In Line with Our Ancestors: Oct-4 and the Mammalian Germ

The transcription factor Oct-4 is expressed specifically in the totipotent germline cycle of mice. Cells that lose Oct-4 differentiate along different paths to form embryonic and extraembryonic somatic tissue. Oct-4 may maintain the potency of stem and germline cells by preventing all other differentiation pathways. Oct-4 may also regulate the molecular differentiation of cells in the germ lineage as it progresses from the fertilized egg, through cleavage stage/morula blastomeres, blastocyst, inner cell mass, epiblast, germ cells, and gametes. The factors that regulate, and are regulated by, Oct-4 are reviewed with respect to the phenomena of cell potency and germ/soma segregation and differentiation.