Toward directed reprogramming through exogenous factors.

Direct reprogramming of one cell type into another provides unprecedented opportunities to study fundamental biology, model disease, and develop regenerative medicine. Different paradigms of reprogramming strategies with different sets of factors have been developed to generate various cell types, including induced pluripotent stem cells, neuronal or neural precursor cells, cardiomyocyte-like cells, endothelial cells, and hepatocyte-like cells. Various exogenous factors, especially small molecules modulating signaling, cellular state, and transcription, have been identified to enhance and enable reprogramming. With an increased understanding of reprogramming mechanisms and discovery of new molecules, it is conceivable that reprogramming can be achieved in a more directed and deterministic manner under entirely chemically defined conditions.