Epidermal Growth Factor, encoded by the EGF gene, has a profound effect on the differentiation of specific cells in vivo and is a potent mitogenic factor for a variety of cultured cells of both ectodermal and mesodermal origin. The EGF precursor is believed to exist as a membrane-bound molecule that is proteolytically cleaved to generate the 53-amino acid peptide hormone that stimulates cells to divide. (From LocusLink)