Nanog is a member of the homeobox family of DNA binding transcription factors that has been shown to maintain pluripotency of embryonic stem cells. Nanog expression is controlled by a network of factors including Sox2 and the key pluripotency regulator Oct-4. Nanog expression is high in undifferentiated embryonic stem cells is down-regulated during embryonic stem cell differentiation, concomitant with loss of pluripotency.