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Genetic engineering: cow gives allergen-free milk

Genetically modified cow bred with allergen-free milk. A common trigger for allergic reactions after milk consumption, according to a New Zealand research team led by Anower Jabed from the Institute of Biology at the University of Waikato in Hamilton (New Zealand), is the protein beta-lactoglobulin (BLG) contained in cow's milk, which is not found in human breast milk . Around two percent of infants are allergic to this protein.

To date, complex processes have been required to produce milk without beta-lactoglobulin, not least because the protein is relatively heat-resistant. The New Zealand researchers had therefore set themselves the goal of genetically modifying cows in such a way that they would give beta-lactoglobulin-free milk directly. As Anower Jabed and Stefan Wagner from the “AgResearch” research center in Hamilton report in the journal “Proceedings of the National Academy of Sciences” (PNAS), they have now succeeded in doing this. They introduced genetic information that contributes to the production of certain microRNAs into the genes of cattle. These injected microRNAs blocked the gene that is responsible for the production of beta-lactoglobulin, the researchers write. As a result, the bred cow delivered allergen-free milk.

Beta-lactoglobulin in cow's milk reduced by up to 98 percent For a long time, researchers at the University of Waikato had been looking for ways to breed cows that supply beta-lactoglobulin-free milk directly. First, they identified ten microRNAs that reduced BLG by up to 98 percent in in vitro screening. The microRNAs block certain genes that are required to produce the protein, the New Zealand scientists report. In a next step, the identified, particularly effective microRNAs were tested in experiments with mice. The researchers implemented the genetic building instructions for the microRNAs in the genome of mouse embryos, and in around 25 percent of the experiments, mice were created that carried the microRNA genes and passed them on to their descendants. The previously established effectiveness was also confirmed in the experiments with mice, write Jabed and colleagues.

RNA blockade through so-called microRNA In a next step, the most effective microRNA variant was built into the fertilized egg cells of cows. The researchers cloned the egg cells, which succeeded, and used five of the embryos resulting from them to act as surrogate mothers. Pregnancy was successfully completed and a female calf was born. At the age of seven months, the calf was stimulated to produce milk by the administration of hormones. The milk was free of beta-lactoglobulin, Jabed and colleagues report. This proves that the microRNAs successfully and specifically block the production of the allergenic protein. The researchers conclude that "this type of RNA blockade proves to be an effective strategy to change the composition of milk, but also other properties of farm animals."

Genetic engineering cows with special features However, the genetically modified cow also showed other special features. On the one hand, their milk contained "significantly more of all other milk proteins, including casein in particular," report the New Zealand researchers. While Jabed and colleagues describe the high casein content of milk as an advantage, since the milk also contains more calcium and is particularly suitable for making cheese, for example, the risk of allergies due to high casein content should also be pointed out. For its part, casein is one of the common triggers of cow's milk allergies. In the end, little may be gained for allergy sufferers by breeding the genetically modified cows.

Doubtful success of genetic manipulation In addition, there are the ethical reservations that generally resonate in such genetic interventions and are of particular importance in the case of inheritable manipulations of the hereditary disposition. In addition, the cow had no tail, but the researchers believe that this was probably not related to the genes introduced. This natural mutation can be observed from time to time in cattle. Jabed and colleagues assume that the cell selected for cloning already happened to carry this mutation. However, they could not completely rule out a possible connection with their manipulation of the genetic material. With a critical attitude towards genetic interventions, the question really arises whether the result of milk that is free of beta-lactoglobulin from the start justifies the intervention. Especially since there are other ways to subsequently rid the cow's milk of the allergy-causing proteins. (fp)

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