A critical event during embryonic development is the segregation of the germ line from the soma. The germ line founders, or primordial germ cells (PO C), are the precursors of the gametes, which enable the transmission of the genetic material to future generations. In rodents, the PGC precursors are segregated from somatic lineages before the start of gastrulation. In several model organisms segregation of the germ line is accomplished by maternally inherited transcriptional repressors contained in the egg's germ plasm. In mammals, PGC specification is regulated by epigenesis, a mechanism by which pluripotent cells ill the epiblast respond to specification signals according to a temporal and spatial program of differentiation. In the mouse embryo, the transcriptional repressor Blimp] plays a fundamental role in restricting nascent POC to somatic differentiation signals. The aim of this project was to determine whether the mechanism of lineage specification is conserved in humans.