FGF-21 is a secreted growth factor that is a member of the FGF family. Proteins of this family play a central role during prenatal development and postnatal growth and regeneration of a variety of tissues, by promoting cellular proliferation and differentiation. FGF-21, in the presence of betaKlotho as a protein cofactor, signals through the FGFR 1c and 4 receptors and stimulates insulin independent glucose uptake by adipocytes. Recombinant human FGF-21 is a 19.5 kDa protein containing 182 amino acid residues.