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L.K. McLoon, K.M. Thorstenson, A. Asakura; Extraocular Muscles Contain More Satellite Cells and More Multipotent Precursor Cells than Limb Muscle . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4679.
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Purpose: The extraocular muscles (EOM) are spared in muscular dystrophy, despite the absence of dystrophin. We have shown that the EOM, unlike limb muscles, remodel continuously throughout life by a process of myonuclear turnover. It is possible that intrinsic differences in satellite cell populations within these muscles may, in part, explain this differential disease susceptibility. We examined the differences in the satellite and precursor cell populations of EOM and limb from adult rabbit and compared both total numbers and expression of markers that identify satellite cells and multipotent precursor cells in muscle. Methods: EOM and tibialis anterior were isolated from adult New Zealand white rabbits and digested with collagenase type B and dispase II to obtain satellite and precursor cells. FACS analysis was performed using a cell sorter with dual lasers and Hoechst 33342 staining with or without verapamil to identify the main population (MP) and side population (SP) cells from these muscles. In a separate series, both MP and SP cells were obtained but sorted by FACS analysis based on staining for each of the following markers: Notch–1, Pax7, Sca–1, and CD34. Results: FACS analysis of cells using Hoechst dye exclusion showed that EOM has significantly more satellite cells in the MP compared to limb muscle, but decreased total numbers of SP cells. Verapamil depleted the SP in both groups. FACS analysis showed that 70% of the live cells in the MP from EOM were Pax7–positive, compared to 45% in the limb MP. The EOM contained significantly greater numbers of CD34– and Sca–1–positive cells compared to limb muscle. Of the MP cells, 65% of the EOM cells were CD34–positive compared to 30% of limb cells. Of the SP cells, 30% of EOM cells were CD34–positive compared with 10% of the limb SP cells. Conclusions: The EOM contain significantly greater numbers of satellite cells compared with limb muscle, as determined by FACS analysis and staining for Pax7 and Notch–1. By Hoechst dye exclusion, there were fewer side population cells in EOM compared to limb muscle. However, when examined by specific markers for multipotent precursor cells (mpc), Sca–1 and CD34, there were significantly greater numbers of mpc in EOM compared with limb. This suggests that the EOM contain greater numbers of both satellite cells and the more multipotent muscle precursor cells compared with limb muscle. These differences in satellite and precursor cell populations between EOM and limb may be responsible, in part, for the differential sparing of the EOM in muscular dystrophy.
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