HB-GAM/pleiotrophin but not RIHB/midkine enhances chondrogenesis in micromass culture

The heparin-binding growth-associated molecule HB-GAM (also named pleiotrophin) and the retinoic acid-induced heparin-binding protein RIHB (chicken midkine) are developmentally regulated proteins forming a new family of heparin-binding molecules with putative functions during cell growth and differentiation. A direct involvement of these molecules during chondrogenesis in vivo was suggested by their patterns of expression. The putative chondrogenic activity of these molecules was investigated in vitro using micromass cultures from chicken limb bud mesenchymal cells. Exogenous HB-GAM, not RIHB, was found to enhance chondrogenesis in this system. These results provide a strong incentive for considering and further investigating the role of this protein in the control of limb cartilage differentiation.