Birth of the first genetically modified and cloned puppies

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Since the emergence of the CRISPR-Cas9 gene editing technique, more daring genetic manipulations have emerged. In particular, scientists began using the technique on dogs. By combining gene editing with somatic cloning through nuclear transfer, Korean researchers have for the first time produced beagles whose modified genes are stronger and spread more evenly, from the first generation . The technique could eventually limit or even eliminate genetic diseases in purebred dogs, or allow the development of more targeted and precise treatments. But the limitations of the method are not yet well known and may raise ethical issues for animal rights defenders.

About 36,000 years ago, humans began domesticating wolves (Canis lupus), from which most of today’s dog breeds (with some exceptions), including companion dogs (Canis lupus familiaris). Thousands of years of domestication of the wolf have thus gradually changed its genome, to gradually adapt to the needs and wants of man. This evolution occurs through the process of natural selection, or through human migration – domesticated dogs of different breeds would have crossed and mixed on the continents.

Today, man seems to want to influence this genetic evolution even more radically thanks to biotechnology. Recently, researchers from the Korean company ToolGen combined CRISPR-Cas9 technology and cloning for the first time, and gave birth to two apparently healthy baby beagles.

In dogs, the CRISPR-Cas9 technique was used for the first time in 2015 by Chinese researchers, in the same breed. The two dogs born from the experiment were surprisingly more muscular than normal, mainly due to the elimination of the myostatin expression gene, which normally limits muscle development. Apparently the goal was to create a new breed better suited for running and hunting.

This precise, affordable technology has inspired many other companies to experiment with new breeds or “revive” the pets of wealthy customers. The advantage of this technology is the elimination of genes responsible for diseases, or even the improvement of cognitive and physical abilities.

However, the basic technique is limited, because the animals born are “chimeras”. With this technique, gene editing takes place directly at the level of the fertilized egg, which is then implanted into a surrogate woman. But since the change is not represented in all cells, breeding is necessary to reproduce the genes at a higher frequency in future generations.

Favorable characteristics resulting from gene editing can be passed from generation to generation “, explained at the time Liangxue Lai, researcher at the key laboratory of regenerative biology at the Institutes of biomedicine and health in Guangzhou, and one of the authors of the Hercules and Tiangou experiment. ” It may be possible to breed large numbers of genetically modified dogs, which can be sold “, he added.

As for somatic cloning by nuclear transfer, it is already used in dogs, in South Korea, to create black and white Afghan hounds. Named Snuppy, the greyhound was born from the skin cells of one of the father’s ears, which were mixed with the eggs of a surrogate.

The advantages of both combined techniques

In a new study, published in the journal BMC Biotechnology, Korean researchers have successfully combined this cloning technique with CRISPR-Cas9 gene editing. Thanks to this combination, no breeding is necessary to fully express the desired genes.

The main advantage of this new method is the possibility of eliminating pathological genetic mutations in purebred dogs. In the latter, in fact, the lack of genetic diversity is often the reason for the more frequent appearance of phenotypically recessive mutations. The ToolGen technique can thus change these genes without the risk of changing other characteristics, and preserve the purity of the dog breed.

Technology can also contribute to the protection and conservation of biodiversity, through its use in species threatened with extinction. For the survival of their species, these animals are often forced to reproduce between close relatives, their number or their territory is very small. Inbreeding, which leads to a more frequent manifestation of genetic pathologies, therefore constitutes an additional threat to the survival of this species. Korean technology can alleviate this problem, by eliminating pathogenic mutations.

In their experiments, the researchers took skin cells in which a mutation in the DJ-1 gene was induced to prevent the expression of the protein it codes for. This gene is particularly associated with various diseases, such as Parkinson’s. Other genes were also added, including one that expresses a green fluorescent protein to facilitate tracking of successfully transformed cells.

For nuclear transfer, cells are placed near the eggs from which the DNA was previously extracted. The cells and the eggs are then brought together by the electrical impulses that are injected into their environment. The 68 embryos obtained were implanted in six surrogate women.

The experiment, however, only gave birth to two puppies, which are now 22 months old and show no abnormalities. However, since diseases caused by DJ-1 are age-related, dogs may develop age-related pathologies.

The researchers also emphasized that these animals will only be used for medical research. Moreover, this type of experiment is still subject to many ethical debates.

Source: BMC Biotechnology

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