SCHWANN-CELLS AND CELLS IN THE OLIGODENDROCYTE LINEAGE PROLIFERATE INRESPONSE TO A 50,000 DALTON MEMBRANE-ASSOCIATED MITOGEN PRESENT IN DEVELOPING BRAIN

The neuronal cell surface is believed to carry a mitogenic signal for peripheral glial cells. We have purified a mitogen from fetal bovine b rain membranes that, in common with the PNS neuronal mitogen, stimulat es the proliferation of Schwann cells in vitro and binds heparin. The purified mitogen has an apparent molecular weight of 50,000 daltons as estimated by elution of activity from non-reducing polyacrylamide gel s. Since the developing central nervous system is a rich source of mit ogen, we tested whether the protein is mitogenic for one or more cell types isolated from the developing brain. Purified mitogen was added t o enriched cultures of astrocytes or developing oligodendrocytes, or t o microglial cells. The analyses demonstrated that the protein is mito genic for developing oligodendrocytes but not astrocytes or microglial cells. These results suggest that during development a membrane-assoc iated mitogen present in the brain might regulate the proliferation of developing oligodendrocytes, and consequently, the population size of oligodendrocytes in the brain.