A team of scientists in China were able to get mice of the same sex to produce healthy, living offspring for the first time, according to a study published Thursday in the journal Cell Stem Cell.
The scientists were able to use sophisticated genetic tools to create offspring from two female mice and from two male mice — though they could only get the ones from female parents to live long enough to reproduce themselves.
Many animals reproduce through methods other than by a male and female having sex. Some animals can reproduce by building clones of themselves, and reproduction with only one sex is possible in many “lower vertebrates” like fish, reptiles and amphibians, the scientists wrote.
In mammals, that’s not the case. The researchers wanted to find out why — and if they could figure out a way to make it work in a lab.
It took sophisticated, complicated genetic tinkering to get the babies born. It wasn’t easy as just taking two X chromosomes from two females and putting them together, or taking an X and Y from two different males and sticking them together. That’s because of something called “imprinting.”
“Imprinting” refers to certain genes that only activate when they come from male or female parents. If you have two female sets of genetic instructions, some genes won’t be “turned on” and will mess up the growth of the embryo. This caused some of the mice to become too small and die before they could mature when the scientists first attempted making babies from two female parents, according to Forbes.
So they turned to a new tool called CRISPR, a set of genetic “scissors” made from bacteria that can snip out troublesome genes. When they carefully cut out the imprinted genes that were preventing things from working correctly, the female pups were born.
It wasn’t perfect. Out of 210 embryos, only 29 were born to live to maturity. In a news release, the scientists said the mice “still showed defective features” and called the method “very impractical and hard to use.”
It was even harder for male mice. In that case, the researchers used CRISPR to delete seven troublesome genes from the mice, then injected the genetic material from two males into an egg cell that had the mother’s genetic information removed before transferring it into a female to develop.
That experiment produced 12 full-term babies, but they all died within 48 hours.
“It really opens your imagination for what you can do in mammals,” said Dr. Nissim Benvenisty of the Hebrew University of Jerusalem, according to STAT News.
So why do it?
“One reason is to understand better how fertilization and embryonic development work,” said Hank Greely of Stanford University, according to Forbes.
As for its use in humans? Not likely — at least not soon, some scientists say.
“There would need to be a decade or more of safety testing before the FDA-approved such a process in humans — and that’s after another several years of concerted work to even get to the point of being able to do enough with human material to even get to safety testing. Its at least 15 years away in humans, I’d guess and maybe forever,” Greely said, according to Forbes.
“Even with two mothers I’m not convinced they’re normal and the success rate is pretty low,” Robin Lovell-Badge of the Francis Crick Institute said, according to the BBC. “It is not something I’d hope anyone would contemplate.”