Establishment of the germ cell lineage in mammals

The germ cell lineage in mice becomes lineage-restricted about 7.2 days pos t coitum. Its progenitors have migrated from the proximal region of the epi blast. Cells from the distal region of the epiblast will also give rise to germ cells, if they are transplanted to the proximal region at the appropri ate time. Cells in this region are subject to a predisposing signal from th e adjacent extra-embryonic ectoderm. It appears that this and other signals determine the emergence of germ cells: unlike in some other organisms, thi s event is not predetermined. (C) 2000 Wiley-Liss, Inc.