Pax7 Reveals a Greater Frequency and Concentration of Satellite Cells at the Ends of Growing Skeletal Muscle Fibers

Mohammed Z. Allouh ¹, Zipora Yablonka-Reuveni ¹ and Benjamin W.C. Rosser ^1*

¹ Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada (MZA,BWCR), and Department of Biological Structure and Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, Washington (ZY-R)

^* To whom correspondence should be addressed. E-mail: ben.rosser{at}usask.ca.

Submitted on July 2, 2007
Accepted on 20 September 2007

	Abstract

The main sites of longitudinal growth in skeletal muscle are the ends of the fibers. This study tests the hypothesis that satellite cells (SCs) are at a greater frequency (#SC nuclei/all nuclei within basal laminae) and concentration (closer together) within growing fiber ends of posthatch chicken pectoralis. SCs were localized by their Pax7 expression, and fiber ends identified by their retention of neonatal myosin heavy chains and small cross-sectional profiles. While SC frequency decreased from about 20% at nine days posthatch to less than 5% at 115 days, fiber ends retained a frequency of about 16%. The calculated mean area of sarcolemma per SC revealed higher concentrations of SCs at fiber ends. There was also a strong inverse correlation between SC frequency and fiber profile cross-sectional size throughout development. This study suggests that SCs at fiber ends play a key role in the longitudinal growth of muscle fibers, and that fiber profile size may impact SC distribution.

Key Words: muscle fibers, muscle growth, myosin, satellite cells, myonuclei, Pax7, fiber ends

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