Figure 1.

Schematic representation of differentiation pathways from ES/iPS cells into germ cells. ES cells are derived from the mouse blastocyst, and iPS cells are reprogramed from adult somatic cells. Both ES/iPS cells can be differentiated into PGCs and further towards either spermatocytes or primary oocytes. Germ cell markers for the corresponding stages are marked as framed. Certain germ-cell-specific genes, like the ones coding for germ granule components like Ddx4/Vasa are active all through germ cell development, while others like Fank1 only expressed at distinctive phases of germ cell development. Abbreviations: ES: Embryonic stem, iPS: Induced pluripotent stem, PGCs: Primordial germ cells, SSCs: Spermatogonial stem cells.