Mice Bred Without Fertilization of Eggs

Mice can be bred without the fertilization of an egg, a new study from the University of Bath in England revealed.

Researchers from the university developed a method where they trick unfertilized mouse eggs into creating embryos and then inject the resulting embryos — called parthenogenotes — with sperm, allowing them to become healthy baby mice with a success rate of up to 24 percent, the University of Bath said in a news release.

"This is first time that full-term development has been achieved by injecting sperm into embryos," molecular embryologist Tony Perry, senior author of the study, said in the study. "It had been thought that only an egg cell was capable of reprogramming sperm to allow embryonic development to take place.

"Our work challenges the dogma, held since early embryologists first observed mammalian eggs around 1827 and observed fertilization 50 years later, that only an egg cell fertilized with a sperm cell can result in a live mammalian birth."

Details of the study were published Tuesday in the journal Nature Communications.

"These studies demonstrate that mitotic embryos are able to remodel sperm chromatin completely, leading to the direct production of healthy animals," the authors said in the Nature Communications report. "Full sperm reprogramming is therefore not unique to oocytes, showing that sperm chromatin reprogramming machinery is present at different development stages and in other cell types."

Biologist Karl Ernst Ritter von Baer was the first scientist to knowingly observe mammalian eggs in dogs in the 1800s, leading the conclusion that all animals are developed from eggs, according to Gizmodo.

"In some vertebrate species, like geckos for example, parthenogenetic embryos can develop fully to produce healthy live young, but there are no examples of parthenogenetic mammals known to science," Perry told Gizmodo. "Instead, development peters out after a few days."

The University of Bath statement said the mice born as a result of its technique appeared to be healthy, but their DNA began with different epigenetic marks compared with normal fertilization. That detail suggests that different epigenetic pathways can lead to the same developmental destination, something that was not previously known.

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