In A First, Researchers Make Eggs From Male Cells, Create Mice With Two Biological Fathers: Reports

The new research marks the first time scientists have created viable eggs from male cells. As part of the research, the scientists turned male XY chromosomes into female XX ones.

Japanese scientists have made a breakthrough in reproduction: creating eggs from male cells, a first in genetics. Scientists at Japan's Kyushu University and Osaka University have created mice with two biological fathers by making eggs from male cells, The Guardian reports. 

The milestone opens up new possibilities in reproduction, and could pave the way for future research that could enable same-sex couples to have biological children. 

Quoting Katsuhiko Hayashi, who led the research, a report by The Guardian says that this is the first case of making robust mammal oocytes from male cells. Hayashi, Internationally renowned as a pioneer in the field of lab-grown eggs and sperm, presented the new research at the Third International Summit on Human Genome Editing at the Francis Crick Institute in London on March 8, 2023. 

The findings of the new research have been submitted for publishing in the journal Nature. 

Potential applications of the technology in the future

According to the report, Hayashi predicts it will be technically possible to generate a viable human egg from a male skin cell within a decade. However, scientists have not yet created human eggs from female cells. 

The new research marks the first time scientists have created viable eggs from male cells. As part of the research, the scientists turned male XY chromosomes into female XX ones, a BBC report says. 

While Hayashi's team is trying to use the same technique to generate eggs from human cells, there will be certain hindrances, such as establishing the safety of lab-grown eggs. 

Currently, Hayashi is working on developing fertility treatments, the BBC report says. 

Quoting Hayashi, the Guardian report says it will be possible to replicate the research in humans even in 10 years. He also said that he would be in favour of the technology being used clinically to allow two men to have a baby if it were shown to be safe. 

According to the reports, Professor George Daley of Harvard Medical School, who is not involved in the research, says there is still a long way to go before society is faced with such a decision because doing the research on humans is harder than the mouse, and researchers still do not understand enough of the unique biology of human gametogenesis, or the formation of reproductive cells, to reproduce Hayashi's provocative work in mice. 

The technology could be used to treat severe forms of infertility

Not only is there a potential to use the technique for creating human eggs in the future, but also to great severe forms of infertility, including women with Turner's syndrome, a genetic condition in whom one copy of the X chromosome is missing or partly missing, and can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop, and heart failure. 

Hayashi said the application of the technique to treat Turner's syndrome and other forms of infertility was the primary motivation for the research.

Some scientists believe that it would be challenging to replicate the technique in human cells because these require much longer periods of cultivation to produce a mature egg, which can increase the risk of cells acquiring unwanted genetic changes, the Guardian report says. 

How the study was conducted

As part of the research, the scientists reprogrammed male skin cells into a stem cell-like state to create cells called induced pluripotent stem (iPS) cells. According to the University of California Los Angeles, iPS cells are cells derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state that enables the development of an unlimited source of any type of human cell needed for therapeutic purposes. A pluripotent cell is one which is able to develop into several different types of cells.

After reprogramming the male skin cells into a stem-like state, the researchers deleted the Y chromosome of the cells and replaced it with an X chromosome borrowed from another cell. In this way, the researchers produced iPS cells with two identical X chromosomes. 

Then, the researchers cultivated the cells in an ovary organoid, which is a culture system designed to replicate the conditions inside a mouse ovary, the report says. After this, the researchers fertilised the eggs with normal sperm, and obtained about 600 embryos. The researchers implanted these embryos into surrogate mice, resulting in the birth of seven mouse pups.

The efficiency achieved with normal female-derived eggs is five per cent, while that in the research was one per cent. This means that one per cent of the embryos went on to produce a live birth in the new research. 

According to the report, the baby mice appeared healthy, had a normal lifespan, and produced offspring as adults. 

Why have scientists not been able to produce human eggs from human cells?

While scientists have created the precursors of human eggs, the cells, until now, have stopped developing before the point of meiosis. According to the United States National Institutes of Health (NIH), meiosis is a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in the gametes. Meiosis maintains the diploid state of humans, or the fact that each somatic cell contains two sets of chromosomes.