Scientists create baby mice from two mouse dads

Scientists in Japan have created mice with two biological fathers and say the possibility of two men producing a biological child is not far behind.

Katsuhiko Hayashi, a pioneer in lab-grown eggs and sperm, announced the fertility breakthrough at the Third International Summit on Human Genome Editing in London on Wednesday.

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Hayashi and his colleagues at Kyushu University in Fukuoka, Japan, used manipulated skin cells from one male mouse and the sperm from another to create seven healthy mouse pups.

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Hayashi was confident he’d soon be able to replicate the process in humans, creating a viable egg from a human male’s skin cells.

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“Purely in terms of technology, it will be possible even in 10 years,” he told the conference. Hayashi and colleagues are already at work on translating their success into the creation of lab-grown eggs using male human cells.

Hayashi’s team previously created mice that were technically from two biological fathers through an elaborate genetic engineering process. This method was more direct.

First, male mouse skin cells were reprogrammed into a stem cell-like state, then the Y-chromosomes of these XY cells were replaced by X chromosomes from another group of cells, producing female XX versions.

“The trick of this, the biggest trick, is the duplication of the X chromosome,” said Hayashi. “We really tried to establish a system to duplicate the X chromosome.”

Those cells were then cultivated into eggs in the mouse version of  “ovary organoid,” a culture system that mimics a mammalian ovary. Scientists fertilized the eggs and created about 600 mouse embryos, which were then implanted in female surrogate mice.

With seven healthy pups born, the efficacy rate was about one percent, compared with five percent for human IVF treatments.

“This is the first case of making robust mammal oocytes from male cells,” Hayashi told the conference.

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The mouse pups went on to have average lifespans and produce their own offspring. “They look OK, they look to be growing normally, they become fathers,” said Hayashi.

Hayashi said the primary motivation for the research was to treat severe forms of infertility, including women with Turner’s syndrome, in which one copy of a woman’s X chromosome is corrupted.

Prof George Daley, dean of Harvard Medical School, described Hayashi’s work as “fascinating”, but said research indicates growing gametes from human cells in the laboratory was a leap from mouse cells. “We still don’t understand enough of the unique biology of human gametogenesis to reproduce Hayashi’s provocative work in mice,” he told The Guardian.

Hayashi said he’s personally in favor of his work being used to help two men to produce their own biological children, provided the technique turns out to be safe for humans.

But “that is not a question just for the scientific program,” he added.

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