Can people of the same sex give birth? It sounds like night talk, but now some technologies have made homosexual reproduction no longer far away. Although there is still a long way to go, these technologies can at least give many same-sex couples hope: Embracing genetically children. This article comes from micro-channel public number: Global Science (ID: huanqiukexue) , author: Roni Dengler, translator: Yang heart boat, topic map from : Picture Worm

Cara Gormally ’s conception has kept her in a gloomy atmosphere. She herself really wants a child, and the only difficulty she and same-sex partners have to face is Selecting the right source of sperm donation strong>. They were relatively easy to find donors, but then, Gormally’s fertilization process became difficult, and she became frustrated and lost every month due to failed fertilization. “In this process, there are too many random factors, and we can only rely on luck.” The dual pressures of economy and physiology made her physically and mentally tired.

But this is not the hardest part. She and his wife have accepted the fact that no matter how much they desire a child, biologically, this child will not have any blood relationship with Gormally’s wife.

“I am very sad to think that the child is not genetically from us,” Gormally said, “I hope to break through this biological impossibility.”

Now, a series of new technologies may have the potential to change this impossibility, allowing same-sex couples to obtain children who fuse the genetic genes of the two people, just like heterosexual couples.

The biggest obstacle to homosexual reproduction

Most cells in mammals carry two sets of chromosomes. One group came from the father and one group came from the mother. However, sperm and eggs are special cases with only one set of chromosomes.When the egg is fertilized, the fertilized egg regains two sets of chromosomes.

For same-sex couples like Goamally and his wife, the biggest obstacle that prevents them from getting together is genomic imprinting. These imprints carry different marks on the parents’ DNA and are passed on to their offspring at the same time. The purpose is to allow certain genes to be expressed only from the DNA of the mother or father. If this process goes wrong, it can lead to miscarriages, developmental defects in offspring, and cancer.

In sperm and eggs, specific imprinted genes on chromosomes are silenced or rewritten, regardless of whether the chromosome was previously from a father or mother.

Jay Smith / Discover

During the genetic imprinting process of DNA, some markers in different areas of the mother’s side will turn off the expression of specific genes. Therefore, this gene can only be expressed by the DNA provided by the father, and vice versa. (Of course, not all imprints will turn off gene expression, and some will also activate genes) . This is the biggest difficulty for same-sex couples to obtain children. If all the DNA from women or men is used, genes in some regions may be turned off, so that the fetus cannot develop normally.

“We cannot guarantee that all genes required for normal development are on unless the embryo receives both paternal and maternal genetic material.” Marisa Bartolomei, a geneticist at the University of Pennsylvania, is exactly what she is The first imprinted gene was found in mice.

Scientists discovered genomic imprints in mammals more than 30 years ago. In experiments in the 1980s, researchers tried to remove mice affected byThe sperm eggs come from the mother or father’s genome, and then a set of genomes are added to this fertilized egg, and finally the embryos are all mother or father genes. The fertilized eggs allowed the mice to conceive, but the embryos were unable to develop and survive.

These experiments show that the normal development of the embryo cannot be separated from the genetic material of both parents, and the DNA of both parents may be expressed differently in some aspects. And subsequent experiments also found that if a pair of DNA copies of a certain region of a mouse embryo are from the same party (instead of each parent providing a copy) < / span>, then the development process of the mouse will appear different.

For example, there is a gene that controls the long tail of a mouse. When researchers deleted regions of related genes in maternal DNA, mouse embryos grew larger and died halfway through development. Deletion of related gene regions on the parental DNA will basically have no effect on mouse development.

In the following 30 years, researchers discovered more and more imprinted genes (They estimated that there should be 100 ~ 200 such genes) and markers that can silence the expression of these genes. In the process, scientists also discovered that these imprinted genes are related to human developmental disorders. They also realized that the biggest difficulty for same-sex couples to obtain genetic offspring is here.

