Lineages of embryo formed in latest stem-cell-based embryo model

An embryo model that has been created from human pluripotent stem cells (hPSCs), without using eggs or sperm, shows how tissues of the developing embryo interact.

Stem-cell-based embryo models (SCBEMs) are entities or materials that – in some respects – resemble embryos in the earliest stages of human development (see BioNews 1194 and 1195). Publishing their research in Nature, scientists report that primed hPSCs can be triggered to self-organise into 3D structures that mimic post-implantation events in early human development. The model created includes both embryonic tissues and extra-embryonic tissues (placenta and yolk sac), allowing researchers to study how these two tissues interact during the gastrulation phase, which occurs around two weeks after fertilisation.

'If we can experimentally model this period, then we can finally start asking questions about how human development happens in those very early stages that are normally hidden within the body of the mother,' said corresponding author Dr Berna Sozen, assistant professor of genetics at Yale School of Medicine, New Haven, Connecticut. This latest research meant scientists would hopefully also be able to study embryonic failure, developmental disorders and pregnancy loss in future, she added.

Dr Sozen and her colleagues grew embryonic stem cells in vitro, transferred the cells into a 3D culture system, and exposed them to conditions that stimulated the cells to spontaneously self-organise and differentiate. The scientists grew the cells for approximately one week, and analysed how they guided each other as they developed. Without any changes being made to the genome, the cells formed the two key embryonic cell populations – the epiblast (precursor to the embryo) and the hypoblast (precursor to the yolk sac).

'The work presented... is a remarkable study that has been carried out with great care. The data show the development and detailed description of the generation of a stem-cell-based embryo model that will allow researchers to carry out precise studies on how the founder lineages of the developing embryo can interact with each other,' said Professor Roger Sturmey from Hull York Medical School, chair of the Guidelines Working Group of the Governance of SCBEMs (G-SCBEM) project.

G-SCBEM – which is led by Cambridge Reproduction in partnership with the Progress Educational Trust (PET) – is a project which involves scientists, ethicists, legal experts and others in developing a recommended governance framework for UK research involving SCBEMs.

Professor Sturmey added: 'Importantly, these data highlight similarities between stem cell-based embryo models and embryos proper – but also reveal subtle differences, which do distinguish these models from embryos proper.'

The authors of the Yale-led study believe that their model for human post-implantation development could offer new insights into why pregnancies can fail, as well as insights into the origins of congenital disorders.