The notch gene belongs to a family of epidermal growth factor (EGF) like homeotic genes, which encode transmembrane proteins with a variable number of cysteine-rich EGF-like repeats in the extracellular region. Four notch genes have been described in mammals, which include notch-1. notch-2, notch-3, and notch-4(Int-3), which have been implicated in the differentiation of the nervous system and other structures. The EGF-like proteins Delta and Serrate have been identified as ligands of notch-1. Mature notch proteins are heterodimeric receptors derived from the cleavage of notch pre-proteins into an extracellular subunit (NEC) containing multiple EGF-like repeats and a transmembrane subunit including intracellular region (Ntm). Alteration of notch-1 signaling or expression may contribute to tumorigenesis.