Induction of neurite outgrowth by a conditioned-medium factor bound to the culture substratum

Abstract

Heart-cell conditioned medium (HCM) induces rapid chick embryo neurite outgrowth from isolated neurons in culture. The following evidence indicates that this action of HCM is due to a trypsin-sensitive factor which attaches to the polyornithine-coated culture substratum. Pretreatment of the culture substratum with HCM allows rapid neurite outgrowth to occur even in unconditioned media. The active factor remains bound to the substratum during the period of neurite outgrowth. The substratum-bound activity is destroyed by trypsin treatment, but is insensitive to collagenase, RNase and DNase. The factor that binds to the substratum is essential for neurite outgrowth, because HCM is no longer active when the material that binds to the polyornithine substratum has been removed by passage of the HCM over a series of culture dishes. This depleted HCM still supports growth of nonneuronal cells. Most significantly, when neurons are cultured in whole HCM, the extent of neurite outgrowth is proportional to the amount of substratum-bound activity and not to the amount in solution, indicating that the substratum-bound form of the factor is more active. Previous observations suggest that HCM promotes neurite outgrowth by increasing the adhesion between nerve cell surface extensions and the polyornithine-coated culture substratum. The factor in HCM that binds to the substratum may possess sites to which nerve cell surface components adhere.