A novel approach for inhibiting growth factor signalling in murine tooth development. Inhibition of FGF's.

Growth factors belonging to the FGF and TGF-beta families, together with other secreted factors such as Sonic hedgehog, have been shown to be spatially and temporally regulated during tooth development. Providing evidence of the functions of these molecules has, however, proved difficult. We have developed a novel strategy for investigating the role of secreted molecules in tooth development using soluble forms of membrane bound receptors to sequester ligands. Chimeric fusion proteins of receptor extracellular domains were cloned into the eukaryotic expression vector pIG-1 and transfected into COS cells. Fusion proteins secreted by the COS cells were purified using Protein A Sepharose. A soluble form of the FGF receptor FGF-1IIIc, which preferentially binds FGF-2 and FGF-4, was produced using this technique and added to mouse mandible cultures. Addition of the soluble receptors to E13 cultures resulted in down-regulation of Sonic hedgehog expression in molar enamel knots, consistent with inhibition of FGF-4 signalling.