavy chain (MHC) isoform expression were investigated in rat soleus muscle unloaded by hindlimb suspension. Changes at the mRNA level were measured by RT-PCR and correlated with changes in the pattern of MHC protein isoforms. Protein analyses of whole muscle revealed that MHCI decreased after 7 days, when MHCIIa had increased, reaching a transient maximum by 15 days. Longer periods led to inductions and progressive increases of MHCIId(x) and MHCIIb. mRNA analyses of whole muscle showed that MHCIId(x) displayed the steepest increase after 4 days and continued to rise until 28 days, the longest time period investigated. MHCIIb mRNA followed a similar time course, although at lower levels. MHCIalpha mRNA, present at extremely low levels in control soleus, peaked after 4 days, stayed elevated until 15 days, and then decayed. Immunohistochemistry of 15-day unloaded muscles revealed that MHCIalpha was present in muscle spindles but at low amounts also in extrafusal fibers. The slow-to-fast transitions thus seem to proceed in the order MHCIbeta --> MHCIIa --> MHCIId(x) --> MHCIIb. Our findings indicate that MHCIalpha is transiently upregulated in some fibers as an intermediate step during the transition from MHCIbeta to MHCIIa.
Stevens
L
L
Faculty of Biology, University of Konstanz, D-78457 Konstanz, Germany.
Sultan
K R
KR
Peuker
H
H
Gohlsch
B
B
Mounier
Y
Y
Pette
D
D
D000818:Animals; D000911:Antibodies, Monoclonal; D002454:Cell Differentiation; D015870:Gene Expression / Q000502:physiology; D006614:Hindlimb; D007103:Immobilization / Q000502:physiology; D007124:Immunoenzyme Techniques; D007536:Isomerism; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology / Q000502:physiology; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000166:cytology / Q000502:physiology; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D009929:Organ Size; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D016474:Weight-Bearing
D000911:Antibodies, Monoclonal; D012333:RNA, Messenger; D018995:Myosin Heavy Chains