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Nature has very varied forms of reproduction: from sexual production between males and females to asexual production, in which a single individual is capable of generating offspring, such as spores. In the latter there is a type, the partogenesis, in which a female is capable of generating offspring using only her ovules, without sex and without their being fertilized. Some fish, reptiles, amphibians, bees, scorpions or mites have offspring in this way. Science has been trying to recreate it artificially in mammals for some time (and apply it in fields such as research or medicine), but until very recently it was believed impossible. Now, a group of Chinese scientists has just achieved it in mice thanks to genetic manipulation.
The results have been published in the journal ‘
Proceedings of the National Academy of Sciences‘ (PNAS).
The main obstacle to this type of reproduction in mammals is the phenomenon known as genetic imprinting, whereby certain genes are expressed in a specific way depending on the sex of the parent that provides them. However, in order for an unfertilized egg to develop into an embryo, it needs to have two sets of DNA, in this case from its mother. And because the imprinting pattern is the same in both sets, some genes collide or don’t turn on at all.
In 2004, Japanese researchers managed to create a mouse by parturition from two females: one of the ovules acted as if it were the material provided by the ‘father’ of the offspring, which they called Kaguya. However, this new technique has allowed an almost ‘virgin’ conception. Yanchang Wei and his colleagues at Shanghai Jiao Tong University, China, created unfertilized mouse eggs with twice the normal number of chromosomes, adding DNA that is expelled in the early stages of the development of the egg. Then they used the gene editing tool CRISPR to target seven imprinted gene regions previously identified as important in embryo development and change epigenetic imprinting. This caused the second copy of the mother’s genetic code to appear as if it were that of a male, ‘trickling’ the ovum into becoming an embryo.
Wei and her team edited 227 unfertilized eggs, which ultimately resulted in 192 embryos. Only 14 of these embryos reached term, but only three survived. Finally, only one mouse reached maturity and might reproduce normally. ‘The live pups were underweight compared to normal mouse pups and showed certain genetic abnormalities. This suggests that there are still imprinting regions involved in embryo development that we do not fully understand », he states for
‘NewScientist’Tony Perry, from the University of Bath (UK), and who was not involved in the study. “Another possibility is that gene editing hasn’t worked as fully as it should.”
It is inevitable to think of the application in people; however, all scientists agree that this is a milestone in gene editing, there is still a long time to see a similar technique in human babies. “The state of knowledge regarding imprinted genes in humans is much lower than it is in mice,” Perry says. We can’t do experiments with them in the same way we can with mice.”
In fact, CRISPR gene therapies being used in humans are still ‘in their infancy’: the first human clinical trials testing cancer immunotherapy treatments for two common blood diseases (sickle cell anemia and beta -thalassemia), and for the deadly condition transthyretin amyloidosis. At the same time, there are dozens of experiments waiting to get the green light for tests on people.