Embryologists have created the first model of an early human embryo from skin cells. This will circumvent the ban on such experiments in most countries. We tell you whether it is possible to consider such an organism as an embryo, how it was created and how it will help science.
What embryos are we talking about?
About blastocyst. This is an early stage in the development of the embryo of mammals (including humans). The blastocyst stage follows the morula stage and precedes the embryonic disc stage. The blastocyst stage refers to the preimplantation period of development, that is, the earliest period of mammalian embryogenesis (before the embryo is attached to the uterine wall).
In the evolution of mammals, the blastocyst as a developmental stage arose to ensure implantation, as well as to organize the spatial basis for the formation of the embryonic disc in the absence of the yolk.
The blastocyst stage is not homologous to the blastula stage. The blastula stage follows later in mammalian ontogeny (embryonic disc), in the so-called. “The first phase of gastrulation”, but traditionally the term “blastula” is not used for mammals and other amniotes. Accordingly, it is a common mistake to use the word “blastocoel” in relation to the blastocyst cavity.
Outwardly, a blastocyst is a ball consisting of several tens or hundreds of cells. The size of the blastocyst ranges from fractions of a millimeter (0.1 mm in rodents and humans) to several millimeters (in artiodactyls).
The blastocyst consists of two cell populations: trophoblast (trophectoderm) and embryoblast (inner cell mass). The trophoblast forms the outer layer of the embryo – a hollow ball or vesicle.
The embryoblast forms the inner layer of the blastocyst is located inside the trophoblastatic vesicle in the form of an accumulation of cells at one of the poles of the ball (inner cell mass).
Trophoblast is involved in implantation (attachment of the embryo to the uterine epithelium, invasion into the endometrium of the uterus, immunosuppressive action, destruction of blood vessels), as well as in the formation of the ectoderm of the chorionic villi (ectodermal part of the placenta).
The embryoblast gives rise to the body of the fetus itself, as well as the mesodermal and endodermal structures of the extraembryonic organs (yolk sac, allantois, amnion, mesodermal part of the chorion).
Typically, embryos are grown in the laboratory from donor fertilized eggs. In the case of cloning, sperm can be discarded.
Since the mid-tenths, it has become clear that it is possible to grow embryos in a test tube without the participation of germ cells at all. The blastocyst consists of three types of cells, from which the tissues of the fetus, the placenta and the yolk sac are then formed. And they get it all from stem cells.
At the beginning of 2000. it was shown that by in vitro treatment of mammalian oocytes (rats, macaques, and then humans) or by preventing the separation of the second polar body during meiosis, it is possible to induce parthenogenesis, while development in culture can be brought to the blastocyst stage.
Thus obtained human blastocysts are potentially a source of pluripotent stem cells that can be used in cell therapy.
In 2004, in Japan, by the fusion of two haploid oocytes taken from different mice, it was possible to create a viable diploid cell, the division of which led to the formation of a viable embryo, which, having passed the blastocyst stage, developed into a viable adult.
It is assumed that this experiment confirms the participation of genomic imprinting in the death of embryos formed from oocytes obtained from one individual at the blastocystal stage.
Stem cell pregnancy
Researchers at the University of Utrecht created a mouse embryo from two types of stem cells – embryonic and trophoblastic. The blastocyst grown by them has formed all types of cells necessary for further development.
Moreover, when implanted into the uterus of an animal, the blastocyst caused pregnancy. True, the authors of the work emphasized that they did not get a completely real embryo and therefore the female could not bear it and give birth.
In 2019, scientists from the Salk Institute for Biological Research also initiated pregnancy in mice by transplanting embryos obtained from just one somatic cell. It was taken from the body of an adult animal, reprogrammed and propagated – thus the culture of embryonic stem cells appeared.
Then they were reprogrammed once again, turning them into the so-called improved pluropotent cells, and treated with a cocktail of special signaling substances – those that, during natural embryonic development, cause the differentiation of the trophoblast (from which the placenta is formed) and the internal cell mass (from which the tissues of the embryo are formed).
