Betacellulin (BTC) is a member of the EGF family of cytokines that also includes EGF, TGF-a, Amphiregulin, HB-EGF, Epiregulin, Tomoregulin and the Neuregulins. It is expressed in most tissues including kidney, uterus, liver and pancreas. BTC also presents in body fluids, including serum, milk, and colostrum. At the amino acid sequence level, human mature BTC protein exhibits 80 % identity with mouse BTC protein. The protein binds to EGFR, ERBB4 and other EGF receptor family members and acts as a potent mitogen for retinal pigment epithelial cells and vascular smooth muscle cells.