Migration of Schwann cells and wrapping of neurites in vitro: a function of protease activity (plasmin) in the growth medium.

In vitro conditions were defined under which Schwann cells, from a population of dissociated embryonic chicken spinal cord cells, migrate along the growing neuronal fibers and wrap bundles as well as individual axons, in a pattern similar to that found in a developing peripheral nervous system in vivo. The migration of Schwann cells and their wrapping of nerve fibers was found to be a function of plasmin activity in the growth medium. It was determined that at least one cell type among the spinal cord cells is producing plasminogen activator, the enzyme that activates the plasminogen that is a constituent of any serum. It is concluded that, to achieve wrapping of neurons by Schwann cells in culture, it is essential to have an active plasmin-generating system in the medium. It is hypothesized that the Schwann cell produces plasminogen activator. The possible role of both the Schwann cell and the plasminogen possible role of both the Schwann cell and the plasminogen activator in the formation of the neuromuscular junction is discussed.