Previous reports have shown that embryonic stem (ES) cells, derived from the inner cell mass of mouse or human blastocysts, could differentiate in vitro into female and male germ cells as well as into the cell types of all three germ layers. While in one case, the ES cell-derived germ cells have been reported to give birth to live offspring in the mouse, these cells differ in fertilization capacity from the sperm and oocytes produced in vivo as they cannot complete meiosis under in vitro conditions. The efficiency of functional germ cell isolation from ES cells is also low. According to published reports, factors such as the proper selection of feeder cells, including ovarian granulosa cells and those which could secrete bone morphogenic protein-4 (BMP4), and the addition of retinoic acid into culture medium, could to some extent establish and improve the microenvironment ES cells rely on for differentiation into germ cells. This review briefly describes the progress of deriving germ cells from ES cells and discusses possible factors that could improve in vitro gamete production.
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