The researchers used pure pluripotent stem cells to create a model embryo that looks and acts like a natural human embryo. They say this is an ethical way to better understand embryonic development, which could lead to new avenues of research on birth defects and infertility.

Between 8 and 10 days after fertilization, the egg travels through the fallopian tubes and penetrates the uterine wall, marking the beginning of pregnancy (medically). After implantation, the embryo continues to grow and develop. The main organs and systems of the body are formed during this period, which makes the developing embryo vulnerable to birth defects.

Working to better understand the complex development of embryos is difficult for ethical and technical reasons. But researchers at the Weizmann Institute of Science in Israel may have found a way to do just that.

“Drama in the first month; the remaining eight months of pregnancy are mostly intense growth,” said study author Jacob Hanna. “It accurately simulates the development of a real human embryo, including the appearance of its exquisite architecture.”

The researchers drew on their previous experience in creating synthetic models of mouse embryos made entirely from stem cells. As in previous studies, they started with pluripotent stem cells capable of differentiating into many, if not all, cell types. But the researchers reprogrammed the pluripotent stem cells to revert to an even earlier state known as the pure state, making them capable of differentiating into any cell type.

They divided pure pluripotent stem cells into three groups. Those that will develop into embryos are left as they are. The cells in the other two groups were treated only with chemicals, meaning they were not genetically modified to turn on certain genes designed to enable them to differentiate into one of the three types of tissue needed to support the embryo. Shortly after mixing, the cells aggregated, and about 1% of them self-organized into complete embryo-like structures.

“An embryo is by definition self-governing; We don’t need to tell him what to do; we just have to unlock its internally encoded potential,” Hannah said. When you do, the embryo-like model itself will say: “Go!”.

The embryo-like structures developed normally outside the womb for eight days and reached a developmental stage that coincides with the 14th day of human embryonic development, when natural embryos acquire structures that allow them to begin developing body organs.

The researchers found that the model embryos were structurally similar to natural human embryos seen in old textbooks. They even observed the presence and activity of cells that produce human chorionic gonadotropin (hCG), the hormone used in pregnancy testing. The use of extracts from these cells for home pregnancy testing has yielded positive results.

“Many miscarriages occur in the first few weeks, often before a woman even knows she’s pregnant,” Hannah said. “There are also a large number of birth defects, although they appear much later. Our models can be used to identify the biochemical and mechanical signals that drive proper development at this early stage, and how that development can go wrong.”

His work has already opened a new direction for future research. The researchers found that if an embryo is not properly enveloped by the cells that make up the placenta, on the third day, corresponding to day 10 of natural embryonic development, its internal structures do not develop properly.

“An embryo is not static,” Hannah said. “It must have the right cells in the right organization and be able to move forward; it is about existence and becoming. Our complete embryo model will help researchers answer fundamental questions about what determines proper embryo growth.”

The researchers say embryo models could reveal the cause of birth defects and types of infertility and lead to new technologies for growing tissues and organs for transplantation. It could also offer a way to conduct experiments, such as determining the effects of drugs on development, without including living embryos. Source