Mice Birthed From Unfertilized Eggs for the First Time

The lab rodent, which only had genes from its mother, grew to adulthood and successfully reproduced, which was thought to be impossible in mammals

A mouse and its babies
The parthenogenetic mouse and the offspring Yanchang Wei

A team of researchers have successfully raised a mouse into adulthood that was produced from a single unfertilized egg. 

This method of asexual reproduction called parthenogenisis occurs naturally in several animal species, including some sharks, lizards and birds. It results in offspring containing either half or all of their mother’s genetic material, but does not require any genetic contribution from a male sex cell. It was previously thought to be impossible in mammals, per New Scientist’s Alex Wilkins.  

“The success of parthenogenesis in mammals opens many opportunities in agriculture, research, and medicine,” write the authors in their study, which was published in the journal Proceedings of the National Academy of Sciences. “Further identification and editing of additional ICRs [imprinting control regions] might improve the efficiency of parthenogenetic development.”

Prior research to force mammals to reproduce via parthenogenesis have failed because of genomic imprinting, per a statement. In normal sexual reproduction, offspring receive two copies of a gene, one from each parent. But genomic imprinting means that certain genes are chemically tagged to indicate which parent they came from, resulting in only one copy of the gene being expressed. 

The research team used the gene-editing tool CRISPR to target seven of these imprinted gene regions and change the tags, making it seem as though the mother’s genetic code came from a male, per New Scientist. They then injected an enzyme into the egg to switch some genes on and others off to mimic an egg that was fertilized by a male, per the statement. 

“It’s going to turn out to be an important piece of the jigsaw about the mechanism of very early embryo development and the way that the two parental genomes are regulated,” says biochemist Tony Perry of the University of Bath in the United Kingdom, who was not involved in the study, tells New Scientist. “And secondly, it’s an important technical demonstration of the kind of potency of these [CRISPR tools].” 

The researchers transferred 192 parthenogenetic embryos into 14 female mice. Three live baby mice were born, but only one survived to adulthood, per the study. The mouse appeared to have a normal body weight at birth, but as it grew to adulthood, it had about a 20 percent reduction in body weight compared to the study’s control mice. Despite this, the mouse was able to reproduce normally with a male.  

“I think there are people who will look at this and say, ‘Oh, is this going to replace reproduction? Get rid of men?’ No, it’s not,” Marisa Bartolomei, a molecular biologist at the University of Pennsylvania who was not involved in the study, tells The Daily Beast’s Miriam Fauzia. It could, however, help with research on diseases caused by genomic imprinting, like Prader-Willi syndrome or Beckwith-Wiedemann syndrome, per the publication. 

Future research will be needed to improve the process and the success rate of viable offspring, write the authors.