Reduced differentiation potential of primary MyoD-/- myogenic cells derived from adult skeletal muscle.
To gain insight into the regeneration deficit of MyoD-/- muscle, we investigated the growth and differentiation of cultured MyoD-/- myogenic cells. Primary MyoD-/- myogenic cells exhibited a stellate morphology distinct from the compact morphology of wild-type myoblasts, and expressed c-met, a receptor tyrosine kinase expressed in satellite cells. However, MyoD-/- myogenic cells did not express desmin, an intermediate filament protein typically expressed in cultured myoblasts in vitro and myogenic precursor cells in vivo. Northern analysis indicated that proliferating MyoD-/- myogenic cells expressed fourfold higher levels of Myf-5 and sixfold higher levels of PEA3, an ETS-domain transcription factor expressed in newly activated satellite cells. Under conditions that normally induce differentiation, MyoD-/- cells continued to proliferate and with delayed kinetics yielded reduced numbers of predominantly mononuclear myocytes. Northern analysis revealed delayed induction of myogenin, MRF4, and other differentiation-specific markers although p21 was upregulated normally. Expression of M-cadherin mRNA was severely decreased whereas expression of IGF-1 was markedly increased in MyoD-/- myogenic cells. Mixing of lacZ-labeled MyoD-/- cells and wild-type myoblasts revealed a strict autonomy in differentiation potential. Transfection of a MyoD-expression cassette restored cytomorphology and rescued the differentiation deficit. We interpret these data to suggest that MyoD-/- myogenic cells represent an intermediate stage between a quiescent satellite cell and a myogenic precursor cell.
Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, Ontario, Canada L8S 4K1.
L A
LA
Sabourin
A
A
Girgis-Gabardo
P
P
Seale
A
A
Asakura
M A
MA
Rudnicki
D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D015870:Gene Expression; D007763:Lac Operon; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D017570:MyoD Protein / Q000235:genetics* / Q000502:physiology*; D010641:Phenotype; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012038:Regeneration / Q000235:genetics / Q000502:physiology
D017570:MyoD Protein; D012333:RNA, Messenger; D019859:Proto-Oncogene Proteins c-met