Origin, Migration, and Proliferation of Human Primordial Germ Cells

The fi rst histological observations about the origin of the precursors of gametes termed primordial germ cells (PGCs) in extragonadal regions and their subsequent migration into the developing gonads in human embryos date back to the early twentieth century. Fuss (Anat Am 39:407–409, 1911, Anat EntwMech 81:1–23, 1912) and Felix (Die Entwicklung der Harnund Geschlechtsorgane. In: Keibel-Mall Handbuch der 1qEntwicklungageschichte des Menshen, vol 2. Leipzig, Hirzel, pp 732–955, 1911) were apparently the fi rst ones to describe the extragonadal location of PGCs in human embryos. In the youngest, 2.5 mm long, embryo examined (23–26 days postfertilization), These authors described PGCs in the endoderm of the yolk sac wall as cells identi fi able by their large size and spherical shape. Subsequently, Politzer (Z Anat Entw Gesch 87: 766–80, 1928, Z Anat Entw Gesch 93:386–428, 1930, Z Anat EntwGesch 100:331–336, 1933) and Witschi (Contr Embryol Carnegie Inst 209:67–80, 1948) studied the distribution of PGCs in a considerable number of embryos from presomite stages (0.3–0.8 mm, about 3 weeks) to 8.5 mm (5 weeks). Both authors described the migration of PGCs from the yolk sac to the developing gonads. Following a hot debate, it is now generally accepted that after their arrival into the gonadal anlage, PGCs give rise to the oogonia/oocytes and gonocytes (or prespermatogonia) in the embryonic ovary and testis, respectively. These germ cells enter a complex series of events that in the Origin, Migration, and Proliferation of Human Primordial Germ Cells