Activin enhances chondrogenesis of limb bud cells: stimulation of precartilaginous mesenchymal condensations and expression of NCAM.

The roles of activin action in chicken limb development were analyzed. Activin enhanced chondrogenesis up to five-fold in a concentration-dependent manner in limb bud micromass cultures, with a half-maximal dose around 30 ng/ml (1.25 nM). The response of limb bud cells (stage 22/23) to activin appeared higher within 24 hr after culture. Activin increased the size of precartilaginous condensations. No corresponding increase in cell number was observed with total DNA or [3H]thymidine incorporation. Activin treatment resulted in increased expression of NCAM in precartilaginous condensations and tenascin in cartilage nodules, suggesting that the mechanism of activin is mediated by increased cell adhesion and recruitment of mesenchymal cells into condensations. Our results demonstrate a novel function of activin and imply that activin, together with other TGF beta superfamily members, is involved in the induction of limb chondrogenesis.