Story at a glance

  • Researchers at the Weizmann Institute of Science developed an ecosystem where mouse embryos successfully developed externally from a maternal uterus.
  • "Our aim was to recreate those conditions, and now we can watch, in real time, as each domino hits the next one in line,” lead scientist Jacob Hanna said.

A new study tells the story of healthy mice embryos, developing into fetuses complete with heartbeats and burgeoning limbs, healthy and growing. 

What makes these embryos special is the fact that they grew without a uterus.

For the study published in Nature, a team of researchers from the Weizmann Institute of Science cultivated sample embryos ex-vitro, meaning outside of a maternal mammal uterus — usually a critical component of gestation.



Spending seven years working on designing the perfect artificial womb to harbor embryos in, researchers led by Professor Jacob Hanna created a culture system that allowed mouse embryos to grow normally from the pre-gestation stage all the way to its organogenesis phase; that is, when the embryo develops cellular germ layers that steadily form internal organs.

The embryos were held ex-vitro for up to six days. Perhaps most critically, during this time, each embryo developed normally.

“In utero and ex utero-grown embryos were equivalent morphologically and in the expression of all lineage markers analyzed,” the report read. 

The idea to grow embryos outside of a uterus has been around since the 1930s, according to researchers, but had small success, especially since the developing fetuses tended to grow abnormally as opposed to an in-utero embryo.

“If you give an embryo the right conditions, its genetic code will function like a pre-set line of dominos, arranged to fall one after the other," Hanna said. "Our aim was to recreate those conditions, and now we can watch, in real time, as each domino hits the next one in line.”

To do so, Hanna and his team sourced several-days old mouse embryos placed on a man-made growth medium that imitates the wall of a uterus. Once they properly attach, the embryos enter the first stages of embryonic development, and grow in size.

Two days later, as organs began forming from the different cellular embryonic layers grown in the previous phase, scientists added a nutrient solution into the dish harboring the embryos. This functioned as a substitution for the nutrients embryos would receive in a maternal womb from the placenta — absent in Hanna’s artificial womb.

Furthering the genetic engineering capacities this experiment holds, scientists tested inserting genes into the embryos that would identify developing organs in fluorescent colors.

This suggests possibilities for other manipulation of the embryos outside of a uterus.

“We think you can inject genes or other elements into the cells, alter the conditions or infect the embryo with a virus, and the system we demonstrated will give you results consistent with development inside a mouse uterus,” says Hanna. 

The lab’s next mission is to see if they can create artificial embryos using stem cells. This could help yield answers to why some people struggle to become pregnant and reveal more about the window into embryo implantation.

Ideally, this successful study can also lead to the reduction of the use of animals in scientific experiments and expedite research. 

Published on Mar 18, 2021