UM chickens are not afraid of blood cancer
Chickens made invulnerable to cancer-provoking virus
The new breed is not affected by the avian leukemia virus
Czech biologists have used the popular CRISPR/Cas9 genomic editor to breed a new breed of chickens that is not affected by the avian leukemia virus – a dangerous pathogen that generates blood cancer epizootics among birds. The significance of this discovery for poultry farming was revealed in an article published in the journal PNAS.
"Our tests show that a single mutation in the chNHE1 gene made chickens invulnerable to the action of five of the most common varieties of this virus at once. However, it remains unclear whether the pathogen will be able to adapt to this change and adapt to the new structure of chNHE1," the researchers write.
Over the past half century, scientists have discovered several types of microorganisms and viruses directly related to the development of cancer in humans, other animals or in plant tissues. For example, the bacteria Helicobacter pylori and Streptococcus gallolyticus are considered today to be the main contributors to the development of stomach cancer.
Similar problems threaten plants whose roots are penetrated by the pathogen Agrobacterium tumefaciens, and a whole group of viruses, the so-called oncoviruses, often increase the likelihood of developing cancer in their victims or directly cause it. These include herpes pathogens, papillomas and the mouse pathogen MMTV, which provokes breast cancer and is transmitted together with the milk of a female to her cubs.
A group of biologists led by Jiri Hejnar, head of the laboratory at the Institute of Molecular Genetics of the Czech Academy of Sciences in Prague, studied avian leukemia virus (ALV) – the first known pathogen of this kind, discovered by Danish biologists at the beginning of the last century. Since the middle of the XX century, this disease has begun to cause massive outbreaks of "contagious" blood cancer among laying hens in the United States and several other countries.
This epizootic was stopped in 1980-1990, but relatively recently there was a new outbreak of this disease in China and Southeast Asian countries, provoked by the virus strain ALV-J. This form of viral leukemia infects virtually all chickens equally well, which prevented breeders from creating a population of birds resistant to the action of this disease and using it to breed new breeds of birds protected from ALV-J.
Absolute protection
Gainar and his colleagues solved this problem by adapting the popular CRISPR/Cas9 genomic editor to work with the embryonic cells of birds. This system, as scientists explain, is quite well adapted to work with mammalian DNA, but it was not quite compatible with birds.
Scientists solved this problem by editing not the genome of eggs or embryos, but male germ cells extracted from the body of young roosters. After genetic manipulations, they returned back to the bird's body, after which it continued the genus and gave offspring already with altered DNA.
Guided by this idea, biologists used CRISPR/Cas9 to remove just one "letter" from the chNHE1 gene, which the ALV-J virus uses to penetrate chicken cells. After several generations of birds, Gainar and his team obtained several healthy males and females, in which both copies of the chNHE1 gene were altered.
Having raised a new generation of these birds, as well as chickens that had only one corrected version of this DNA site, the scientists tested what would happen if they tried to infect them with huge doses of ALV-J. They conducted similar experiments with other viruses that use the same gene to enter bird cells.
These experiments showed that the appearance of two corrected copies of chNHE1 gave birds absolute protection from infection, and one copy of this gene significantly increased the resistance of birds to small doses of viruses. At the same time, as scientists note, the removal of a gene fragment did not affect the health of birds and did not change their behavior, and the editing of the genome itself did not lead to the appearance of new "typos" in their DNA.
All this, according to the researchers, suggests that the breed of chickens created by them, as well as new varieties of birds obtained in a similar way, can be used to combat various retroviral infections affecting poultry on large farms and in small households.
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