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© The Rockefeller University Press, 0021-9525/1999//631 $5.00
The Journal of Cell Biology, Volume 144, Number 4, , 1999 631-643


Regular Articles

Reduced Differentiation Potential of Primary MyoD–/– Myogenic Cells Derived from Adult Skeletal Muscle



Luc A. Sabourin, Adele Girgis-Gabardo, Patrick Seale, Atsushi Asakura, and Michael A. Rudnicki

Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, Ontario, Canada L8S 4K1

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.

Key Words: MyoD • myogenic regulatory factor • satellite cell • differentiation • proliferation



Abbreviations used in this paper: BrdU, 5-bromo-2'-deoxyuridine; MHC, myosin heavy chain; MRF, myogenic regulatory factors.

Address correspondence to Dr. Michael Rudnicki, Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, Ontario, Canada L8S 4K1. Tel.: (905) 525-9140. Fax: (905) 521-2995. E-mail: rudnicki{at}mcmaster.ca

M.A. Rudnicki is a research scientist of the National Cancer Institute of Canada, and a member of the Canadian Genetic Disease Network of Excellence. L.A. Sabourin is a postdoctoral fellow of the Medical Research Council of Canada, and P. Seale is supported by an National Science and Engineering Research Scholarship.



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