‘Revolutionary’: Scientists create mice with two fathers

PARIS — Scientists have created eggs from the cells of male mice for the first time, resulting in the birth of seven mice with two fathers, according to research hailed as “revolutionary”.

The technique developed in the proof-of-concept experiment is a long way from potentially being used in humans, with obstacles such as a low success rate, adaptation concerns, and wide-ranging ethical considerations.

But the breakthrough raises the prospect of a range of new reproductive opportunities, including gay male couples – or even a single man – being able to have a biological child without the need for a female egg.

The study, published in the journal Nature, was carried out by a team of scientists in Japan led by developmental biologist Katsuhiko Hayashi of Osaka and Kyushu Universities.

Hayashi and his team previously found a way to take skin cells from a female mouse and turn them into an egg that could be used to birth healthy pups.

For their latest research, the team wanted to do the same for male cells.

Just like humans, male mice have both an X and a Y chromosome, while females have two X chromosomes.

The scientists took skin cells from the tail of a male mouse and transformed them in a dish into so-called induced pluripotent stem cells, which can become any type of cell.

Around six percent of the cells lost their Y chromosome, leaving only one X chromosome – the so-called XO.

Using a fluorescent protein and a drug called reversin, the researchers were able to duplicate the existing X chromosome in these cells, creating an XX set.

– One percent success rate –

The cells were then used to create eggs, which were fertilized with sperm from another male mouse and implanted in the uterus of female surrogate mice.

Of 630 attempts, seven puppies were born, which corresponds to a success rate of just over one percent.

The pups show no signs of abnormalities and are self-fertile, the study said.

Hayashi, who first presented the results at the Third International Summit on Human Genome Editing in London last week, warned that there were still many obstacles to overcome before the technology could be used in humans.

“There’s a big difference between a mouse and a human,” he told the summit.

Nitzan Gonen, head of the sex determination laboratory at Israel’s Bar-Ilan University, told AFP it was a “revolutionary paper” but warned there was still a long way to go.

In theory, the technique could allow two same-sex male partners to have a baby, with one providing the sperm and the other providing the egg, said Gonen, who was not involved with the research.

A male could even provide both the sperm and the egg, which Gonen says “might be a little bit more like cloning, like what they did with Dolly the sheep.”

– “Milestone” –

Jonathan Bayerl and Diana Laird, stem cell and reproductive experts at the University of California, San Francisco, said it was not yet known if the procedure would even work with human stem cells.

Nevertheless, the research is “a milestone in reproductive biology,” they commented in Nature.

A possible future application could be to bring an endangered species back from the brink with only one surviving male, assuming there is a suitable female replacement from another species, they said.

But Gonen warned that the process is currently “extremely inefficient” as 99 percent of the embryos would not survive.

And while gestation lasts just three weeks in mice, it lasts nine months in humans, giving much more time for things to go wrong, she added.

If she had to guess, Gonen estimated that the technology could be ready for humans “scientifically” in about 10 to 15 years.

But that included the time it might take to work through the ethical considerations that might arise, she added.

“The fact that we can do something doesn’t necessarily mean that we want to do it – especially when it involves a new person.”