Scientists say they created mice with two biological fathers


Microscopic view of cells on the left, next to an archive image of mice
K. Hayashi/Kyushu University

  • Scientists said they created a mouse from two biological fathers.
  • At a conference they said they made female eggs from male cells.
  • The very early study raises hopes that same-sex partners could have biological children.

Scientists claim they created mice with two fathers in a breakthrough that could one day be replicated in humans.

Osaka University’s Katsuhiko Hayashi said at the Human Genome Editing Conference on Wednesday that he made his breakthrough after changing chromosomes from XY to XX in a male cell.

He then used this technique to create female eggs, called oocytes, from male cells and fertilized them to create seven mice with two biological fathers.

The discovery has yet to be validated by peer review and is still in the early stages of development. However, if confirmed, it increases the possibility that male couples will one day have their own biological children.

The eggs transferred from male to female were made from skin cells

Cells are flexible, and scientists have learned to change them from one cell type to another with the right instructions.

To create the egg, the scientists took male skin cells with X and Y chromosomes and reprogrammed them to turn into what are known as pluripotent stem cells, cells that can turn into any other type of cell.

A picture shows a colony of human stem cells viewed through a microscope.
REUTERS/Alan Trounson/California Institute for Regenerative Medicine/Handout

They then deleted the Y chromosomes in the cells and duplicated the cells’ X chromosomes before causing the cells to turn into eggs with two X chromosomes.

“The trick to this, the biggest trick, is the duplication of the X chromosome,” Hayashi told The Guardian. “We really tried to establish a system for replicating the X chromosome.”

The technique was used to create seven mouse pups that scientists said appeared healthy.

Hayashi says it could be used in humans within a decade, while others disagree

It will be a while before the technology can be safely used on humans.

Mice are very different from humans, and even in mice, the eggs aren’t of great quality – only one in 100 fertilized eggs resulted in a live birth, Hayashi told the Guardian.

Still, Hayashi is optimistic. From a purely technological point of view, he predicts that making eggs from male cells in humans “will be possible even in 10 years,” he said, according to The Guardian.

He told the BBC he would like to see technology bring fertility options to same-sex partnerships of all sexes down the line. The technique could also help women and people with two X chromosomes who have a genetic problem involving one of the X chromosomes to have children, he said.

He warned that the harmlessness had to be proven beforehand.

“Technically it’s possible. I’m not sure if it’s safe or socially acceptable at this point,” he said.

George Daley, dean of Harvard Medical School, who is not involved in the research, told the BBC the work was “intriguing” and “provocative” but he wasn’t sure if this technology would work in human cells any time soon would.

Human reproductive cells are very complex and much less well known than mouse cells. So there is still a long way to go before these fertility options can be offered to people, Daley told the Guardian.

The discovery is promising, although this isn’t the first time a mouse has been born to two fathers. A 2010 study managed to do this, but their technique required many more steps and manipulations on the embryo and did not produce a viable egg. According to the Guardian, Hayashi’s approach is much simpler.

Hayashi has also previously made mice with two birth mothers using the same technique dating back to 2016. We are yet to be able to create a viable human egg from female skin cells, seven years after Hayashi’s work on female mice, The Guardian reported.

“Scientists never say never, basically it’s been done in mice, so of course it could be possible in humans,” Haoyi Wang of the Chinese Academy of Sciences told the BBC. But he added, “I can foresee a lot of challenges and I couldn’t predict how many years that would be.”

It may be possible, but is it ethical?

If technology progressed to this point, it would be up to society to decide whether we would allow humans to use it to create children.

Germline gene editing in humans – when the DNA is altered in a way that the manipulation made by scientists is passed on to the offspring of the children themselves – has usually been a solid red line for scientists.

When scientist He Jankui crossed that line in 2019 and revealed that he had altered the genes of two babies, he received an international warning and was sentenced to prison.

However, if Hayashi’s research can open up new possibilities for human reproduction, the technology could be considered in the future.

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