For the first time, researchers from the Weizmann Institute of Science in Israel have demonstrated the creation of mouse embryos without using eggs or sperm. The findings were reported in a peer‑reviewed journal article.
Embryonic stem cells formed the foundation of these embryos. These cells can become cells from the three primary germ layers yet cannot alone produce extra‑embryonic tissues. The scientists reprogrammed some of the cells so they could contribute to the placenta and yolk sac, tissues that support blood formation at a specific stage of development.
The team achieved clusters consisting of about ten thousand cells, but only a small fraction—roughly fifty cells—continued to develop. The embryos remained in an artificial womb for about 8.5 days, which corresponds to half of a typical mouse gestation. They were placed in small vessels containing a nutrient solution, and these vessels were mounted on a rotating cylinder to imitate blood flow and nutrient delivery to the developing placenta, while also reproducing the uterus‑like pressure.
By day six, areas that would form the central nervous system began to appear, and soon the brain started to take shape. By day eight, the heart, vessels, and intestines formed. In both structure and genetics, the embryos closely resembled natural mouse embryos.
The study authors note that the next objective is to understand how stem‑cell groups know what to do: how they assemble into organs and move to their designated locations within the embryo. Since the artificial uterus is transparent, unlike a natural one, this platform could be used to model congenital and acquired defects in human embryos and may offer a clearer view of developmental processes that are hard to study in vivo.
Beyond basic insight, the bioreactor system holds potential as an incubator for cells, tissues, and organs grown for transplantation, contributing to future therapeutic possibilities.