Meanwhile, Hannah’s team in Israel had grown a mouse embryo model in a similar fashion, as described in the paper. with paper cell This was published just before the paper by Zernicka-Goetz’s group. Hannah’s model was also made entirely of embryonic stem cells, some of which were genetically induced to become her TSCs and her XEN cells. “Whole embryos filled with synthetic organs, including extraembryonic membranes, can be generated all by starting with naive pluripotent stem cells,” Hannah said.
Hannah’s model of the fetus, like the one made by Zernika-Goetz, went through all the expected early developmental stages. After 8.5 days, they had crude bodies with heads, limb buds, hearts and other organs. Their bodies were attached to a TSC-made pseudoplacenta by umbilical cord-like columns of cells.
“These embryo models mimic natural embryogenesis very well,” Zernika Goetz said. The main difference may be the result of improper formation of the placenta as it cannot contact the uterus. An imperfect signal from a defective placenta can impair the healthy growth of some fetal tissue structures.
Without a better substitute for the placenta, “we still don’t know how well these structures will develop,” she says. That’s why she believes the next big challenge will be to address developmental stages in embryonic models that normally require the placenta as an interface between the maternal and fetal circulatory systems. No one has yet found a way to do it in vitro, but she says her group is working on it.
Hanna admitted that she was surprised that the embryo model continued to grow well past gastrulation. However, after working on this for 12 years, he added, “I get excited and surprised at every milestone, but after a day or two, I get used to it and think it’s normal and focus on the next goal.”
Jun WooA stem-cell biologist at the University of Texas Southwestern Medical Center, Dallas, was also surprised that an embryo model made entirely from embryonic stem cells could evolve so far. “The fact that they can form embryo-like structures with distinct early organogenesis suggests that seemingly functional tissues can be obtained ex utero based purely on stem cells,” he said.
To make matters worse, it turns out that the embryo model doesn’t need to be grown from literal embryonic stem cells—stem cells taken from a real embryo. They can also grow from mature cells taken from you or me and regress to a stem cell-like state. The possibility of such “rejuvenation” of mature cell types is revolutionary discovery Awarded by Japanese biologist Shinya Yamanaka 2012 Nobel Prize Doctor of physiology or medicine. Such reprogrammed cells, called induced pluripotent stem cells, are created by injecting mature cells (such as skin cells) with several key genes that are active in embryonic stem cells.
So far, induced pluripotent stem cells appear to be able to do almost anything that real embryonic stem cells can do, including growing into embryo-like structures in vitro. And its success appears to sever the last crucial link between the embryo model and the real embryo. Because you don’t need an embryo to make them, they fall outside most of the existing regulations.
Growing Organs in the Lab
Even if the embryo model bears unprecedented similarity to the real embryo, it still has many shortcomings. Nicholas Libron“Embryonic models are rudimentary, incomplete, inefficient and lack the ability to give birth to organisms,” admits the stem cell biologist and embryologist at the Institute for Molecular Biotechnology in Vienna.
The failure rate of developing embryo models is very high, with less than 1% of the initial cell clusters growing. Subtle anomalies are mostly related to disproportionate organ sizes, and often obliterate them, Hanna said. Wu believes more research is needed to understand both the similarities with normal embryos and the differences that might explain why the mouse embryo model is unable to grow beyond 8.5 days.
