OCT4

OCT4, also known as POU5F1, is a transcription factor in the POU family that binds the octamer motif ATTTGCAT and is essential for maintaining pluripotency in early embryonic cells. In humans it is encoded by the POU5F1 gene on chromosome 6p21.3. OCT4 is a key component of the core transcriptional network together with SOX2 and NANOG that sustains self-renewal of embryonic stem cells.

OCT4 consists of a POU domain structure comprising a POU-specific domain and a homeodomain, enabling sequence-specific DNA binding and transcriptional regulation. Alternative splicing yields several isoforms; the main pluripotency-associated isoform is OCT4A, while OCT4B and OCT4B1 have distinct expression patterns and are not required for maintaining pluripotency.

Expression is high in the inner cell mass of the blastocyst, embryonic stem cells, and primordial germ cells, and is downregulated upon differentiation. It functions in a regulatory network with SOX2 and NANOG, and its expression level is dosage-sensitive for pluripotency. OCT4 is also used in reprogramming somatic cells to induced pluripotent stem cells, along with other factors; sustained OCT4 expression is required, but misexpression can promote differentiation or, in some contexts, tumorigenic traits.

In research and clinical contexts, OCT4 serves as a canonical marker of pluripotency in stem cell studies; detection can be complicated by OCT4 pseudogenes and transcript variants. Aberrant OCT4 expression has been reported in some cancers and germ cell tumors, where it is investigated as a marker of stem-like cells.