Oct4 (Octamer Binding Transcription Factor 4) is part of the POU family, whose members contain a bipartite DNA-binding domain consisting of the POU-specific (POUS) and POU homeo-domain (POUHD). Connection of these subdomains by a flexible linker gives POU transcription factors the intrinsic ability to adopt several binding configurations on DNA. POU transcription factors were originally identified as proteins able to activate genes bearing cis-acting elements containing an octameric sequence within their promoter region. They bind to the consensus sequence ATGCAAAT.

The Oct4 gene has only been found in mammals. In mice, it is located on chromosome 17 and is separated into five exons, which encode a mRNA transcript of 1.5 kb. The human Oct4 is 87% identical to that of the mouse, and is located on chromosome 6. In humans, two transcripts are produced through alternative splicing, while mice produce only one transcript. Oct4 has also been found in other mammalian species including bovine and rat. Oct4 mRNA and protein are present in unfertilized oocytes and expression is abundant and uniform in all cells of the embryo through the morula stage (32-64 cells). After day 7.5, Oct4 is strictly confined to the primordial germ cells (PGCs), precursors of the gametes. Oct4 is also expressed in embryonic stem (ES) and embryonic carcinoma (EC) cells.

The first morphological indication of differentiation in mammalian embryogenesis is the formation of the trophectoderm (TE) at the early blastocyst stage. While TE cells are restricted to extra-embryonic cell lineages, inner cell mass (ICM) cells remain totipotent. During this phase, Oct4 is downregulated in cells that form the TE, while the cells in the ICM maintain a high level of Oct4. Consequently, a high level of Oct4 expression is thought to keep cells in a totipotent stage, whereas down-regulation is associated with differentiation. Several genes have been found to contain Oct4 binding sites; some positively and some negatively regulated. The α and β subunits of human chorionic gonadotrophin (HGC) are negatively regulated by Oct4 while platelet-derived growth factor (PDGF) α is activated by Oct4.