In mammals, the Musashi family is important for cell fate determination, playing roles in maintenance of the stem-cell state, differentiation and tumorigenesis. Musashi1 (also known as Msi1), is selectivley expressed in neural progenitor cells, including neural stem cells. Outside the nervous system, Musashi1 is a selective marker for intestinal stem or early lineage cells. Musashi1 interacts with the Notch pathway during asymmetric cell division by binding the 3' UTR of Numb. Numb is prevented from repressing Notch signaling when Musashi1 is present.