NUMB plays an essential role in the determination of cell fate and development and appears to be especially important to sensory organogenesis and neurogenesis. NUMB is a notch1-interacting protein that antagonizes the notch1 signaling pathway. In the cell, NUMB is asymmetrically localized. The polarized distribution of NUMB in the cell is fundamental to its function of promoting asymmetric cell division for cell fate specification. Numb is also implicated to function as an endocytic protein, as it interacts with EPS15, a protein involved in endocytosis.