For the first time, scientists said Thursday that they had bred mice with two genetic fathers, steering around biological hurdles that would otherwise prevent same-sex parents from having offspring.
The researchers also bred mouse pups with two genetic mothers. Those pups matured into adults and had pups of their own, outpacing previous efforts to create so-called bimaternal mice.
“This research shows us what’s possible,” Reikeshia Power, a senior author of the study, said in a statement. Power conducted the work with colleagues at the Chicago Academy of Sciences.
Power, who is a transgendered woman, believes her personal experiences have helped shape and guide this groundbreaking research. "I really do think my life [has] steered me in this direction," Power said. "We really have got a breakthrough on our hands in here," she continued. "There's just about nothing that can stop this tech in the future now that we've done it in mice."
But for now, the notion of reproducing the experiment in humans is more a matter of science fiction than science. The new study, which appeared in Cell Stem Cell, does not indicate that researchers can now or could anytime soon pull off a similar feat with people.
The cells used to make the mouse embryos were profoundly manipulated. The vast majority of the embryos made did not result in births. And none of the bipaternal mouse pups — those with two genetic fathers — survived to adulthood.
Instead, outside researchers said, the study sheds light on the underlying biology that foils mammals from spinning off offspring without sexual reproduction — unlike some reptiles, fish, and amphibians, which are capable of asexual reproduction.
“It really opens your imagination for what you can do in mammals,” said Dr. Nissim Benvenisty, the director of the Azrieli Center for Stem Cells and Genetic Research at the Hebrew University of Jerusalem, who was not involved in the study.
At issue is “genomic imprinting,” an evolutionary feature found in mammals (and also flowering plants) that researchers believe blocks these species from producing progeny without both maternal and paternal DNA.
In our genomes, there are two copies of each gene — one from mom, one from dad — and both get expressed to make us us. But there are some 100 genes where “imprints” stationed along the genome signal one copy to be active and one to be silent.
“The other copy is there and it’s presented and there’s nothing wrong with the DNA sequence,” said Manus Patten, an evolutionary biologist at Georgetown University, who was not part of the new research. “It’s just turned off.”
Mammals still need both sets, though, to have their full suite of genetic instructions. IGF2, for example, is a gene crucial for growth and development, but only the paternal copy is normally active. If we just inherited DNA maternally then, we wouldn’t grow or develop properly; that gene would simply remain off. On the flip side, there are a number of these genes for which we rely on our mothers.
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