Editing the embryo genome

Anna Utkina, Konstantin Severinov, "Orthodoxy and Peace" 

The UK Ministry of Health has issued the first permission to edit the genome of human embryos for research purposes. Konstantin Severinov, a specialist in molecular biology (regulation of bacterial gene transcription), professor at Rutgers University (New Jersey, USA), head of laboratories at the Institute of Molecular Genetics of the Russian Academy of Sciences and the Institute of Gene Biology of the Russian Academy of Sciences, tells about what it is and why.

– What is the editing of the human embryo genome, why are these studies conducted, what is their purpose?

– Human genome editing is a new technology that emerged shortly after the discovery of protective systems called CRISPR–Cas, with which bacteria fight viruses. These systems consist of RNA and a protein part, while the nucleic acid, a small RNA, directs the protein to the strictly corresponding DNA site, and the protein splits both DNA strands at the recognition site.

It turned out that this system, created by evolution to fight bacteria against viruses, can be used as a programmable system for introducing directed cuts into DNA molecules in the cells of any organism.

The idea is this: you introduce the bacterial Cas9 protein into the cell of the organism you are interested in, and CRISPR RNA, which corresponds to the DNA site you are interested in, the gene of this organism. The Cas9 protein, "guided" by an RNA molecule, finds a place corresponding to this RNA in DNA and cleaves it.

Nothing else is required. Because the cells of higher organisms, in particular ours, contain two sets of chromosomes from dad and mom, and each gene, therefore, is present in two copies. And if a DNA molecule breaks in one copy, it will "automatically" heal according to a healthy copy.

Therefore, if you imagine a situation that one copy of the gene is not very "good", there is some kind of mutation, that is, a change in the DNA sequence, and the other is normal, then using CRISPR/Cas9 technology (genome editing), you can make a crack in a bad copy of the gene (just apply the corresponding CRISPR RNA, in order to to program the Cas9 protein to contact exactly a copy of the gene with an altered DNA sequence), and after a raskus is inserted into this DNA, the cell will heal it by itself, without any additional impact, using a "good" copy as a matrix. In this case, editing will occur – a "bad" DNA sequence with a mutation leading to a defect will be replaced by a functional one.

Editing the human genome does not present any particular technical complexity compared to others. CRISPR/Cas9 technology is common and allows you to edit cells of any organisms – yeast, plants, animals and, of course, humans.

Why do such studies? A lot is "written" in the genes, in particular a variety of genetic diseases or predisposition to them.

If for some reason two copies of some important gene in a fertilized egg - both from dad and mom – turn out to be defective, then this is a verdict: either a seriously ill person who cannot be cured will develop, or development will stop in utero, a miscarriage will occur. All cells of such an organism carry a mutation, do not have a healthy copy of the gene.

On the other hand, harmful mutations can appear during life in the cells of individual tissues. Cancer, for example, is generally not a hereditary disease, it's just that in the course of life we accumulate mutations, and some of them lead to various lesions in some of our tissues, in particular cancer.

Nevertheless, diseases with a genetic background, ideally, can be completely cured using genome editing technology – simply replace the corrupted gene text with normal in certain cells.

– Why are manipulations with the genome of human embryos prohibited in 15 out of 22 Western European countries? What are the pros and cons?

– The debate about the ethical standards of working with an embryo or embryonic cells arose at the end of the last century in connection with the development of embryonic stem cell technology, and even earlier – when IVF was introduced into widespread practice. At the philosophical/religious level, it all boils down to the question: when does a person's soul originate?

 After all, an embryo can develop into a human. When does the moment come after which he is a person?

If you do some experiments on an embryo, and then plant this embryo to a surrogate mother and a person, a personality, is born, then you can imagine a number of problems that will arise later. After all, no one asked for his opinion and permission when experiments were being conducted on him. And how to guarantee the safety of these experiments is unclear. And who is responsible for him if there are any problems, or, for example, he declares that he would not mind being sick at all.

