They believe it “holds huge potential” to help understand causes of genetic birth defects and infertility and develop tests for pregnant women.
The Cambridge university research enables scientists to examine what occurs in the largely unknown “black box development” period of embryos between 14 and 21 days.
Ethical and legal restrictions prevent embryos being developed in the lab beyond day 14, forcing scientists to rely on mouse embryos, which have limitations for understanding human development.
The embryo-like “gastruloid” model does not have brain cells and is not capable of being implanted into the womb and developing into a baby.
But it resembles some key elements of an embryo at about 18-21 days, showing the processes underlying the formation of the human body plan, or blueprint, never directly observed before.
The body plan happens via a process called “gastrulation”, when three distinct layers of cells are formed in the embryo that will later give rise to the body’s major systems: the ectoderm will make the nervous system, mesoderm the muscles, and endoderm the gut.
Many birth defects originate during this “black box” period, with causes including alcohol, medications, chemicals and infections. A better understanding of human gastrulation could also shed light on many medical issues including infertility, miscarriage, and genetic disorders.
Professor Alfonso Martinez-Arias, who led the study, said: “Our model produces part of the blueprint of a human. It’s exciting to witness the developmental processes that until now have been hidden from view – and from study.”
Dr Naomi Moris, the first author of the report, said the research “could prove useful for studying what happens when things go wrong, such as in birth defects”.
Dr Teresa Rayon, of the Francis Crick Institute, said the research “adds into the ‘in vitro toolkit’ that scientists can now use to study the most unknown stages of human pregnancy – between weeks two and four, where women wouldn’t normally know if they are pregnant.
“Over this time period, many birth defects originate. Therefore, models that mimic this process and are reproducible will help to increase our understanding and allow testing how and when things can go wrong.”
Prof Joyce Harper, of the Institute of Women’s Health at University College London, said: “This exciting work will allow many key studies to be done so we can learn about early human development and when it goes wrong. This will help us learn more about genetic diseases and infertility.”