Schwann cell myelination in a chemically defined medium: demonstration of a requirement for additives that promote Schwann cell extracellular matrix formation.

Primary cultures of embryonic rat Schwann cells and sensory nerve cells can be grown in the serum-free defined medium N2, but the Schwann cells fail to deposit extracellular matrix and do not ensheath or myelinate axons. Previously these functions could be induced only in media supplemented with serum and chick embryo extract. Here we show that supplementing N2 medium with ascorbic acid and a commercial preparation of the glycoprotein fetuin or purified bovine serum albumin in the absence of serum or other undefined media components leads to increased production of Schwann cell extracellular matrix and extensive myelin formation by Schwann cells. Ascorbic acid is required for production of collagen type IV. Both ascorbic acid and one of the proteins are required for optimal extracellular matrix formation and myelination. These results lend support to the hypothesis that production of extracellular matrix by Schwann cells is necessary for myelination of nerve fibers.