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17.11.2006
Specialists of the All-Russian State Research Institute of Cattle Breeding have obtained transgenic animals, which give milk with the proteins participating in haemopoiesis. However, these are not ordinary transgenic animals, but somatic ones: the transgene is present not in every cell of the body, but only in the organ where it should work – in the udder.

The researchers started the effort for creation of somatic transgenic animals several years ago (InformNauka described these investigations in the material entitled “Transgenic Cows and Pigs” in 2002). Since then, they have obtained transgenic goats and specified influence of various factors on protein produce.

Utilization of transgenic agricultural animals as fermenters bodes well for pharmaceutical industry. However, the traditional method of getting them (when the DNA is introduced directly into the impregnated ovule) is inefficient. Only 1 percent of transplanted embryos turn out to be transgenic, and only 60 percent of transgenic animals provide at lease some amount of the required protein. Moreover, it would be clear who will give protein and how much of it several years after the DNA introduction when the transgenic ovule would turn into an animal of a proper age. Fortunately, there is a less lengthy and expensive way of gene transfer – the required gene is introduced directly into the mammary gland of a cow, goat or a sow.

Of course, the method is rather troublesome. First, the required gene should be built into the retrovirus’ genome, and the viral DNA should be introduced into the cell culture. Retroviruses possess a property very precious to genetic engineering – to survive in the cell, they must necessarily build their DNA into the cell’s chromosome.

The cells are reproducing and along with that they are producing new viral particles, and when they are introduced into the mammary gland, the viral particles penetrate the gland’s cells and build their DNA in the cellular genome. Thus, the mammary gland’s cells get the required gene and start producing the useful protein together with milk.

The researchers dealt with genes of two proteins participating in maturation of blood cells: erythropoietin and granulocyte-colony-stimulating factor. The maximum concentrations of these proteins in milk reached about 1,000 and 200 nanogram per milliliter, respectively. However, contemporary technologies allow to educe proteins from milk at ten times lower concentrations (only 25 nanogram per milliliter).

Practically all laboratory animals synthesized the required proteins during the entire period of lactation. However, the quantity of protein in milk changes from day to day. The first third of lactation is more productive than the two following ones. The researchers have determined that the highest possible production of proteins requires that gene constructions should be introduced into the mammary gland of cows in the 4th –6th month of pregnancy, that of goats – in the 4th –5th month of pregnancy, and that of sows – during the last trimester of pregnancy. The maximum production of proteins was achieved with cows, but the average concentration of proteins turned out to be higher in the milk of goats and sows.

In the researchers’ opinion, they have developed a technology, which allows to get the highest quantity of industrially important protein from the milk of an animal as compared to other existing gene transfer methods. Although transgenic animals, obtained by this method, do not transmit the new gene to descendants, they efficiently produce biologically active proteins in required quantities.

Nadezda Markina | alfa
Further information:
http://www.informnauka.ru

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