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takyon writes:

Scientists have coaxed mouse egg precursor cells, created from stem cells, into producing fertile egg cells. The egg cells were created in ovaries outside of a living mouse, but the "lab-based ovaries" were small cell clusters taken from existing fetal mouse ovaries:

In work that raises the prospect of new infertility treatments and designer babies, researchers have used stem cells to grow fertile mouse egg cells for the first time entirely in a lab dish. The eggs gave rise to pups after being fertilized and implanted into rodent foster mothers. The method—which sometimes produced defective eggs and had a success rate of less than 1%—won't be producing human egg cells any time soon, but the technique could help researchers identify key genes involved in egg development and maturation. The work is a "stunning achievement," says George Daley of Harvard Medical School in Boston, who was not involved in the project.

Egg cells are uniquely powerful, containing the instructions needed to start the development of a new organism. Deriving such cells in the lab has long been a goal for researchers who want study their development in more detail. It also raises a futuristic possibility: being able to make human eggs in the lab from skin or other donor cells—and even being able to make genetically altered egg cells. However, any application to human cells is a very long way off, says Katsuhiko Hayashi, a stem cell biologist at Kyoto University in Japan, who led the new mouse egg studies.

[...] The work published today combines the insights gained from that study with the earlier techniques for turning ES and iPS cells into egg precursor cells. First, the scientists used ES and iPS cells to make immature egg precursor cells. Then they inserted those precursors into clusters of cells taken from fetal mouse ovaries. They carefully cultured those cell clusters for more than a month. [emphasis mine]

The team's lab-based ovaries produced more than 50 mature egg cells each, the scientists report. The labmade eggs had higher rates of chromosome abnormalities than is usually observed in eggs in normal mouse ovaries, but more than 75% had the correct number of chromosomes. The scientists mixed some of those eggs with mouse sperm, producing more than 300 two-cell embryos, which researchers then implanted into foster mothers. However, only 11 of those embryos—or 3%—grew into full-term pups, compared with 62% for eggs taken from adult mice and fertilized in vitro. The reasons for that are still unclear, Hayashi says. The pups that did survive grew into apparently healthy, fertile adults. The researchers also showed that they could derive new ES cell lines from embryos generated from the labmade eggs. That recreates, they note, a full cycle of female germ cell development in the lab.

If scientists can develop suitable lab-grown ovaries and artificial wombs, it won't matter if the success rate is in the single digits (and the technique will probably be improved over time), and human embryos could be grown as desired without requiring human participants. There would be no need to "exclude a risk of having a baby with a serious disease" as one of the authors warns, if the purpose is experimentation rather than fertility treatment.

Reconstitution in vitro of the entire cycle of the mouse female germ line (DOI: 10.1038/nature20104) (DX)

[Continues...]

The female germ line undergoes a unique sequence of differentiation processes that confers totipotency to the egg. The reconstitution of these events in vitro using pluripotent stem cells is a key achievement in reproductive biology and regenerative medicine. Here we report successful reconstitution in vitro of the entire process of oogenesis from mouse pluripotent stem cells. Fully potent mature oocytes were generated in culture from embryonic stem cells and from induced pluripotent stem cells derived from both embryonic fibroblasts and adult tail tip fibroblasts. Moreover, pluripotent stem cell lines were re-derived from the eggs that were generated in vitro, thereby reconstituting the full female germline cycle in a dish. This culture system will provide a platform for elucidating the molecular mechanisms underlying totipotency and the production of oocytes of other mammalian species in culture.

Previously: Mice Created from Artificially Developed Embryos

Original Submission