STRUCTURE AND EXPRESSION OF THE MESSENGER-RNA ENCODING A NOVEL FIBROBLAST-GROWTH-FACTOR, FGF-18

We isolated the cDNA encoding a novel member (207 amino acids) of the fibroblast growth factor (FGF) family from rat embryos. Because this p rotein is the 18th documented member of the FGF family, we tentatively termed it FGF-18, We have also determined mouse and human FGF-18 with high amino acid identity (99.5 and 99.0%) to rat FGF-18, respectively . Among FGF family members, FGF-18 is most similar (52.7% amino acid i dentity) to FGF-8 and FGF-17, FGF-18 has a typical signal sequence at its amino terminus. Recombinant rat FGF-18, which was efficiently secr eted by High Five insect cells infected with recombinant baculovirus c ontaining the cDNA, induced neurite outgrowth in PC12 cells. The expre ssion of FGF-18 mRNA was examined in adult rat tissues and embryos by Northern blotting analysis and in situ hybridization, FGF-18 mRNA of s imilar to 2.7 kilobases was preferentially detected in the lung among adult rat tissues examined. In rat embryos, FGF-18 mRNA was detected i n several discrete regions at embryonic days 14.5 and 19.5 but not at E10.5, The temporal and spatial patterns of FGF-18 mRNA expression in embryos are quite different from those of FGF-8 and FGF-17 mRNAs repor ted. The present results indicate that FGF-18 is a unique secreted sig naling molecule in the adult lung and developing tissues.