Mouse embryos grown outside a uterus for 11 days

Researchers have devised a method for growing mouse embryos up to the point they start growing limbs and organs, outside of the uterus.

The work was published in Nature and performed by scientists at the Weizmann Institute of Science in Rehovot, Israel. Embryos collected from pregnant mice were kept alive for up to 11 days, a week longer than previously possible, by culturing them in rotating flasks containing nutrient solution with carefully controlled gas concentration and pressure. Because the embryos reached organogenesis, the process by which the internal organs and specific structures such as limbs are formed, outside of the uterus researchers were able to observe the early development of limbs and organs.

'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,' said Professor Jacob Hanna, who led the work. He continued: 'Our aim was to recreate those conditions, and now we can watch, in real time, as each domino hits the next one in line.'

Until now, embryologists have needed to remove developing embryos from within the uterus of a mouse in order to gather information about developmental progress. This obstacle means that research can only provide snapshots of development and not the ability to track these processes in real time.

Markers were used which detect the expression of specific development related genes to see whether or not the culture method affected the development of the embryos. These developmental markers were found to be identical between the cultured embryos and those extracted from mice at the same developmental stage, showing that the  embryos grown outside of the uterus developed just as they would in the uterus.

The new method 'opens new doors by making embryos accessible for a detailed study of many aspects of their development,' Professor Magdalena Zernicka-Goetz, a developmental biologist at the University of Cambridge and California Institute of Technology, not involved in the study, told Science.

Growing embryos fertilised using IVF rather than collected from pregnant mice, is the next step for researchers. This will allow the earliest stages of development to be studied as well. It is hoped achieving this could provide some insight into developmental diseases and why implantation and early development of the embryo sometimes fails during pregnancy in mammals.

It is currently against guidance from the International Society for Stem Cell Research to carry out research on human embryos beyond 14 days. At this stage the embryo 'gastrulates' into layers of cells that go on to differentiate into different parts of the body. Updated guidance on this is expected in May.