Replicative and differentiative behavior in daughter pairs of myogenic stem cells

Time-lapse microcinematography was used to trace the migration and subsequent fate of daughter pairs from single myogenic stem cells. The generation times of siblings which divide are closely correlated (r, 0.73) compared with randomly selected cells (r, 0.059), suggesting the more or less equal partition of stem cell components. The commitment to differentiative expression, however, is not inherited and must occur following stem cell division. Within the combined group in which at least one sibling fused, the ratio of pairs in which both fuse to pairs in which one divides and one fuses is 21:18. X2 for this ratio (compared with 1:1) is 0.103 indicating that it is just as likely that one daughter fuses and the other divides as that both fuse. We see no evidence of an intrinsic mitotic clock. If there were, one would expect that both or neither daughter would differentiate, depending on whether or not the 'clock' had run out for a particular stem cell.