A similar problem with cloning. If you clone someone, will it be the same person or another? Now they use a genetic definition of personality, which means that the clone will be absolutely identical to the original one from the point of view of, for example, the judicial one? In general, there are a lot of interesting problems.

Accordingly, experiments on human embryos are prohibited. For example, in the United States during the time of George W. Bush, federal funding was prohibited, that is, the allocation of grants for research on human embryonic stem cells, now the ban has been lifted, but there is serious regulation.

But you also need to understand that ultimately scientists are engaged in research and spend taxpayers' money precisely in order to cure diseases and ensure a long and happy life for everyone. It is quite obvious that people have a lot of problems, diseases, physical lesions, defects associated with embryonic development and because of this - a lot of crippled destinies. But if we intervene at the embryo stage and change some genes, it will probably be possible to solve all these problems. This is obviously a good thing, and just like with IVF, the introduction of editing into practice is only a matter of time.

– What is the difference between the technology of editing the genome of individual (somatic) cells, for example, retinal cells or stem cells, from editing the genome of the embryo as a whole?

– There is no difference in technology. With some experience in the molecular genetic craft, all this can be done both with individual cells and with an embryo. It's just that an entire organism can develop from an embryonic cell, but a whole organism cannot formally develop from a somatic cell after genetic modification. But, on the other hand, it is possible to make induced pluripotent stem cells from edited somatic cells, and from them come to the same thing, that is, an organism with an edited genome.

– Is there a danger that the changes will also affect the germ cell line and, therefore, will be transmitted in generations?

– Why "danger"? When we decide to reproduce, then, having half of the genes from dad and mom, we transfer to the embryo in our germ cells – the woman in the egg, and the man in the sperm – some random combination of various genes from both dad and mom. As a result, we give offspring half of all the genetic information that we have, but this "half" is always different, each sperm or egg is completely unique from a genetic point of view, a set of variants of copies of genes. Why, strictly speaking, is there a situation when one family can have one sick child and the other healthy, despite the fact that genetically, it would seem, their parents are the same, they are simply carriers of some kind of disease.

An embryo develops from a single cell – a fertilized egg, from it develop several trillion cells that make up you or me, including germ cells. Of course, if something changes at the embryo stage, then there will be changes everywhere.

– While research is being conducted with "extra" embryos that are obtained but not used during the in vitro fertilization (IVF) procedure, but can scientists seriously talk about the possibility of conducting research on humans, in which cases there may be a need for such an intervention?

– Genome editing technologies will be developed not only for embryonic editing. For example, now people who get sick with lymphoma are first irradiated, and then they are looking for a donor to plant bone marrow in place of the destroyed affected hematopoietic cells. It is long and difficult to find immunocompatible donors. And with technology, when the patient's hematopoietic stem cells are taken, edited (that is, the genetic error is changed using CRISPR/Cas9 technology), and then multiplied and injected back into the person, but no longer contain a mutation, the problem of donation and compatibility is completely solved. The same is true for some other forms of cancer, as well as for hemophilia, thalassemia…

 The main problem is that it is now difficult to guarantee the absolute accuracy of editing.

And the experiments, which, in particular, were done by the Chinese on early human embryos, showed that in addition to "curing" the right place, mutations are induced in other places, because the CRISPR/Cas9 RNA-protein complex makes mistakes and learns (and discovers) not just the areas where you want it to go. This is a question of improving technology, specificity, which is being solved now.

And transgenic animals using these CRISPR/Cas9 technologies are already being made without problems. Technically, from the point of view of a molecular biologist, there is no difference between a pig and a human. Recently, for example, they made a pig, from whose genome they removed all the viruses that are always there and can sometimes be activated. Since pigs may soon be used as an organ factory for humans, because pigs are like us, the viruses that they have in their genome should be removed to prevent the possibility of their transmission to humans. And these pigs were obtained by the CRISPR/Cas9 method. So the issues of human research are purely regulatory, not technical.

Portal "Eternal youth" http://vechnayamolodost.ru

05.02.2015