Programmed cell death in mouse primordial germ cells.

In a number of mammalian species, the main events of development of the primordial germ cells (PGCs), the embryonic precursors of the oocytes and spermatozoa, were described during the early twentieth century. Actually, the concept of the origin of germ cells in extragonadal sites before the formation of the gonadal anlagen, was put forward for the human embryo around the first decade of the 1900s (for a review, see De Felici, 2013). PGC development is characterized by two major cellular processes, a movement from the wall of the yolk sac, where the germline is determined, to the gonadal anlagen and an increase in number due to active proliferation. As far as we know, the notion that programmed cell death (PCD) might physiologically occur in mammalian PGCs was for the first time put forward by us in 1993 in the case of the mouse. How we arrived to such a concept and the progress made up to now in the characterization of this process in our and other laboratories mainly in the mouse are the topics of the present review