The Chinese team of scientists was able to achieve the appearance of healthy offspring in a same-sex pair of mice. The experiment to change the genetic code was carried out with the participation of a pair of males and a pair of females. Mice, which had only paternal genes, died two days after birth, while mice born with the DNA of two mothers feel good and do not look different from ordinary individuals of their species - they even managed to give birth.
This event is called a breakthrough in genetic engineering: until now, mammals have been able to reproduce only with the participation of genetic material from males and females - this combination has been mandatory. Representatives of other classes of animals - including fish, reptiles and amphibians - can produce offspring without the participation of another partner, but in the mammalian world there was an unshakable rule of imprinting.
The biological phenomenon of imprinting is not fully understood, but in general it is generally accepted to consider it a kind of competition between two DNAs, maternal and paternal, for whose genes the offspring will receive. As a result of this process, offspring inherits part of the genetic code from females, another part from males, and unused genes in each of the chains are “turned off” by natural chemical “silencers”. In the case of mixing genes of same-sex parents, a failure usually occurs due to the fact that the same DNA strands remain either simultaneously "on" or simultaneously "off". This leads to genetic abnormalities already at the stage of fetal development and - most often - to miscarriage.
Is it possible to deliberately edit the DNA so that the genes are “on” and “off” in the correct way and make a complete combination that will ensure the birth of healthy offspring? This question was asked by Chinese researchers and received a partly positive answer. First, they needed to identify those areas of DNA that are responsible for imprinting, and remove them so as not to damage other vital areas. For this jewelry operation, CRISPR / Cas9 technology was applied, which allows editing genetic chains. In both experiments, scientists created haploid (containing half a set of chromosomes) cells from stem cells of mice, some of which were turned into "pseudosperm" by means of genetic editing, others into imitation of eggs.
In the case of male mice, editing the haploid cell turned out to be much more difficult: to do this, seven genetic regions had to be removed instead of three (as in the case of a pair of females), and even that was not enough, judging by the fact that the experiment on males ended in failure. “The rapid death of the offspring [of the two males] indicates that there are still unknown barriers to reproduction and development,” said one of the study's authors, Dr. Hu Baoyang. "Successful reproduction of offspring from two males happens very rarely, we observe it only in certain species of fish and only in laboratory conditions."
Although mice born to two mothers look healthy, genetic abnormalities in both them and their offspring may appear much later.
The experiment with the DNA of two females turned out to be much more successful: out of two hundred and ten embryos obtained, twenty-nine were born alive, of which seven, in turn, were able to give birth (already without the intervention of geneticists, in a way familiar to mice).
Does this mean that reproductive technologies are one step away from allowing same-sex parents to have one hundred percent “their” (from a biological point of view) children? Don't jump to conclusions. Chinese scientists have done an outstanding job, but they do not set themselves the task of moving from mice to humans.In addition, as noted by Dr. Zhang Yi of Harvard Medical School, the transition is "at least ten times more difficult."
This opinion is shared by many commentators from the scientific world. They agree that developing genetic editing for human genes will take much longer and doesn't look realistic in the short term. Including for ethical reasons: although mice born to two mothers look healthy, genetic abnormalities in both them and their offspring may appear much later. In the case of humans, scientists simply cannot afford the risk. “In these things, security is the first thing that matters to me,” says lawyer Sonia Suter, professor of bioethics at George Washington University.
"To create a human child in this way looks like an unthinkable task," says Christophe Galichet, a scientist at the Francis Crick Institute in London, while noting that "the authors [of the study] have taken an extremely important step in the study of why mammals can only reproduce sexually." …
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