Mouse Embryos Grown WITHOUT Eggs or Sperm

[Tom.G]

https://www.nature.com/articles/d41586-022-02334-2

That period (8.5 days) is long enough for the brain regions to develop, the heart to start beating, and the neural and gut tubes to form. These synthetic embryos look a lot like natural embryos that form when mouse sperm meets egg, but they “were not 100% identical”, Hanna says. “You can see some defects and some changes in the organ size.”

 

[BillTre]

They were made from stem cells (rather than egg and sperm cells).
Mice are mammals and normally develop in the mother receiving nourishment from the placenta.
Late implantation in mice is at 8 to 10 days post fertilization, so (assuming a similar rate of development) these could be similar to preimplantation embryos. This may be why they did so well. Thay had not yet run into the requirement for nourishment from the mother. Implanted embryos would also be in a different environment and would receive different signals of various kinds from the mother's uterus. These may be important for normal subsequent development.

Growing mammalian embryos to later stages in a dish is a dream of a lot of researchers. They have to be removed from the mother for any really intensive observations. This is why zebrafish are considered a much more optimal prep for observing development. The eggs are externally fertilized and all development is easily observed in a microscope, with lot of observational and manipulative tricks available.