NANOG is a transcription factor critically involved with self-renewal of undifferentiated embryonic stem cells. NANOG is thought to function in concert with other factors such as POU5F1 and SOX2 to establish ESC identity. Overexpression of NANOG in mouse embryonic stem cells causes them to self-renew in the absence of Leukemia inhibitory factor. NANOG overexpression in human embryonic stem cells enables their propagation for multiple passages during which the cells remain pluripotent.