Figure 1

Schematic diagram indicating timing of germ cell specification and migration in mouse and likely timings in the rat. The timing of germ cell specification is well-described in the mouse in which PGCs specified from epiblast cells at around e6.25–7 migrate along the developing hind-gut endoderm (from e8.5) and colonise the genital ridges from e10.5. The process is less well-reported in the rat and probably occurs later than in the mouse [9].