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The First Mice Bred from 2 Dads Died Gruesome Deaths—But They May Hold Clues to Saving Endangered Species

Lab Mice Live In Individually Ventilated Cages Worth 100 Thousand Yuan Per Square Meter In GuangzhouLab Mice Live In Individually Ventilated Cages Worth 100 Thousand Yuan Per Square Meter In Guangzhou
Mice live in individually ventilated cages (IVC) worth about 100 thousand yuan ($14,700) per square meter at a laboratory animal center at the Sixth Affiliated Hospital of Sun Yat-sen University on September 3, 2018 in Guangzhou, Guangdong Province of China. With a total budget of about 10 million yuan ($1.5 million), the laboratory animal center in Guangzhou has 2,000 individually ventilated cages.He Yushuai—Southern Metropolis Daily/VCG via Getty Images

Using a gene-editing method that has emerged in the last few years, Chinese researchers have created viable mouse embryos using cells from two males and, separately, from two females. The implanted embryos grew to term but the male-only pups died a few days after birth, the researchers report in Cell Stem Cell.

It is the first case of mammals with two fathers and no mothers, though Japanese researchers created fatherless mice with two mothers in 2004. That time, researchers converted an immature female egg into a sperm-like cell and removed a pair of genes involved in fetal growth. Most of the pups did not survive to adulthood, probably due to the interference with their genes, but one did and had pups of her own.

Other animals—including turkeys and many reptiles, amphibians and fish—can self-fertilize when unable to find members of the opposite sex. Some can even change their sex in order to reproduce in the local male-heavy or female-heavy community.

In the recent Chinese project, researchers used a more precise gene-editing tool called CRISPR/Cas9, which allowed them to trim three stretches of genetic information known to otherwise interfere with single-sex embryo development. The pups grown this way from two female parents grew up and had normal fertility, though they did suffer from some abnormalities.

Forming embryos from two male parents required trimming more genetic material in six places. However, the interference caused those pups to grow in grotesque proportions, inflated by internal fluid until their guts leaked, their tongues swelled and they could not close their eyelids. They lived only 48 hours.

The researchers have no plans to do similar experiments in humans, they told Science News. Because of differences between the genetic code in each species, it may not even work in humans. But if researchers could adapt it to other species, they might be able to help save endangered ones such as the northern white rhinoceros, of which only two females remain.

Studying the effects of suppressing different genetic passages on embryos in the laboratory might also teach researchers more about how genes guide normal development. But as soon as they turn to humans, “It is really a big ethical question mark,” Monika Ward of the University of Hawai’i told National Geographic.