TY - JOUR
T1 - Failure of Myf5 to support myogenic differentiation without myogenin, MyoD, and MRF4
AU - Valdez, M. Renee
AU - Richardson, James A.
AU - Klein, William H.
AU - Olson, Eric N.
N1 - Funding Information:
We thank Michael Rudnicki for MyoD mutant mice. We are also grateful to J. Page for editorial assistance and A. Tizenor for graphics. This work was supported by grants from the NIH, the Muscular Dystrophy Association, and the American Heart Association to E.N.O. R.V. was supported by a predoctoral training grant from the NIH.
PY - 2000/3/15
Y1 - 2000/3/15
N2 - The basic helix-loop-helix (bHLH) transcription factors - MyoD, Myf5, myogenin, and MRF4 - can each activate the skeletal muscle-differentiation program in transfection assays. However, their functions during embryogenesis, as revealed by gene-knockout studies in mice, are distinct. MyoD and Myf5 have redundant functions in myoblast specification, whereas myogenin and either MyoD or MRF4 are required for differentiation. Paradoxically, myoblasts from myogenin mutant or MyoD/MRF4 double-mutant neonates differentiate normally in vitro, despite their inability to differentiate in vivo, suggesting that the functions of the myogenic bHLH factors are influenced by the cellular environment and that the specific myogenic defects observed in mutant mice do not necessarily reflect essential functions of these factors. Understanding the individual roles of these factors is further complicated by their ability to cross-regulate one another's expression. To investigate the functions of Myf5 in the absence of contributions from other myogenic bHLH factors, we generated triple-mutant mice lacking myogenin, MyoD, and MRF4. These mice appear to contain a normal number of myoblasts, but in contrast to myogenin or MyoD/MRF4 mutants, differentiated muscle fibers fail to form in vivo and myoblasts from neonates of this triple-mutant genotype are unable to differentiate in vitro. These results suggest that physiological levels of Myf5 are insufficient to activate the myogenic program in the absence of other myogenic factors and suggest that specialized functions have evolved for the myogenic bHLH factors to switch on the complete program of muscle gene expression. (C) 2000 Academic Press.
AB - The basic helix-loop-helix (bHLH) transcription factors - MyoD, Myf5, myogenin, and MRF4 - can each activate the skeletal muscle-differentiation program in transfection assays. However, their functions during embryogenesis, as revealed by gene-knockout studies in mice, are distinct. MyoD and Myf5 have redundant functions in myoblast specification, whereas myogenin and either MyoD or MRF4 are required for differentiation. Paradoxically, myoblasts from myogenin mutant or MyoD/MRF4 double-mutant neonates differentiate normally in vitro, despite their inability to differentiate in vivo, suggesting that the functions of the myogenic bHLH factors are influenced by the cellular environment and that the specific myogenic defects observed in mutant mice do not necessarily reflect essential functions of these factors. Understanding the individual roles of these factors is further complicated by their ability to cross-regulate one another's expression. To investigate the functions of Myf5 in the absence of contributions from other myogenic bHLH factors, we generated triple-mutant mice lacking myogenin, MyoD, and MRF4. These mice appear to contain a normal number of myoblasts, but in contrast to myogenin or MyoD/MRF4 mutants, differentiated muscle fibers fail to form in vivo and myoblasts from neonates of this triple-mutant genotype are unable to differentiate in vitro. These results suggest that physiological levels of Myf5 are insufficient to activate the myogenic program in the absence of other myogenic factors and suggest that specialized functions have evolved for the myogenic bHLH factors to switch on the complete program of muscle gene expression. (C) 2000 Academic Press.
UR - http://www.scopus.com/inward/record.url?scp=0034643095&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034643095&partnerID=8YFLogxK
U2 - 10.1006/dbio.2000.9621
DO - 10.1006/dbio.2000.9621
M3 - Article
C2 - 10694423
AN - SCOPUS:0034643095
SN - 0012-1606
VL - 219
SP - 287
EP - 298
JO - Developmental Biology
JF - Developmental Biology
IS - 2
ER -