For the first time ever, healthy mice with two mothers have been born in a study that challenged scientific boundaries, the Guardian reports.
Mice with two fathers were also born, but survived only for a few days, according to the Chinese team that conducted the research. Although the results proved that barriers to same-sex reproduction in humans can be overcome, there is no prospect for that to take place in the near future.
“This shows us what’s possible,” said senior author of the paper, Wei Li, of the Chinese Academy of Sciences.
This is the first time scientist have managed to produce healthy baby mice with same-sex parents, as in previous experiments the animals had serious abnormalities, and the methods used usually required “convoluted sequences of genetic manipulations, sometimes involving several generations of mice,” the Guardian said.
The study worked towards finding an explanation for a subject that scientists have been debating for a long time, which is why mammals require genetic contribution from both a female and a male in order to reproduce. Many other species of animals do not require said equal genetic contribution, such as hammerhead sharks and komodo dragons, where genes from the father are not necessary for the reproduction process.
A phenomenon known as “imprinting” takes place in mammals during reproduction, where for 100 or so genes, only the copy that came from the mother or the father are ever used. It is possible to know from which parent a gene originated from in the first place, even though maternal and paternal genetic contributions are all mixed together in the genome, because all genes carry their own chemical tag. Usually, a healthy and viable embryo cannot be produced without the correct pattern of male and female imprinting.
This study shows that this problem can technically be solved. When it came to the mice born from two mothers, researchers grabbed embryonic stem cells from a female mouse, and by using the gene-editing tool Crispr-Cas9, they removed maternal imprinting from three crucial regions of DNA “by snipping out a single letter of the genetic code where the chemical tag was attached,” the Guardian reported. This resulted in the genetic material appearing more “male” in its imprinting pattern.
Scientists then injected the modified cells into the unfertilized egg of another female mouse, and the genome from the two females combined formed a healthy embryo. The study was a success as they managed to produce 29 live mice from 210 embryos, and the animals lived on to become adults and to have their own babies.