Male obsolescence may be approaching
HEALTHY mice have been bred from two mums and gone on to have normal pups of their own.
Researchers from China altered stem cells from a female mouse and injected them into the eggs of another, with 29 out of 210 embryos surviving.
Mice pups from two dads were also born using a similar but more complex approach, but they only survived for a couple of days.
The researchers were examining what makes it so challenging for mammals of the same sex to reproduce and found that some of these barriers can be overcome using stem cells and targeted gene editing.
But they warned there were still obstacles to using these methods in other mammals.
Researchers at the Chinese Academy of Sciences said they were interested in why mammals could only undergo sexual reproduction.
While some reptiles, amphibians, and fish can reproduce with one parent of the same sex, it's challenging for mammals to do the same even with the help of fertilisation technology.
In mammals, because certain maternal or paternal genes are shut off during germ line development by a mechanism called genomic imprinting, offspring that don't receive genetic material from both a mother and a father might experience developmental abnormalities or might not be viable
Co-author Qi Zhou said by deleting these imprinted genes from immature eggs, researchers had produced bimaternal mice - mice with two mothers - in the past.
"However, the generated mice still showed defective features, and the method itself is very impractical and hard to use," Zhou said.
To produce their healthy bimaternal mice, then team used haploid embryonic stem cells (ESCs), which contain half the normal number of chromosomes and DNA from only one parent and which the researchers believe were the key to their success.
The mice were normal, lived to adulthood, and had babies of their own.
Twelve live, full-term mice with two genetic fathers were produced using a similar but more complicated procedure.
These embryos were transferred along with placental material to surrogate mothers, who carried them to term.
These pups survived 48 hours after birth, but the researchers are planning to improve the process so that the bipaternal mice live to adulthood.
Similar results were achieved in 2011 but using a method that relied on a female intermediary produced from the first father's stem cells to mate with the second father.
That method sidestepped the problem of genomic imprinting but presents ethical and practical hurdles if this technology were to ever be considered for humans.
Co-author Wei Li said researchers would need to identify problematic imprinted genes that were unique to each species.
They would also have concerns for the offspring that don't survive or that experience severe abnormalities.
But the team still hope to explore these techniques in other research animals in the future.
"This research shows us what's possible," he said.
"We saw that the defects in bimaternal mice can be eliminated and that bipaternal reproduction barriers in mammals can also be crossed through imprinting modification.
"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."