THE ROLE OF TENASCIN-C AND RELATED GLYCOPROTEINS IN EARLY CHONDROGENESIS

A number of large multidomain extracellular matrix glycoproteins, incl uding fibronectin and members of the tenascin and thrombospondin famil ies, are expressed in locations that suggest they may be involved in t he process of chondrogenesis. During early limb morphogenesis, tenasci n-C is selectively associated with condensing chondrogenic mesenchyme. With progressive development of endochondral bones, tenascin-C is abs ent from the matrix surrounding proliferating and hypertrophic chondro cytes, but remains in a restricted distribution in peripheral epiphyse al cartilage. During long bone development, patterns of expression of tenascin-C splice variants differ between chondrogenic and osteogenic regions, suggesting that different isoforms may have different functio nal roles. Tenascin-C presented as a substratum for chick wing bud mes enchymal cells induces chondrogenic differentiation. In early studies, fibronectin was found to inhibit chondrogenesis, despite being abunda nt in early chondrogenic mesenchyme. Recent studies showing differenti al effects of fibronectin splice variants on prechondrogenic mesenchym al condensation may explain this paradox. Members of the thrombospondi n gene family are expressed in chondrogenic tissues at different stage s, suggesting that they each play a unique role in cartilage developme nt. Microsc. Res. Tech. 43:102-110, 1998. (C) 1998 Wiley-Liss, Inc.