SCIATIC-NERVE PROTEIN HAS A TROPHIC EFFECT ON DEVELOPMENT AND MAINTENANCE OF SKELETAL-MUSCLE CELLS IN CULTURE

Citrate-soluble extracts of chicken sciatic nerve were fractionated biochemically and added to cultures of embryonic chicken skeletal muscle in order to identify the component that exerted trophic influences on the muscle. A protein fraction that expressed trophic activity was obtained by ion-exchange chromatography on DEAE-cellulose followed by gel filtration on Sephadex G-100 superfine. This fraction enhanced the rate and degree or morphological maturation and the level of protein synthesis in embryonic muscle cells. Muscle fibers treated with this fraction after maturation in culture survived for longer periods in vitro than did comparable controls. Characterization of the active protein fraction by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed the presence of one major protein (molecular weight 84.000) and three minor proteins. Electrophoretic analysis of biologically inactive gel filtration fractions indicated that the three minor proteins were contaminants and that biological activity was associated with the protein of molecular weight 84.000. Analytical isoelectric focusing revealed that the active protein was acidic and focused as four species with isoelectric points (pI) of 5.74, 5.77, 5.92, and 6.15. Maximal incorporation of [14C]-leucine into muscle cell protein was elicited by 20 μg of active protein per culture dish. These data suggest that an acidic protein having trophic influences upon muscle has been identified and partially purified.