Defects in stem cell quiescence, activation, or self-renewal have been implicated in diseases including aging-associated sarcopenia, muscular dystrophy, and cancer cachexia. However, identifying the molecules that control whether or not a cell enters quiescence, activation, or self-renewal has been difficult. Here the authors report a live imaging screen to identify such factors. They identify Oncostatin M as a reversible quiescence inducer.