A discrepancy resolved: human satellite cells are not preprogrammed to fast and slow lineages.

Satellite cells from chicken and mouse muscle when differentiated in vitro have been shown to display a myosin heavy chain phenotype that corresponds to the fibre from which they originated. Indirect evidence has suggested that this might not be the case for human satellite cells. In the present study we have compared the myosin heavy chain (MHC) profile expressed by differentiated cultures of satellite cells isolated from single fast or slow muscle fibres. The MHC composition of the isolated fibres was determined by sodium dodecyl sulfate glycerol gel electrophoresis and Western blotting. The MHC profile expressed by the differentiated myotubes was identified by immunostaining using specific antibodies. Our results show that all human satellite cells isolated from either fast or slow fibres form myotubes in vitro which co-express both fast and slow MHCs independently of the fibre type from which they originated. These results confirm that human satellite cells, in contrast to those of birds and rodents, are not confined to distinct fast and slow lineages.