Producing germ cells in vitro would ... be either maintained in an uncommitted and self-perpetuating state or induced to differentiate into any or all of the three germ layers of the early embryo.

Using a noninvasive method to assess germ cell turnover time accurately in vivo with stable isotope labeling (2 H 2 0) ... In Vitro Fen. Embryo Transf. 2(3), 119-122(1985).