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Published 13 September 2004. doi:10.1083/jcb.200403004
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 166, Number 6, 865-876
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Article

 Rb is required for progression through myogenic differentiation but not maintenance of terminal differentiation

Michael S. Huh1, Maura H. Parker1,2, Anthony Scimè1, Robin Parks1, and Michael A. Rudnicki1,2

1 Molecular Medicine Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada, K1H 8L6
2 Medical Sciences Program, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada, L8N 3Z5

Address correspondence to Michael A. Rudnicki, Molecular Medicine Program, Ottawa Health Research Institute, 501 Smyth Rd., Ottawa, Ontario, Canada, K1H 8L6. Tel.: (613) 739-6740. Fax: (613) 737-8803. email: mrudnicki{at}ohri.ca

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.

Key Words: pRb; primary myoblasts; proliferation; MyoD; myogenin

Abbreviations used in this paper: Ad-Cre, Cre-expressing adenovirus; Ad-Lac-Z, Lac-Z–expressing adenovirus; DM, differentiation media; MHC, myosin heavy chain; MRF, myogenic regulatory factor.


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