Artificial gametes: Where are we in 2021?

Pluripotent stem cells and spermatogonial stem cells are stem cell types specialized for reconstitution of germ cell development in vitro, as they are capable of differentiating into gametes. Reconstitution of germ cell development, termed in vitro gametogenesis, will provide an experimental platform for a better understanding of germ cell development, as well as an alternative source of artificial gametes for reproduction, with the potential to treat and cure infertility. Since germ cells are especialized cells that will pass all genetic information into the next generation, both the in vitro culture system and its derived-cells from stem cells must be carefully evaluated. In this review, we summarize the progress in in vitro gametogenesis, most of which has been made using mouse models, as well as the future challenges in this field.