Asexual reproduction or parthenogenesis – a Greek term meaning ‘virgin creation’ – has been achieved for the first time in a mammal; specifically, in a mouse that has given birth to a live offspring from an unfertilized egg genetically edited by a team of Chinese scientists. Parthenogenesis defines the ability of certain animals and plants to reproduce from their own reproductive cells and without needing the genetic material of the male to do so, but it was believed that this phenomenon was not possible in the case of mammals.
This type of reproduction presents a problem in mammals, in that for the unfertilized egg to become an embryo, it needs two sets of DNA – that of the father and that of the mother. When a sperm enters the egg, a phenomenon called genetic imprinting occurs, which means that the functioning of some genes differs depending on whether they are inherited from the father or the mother, and in certain cases some imprinting genes are related, for example , with a higher risk of developing diseases such as cancer.
A pregnancy from a single unfertilized egg
In 2004, Japanese researchers managed to create a mouse – which they called Kaguya – by parthenogenesis, and for this they used two ovules, one of which acted as the authentic ovule, while the other simulated the genetic contribution of the sperm. The calf was, therefore, the daughter of two females.
In the new research, the results of which have been published in the Proceedings of the National Academy of Sciences’ (PNAS), scientists at Shanghai Jiao Tong University in China, led by Yanchang Wei, a reproductive medicine researcher at Ren Ji Hospital in Shanghai, have achieved a pregnancy from a single unfertilized egg with a genetic editing technique very similar to CRISPR or genetic ‘cut and paste’.
“The success of parthenogenesis in mammals opens up many possibilities in agriculture, medicine and research”
The researchers used the gene-editing tool to mimic genetic imprinting at seven different points in the genome of an egg cell that had two copies of each gene and had previously been identified as important in embryo development. This caused the second copy of the mother’s genetic code to appear as if it were from a male and began the biochemical process equivalent to fertilization; thus, the ovule went from being a single cell to a 140-cell blastocyst.
Of the 227 unfertilized ovules edited, they obtained 192 embryos, which they implanted in as many females. Only 14 of them made it to term, and only three survived, although two died after delivery. Only one of the offspring – a female – reached adulthood and was able to reproduce normally.
The authors of the study have highlighted that “parthenogenesis in mammals can be achieved through epigenetic regulation”, and believe that it would be possible to perfect this technique so that the rate of successful births increases. “The success of parthenogenesis in mammals opens up many possibilities in agriculture, medicine and research”, they conclude.
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