Expression of MRF4, a myogenic helix-loop-helix protein, produces multiple changes in the myogenic program of BC3H-1 cells.
Expression of MRF4, a myogenic regulatory factor of the basic helix-loop-helix type, produced multiple changes in the myogenic program of the BC3H-1 cell line. BC3H-1 cells that stably expressed exogenous MRF4 were prepared and termed BR cell lines. Upon differentiation, the BR cells were found to have three muscle-specific properties (endogenous MyoD expression, myoblast fusion, and fast myosin light-chain 1 expression) that the parent BC3H-1 cells did not have. Of the four known myogenic regulatory factors (MyoD, myogenin, Myf-5, and MRF4), only MRF4 was capable of activating expression of the endogenous BC3H-1 myoD gene. In addition, the pattern of Myf-5 expression in BR cells was the opposite of that in BC3H-1 cells. Myf-5 expression was low in BR myoblasts and showed a small increase upon myotube formation, whereas Myf-5 expression was high in BC3H-1 myoblasts and decreased upon differentiation. Though the MRF4-transfected BR cells fused to form large myotubes and expressed fast myosin light-chain 1, the pattern of myosin heavy-chain isoform expression was the same in the BR and the nonfusing parent BC3H-1 cells, suggesting that factors in addition to the MyoD family members regulate myosin heavy-chain isoform expression patterns in BC3H-1 cells. In contrast to the changes produced by MRF4 expression, overexpression of Myf-5 did not alter BC3H-1 myogenesis. The results suggest that differential expression of the myogenic regulatory factors of the MyoD family may be one mechanism for generating cells with diverse myogenic phenotypes.
Block
N E
NE
Neuromuscular Laboratory, Massachusetts General Hospital, Charlestown 02129.
Miller
J B
JB
D000818:Animals; D002454:Cell Differentiation; D002459:Cell Fusion; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation; D066298:In Vitro Techniques; D051379:Mice; D009124:Muscle Proteins / Q000502:physiology*; D009132:Muscles / Q000166:cytology*; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D009218:Myosins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D015534:Trans-Activators; D014162:Transfection
D004268:DNA-Binding Proteins; D009124:Muscle Proteins; C497418:Myf5 protein, mouse; C503801:Myog protein, mouse; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D012333:RNA, Messenger; D015534:Trans-Activators; C063403:myogenic factor 6; D009218:Myosins