Further stages of development observed in mouse embryo models
Dr Rachel Montgomery
Progress Educational Trust06 September 2022
'Synthetic' model embryos made using mouse stem cells and an artificial incubator are the closest a stem-cell-derived embryo model has ever come to resembling a naturally developing embryo in the uterus.
Researchers from the University of Cambridge and the California Institute of Technology grew the so-called 'integrated stem cell-based embryo models' for 8.5 days (complete mouse gestation is 18-21 days) – long enough to develop a beating heart and the foundations of all other organs.
'The stem cell embryo model is important because it gives us accessibility to the developing structure at a stage that is normally hidden from us due to the implantation of the tiny embryo into the mother's womb' said lead researcher Professor Magdalena Zernicka-Goetz from the University of Cambridge.
As reported in Nature, the models were developed by combining three different and specific types of stem cells: one that will develop into the embryo, with the other two developing into extraembryonic structures including the placenta and yolk sac which provides the early embryo with nutrients.
When combined in an artificial incubator, the stem cells were found to signal to each other via touch and chemical messengers, allowing them to spontaneously self-organise into embryos. These synthetic models also reached the point where the entire brain, including the anterior forebrain, began to develop.
'The embryos struggle to grow beyond that point because they require a placenta which we cannot reproduce in vitro', first author Dr Gianluca Amadei from the University of Cambridge told the Financial Times.
The recent work builds on very similar work published earlier this month by Professor Jacob Hanna at the Weizmann Institute of Science in Israel, who genetically altered stem cells to create mouse embryo models and also allowed them to develop for 8.5 days. Both studies found the process highly error-prone, with only one in 100 attempts being successful.
Nonetheless, the team hope that their findings could have a number of implications, from improving the understanding of normal development and helping to better understand why some embryos go on to develop into a healthy pregnancy, while many others fail.
The team are also working on developing human embryo models, but stress that these efforts are considerably further behind given the differences in understanding between early human and mouse development.
Having a lab-grown human embryo model available for research could be a major advance for the study of fertility and common developmental disorders, but also highlight the importance of ongoing ethical and legal conversations about the status and use of model embryos and natural human embryos in research.
Sarah Norcross, director of PET, said: 'Unlike actual human embryos, stem-cell-based embryo models in humans and other organisms are not restricted by a 14-day rule…These models are extremely helpful for research, but there still remains a case for changing the law to extend the 14-day rule, so that we can continue to learn from the precious embryos that have been kindly donated by fertility patients following their treatment.'
Sources and References
25 August 2022. University of Cambridge
‘Synthetic’ embryo with brain and beating heart grown from stem cells by Cambridge scientists
25 August 2022. Nature
Synthetic embryos complete gastrulation to neurulation and organogenesis
25 August 2022. New Scientist
Synthetic mouse embryos with rudimentary brain grown in the lab
25 August 2022. Nature
Mouse embryos grown without eggs or sperm: why and what’s next?
25 August 2022. Financial Times
Scientists create ‘synthetic’ mouse embryos with brains and beating hearts
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.