Germ cells and pluripotent stem cells in the mouse.

For many years, attempts to achieve long-term culture of mouse primordial germ cells (PGCs) proved unsuccessful, even when feeder layers were used and individual growth factors were added to the medium. However, when three growth factors were added simultaneously to the medium, some of the cells continued to proliferate indefinitely. Similar to embryonic stem cell lines, these embryonic germ (EG) cell lines were capable of giving rise to embryoid bodies in vitro, and colonizing all cell lineages in chimeras, including the germline. Initially, EG cells were made from PGCs before migration, 8.5 days post coitum (dpc), and after entry into the genital ridge, 11.5 and 12.5 dpc. New EG cell lines from 9.5 dpc (migrating) and 11.5 dpc PGCs, carrying either a LacZ or GFP transgene, are described here. The developmental potential of the new EG cell lines in vitro, in vivo in chimeras, and in tissue aggregates in organ culture was studied. The EG cells were compared with PGCs at the stage from which the EG cells were derived. The two cell types show several similarities, but also some differences in gene expression and cell behaviour, which require further exploration.