Germline cells transmit genetic information from generation to generation, making them the focus of reproductive studies. In mice, primordial germ cells (PGCs) appear in gastrulating embryos at embryonic day 7.25 and have been generated in vitro from the outer germinal membrane of an ovum (epiblast), provided the epiblast is cocultured with cells expressing bone morphogenic protein (BMP) 4 and 8b. How the founder population of PGCs is separated from the rest of the pluripotent epiblast has been unclear because of technical difficulties in distinguishing PGCs from embryonic stem (ES) cells, since standard PGC markers (OCT4 and alkaline phosphatase) are also positive in ES cells. In the September 15
Toyooka et al. targeted the
This suggests that the ES cell line used could generate PGCs in culture, but it gave no clue as to the developmental potential of these cells. Therefore, Toyooka et al. performed transplantation experiments with purified LacZ-positive ES-derived cells. After coculture with gonadal cells and transplantation into the male gonad, ES-derived PGCs differentiated into spermatogenic cells and, ultimately, sperm.
"We have demonstrated that ES cells are able to differentiate into germ-line cells in vitro" and "have the potential to undergo meiosis and produce sperm," conclude the authors. The easy detection of differentiating PGCs could facilitate advances in reproductive engineering.