Comparative genomics on FGF8, FGF17, and FGF18 orthologs

FGF and WNT signaling pathways network together during embryogenesis and carcinogenesis. Among 22 FGF family members within human and rodents genomes, FGF20 orthologs are evolutionarily conserved targets of the WNT/β-catenin signaling pathway. FGF8, FGF17, and FGF18 constitute one of FGF subfamilies. Here, comparative proteomics and comparative genomics analyses on FGF8, FGF17, and FGF18 orthologs were performed. Rat Fgf8 and Fgf17 genes, consisting of five exons, were located within AC096326.7 and AC097410.12 genome sequences, respectively. FGF8, FGF17, and FGF18 orthologs were FGF family members with the N-terminal signal peptide. Human FGF8 isoform F showed 90.6% total-amino-acid identity with rat Fgf8 (268 aa). Human FGF17 showed 98.6% total-amino-acid identity with rat Fgf17 (216 aa). Human FGF18 also showed 98.6 total-amino-acid identity with rat Fgf18. FBXW1 (βTRCP1 or BTRC1)-FGF8-NPM3 locus at human chromosome 10q24.32, FBXW11 (βTRCP2 or BTRC2)-FGF18-NPM1 locus at human chromosome 5q35.1, and FGF17-NPM2 locus at human chromosome 8p21.3 were paralogous regions within the human genome. FGF8 mRNA was expressed in DMSO-treated embryonic stem (ES) cells. FGF17 mRNA was expressed in ES cells differentiated to an early endodermal phenotype. FGF18 mRNA was expressed in fetal lung, fetal heart, lung carcinoid, colorectal cancer, and ovarian cancer. FGF18 promoter with double TCF/LEF binding sites rather than FGF8 promoter and FGF17 promoter was more conserved between human and rodents. These facts indicate that FGF18 orthologs were evolutionarily conserved targets of the WNT/β-catenin signaling pathway.