An incredible new study from researchers at the Hebrew University of Jerusalem has for the first time found a way to transform skin cells into all three of the stem cell types that make up an early-stage embryo. This extraordinary discovery points a way toward creating an embryo without the need for an egg or sperm.
Over a decade ago Japanese researcher Shinya Yamanaka at Kyoto University made a radical breakthrough. He and his team found a way to take regular mouse skin cells and make them revert into embyronic-like stem cells. The ability to easily create these cells, called induced-pluripotent stem cells (iPSCs), was a true revolution in medical science, leading to a number of amazing innovations.
While iPSCs offered scientists spectacular new opportunities, from regrowing human hearts to repairing damaged spinal cords, the innovation had its limitations. If one wanted to build an entire human embryo other novel stem cells were necessary. iPSCs may constitute the bulk of a growing body, but they do not generate several fundamentally important extra-embryonic tissues.
Two other novel types of stem cells are vital to the development of a healthy embryo: trophoblast stem cells (TSCs) and extraembryonic endoderm stem cells (XENs). These are the stem cells that generate the placenta and other important embryo-surrounding tissues, including the umbilical cord and the yolk sac.
Last year a team of Cambridge scientists led a study demonstrating the creation of an artificial mouse embryo generated by combining these three types of stem cells. That research was the first time an embryo was effectively created without a sperm or egg.
Where the Cambridge research captured the three stem cell types from a developing mouse embryo, this new Israeli study indicates these three stem cell types can be generated from adult skin cells, with a combination of five genes responsible for triggering the transformation of the skin cells into each of three embryonic cell types.
Speaking to The Jerusalem Post, corresponding author on the new study Yosef Buganim said that, while the race is on to birth a live mouse created from these transformed skin cells, the science is still potentially decades away from replicating the process in humans.
"To make a baby, we need to organize the cells into a 3-D structure," says Buganim. "Then, if done correctly – if we find the exact ratio between the cell types and the right environment – we could generate an embryo."
Creating entire human embryos from skin cells without the need for sperm or eggs may be the most extreme hypothetical outcome from this research, and one that dramatically reframes human fertility processes. But earlier, more immediate and less controversial, uses for this kind of innovation would be the ability for scientists to better understand embryonic defects or placental dysfunction by modeling the development of an embryo in laboratory conditions.
The new research was published in the journal Cell Stem Cell.
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