Octamer-4 (Oct-4), a member of the POU family of transcription factors, has been demonstrated to be vital for the formation of self-renewing pluripotent stem cells. During embryogenesis, expression of Oct-4 is limited to pluripotent cells of the inner cell mass (ICM) that contribute to the formation of all fetal cell types. This relationship between Oct-4 and pluripotency has seen this transcription factor emerge as a marker of pluripotent stem cells. Undifferentiated human and murine pluripotent Embryonic Stem (ES) and Embryonic Carcinoma (EC) cells express Oct-4. Additionally, murine Embryonic Germ (EG) cells are also known to express Oct-4. Following stem cell differentiation, the level of Oct-4 expression decreases. Oct-4 expression by human EG cells is not known.