Scientists have created a creature that closely resembles a human embryo – without sperm, eggs or a uterus.
The embryo has even released so much of the hormone that pregnant women produce that a pregnancy test turns positive, leading to a positive test result in the laboratory.
Researchers at the Weizmann Institute of Science in Israel created complete models of human embryos from stem cells created in the laboratory, building on previous research in which they created mouse embryos.
The researchers’ goal is to ethically study what happens in the very early stages of pregnancy without having to experiment with real human embryos. The model developed by the team is a collection of cells that cannot grow into a human.
The embryo is not human and could not become one because the artificial embryo could not be successfully implanted into the uterine lining. An embryo is typically considered a fetus between weeks 9 and 12, when it has all major organ systems and is clearly a human being.
Pictured: the 14-day embryo, including the yolk sac (yellow) and the part that will become the embryo itself, topped by the membrane (blue) – all encased by cells that will become the placenta (pink).
Pictured: A human embryo model derived from stem cells at a developmental stage corresponding to that of a human embryo on day 14. It shows the hormone used in pregnancy tests (green) and the outer layer that becomes the placenta (pink).
The artificial embryo model contained all the elements that would be expected in a 14-day-old human embryo, including the placenta, yolk sac, membranes and other external tissues.
Many miscarriages and birth defects occur in this early period, but little is currently known about them.
Professor Jacob Hanna, who led the research team, said: “The drama unfolds in the first month; The remaining eight months of pregnancy are mainly characterized by strong growth.’
“That first month is still largely a black box.” Our stem cell-derived human embryo model offers an ethical and accessible way to look into that box.
“It closely mimics the development of a real human embryo, particularly the emergence of its extremely delicate architecture.”
Previously, models of human embryos were not accurate because they did not contain cell types that are critical to an embryo’s development, including cells that make up the placenta and membrane.
They also didn’t grow past the 14-day mark.
Instead of a sperm and an egg, the Israeli researchers used naive stem cells, which they reprogrammed so that they could develop into any type of tissue in the body.
This is the same stage as the seventh day of the natural human embryo, just prior to implantation in the uterus.
Chemicals were used to stimulate the stem cells to transform into four types of cells needed to form an embryo: epiblast cells, from which the fetus develops; trophoblast cells that become the placenta; hypoblast cells, which become the supporting yolk sac; and extraembryonic mesodermal cells, which become part of the amniotic sac.
About 120 of the cells were mixed together in a precise ratio, totaling about 0.01 millimeters.
By day 14, only one percent of the mixture had spontaneously multiplied into around 2,500 cells measuring half a millimeter.
However, the other 99 percent did not develop. Other scientists suspected that it would be difficult to determine what would happen in a miscarriage – something the researchers hoped might be possible by studying the embryo model – if 99 percent of the cell mix was unable to to assemble yourself.
Professor Hanna said: “An embryo is by definition self-directed; We don’t have to tell it what to do – we just have to unleash its internally coded potential.
“It’s critical to get the right types of cells mixed in early on, which can only be obtained from naïve stem cells that have no developmental constraints.” Once you do that, the embryo-like model itself says, “Go!”
The embryo model was then allowed to grow until it could be compared to an embryo 14 days after fertilization.
In most countries, this is the legal limit for normal embryo research.
The researchers emphasized that it was unethical, illegal and impossible to create an actual pregnancy from the embryo models.
Because as the 120 cells assemble, they exceed the point at which an embryo could be successfully implanted into the uterine lining.
One way to use the embryo model is to create organs for transplantation, Professor Hanna told The Guardian.
Model embryos could be created from skin cells from diseased patients, from which organs could grow after a month or two, which could then be used for transplantation into the patients.
The research was published today in the journal Nature.