Early embryology; the earliest blastocyst runs the show (Introduction)

by David Turell , Thursday, July 07, 2022, 16:57 (660 days ago) @ David Turell

Tells the uterus what to do:

https://phys.org/news/2022-07-life-early-embryo-driver-seat.html

"One often thinks that the early embryo is fragile and needs support. However, at the earliest stages of development, it has the power to feed the future placenta and instructs the uterus so that it can nest. Using blastoids, in vitro embryo models formed with stem cells, the lab of Nicolas Rivron at IMBA showed that the earliest molecular signals that induce placental development and prepare the uterus come from the embryo itself.

"Who takes care of whom at the onset of life? The placenta and the uterus nurture and shelter the fetus. But the situation at the very early stage of development, when the blastocyst still floats in the uterus, was unclear so far. Now, the research group of Nicolas Rivron at IMBA (Institute of Molecular Biotechnology of the Austrian Academy of Sciences) uncovered basic principles of early development using blastoids.

"Blastoids were first developed by the Rivron lab from mouse stem cells (Nature, 2018) and then from human stem cells (Nature, 2021). Blastoids provide an ethical alternative to the use of embryos for research and, importantly, enable multiple discoveries.

"Now, blastoids have settled a "chicken or egg" dilemma. Using mouse blastoids, the researchers found that the early embryonic part (~10 cells) instructs the future placental part (~100 cells) to form, and the uterine tissues to change. "By doing this, the embryo invests in its own future: it promotes the formation of the tissues that will soon take care of its development. The embryo is in control, instructing the creation of a supporting surrounding," says Nicolas Rivron.

"Indeed, the team discovered several molecules secreted by the few cells from which the fetus develops, the epiblasts. They observed that these molecules tell other cells, the trophoblasts that later form the placenta, to self-renew and proliferate, two stem cell properties that are essential for the placenta to grow.

"The team also found that these molecules induce the trophoblasts to secrete two other molecules, WNT6 and WNT7B. WNT6 and WNT7B tell the uterus to wrap around the blastocyst. "Other researchers had previously seen that WNT molecules are involved in the uterine reaction. Now we show that these signals are WNT6/7B and that they are produced by the blastocyst trophoblasts to notify the uterus to react. The relevance could be high because we have verified that these two molecules are also expressed by the trophoblasts of the human blastocyst," states Nicolas Rivron."

Comment: this shows how one new organism tells another what to do. Molecular reactions control the process automatically. The two work together despite being different genetically, a major problem in transplantation of organs. This is an irreducibly complex arrangement and must be designed. Chance mutations to create this mechanism are not possible.