As a result, in 15% of cases, blastoids grew from them – structures similar to blastocysts in cellular composition and gene expression.
Human embryo status
The question of the status of the human embryo is addressed, inter alia, within the framework of bioethics. Of key importance in this consideration is the recognition or non-recognition of the “human” content in the embryo.
At the moment, the status of the embryo in Russian legislation is not completely clear, since it is difficult “to answer the question of whether the law perceives the idea of the existence of an embryo as a subject of legal relations.”
In particular, the law “On transplantation of human organs and (or) tissues” considers embryos as a type of human organs, although its effect on embryos does not apply. Further, there is an idea of the impossibility of considering the embryo a human, “since it does not have legal capacity.”
At the same time, legal thought recognizes that the embryo cannot be attributed to human organs, since it is a new organism with its own organs.
The fact that “all the foundations of life are laid in the embryo” is also realized. Thus, the situation should be recognized as difficult due to the duality of the legal nature of embryos, which creates serious legal problems, because “the question arises as to whether the embryo can be an object of legal relations.”
Ownership of embryos
Embryos are the subject of property disputes in various countries, including the United States. The so-called Davis case (heard in 1989 in Tennessee) is well known, when, in the process of dividing the property of divorcing spouses, the question of the rights to previously frozen embryos arose.
As a result, the court transferred the mother’s embryos to temporary possession for implantation purposes. In addition, the court found that human life begins from the moment of conception and that for this reason the embryo is not an object of property rights.
However, in another case, which was heard in New York in 1995, the embryos were transferred to the ex-wife’s property. There is also a known case when the spouses demanded to remove the embryo that they had previously transferred for research from the laboratory.
As a result, the court demanded that the embryo be transferred to the spouses, without, however, discovering the existence of ownership and confirming that “the human embryo is not an object of ownership.”
Thus, American legal thought, in principle, is ready to recognize the embryo as an object of legal relations, but this object is very specific: as a rule, courts do not recognize the ownership of embryos, since the latter are the beginning of a new human life.
In discussions about the acceptability or unacceptability of certain manipulations with embryos, the concept of the rights of the embryo occupies an important place. In particular, the prohibition on the use of embryos or embryonic tissues for medical research purposes is based on the recognition of such rights.
Their defenders, supporters of the so-called “conservative position”, refer to the fact that from the moment of conception, human life is sacred and inviolable, and also argue that the embryo has all human rights.
Supporters of the so-called “liberal position”, even at the very late stages of pregnancy, refuse to recognize the independent status of the fetus, and the decision of its fate is left to the mother or doctors.
Natural inalienable human rights include, inter alia, the right to life. The question of what is the moment of the emergence of the right to life, from which legal personality begins, is extremely important for criminal and civil law and for jurisprudence in general.
There is a concept according to which the legal status of the embryo should be determined on the basis of the fact that the embryo is the beginning of a new life, and not part of the human body. Supporters of this position proceed from the fact that a person as a new creature (biological individual) arises immediately after the fusion of parental germ cells.
Why grow embryos?
In order to circumvent the rather harsh rules that directly prohibit the creation of human embryos for research purposes. And without this, it is impossible to figure out what actually happens in the early stages of development.
It is likely that society as a whole will be more tolerant of research on such models than experiments on real embryos, researchers from the University of Michigan (USA) say in the Nature editorial. So far, the main ethical question that needs to be addressed is whether the 14-day rule applies to them.
Today, human embryos obtained experimentally are destroyed 14 days after fertilization. In some countries, violation of this norm is punishable by law, in others – experiments with such embryos reject ethical committees and deprive them of funding.
If the ban is lifted in relation to blastoids, then scientists will probably be able to understand not only the causes of miscarriages and failures in IVF, but also to find out the mechanisms of a number of hereditary pathologies, including cardiovascular diseases and some types of diabetes.