THE FIBROBLAST GROWTH-FACTOR RECEPTORS - A GROWING FAMILY

The fibroblast growth factors (FGF) are a family of seven polypeptides, the physiological importance of which has been early recognized. By contrast, their receptors have been identified only recently : they consist of protein tyrosine kinases, and of proteoglycans that serve as accessory molecules. Four genes code for receptor tyrosine kinases that, through alternative splicing mechanisms, generate multiple receptor moieties. A single proteoglycan has been formally identified as receptor for the FGFs, but several clues led to suggest that this syndecan is but one member of a whole family of proteins. The FGFs and their receptors constitute a unique example of double redundancy, as each FGF seems to associate to several receptor molecules, which in turn bind several FGFs. The advantages of such a profusion are not well understood, and several explanations are discussed.