Transcription factor required for the maintenance of pluripotency and self-renewal of embryonic stem cells. During embryonic development, expressed preferentially in epiblastic cells and germ cells. In pre-streak embryos, detected in the whole epiblast, but not in the forming hypoblast (stages XI through XIII) (at protein level). As the primitive streak starts to form, disappears from the primitive streak epiblast, but still expressed throughout the area pellucida epiblast (stage XIV -> 3+). At the end of gastrulation (stage 4+), quickly decreases in the epiblast and persists in a crescent anterior to the emerging head process (stages 4+ through 6). At stage 5, strongly expressed in some of the cells in the germinal crescent, probably corresponding primordial germ cells. At stage 7 (neurula stage), undetectable in differentiated cells (at protein level). As the neural plate forms (stages 6-8), expression in the epiblast is restricted to the anterior neural plate. At stage 33, still expressed in germ cells. At stages 42-43, expressed in gonads, as well as in brain, kidney and heart, but at much lower levels than in proliferating embryonic stem cells. Strongly down-regulated during embryonic stem cell differentiation, induced either by retinoic acid treatment, or by cell adhesion prevention leading to embryoid body formation. Belongs to the Nanog homeobox family.