Oct-4 (POU5F1) is a transcription factor expressed in the totipotent and pluripotent stem cells of the pregastrulation embryo. It is also expressed in primordial germ cells and in the female germ line. OCT4 binds to the octamer motif (5'-ATTTGCAT-3') and forms a trimeric complex with SOX2 on DNA and controls the expression of a number of genes involved in embryonic development such as YES1, FGF4, UTF1 and ZFP206. It is critical for early embryogenesis and for embryonic stem cell pluripotency.