The most complete human embryo model to date has been created, mimicking all of the key structures that emerge in the early embryo by day 14 of development.
Scientists at the Weizmann Institute, Israel have improved upon other recently created stem-cell-based embryo models (SCBEMs) (see BioNews 1194, 1195, 1196 and 1200) which have lacked most of the defining hallmarks of a post-implantation embryo.
'The drama is in the first month, the remaining eight months of pregnancy are mainly lots of growth,' said Professor Jacob Hanna, who led the study published in Nature. 'But that first month is still largely a black box. Our stem-cell-derived human embryo model offers an ethical and accessible way of peering into this box. It closely mimics the development of a real human embryo, particularly the emergence of its exquisitely fine architecture.'
Professor Hanna and his colleagues used human naïve pluripotent stem cells (see BioNews 1204) to create types of cell that – in an actual human embryo – would go on to form the embryo proper (and subsequently the fetus), the placenta, and the yolk sac.
The researchers mixed 120 such cells in a particular ratio, and placed them on a shaker, causing cell clumps to grow. About one percent spontaneously self-organised into embryo-like models, with structural and morphological similarity to an actual human embryo after 14 days of development.
Professor Hanna explained: 'It's critical to mix in the right kinds of cells at the beginning, which can only be derived from naïve stem cells that have no developmental restrictions. Once you do that, the embryo-like model itself says, "Go!"'
Comparison with textbook illustrations, from some of the most comprehensive embryology atlases from the 1960s, demonstrated that these SCBEMs are unprecedentedly similar to – but not identical to – actual post-implantation human embryos. It would not be possible (or permissible) to establish a pregnancy using these SCBEMs, but nonetheless, secretions from the SCBEMs did turn a pregnancy test positive.
The researchers hope that their models will advance research into infertility, drug testing and tissue transplants, as well as expanding our understanding of the first weeks of embryonic development.
'Many failures of pregnancy occur in the first few weeks, often before the woman even knows she's pregnant,' said Professor Hanna. 'That's also when many birth defects originate, even though they tend to be discovered much later. Our models can be used to reveal the biochemical and mechanical signals that ensure proper development at this early stage, and the ways in which that development can go wrong.'
Professor Robin Lovell-Badge from the Francis Crick Institute, London, who was not involved in the study (and who is chair of trustees at PET, the charity that publishes BioNews) told BBC News that these SCBEMs 'look pretty good' and 'look pretty normal'. But he cautioned that the current 99 percent failure rate in the creation of the SCBEMs will need to be improved, if they are to prove insightful in research.
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