Scientists have bred a creature that closely resembles a human embryo — with no sperm, eggs, or a uterus.
The embryo even secreted hormones, which resulted in a positive pregnancy test in the laboratory.
Researchers at the Weizmann Institute of Science in Israel created complete models of human embryos from lab-created stem cells, building on previous research in which they made mouse embryos.
Her goal is to ethically examine what happens in the very early stages of pregnancy. The embryo model is not a viable human.
Professor Jacob Hanna, who led the research team, said: ‘The drama plays out in the first month; The remaining eight months of pregnancy are mainly characterized by strong growth.’
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).
The artificial embryo model contained all the elements that a 14-day-old human embryo would expect, including the placenta, yolk sac, membranes and other external tissues.
The hope is that the model will allow researchers to ethically explore what happens in a human embryo in the first few weeks after a sperm fertilizes an egg.
Many miscarriages and birth defects occur during this period, but little is known about them at this time.
Professor Hanna said: “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.”
Until now, models of human embryos have not been accurate because they did not contain cell types critical to embryo 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 egg, the Israeli researchers used naïve stem cells, which they reprogrammed to transform 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 on a shaker in a precise proportion totaling about 0.01 millimeters.
By day 14, they had spontaneously multiplied in around 2,500 cells and were half a millimeter in size.
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 grown 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 research was published in the journal today Nature.
