Glial growth factor: a mitogenic polypeptide of the brain and pituitary.

Purified rat Schwann cells divide slowly in tissue culture medium containing 10% fetal calf serum. They are stimulated to divide by a polypeptide growth factor present in extracts of the bovine brain and pituitary, but not by a variety of purified growth factors and hormones, nor by extracts of nonneural tissues. The activity resides in a component of Mr = 31,000, as evidenced by purification, reactivity with a set of monoclonal antibodies, and recovery of mitogenicity after sodium dodecyl sulfate gel electrophoresis. The activity is present in comparable levels in the anterior and posterior lobes of the pituitary and shows a regional variation in specific activity in different areas of the bovine brain. The caudate nucleus has a higher (1.2-fold) specific activity than the pituitary. When incubated with dissociated cultures of the rat corpus callosum, the purified factor stimulated division of astrocytes, but not of oligodendrocytes or macrophage-like microglial cells. It was also active on fibroblasts derived from newborn rat muscle cultures. In view of the importance of the Schwann cell in its definition, as well as its action on astrocytes, the factor has been tentatively named glial growth factor.