Model exemplifying downstream mediators of Musashi’s impact in development and cancer. (a) In normal stem cells, Musashi expression suppresses Numb translation, leading to increased Notch signaling and maintenance of an undifferentiated state. Musashi can also suppress p21 (also known as Cdnk1a), which normally blocks cell cycle progression, thus promoting cell proliferation. (b) As Musashi expression is extinguished, suppression of Numb is lost and Notch signaling is inhibited, thus triggering differentiation. In parallel, reduced Musashi expression results in increased levels of p21 and reduced cell proliferation. (c) In the context of cancer, increased levels of Musashi suppress Numb and p21, among other genes, leading to sustained self-renewal of the cancer stem cell pool.