| Popis: |
The influence of external diffusible factors on the terminal differentiation of cells of the myogenic line L 6 has been studied. The cultures were fed either with medium which had been depleted of mitogenic factors by previous incubation in the presence of myogenic cells, or with standard medium to which proteins secreted by myoblasts had been added. We present evidence that the length of the proliferative phase of the cultures is largely dependent upon environmental cues. However, by inhibiting DNA replication by a variety of means during this phase, we show that in order to differentiate, DNA synthesis is needed for myogenic cells of this line. Once the myoblasts have initiated their last presumptive round of DNA synthesis, they cannot be induced to undergo further DNA replication by environmental factors. Cloning experiments showed that, at this time, the cells lose their proliferative capacity. Our data strongly suggest that, at this stage, cells of line L 6 become irreversibly committed for differentiation. The fusion rate of the committed myoblasts could be significantly increased by proteins secreted by proliferating myogenic cells, but not by those secreted by myotubes. |
