Derivation of germ cells from mouse embryonic stem cells

Deriving oocytes from mouse embryonic stem (ES) cells in the laboratory would be a major advance in therapeutic cloning from today's insufficient process. The first step in this attempt is to study the precursors - primordial germ cells (PGCs), including their emergence, presentation, migration and differentiation. By comparing various reported antigens of germ cells, we found stage-specific embryonic antigen-1 (SSEA-1) and Octamer-4 (Oct-4) are the most useful markers to verify the growth and maturation of germ cell culture from mice. Transgenic mice with specific antigens such as SSEA-1 or Oct-4 are helpful to pick up colonies and follow PGC differentiation. We also delineate the physiological structure for germ cell development by reviewing important studies which employed re-aggregation methods to make germ cells more mature and ready for clinical use. Although some mysteries about reprogramming and intragonadal signal interactions still remain unsolved, each step in uncovering these mechanisms will bring us closer to establishing an unlimited source of germ cells from ES cells.