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Artificially Induced Oocytes
In mice, male embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have been shown to differentiate into primordial germ cell–like cells (PGCLCs) in vitro. Upon transplantation into testes, these PGCLCs can form fully functional sperm. Again working in mice, Hayashi et al. (p. 971, published online 4 October) found that female ESCs and iPSCs can also differentiate into PGCLCs, which, when aggregated in reconstituted ovaries, exhibited epigenetic reprogramming and meiotic potential in vitro. Upon transplantation of the reconstituted ovaries under ovarian bursa, female PGCLCs developed into fully grown oocytes that contributed to healthy offspring upon in vitro maturation and fertilization.
Reconstitution of female germ cell development in vitro is a key challenge in reproductive biology and medicine. We show here that female (XX) embryonic stem cells and induced pluripotent stem cells in mice are induced into primordial germ cell–like cells (PGCLCs), which, when aggregated with female gonadal somatic cells as reconstituted ovaries, undergo X-reactivation, imprint erasure, and cyst formation, and exhibit meiotic potential. Upon transplantation under mouse ovarian bursa, PGCLCs in the reconstituted ovaries mature into germinal vesicle-stage oocytes, which then contribute to fertile offspring after in vitro maturation and fertilization. Our culture system serves as a robust foundation for the investigation of key properties of female germ cells, including the acquisition of totipotency, and for the reconstitution of whole female germ cell development in vitro.