Researchers just made healthy baby mice with two mothers & no father

Mouse pups born to two fathers like the one shown here only survived a few days. Credit Leyun Wang

Mouse pups born to two fathers like the one shown here only survived a few days. Credit Leyun Wang

In creating the "mothers only" mice, the researchers simply injected edited stem cells directly into the egg, which was then implanted into another female mouse. In total, they produced 29 live mice from 210 embryos.

Another view of a healthy adult bimaternal mouse, born to two mothers, with offspring of her own.

Just as impressively, the created mice were able to live to adulthood and have offspring of their own.

Some reptiles, amphibians, and fish, however, have the benefit of parthenogenesis: a natural form of asexual reproduction in which growth and development of embryos occur without fertilization.

But while the team was able to produce viable babies from female pairs of mice, whose offspring went on to have their own progeny, the mice produced from male pairs fared less well.

Japanese scientists in 2004 duplicated this phenomenon using mice; they grew healthy female pups that lacked any paternal genes.

Zhou said same-sex reproduction was hard for mammals because of a mechanism called genomic imprinting, while it was much easier for some reptiles, amphibians and fish.

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Dr Hu said: 'We found in this study that haploid ESCs were more similar to primordial germ cells, the precursors of eggs and sperm. For example, there is a need to identify problematic imprinted genes that are unique to each species and ongoing concerns for the offspring that don't survive or that experience severe abnormalities. Haploid ESCs containing only a male parent's DNA were modified to delete seven key imprinted regions.

Then CRISPR-Cas9 gene editing - which uses DNA and RNA sequences culled from bacteria to pinpoint and delete human genes - turns off the genes that tell the remaining cells to be female, encouraging the egg to behave like sperm.

According to one evolutionary hypothesis, parents' sex cells resolve this difference by shutting off regions of their offspring's DNA that would benefit their partner's desires in a process called genomic imprinting. These embryos were transferred along with placental material to surrogate mothers, who carried them to term. However, the bipaternal mice pups only survived for 48 hours after birth.

This field of research treads on tricky ethical ground, with previous studies involving genetic editing and novel methods of reproduction prompting fears about the implications if similar processes were eventually applied to humans.

A bipaternal mouse pup born to two fathers.

"The tremendous amount of genetic modification needed in order to do what they (Chinese researchers) did, makes it implausible to use it in anything other than research in the way that they've done", he said. They do hope, however, to explore these techniques in other research animals in the future.

"If the research is reproducible, and also works in humans, it still has to be shown to be safe,"Bob Williamson, the chair of the Board of Stem Cells Australia, said. We also revealed some of the most important imprinted regions that hinder the development of mice with same sex parents, which are also interesting for studying genomic imprinting and animal cloning".

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