The FGF family plays a central role during prenatal development and postnatal growth, and the regeneration of a variety of tissues, by promoting cellular proliferation and differentiation. The FGF ligands bind to a family of type I transmembrane tyrosine kinase receptors, which leads to dimerization and activation by sequential autophosphorylation of specific tyrosine residues. Four genes encoding structurally related FGF receptors (FGFR-1 to -4) are known. Alternative splicing of the mRNAs generates numerous forms of FGFR-1 to -3. Alternate forms of FGF receptors can exhibit different specificities with respect to ligand binding. For example, the form designated as FGFR1a (IIc) interacts predominantly with FGF-acidic (FGF1) and FGF-basic (FGF2). A frequent splicing event involving FGFR-1 and -2 results in receptors containing all three Ig domains, referred to as the alpha isoform, or only IgII and IgIII, referred to as thebeta isoform. Only the alpha isoform has been identified for FGFR-3 and FGFR-4. Additional splicing events for FGFR-1 to -3, involving the C-terminal half of the IgIII domain encoded by two mutually exclusive alternative exons, generate FGF receptors with alternative IgIII domains (IIIb and IIIc). PeproTech's CHO cell-derived Recombinant Human FGFR3 (IIIc) Fc is a glycosylated, disulfide-linked homodimer of 1,170 amino acid residues whose monomer consists of the 353-amino-acid length extracellular portion of FGFR3a (IIc) fused to the 231-amino-acid length Fc portion of human IgG1 by a single glycine. The calculated molecular weight of CHO cell-derived Recombinant Human FGFR3 (IIIc) Fc is 128.3 kDa, however, it migrates at an apparent molecular weight of approximately 100-110 kDa by SDS-PAGE analysis under reducing conditions due to glycosylation.