A NOVEL-APPROACH FOR INHIBITING GROWTH-FACTOR SIGNALING IN MURINE TOOTH DEVELOPMENT - INHIBITION OF FGFS

Growth factors belonging to the FGF and TGF-beta families, together wi th other secreted factors such as Sonic hedgehog, have been shown to b e spatially and temporally regulated during tooth development. Providi ng evidence of the functions of these molecules has, however, proved d ifficult. We have developed a novel strategy for investigating the rol e of secreted molecules in tooth development using soluble forms of me mbrane bound receptors to sequester ligands. Chimeric fusion proteins of receptor extracellular domains were cloned into the eukaryotic expr ession vector pIG-1 and transfected into COS cells. Fusion proteins se creted by the COS cells were purified using Protein A Sepharose. A sol uble form of the FGF receptor FGF-1IIIc, which preferentially binds FG F-2 and FGF-4, was produced using this technique and added to mouse ma ndible cultures. Addition of the soluble receptors to E13 cultures res ulted in down-regulation of Sonic hedgehog expression in molar enamel knots, consistent with inhibition of FGF-4 signalling.