Notch1 is the human homolog of the D. melanogaster Notch gene first reported as the gene responsible for the presence of notches in the wingblades of a specific strain of flies. The Notch protein is a transmembrane receptor that mediates juxtacrine signals between adjacent cells. Mammalian Notch1 ligands include Delta-like and Jagged. Upon ligand binding, Notch1 undergoes two proteolytic cleavage events that result in the release of the intracellular Notch1 domain and its translocation to the nucleus where it can participate in gene transactivation. Notch 1 signals mediate cellular fate, differentiation, and development.