TVP WEEKLY: "Mouse embryos formed without an oocyte or spermatozoa - what for.. and what else is there to face?" – asked recently “Nature”, the scientific journal. Can you explain simply what happened?

ANNA AJDUK: "Synthetic embryos" have been created for several years from stem cells that have the ability to develop into other various types of cells. It turned out that they can be used “to glue" (scientifically speaking – “to aggregate”) formations resembling embryos. They are called differently: synthetic embryos, artificial embryos or embryoids.

The “Nature” article comments on two recent documents concerning the subject. One comes from Israel – from the group of Jacob Hanna Lab, part of the Department of Molecular Genetics at the Weizmann Institute of Science in Rehovot; The other we owe to the team led by a Polish woman - Magdalena Żernicka-Goetz, who comes from the Department of Embryology at the University of Warsaw and has been working for years at the University of Cambridge in Great Britain, currently also at Caltech (California Institute of Technology) in Pasadena, USA.

The first embryoids were created about five years ago, and Magda Żernicka-Goetz's group has been developing this research from the beginning. The artificial embryos resemble the ordinary ones in their structure, and many processes taking place in them happen similarly. Thanks to this, they can be a great tool for investigating the mechanisms of embryonic development and reasons for diverse diseases arising in fetal life.

“Stem cells” is a broad term. What is it about in this case?

Embryoids are made of pluripotent stem cells, i.e. stem cells that can develop into many other types of cells. The easiest way to obtain them is from an embryo at a very early stage of development (called a blastocyst – usually a ball of cells that forms early in a pregnancy, about five to six days after a sperm fertilises an egg) - just before implantation in the uterus. In natural conditions, embryonic tissues develop from them, but not other tissues necessary for development, such as the placenta or some fetal membranes.

Currently, an almost perfect embryo has been created by glueing together three types of such embryonic stem cells. One that forms the body of the embryo, and two that have been altered to become the cells of the placenta and one of the fetal membranes (yolk sac), respectively. This was done using murine material, not a human one.

So what is new about the research work from Cambridge and Rehovot that it stormed through the scientific media?

True success is the cultivation - longer than ever before – of the mouse embryos and following observation of embryonic processes, such as the formation of the nervous system or the heart. Previously, we could not observe them in vitro, so we were unable to study them in detail.     SIGN UP TO OUR PAGE 
  Moreover, until recently, mouse embryos or embryoids have been successfully maintained in culture only up to the sixth or seventh day of development. And the work we are talking about lasts already eight days and a half. The difference seems small, but scientifically speaking, that is very important.

Indeed - after all, the mouse's pregnancy lasts up to 20 days, so - if we try hard enough - we may reach halfway in the incubator.

Here, it turned out to be essential to combine stem cells capable of producing an embryo body with those capable of producing extra-embryonic structures. Moreover, the cells that create them provide numerous signals that act as signposts, telling the cells of the embryo where to locate so that the embryo knows, for example, where to find its front or back. In this phase of development, cells not only divide intensively (which is why the embryo grows) and differentiate (thanks to which many different tissues are formed), but they also move en masse to find the right place.

The second technical innovation is a special incubator from the Weizmann Institute.

Normally, the development of such embryos occurs in the womb, so to study them, these must be collected from animals. Embryoids allow research to be carried out without sacrificing pregnant laboratory animals. However, to grow both – the natural embryos and embryoids - a special incubator is required in which the tubes containing the embryos are rotated to allow mixing and oxygenation of the culture medium. This is necessary because - compared to classical tissue cultures that are plated - these embryos are massive and fast-growing structures.

So, is this some kind of an "artificial uterus" that can keep embryos beyond the stage of organ formation? Could it be applied to humans?

It is much easier to conduct such experiments on mouse embryos, where the development is very fast and the embryo size is small compared to humans. Let's imagine this: we start with single-cell embryos, which in humans and mice are of a similar size, and we end with new-borns, one of which - the human one - could easily hold the other in the palm of his hand. In addition, the human embryo takes more than ten times longer to develop than the mouse. Thus, the developmental processes we can already observe in mice today - in laboratory conditions - are still difficult to notice in humans. This technical challenge is still difficult to overcome today.

Can embryos develop into an adult being?

NO. Even if we wanted to, we are currently unable to complete their development.

Ok.. Not within this 'artificial rotating uterus'. What if they were implanted in real wombs?

We can't implant them. For a simple reason - the moment for implantation is strictly defined and very short in the whole process of evolution. Additionally, embryoids are unable to settle themselves properly in the uterus, even if their development is stopped at an earlier stage, where the natural embryo usually gets installed in the womb; Although – roughly or even with the eye armed with a solid microscope and molecular analysis techniques, embryoids only resemble the natural ones, those resulting from fertilisation. They are similar, but they are different. The devil is in the details. In addition - in its recommendations - the scientific community and the law prohibit any transplantation of artificial embryos into the human womb and human embryos into the uterus of other mammals.

