Golding, J.P.; Beauchamp, J.R.; Partridge, T.A. and Zammit, P.S.
Not all activated satellite cell progeny commit to differentiation.
In: 32nd European Muscle Conference, 7-10 Sep 2003, Montpellier, France.
Satellite cells provide skeletal muscle with a remarkable capacity for repeated repair and regeneration. Quiescent satellite cells are MyoD-ve, with MyoD being induced in >98% of satellite cells within 24hrs of activation (Zammit, Exp. Cell Res. 281, 39, 2002). Here, we explore the subsequent fate of these satellite cells, as they proliferate and begin to differentiate. Satellite cells associated with myofibres, cultured without exposure to serum/CEE, still activated MyoD but the majority failed to divide, demonstrating an uncoupling of the two events. In contrast, myofibres cultured with serum/CEE had clones of satellite cells. MyoD-ve cells were detected in these clones, in which the rest of the cells were MyoD+ve, implying they had arisen after division but were not adopting the same fate. Three possible explanations for MyoD-ve cells were explored: phosphorylated histone markers and BrdU labelling showed that the lack of MyoD was not cell cycle dependent; myogenin immunostaining demonstrated that satellite cells committing to differentiation initially contained MyoD; Pax7 expression was generally down-regulated in the majority of satellite cells by 72hrs, but some remained strongly Pax7+ve. Together, these data suggest that MyoD-ve cells are returning to a quiescent state.
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