Break through obstacles

In October 2018, scientists broke this impossibility in mice. Li Wei’s group at the Institute of Zoology, Chinese Academy of Sciences deleted two female mice with healthy offspring after deleting some imprinted gene regions. They also tried in two male mice, but the embryos obtained by the two male mice died a few days after birth. Although unsuccessful in two male rats, Li Wei is still optimistic: “This study shows us some possibilities.”

In order to break the barrier of imprinted genes, Li Wei and colleagues chose a female mouse to provide embryonic stem cells and deleted some gene regions using CRISPR / Cas9 technology. They then injected the edited embryonic stem cells into the eggs of another female mouse. Finally, the surrogate mice gave birth to the embryos and gave birth to offspring.

In the first two years of this experiment, Li Wei’s group has beenExperiments with fertile offspring of same-sex mice have had some success. At that time, they deleted two imprinted gene regions. These offspring of two female mice can still survive to adulthood and have their own offspring, but they will have some growth defects. On average, offspring born from two females are 20% lighter than males and females. In the 2018 study, they deleted the third imprinted gene region, and the mice could Grows normally .

But scientists are still unable to repeat the results on two male mice, and the related experiments are more difficult than two female mice. They found that if two male mice were to have genetically common offspring, the area of ​​the imprinted genes that needed to be deleted could be twice that of two female mice. Therefore, in Li Wei’s research, he deleted a total of seven imprinted gene regions to successfully give offspring to two male mice.

Although they have worked hard to get offspring, the number of surviving mice is very few. Only 2.5% of the embryos will begin to develop, 0.5% of the mice will survive for two days, and no mouse will reach adulthood.

“At present, two male mice cannot produce healthy offspring. We need to overcome more obstacles to ensure that these mice can survive after birth”, said Li Wei. “The lower the birth rate, the more It can explain that there are some unknown obstacles in the reproduction of the two males that are preventing the development of the embryo. “

In contrast, the reproduction of the two females is much better. The offspring they produce can live to adulthood, can mate with other male mice to give birth to their own children, and behave the same as other mice, no different. As far as their research is concerned, Mice obtained from both sexes are as healthy as other mice in the laboratory .

“This does not mean that these mice are normal in all aspects,” Li Wei reminded, “under severely restricted experimental conditions and a limited number of animals, we cannot detect problems in all aspects.” Of course, despite the success of this experiment in mice, it is not meant to be available to humans. “Before human trials, no more safety and risk considerations can be overemphasized,” especially male and female reproduction. As far as current technology is concerned, the offspring produced by two male mice will be very abnormal and will not survive.

Because the two females look more promising, they are now preparing to apply the technology to monkeys. If it succeeds in monkeys, it means that homosexual reproduction is one step closer to humans.

Another hope

ExhaustedAlthough the research above is encouraging, people like Gormally and her partner still don’t have access to this technology. However, this is not the only way for same-sex couples to count on. Another technique called “in vitro gamete development” (IVG) may be Their second option.

Scientists can use IVG technology to turn other types of cells in the body into eggs or sperm. And some biologists have tried IVG to reprogram adult skin cells into stem cells, and then promote them to differentiate, so that these stem cells differentiate into egg cells or sperm.

Some Japanese research teams are already very skilled in IVG technology. Saito Saito and Lin Keyan of Kyoto University in Japan once used cells on the tail of mice to regenerate functional eggs.

Then they fertilized the reprogrammed egg and transplanted it into a surrogate mouse. As a result, embryos can develop normally and the offspring produced are not only healthy but also fertile. Therefore, in theory, if it is two women, only one woman’s skin cells need to be transformed into sperm, and then her partner’s egg can be fertilized to produce offspring.

IVG technology can indeed change the likelihood that same-sex couples will have offspring. “If this method is feasible, we will definitely try it,” Gormally said. Now, all the babies born from the donor’s sperm have started to learn to walk. “This can completely change some rules that cannot be broken.”

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This article comes from WeChat public account: Global Science (ID: huanqiukexue) , author: Roni Dengler, translator: Yang heart boat