Neurite‐promoting activity from fetal skeletal muscle: Partial purification of a high‐molecular‐weight form

Abstract Neurite extension from sensory neuroblasts dissociated from chick embryo dorsal root ganglia can be stimulated by precoating the polylysine culture surface with extracts of skeletal muscle from bovine fetuses. The active factor(s) may be partially purified from cytosolic extracts of muscle by chromatography on Sepharose 6B and affinity chromatography on wheat germ agglutinin or Helix pomatia agglutinin columns. Extract concentrations of 10–50 μg protein per 1 ml were active in promoting neurite extention when the neurons were cultured without serum or nerve growth factor (βNGF). However, levels of 1–10 μ/m1 produced dramatic neurite extension when 10% (v/v) fetal or newborn calf serum or 0.5 ng/ml βNGF was added to the medium. The biological activity was not blocked by antiserum that was raised against purified mouse laminin and that abolished the neurite‐promoting activity of mouse laminin. The activity of the muscle extract was destroyed by trypsin or heparitinase, in contrast to the biological activity of purified mouse laminin, which was not abolished by heparitinase treatment. The activity could be resolved into two broad peaks on a Sepharose 2B column (apparent Mr between 2 × 10 6 and in 10 × 10 6 in native form). Treatment with dithiothreitol was necessary to dissociate the factor for electrophoresis in 4.25% polyacrylamide‐SDS gels, revealing three major polypeptide bands at Mr = 160,000, 195,000 and 200,000. This preliminary charcterization indicates that the neurite‐promoting activity from bovine skeletal muscle tissue consists of a high‐molecular‐weight complex, one essential component of which is a heparan sulfate.