So these "germ-like formations", as you put it, are – somehow and for unknown reasons - weaker than naturally formed embryos?

Each day of thein vitro culture negatively affects the well-being of both, the foetus and the embryoid. The embryo is always better off inside the female's body than in breeding conditions, even though the latter have been optimised for years. In addition, sticking together several types of stem cells does not, as you can see, perfectly replace the natural forming processes of the embryo.

What do we need such embryonic models for then… apart from "pure science", of course?

These models can be used to test the toxicity of various substances, e.g. medicine, to study their biological activity or influence on the early embryonic development. Now it is not always possible to test the effect of a drug that it could make during the growth of the foetus; hence many medicaments are advised against pregnant women. Embryoids may help here in the future.

Nevertheless, I have a problem with accepting embryoids the same way as the other organoids, increasingly used in biomedical sciences, even in the form of the so-called mini-brains. Embryology has always taught us that an embryo is something special...

This is a fundamental question: should we treat the embryoid as a normal embryo? And if not, what is the differentiator here? Where is the limit if we keep improving this technology, and one day it turns out that – structurally, molecularly and otherwise - we are unable to distinguish between the man-maid embryoids and embryos resulting from fertilisation? In that case, should we grant them "germinal rights"?

In various recommendations, legislators and the scientific community usually use a simple distinction: a true embryo is formed from the union of two gametes - a sperm cell and an egg cell. It is difficult to determine other criteria for acknowledging what a true embryo is. So far, everything indicates that embryoids do not have a full potential for growth and development, i.e. they cannot evolve into a mature organism. They are only simplified models of the embryonic forming processes. We are still to face it over the next several years.

One of the solutions could be - to make the embryoids never reach their full development capacity by using molecular biology methods. For example, they could be constructed using stem cells with a certain defect, which should cause the death of such an embryo at a specific growth stage. This could be done in such a way as to avoid interfering with the development processes of the model which we want to study.

Recommendations developed probably in the 1980s, irrespectively in the USA and Great Britain, blocked the cultivation of human embryos outside the mother's body at the stage of 14 days.

Techniques of in vitro embryo culture developed most strongly in those countries due to the admissibility and popularity of fertilisation beyond the mother’s body. However, the recent recommendations of the International Society for Stem Cell Research argue that the 14-day rule should be made more flexible. The truth is that those 14 days were chosen on the basis of "we will be unable to grow human embryos that long anyway, so...". Now when it turns out that we can grow human embryos up to the 14th day of development, scientists would like to study the subsequent embryonic processes. The appetite grows with eating.

It is worth noting here that normally the implantation of a human embryo takes place on the seventh-tenth day after fertilisation.

On the 14th day, the process called gastrulation begins, which is crucial for the further development of the embryo. Therefore, the scientific community began to push to move this 14-day barrier further. Only again: by how much longer? By 3, 7, or 10 days? Consensus could not be found, so the latest recommendations propose that every experiment in which researchers would like to grow human embryos for longer than 14 days should be subject to a thorough substantive assessment. Only experiments that have a chance to really and significantly expand our knowledge - and at the same time impossible to perform in any other way - would be allowed to extend the breeding in this way. Let us remember that the opportunity of working on human embryos exists in only a few countries. It is illegal in Poland, and this discussion is basically and completely beyond us.

Anyway, the recommendations mentioned above also try to regulate the rules of working with stem cells and embryonic pluripotent cells (those that can develop into many different types of cells or tissues in the body), both in the context of creating embryos and other applications. For example, attempts are made to obtain gametes from them, i.e. eggs and sperm cells.

Scientists emphasise that any changes in the law in this matter should be associated with making the public aware of both, the risks associated with these technologies and, in my opinion, huge benefits. Rules need to be designed to align with what society considers ethical. It is obvious to scientists that if they move too fast in their research, they may cause public fear and resentment, eventually leading to their research being banned.

This reaction may be caused by fear, or by the fact that researchers would make a breakthrough earlier than lawmakers and bioethicists could be ready for it.

The creation of artificial embryos is not the first technology to give cause for our concerns; also not the first one that we get excited about, probably raising too many hopes. It was the same with the cloning of mammals. We were threatened that after the birth of Dolly-the-sheep, cloned people would soon appear ... Then, a quarter of a century passed by and nothing happened. The cloning technique is still challenging and effective. Additionally, there is a widespread legal blockade for this type of human cell experimentation. Whether this will also be the case with the techniques we are talking about today, using embryonic stem cells, I do not know. Time will tell.

–interview by Magdalena Kawalec-Segond

TVP WEEKLY. Editorial team and journalists

–translated by Katarzyna Chocian
Dr Anna Ajduk is a professor at the University of Warsaw, Department of Embryology, Institute of Evolutionary Biology and Biomedical Sciences, Faculty of Biology Council.

Sources:
https://www.cell.com/cell/fulltext/S0092-8674(22)00981-3
https://www.nature.com/articles/s41586-022-05246-3