Fig. 1.

Traditional induction of germ cells from ESCs in the 2000s. A Schematic of mouse germ cell specification in the 2000s. (i) mESCs were cocultured with M15 cells or trophoblast cells that secreted BMP4 or BMP8b to induce the specification of mPGCs [22]. (ii) gcOct4-GFP mESCs were cultured for 7 days in the presence of FBS to induce early germ cells, from which the VASA+ cells were enriched by fluorescence-activated cell sorting (FACS) and further cultured to generate oogonia [23]. gcOct4-GFP,conserved region 2 (CR2) and CR3, also termed the proximal enhancer, were deleted from the 5’ regulatory region of Oct4. OCT4 and GFP were driven by the distal enhancer. FBS, fetal bovine serum,VASA, a marker of postmigratory germ cells. (iii) EBs were formed from ESCs, and EB-derived SSEA1⁺ cells were enriched by FACS and further cultured with RA to induce mPGCs [24]. RA, retinoic acid. B Schematic of human germ cell specification in the 2000s. (i) hESCs were aggregated into hEBs when treated with BMPs, from which VASA+ and SYCP3+ double-positive cells with PGC identities were enriched by FACS [26]. (ii) hPGCs can be produced by reducing the size and confluence of plated hESC colonies. These cells could be purified by sorting with CXCR4 antibody [27]. (iii) hESCs were cocultured with human fetal gonad stromal cells to facilitate the production of hPGCs [28]. (iv) Overexpression of DAZL could promote the efficiency of hPGC (VASA+ cells sorted by FACS) specialization from hESCs with BMPs. In addition, co-overexpression of DAZ and BOULE could promote the meiosis of PGCs [29].