In 1995a boy did medical background when scientists learned it was partially the product of parthenogenesis – a process that occurs when offspring results from an unfertilized egg.

More than two decades after the discovery, scientists are still trying to understand how parthenogenesis works, but a new study takes a big step forward in answering this question, finding further evidence that parthenogenesis can occur in mammals, at least under laboratory conditions.

The latest research focuses on parthenogenesis in mouse offspring, using a unique genetic technique to overcome challenges encountered in previous research. The results were recently published in the journal Proceedings of the National Academy of Sciences.

A mouse – produced by parthenogenesis – and its offspring.Yanchang Wei

What’s new – The researchers used what are called epigenetic rewriting techniques – a method that does not alter an animal’s actual DNA but rather alters gene expression and activity – to create unfertilized parthenogenetic embryos without male sperm.

After transferring the embryos to female mice, the scientists were able to bring a parthenogenetic mouse into adulthood, which then successfully bred – with a male – to create viable offspring. Further experiments brought two additional offspring of living mice, which also survived to adulthood.

Why is it important – Parthenogenesis challenges one of the fundamental principles of sexual reproduction – that is, you need genetic data from both a father’s sperm and a mother’s eggs to produce a offspring.

Yet it is no scientific secret that other animals that normally reproduce sexually can occasionally produce asexual offspring from parthenogenesis. Sharks, snakes and even California condors are among the species scientists have observed breeding without a male’s sperm.

Scientists have not yet observed parthenogenesis in wild mammals, although Previous search published in 2004 found that parthenogenetic laboratory mice could survive to adulthood. Further research will be needed to understand whether parthenogenesis will ever be possible in humans.

This latest study builds on previous research, finding a new genetic way to generate parthenogenetic mammals. Their research supports the parental conflict hypothesis, also known as the “Haig’s hypothesis, which finds that the conflict between maternal and paternal embryonic genes results in differential expression of genes depending on whether they come from sperm or from an egg. This differential expression, known as “gene fingerprinting”, has generally made parthenogenesis difficult to generate in mammals – until now.

How they made the discovery — The researchers used a technique called methylation rewriting, which alters gene expression without altering the DNA itself. Methylation refers to the process of adding or removing chemical groups – called methyl groups – at specific locations on DNA called loci.

Indeed, the scientists used this technique to rewrite seven imprinting control regions in immature eggs called oocytes. Imprinting control regions play a key role in the expression of imprinted genes that derive from the mother or the father.

The researchers successfully used methylation rewriting to activate oocytes – a process that normally occurs during sperm fertilization of the egg – to create parthenogenetic embryos, which were then transferred to host mothers, who gave birth birth to offspring. All this without a single male sperm. The researchers compared the development of the parthenogenetic animals to a control group of mice.

And after – The researchers are quick to find that their procedure for generating parthenogenetic mammals is not extremely efficient. After all, only one offspring – out of hundreds of parthenogenetic embryos created by researchers – has successfully survived into adulthood. Further investigation will help clarify why others have failed and how to successfully edit mammalian parthenogenetic embryos to better ensure their survival.

The researchers also hope that their findings may provide another stepping stone in medical research on parthenogenesis, which has applications for infertility treatments and regenerative medicine.

“The success of parthenogenesis in mammals opens up many opportunities in agriculture, research and medicine,” the researchers conclude.

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