Mouse primordial germ cells (PGCs) are specified between embryonic day 6.5
(E6.5) and E7.5, when they have been visualized as an alkaline phosphatase-
positive (AP+) cell population in the developing allantois. By E8.5, they a
re embedded in the hind-gut epithelium. Previous experiments have suggested
different sites for PGCs' origin, and it is unclear how they reach the gut
epithelium. We have used transgenic mice expressing GFP under a truncated
Oct4 promoter to visualize living PGCs. We find GFP+/AP+ cells in the poste
rior end of the primitive streak as a dispersed population of cells activel
y migrating into the allantois, and directly into the adjacent embryonic en
doderm. Time-lapse analysis shows these cells to be actively migratory from
the time they exit the primitive streak. (C) 2000 Elsevier Science Ireland
Ltd. All rights reserved.