Rb is required for progression through myogenic differentiation but not maintenance of terminal differentiation.
To investigate the requirement for pRb in myogenic differentiation, a floxed Rb allele was deleted either in proliferating myoblasts or after differentiation. Myf5-Cre mice, lacking pRb in myoblasts, died immediately at birth and exhibited high numbers of apoptotic nuclei and an almost complete absence of myofibers. In contrast, MCK-Cre mice, lacking pRb in differentiated fibers, were viable and exhibited a normal muscle phenotype and ability to regenerate. Induction of differentiation of Rb-deficient primary myoblasts resulted in high rates of apoptosis and a total inability to form multinucleated myotubes. Upon induction of differentiation, Rb-deficient myoblasts up-regulated myogenin, an immediate early marker of differentiation, but failed to down-regulate Pax7 and exhibited growth in low serum conditions. Primary myoblasts in which Rb was deleted after expression of differentiated MCK-Cre formed normal multinucleated myotubes that did not enter S-phase in response to serum stimulation. Therefore, Rb plays a crucial role in the switch from proliferation to differentiation rather than maintenance of the terminally differentiated state.
Huh
Michael S
MS
Molecular Medicine Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada, K1H 8L6. mrudnicki@ohri.ca
Parker
Maura H
MH
Scimè
Anthony
A
Parks
Robin
R
Rudnicki
Michael A
MA
D000256:Adenoviridae / Q000235:genetics; D000483:Alleles; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008807:Mice, Inbred BALB C; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology; D032446:Myoblasts / Q000166:cytology / Q000502:physiology*; D018008:Myogenin / Q000502:physiology; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015854:Up-Regulation
D016895:Culture Media, Serum-Free; C503801:Myog protein, mouse; D018008:Myogenin; D016160:Retinoblastoma Protein