TFGwas discovered as a fusion partner ofNTRK1in human papillary thyroid carcinoma. We assembled the mouseTFGcDNA from EST sequences and 5' end RACE product, identified full coding lengthTFGEST clones in pig (c17b07) andSchistosoma mansoni(SMNAS62), and analyzed the genomic structure ofTFGinCaenorhabditis elegans(Y63D3A). The protein sequences of mouse, pig, andS. mansoniTFG are highly homologous to human TFG. TheC. eleganssequence has diverged, but its predicted secondary structure is remarkably conserved. Human, mouse, andC. elegansTFG contain a putative trimeric N-terminal coiled-coil domain, glycosylation, myristylation, and phosphorylation sites, and SH2- and SH3-binding motifs. The SH2-binding motif is absent inC. elegansTFG. The expression ofTFGdoes not vary among 7, 11, 15, and 19 day mouse embryonal stages.In situhybridization with aTFGprobe in 10, 5-day whole mouse embryos showed preferential staining of the limb buds, branchial arches, nasal processes, and brain, and weak staining of the primitive spinal cord and dorsal root ganglia.