Oct4

Oct4, also known as POU domain transcription factor, Octomerbinding transcription factor 3 and Oct3, is expressed in human and mouse totipotent embryonic stem and germ cells. It may function in preventing these cells from differentiating. Each type of established mammalian pluripotent stem cell line (embryonal carcinoma (EC) cells, embryonic stem (ES) cells and embryonic germ (EG) cells) expresses Oct4, which disappears rapidly when the cells differentiate. Most studies on Oct4 have been performed on murine embryos. In human oocytes of various maturity and normally developing preimplantation/cleavage embryos, a variable Oct4 expression pattern has been revealed, concomitant with a pure cytoplasmic localization of the protein. This variability in expression fades away during compaction, indicating embryonic Oct4 expression; the protein appears in the nucleus, implying biological activity.

Functional Oct4 has been found in human amniotic fluid. As Oct4 transcripts have also been found in various differentiated cells, the presence of Oct-4 transcripts or proteins may not be sufficient for identifying undifferentiated cell lines in humans. It may also be important to examine the localization of Oct4 proteins within a cell. Oct4 has been shown to interact with Nanog and with proteins from multiple repression complexes, including the NuRD, Sin3A and Pml complexes, possibly to control ES fate. Reactivation of Oct4 expression is postulated to occur in differentiated cells that have undergone carcinogenesis, or tumor formation.