Modulation of differentiation in vitro. II. Influence of cell spreading and surface events on myogenesis.

We examined the influence of attachment and spreading on myogenesis by adding polylysine-covered beads at different times after plating the cells on a plastic substratum. We show that polylysine per se acting on the cell surface can modulate myogenesis independently of cell spreading. Thus cell shape would not be the limiting factor for the division and differentiation of L6 myoblasts. Multinucleation of the cells was found to be first enhanced by the addition of polylysine-covered beads to replicating myoblasts, although the final percentage of fusion attained by these cultures was lower than in the controls. A similar phenomenon was observed concerning myosin synthesis. No such effect could be observed when the beads were added to a nonfusing mutant or to fibroblasts. Our results show that this phenomenon is specific. We postulate that some of the surface molecules necessary for this process appear on myoblasts shortly before they fuse.