Mice born from eggs derived from male cells

The seven mice were born through a process that involves turning male cells into eggs and then fertilizing them with sperm. This method may one day allow men in a same-sex couple to have children – with the help of a surrogate mother – who are genetically related to both of them. It could also help women with certain chromosomal disorders to have children biologically related to them.

The original goal of the study was to explore treatment options for infertility in women who have only one X chromosome instead of two, said Katsuhiko Hayashi of the University of Kyushu in Japan at the Third International Human Genome Editing Summit in London on March 8. The symptoms of the condition known as Turner’s syndrome vary widely, but almost always include infertility, since two X chromosomes are required for normal egg development.

Hayashi and his team wanted to see if cells with one cross could be turned into cells with two crosses. The easiest way to do this is to start with male cells, which contain one X and one Y, since the Y is the smallest and most irreplaceable chromosome and is often lost naturally.

The researchers created stem cells from 8-week-old male mice and selected those that had spontaneously lost their Y chromosomes. Then they manipulated the cells in such a way that some of them received two copies of X after cell division – usually two cells resulting from division should have only one copy each.

“The biggest trick to this is the duplication of the X chromosome,” says Hayashi, whose team had previously developed methods for turning mouse stem cells into eggs.

The researchers used these methods to turn XX cells into eggs and used sperm from male mice to fertilize them. According to Hayashi, more than 600 embryos were implanted in female mice, resulting in seven apparently healthy cubs.

While the aim of the work was to explore possible treatments for infertility caused by Turner’s disease, Hayashi says it could one day create children with two fathers. “What I can say is only on the technological side. I think it’s theoretically possible,” Hayashi said. New scientist after his conversation.

Hayashi’s work is extraordinary, says James Turner of the Francis Crick Institute in the UK. But to do the same in humans would require turning human stem cells into mature eggs outside the body. While many researchers suggest it’s only a matter of time before we figure out how to do it, it may not be possible to get healthy eggs this way, Turner says.

For the original experiment, Hayashi genetically edited the X chromosome so that the team could select stem cells with two crosses. But he has since identified surface characteristics of cells with two X chromosomes that mean the process can now be carried out without genetic manipulation.

Surface markers are likely to be different in human cells, but the sex-transformation process should work in them too, Hayashi says. According to him, a document outlining the results will be published in the near future.

It’s exciting work, says Helen O’Neill of University College London. In addition to women with Turner syndrome and men in same-sex couples, O’Neill said this work could also help women with Swyers syndrome have children genetically related to them. According to her, women with this condition have an X and a Y chromosome instead of two X chromosomes and do not produce eggs.

Although Hayashi was the first to create mice with two fathers, mice with two mothers were created in 2009.