FGF-10 is involved in the initial budding as well as the continuous outgrowth of vertebrate limbs. FGF-10 mRNA is expressed preferentially in neurons but not in glial cells and may have a distinct role in the brain. Human FGF-10 is mitogenic for fetal rat keratinizing epidermal cells but not for NIH 3T3 cells. Recombinant FGF-10 induces the proliferation of human urothelial cells in vitro and induces the proliferation of transitional epithelium. FGF-10 is secreted by cultured mouse pre- adipocytes, prevention of FGF-10 signaling inhibits subsequent differentiation. The ability of embryonic fibroblasts derived from FGF-10 knock-out mice to differentiate into adipocytes is also impaired.