The successful production of functional mouse eggs entirely in cell culture is described in a study published in Nature this week. The eggs, which were generated using pluripotent stem cells, gave rise to healthy and fertile mouse pups, report the authors.

The egg is the only cell type that is capable of totipotency - the ability to divide and produce all of the differentiated cells in an organism - although how this occurs is not well understood. Female germ cells, which give rise to egg cells, undergo a series of differentiation processes leading to the development of a fully functional egg. A longstanding goal in developmental biology has been to reconstitute the development of egg cells that yield functional eggs using pluripotent stem cells.

Katsuhiko Hayashi and colleagues generated mature egg cells in culture from embryonic stem cells and from induced pluripotent stem cells derived from both embryonic and adult mouse cells. The authors subjected the newly generated egg cells to in vitro fertilization, and the embryos that developed could be transferred into surrogate mice, which for some resulted in the birth of healthy pups. They further show that both male and female pups from induced pluripotent stem cell-derived egg cells were fertile by producing a further generation from these pups. In addition, embryonic stem cells could also be re-derived from the eggs generated in culture and fertilized in vitro.