Gene Silencing to Produce Milk with Reduced Blg Proteins

The process of "knocking down" an undesirable gene is called gene silencing and may be carried out via RNA interference (RNAi). RNAi is a way of silencing the BLG gene using specifically designed molecules of RNA that target the mRNA from the BLG gene and cause it to produce only a very small amount of BLG proteins. Gene silencing is carried out by first making RNAs that are complementary to the mRNAs coding for the BLG proteins that are to be "knocked down". These RNAs are introduced into the cow's cells. They bind to micro RNAs and Argonaute proteins to from a silencing complex. The silencing complex binds to the mRNA for BLG by base pairing of the RNA. This occurs because the RNA introduced into the cell was specially made to be complementary to the mRNA for the BLG protein. This ensures the silencing complex only binds to the mRNA for this protein. When the silencing complex cleaves the mRNA for the BLG protein, the small fragments of mRNA that result, cannot be translated into complete proteins. By cleaving the mRNAs into fragments that cannot be completely translated into proteins, the BLG gene has been "knocked down". However, RNAi does not completely destroy expression of the BLG gene.

Some translation can still occur and thus BLG proteins are still produced. This means that the BLG gene will still produce a very small amount of BLG protein so the cow's milk will contain low levels of BLG proteins. The milk produced by these cows with "knocked down" BLG gene will no longer contain high levels of the BLG protein. When the cow's milk is drunk, it will not cause the same extent of allergic reactions in susceptible people because the production of the BLG proteins which cause these reactions has been reduced.

There are both advantages and disadvantages of producing a transgenic cow which produces milk containing the human myelin sheath protein (a therapeutic protein). Advantages are that the protein can be readily extracted from the milk of the cows and given to people with certain human diseases. The human myelin sheath protein can be used to treat these people. This means that those people do not have to live with that disease and may live longer than expected as a result. Another advantage of making this therapeutic protein in transgenic cows is that a large capacity of the protein can be made. The average dairy cow can produce a large amount of the therapeutic protein (about 5-10g/L). Transgenesis is also very economical and it is easy to scale production up or down to meet demand. Genetic manipulation in cows is more specific than conventional breeding as a specific trait can be focused on and is quicker than conventional breeding which is slow and unpredictable.

Disadvantages are the time taken to create a transgenic cow. It takes a long time to generate and validate transgenic cows and this could outweigh the benefits the transgenic cow's milk will have on humans. Also, the proteins produced in the cow's milk can't be harvested until lactation begins in the cow. Another disadvantage is that the human gene inserted into the genome of the cow (transgene) may affect the cow by disrupting a gene required for an important function. This is because the transgene inserts itself randomly into a chromosome. Enzymatic pathways may be affected and novel molecules may result with unknown effects. There are also fears that new viruses may be created and unknown diseases emerge. There are ethical concerns of the health of the transgenic cows. Many transgenic cows die or are short lived in comparison to non-transgenic cows so many people think it is not ethical to produce these cows due to any suffering they may endure.

There are both advantages and disadvantages of "knocking down" the BLG gene produced in cow's milk in order that milk with reduced BLG proteins is produced. Advantages of using RNAi (RNA interference) to "knock down" the undesirable BLG gene is that the BLG gene coding for the BLG protein is mostly silenced and only a small amount of BLG protein can be produced. This means that the cow's milk no longer contains high levels of BLG proteins and will not cause milk allergies in susceptible people. Milk allergies can result in problems with digestion and sometimes breathing and circulation. These allergies cause suffering so the advantage of the cow's milk with reduced BLG protein production is that this suffering can be alleviated and the people with the milk allergies can drink cow's milk. This can also be cheaper for a lot of people as they would otherwise have had to buy a substitute such as almond milk or soya milk which is a lot more expensive than cow's milk. The cost of the technology involved in producing the genetically modified cows is worth it, as suffering is ceased and extra costs for the allergy sufferers is reduced. The advantages of using RNAi to silence the BLG gene include the high efficiency of the BLG gene knockdown, the ability to easily target the BLG gene, as well as stable and long-term silencing. This makes for a powerful tool that has been successfully applied to cell biology.

Disadvantages of using RNAi to reduce the high levels of BLG proteins in cow's milk are that RNAi sequences do not only bind to one target. These changes in the gene expression pattern of the cell and potentially of the phenotype, can give rise to an unexpected result. The unidentified effects of such a problem bear a high risk to create negative outcomes that can bring the whole cow project into jeopardy.