The enhancement of in vitro survival and chondrogenesis of limb bud cells by cartilage conditioned medium

Dissociated stage 21–28 chick embryo limb bud cells showed an increasing ability to produce cartilage colonies in vitro with in vivo maturation. In addition dissociated stage 21–28 chick embryo limb bud cells exposed to cartilage conditioned medium continuously or only for 48 hr prior to subculture showed an enhanced (as much as 15-fold) ability to form differentiated cartilage colonies. By this criterion, cells were more responsive to conditioned medium prior to stage 25. Conditioned medium from fibroblast cultures caused an inhibition of cartilage colony formation, suggesting that the effect is cell-type specific. Besides increasing cartilage colony formation by enhanced cell survival, the incorporation of S³⁵O₄ into isolated glycosaminoglycans is also stimulated when limb bud cells are exposed to cartilage conditioned medium. The results support a model for cell differentiation which involves the enhancement of a particular differentiated capacity by a diffusible cell-type-specific macromolecule.