Developmental biologists have devised a method for growing mouse embryos outside a uterus for longer than ever before, giving them an unprecedented view of how mammalian organs and limbs form—a process previously hidden inside a mother’s body. Researchers in Israel report today that the new system, which includes rotating bottles filled with nutrients, kept the mouse embryos alive from roughly day five of development until day 11, about halfway through the animals’ 20-day gestation. By that time the embryos have formed hind limbs and all their major organs.
“It looks very spectacular,” says Max Planck Institute for Molecular Genetics developmental biologist Alexander Meissner, who was not involved in the work. “The fact that [the researchers] can culture these embryos and keep them alive for such a long time—it’s amazing.”