The POU5F1 gene, which encodes the POU domain, class 5, transcription factor 1 (also known as Oct-4), is expressed in embryonic stem cells where it regulates pluripotency and proliferation.The POU5F1 gene encodes one of the "core" transcription factors necessary to establish and maintain pluripotency in mammals. Its function depends on its precise level of expression, so its transcription has to be tightly regulated. POU5F1 is a key regulator of self-renewal and differentiation in embryonic stem cells and may be associated with initiation, promotion, and progression in cancer. POU5F1 is a transcription factor and master regulator of cell pluripotency with indispensable roles in early embryo development and cell lineage specification. The role of embryonic POU5F1 in blastocyst formation and cell lineage specification differs between mammalian species .