PRODUCTION OF TRANSGENIC COW MILK & ITS APPLICATION IN HUMAN WELFARE
Recently we have read in the news paper that Scientists have created genetically modified cattle that produce “human” milk in a bid to make cows’ milk more nutritious.
The scientists have successfully introduced human genes into 300 dairy cows to produce milk with the same properties as human breast milk.
Human milk contains high quantities of key nutrients that can help to boost the immune system of babies and reduce the risk of infections.
The scientists behind the research believe milk from herds of genetically modified cows could provide an alternative to human breast milk and formula milk for babies, which is often criticised as being an inferior substitute.
They hope genetically modified dairy products from herds of similar cows could be sold in supermarkets. The research has the backing of a major biotechnology company.
Over centuries animal breeding practices were performed to improve the genetic potential of animals and to introduce new traits, through genetic selection. But the number of gene combinations achieved through this process has limitations, since breeding is only possible between animals of same or closely related species. Transgenesis is a revolutionary technology which introduces new genes to a species, which belong to an entirely different species. The chemical combination of DNA is same in all eukaryotic species. Theoretically genes can be transferred between any species. So the resulting species will be having the desired characteristics of another species. Result of human genome project and other similar projects to reveal the genetic code has opened new arenas in medical research in combination with transgenics.
What is a transgenic cow?
Transgenic cows are genetically modified (GM) cows. They have an extra gene or genes inserted into their DNA. The extra gene may come from the same species or from a different species.
Transgenic cows produce proteins in their milk
The extra gene (transgene) is present in every cell in the transgenic cow. However, it’s only expressed in mammary tissue. This means that the transgene’s protein will only be found in the cow’s milk and can only be extracted from there.
By genetic engineering, the gene for a protein drug of interest can be transferred into another organism that will produce large amounts of the drug. Transgenic technology led to the emergence of a new kind of farming from research and development labs of several universities and small biotechnology companies- they even changed the spelling to “pharming”. “Pharming” is the production of human pharmaceuticals in farm animals. Gene “Pharming” enables production of recombinant biologically active proteins in the mammary glands of transgenic animals. This technology overcomes the limitations of conventional and recombinant production system for pharmaceutical proteins. Mammary gland is the preferred production site, mainly because the qualities of protein that can be produced in this organ using mammary gland specific promoter elements and established methods for extraction and purification of that proteins. Numerous monoclonal antibodies are being produced in the mammary gland of transgenic goats. Cloned transgenic cattle can produce a recombinant bispecific antibody in their blood. Purified from serum, the antibody is stable, mediates target cell restricted T cell stimulation and tumor cell killing. An interesting new development is the generation of Transchromosomal animals. A human artificial chromosome containing the complete sequence of human immunoglobulin heavy and light chain loci was introduced into bovine fibroblasts, which were then used in nuclear transfer cloning. Trans-chromosomal bovine offsprings were obtained, that expressed human immunoglobulin in their blood. This system could be a significant step forward in the production of human therapeutic polyclonal antibodies.
HOW ARE TRANSGENIC ANIMALS PRODUCED?
Since the discovery of the molecular structure of DNA by Watson and Crick in 1953, molecular biology research has gained momentum. Molecular biology technology combines techniques and expertise from biochemistry, genetics, cell biology, developmental biology, and microbiology.2
Scientists can now produce transgenic animals because, since Watson and Crick’s discovery, there have been breakthroughs in:
The insertion of a foreign gene (transgene) into an animal is successful only if the gene is inherited by offspring.
The success rate for transgenesis is very low and successful transgenic animals need to be cloned or mated.
• recombinant DNA (artificially-produced DNA)
• genetic cloning
• analysis of gene expression (the process by which a gene gives rise to a protein)
• genomic mapping
The underlying principle in the production of transgenic animals is the introduction of a foreign gene or genes into an animal (the inserted genes are called transgenes). The foreign genes “must be transmitted through the germ line, so that every cell, including germ cells, of the animal contain the same modified genetic material.” (Germ cells are cells whose function is to transmit genes to an organism’s offspring.)
To date, there are three basic methods of producing transgenic animals:
• DNA microinjection
• Retrovirus-mediated gene transfer
• Embryonic stem cell-mediated gene transfer
Gene transfer by microinjection is the predominant method used to produce transgenic farm animals. Since the insertion of DNA results in a random process, transgenic animals are mated to ensure that their offspring acquire the desired transgene. However, the success rate of producing transgenic animals individually by these methods is very low and it may be more efficient to use cloning techniques to increase their numbers. For example, gene transfer studies revealed that only 0.6% of transgenic pigs were born with a desired gene after 7,000 eggs were injected with a specific transgene.
DNA microinjection is the predominant transgenesis method.
- DNA Microinjection
The mouse was the first animal to undergo successful gene transfer using DNA microinjection. This method involves:
• transfer of a desired gene construct (of a single gene or a combination of genes that are recombined and then cloned) from another member of the same species or from a different species into the pronucleus of a reproductive cell
• the manipulated cell, which first must be cultured in vitro (in a lab, not in a live animal) to develop to a specific embryonic phase, is then transferred to the recipient female - Retrovirus-Mediated Gene Transfer
The second method produces chimeras, altered animals with mixed DNA.
A retrovirus is a virus that carries its genetic material in the form of RNA rather than DNA. This method involves:
• retroviruses used as vectors to transfer genetic material into the host cell, resulting in a chimera, an organism consisting of tissues or parts of diverse genetic constitution
• chimeras are inbred for as many as 20 generations until homozygous (carrying the desired transgene in every cell) transgenic offspring are born
The method was successfully used in 1974 when a simian virus was inserted into mice embryos, resulting in mice carrying this DNA. - Embryonic Stem Cell-Mediated Gene Transfer
The presence of transgenes can be tested at the embryonic state in this third method.
This method involves:
• isolation of totipotent stem cells (stem cells that can develop into any type of specialized cell) from embryos
• the desired gene is inserted into these cells
• cells containing the desired DNA are incorporated into the host’s embryo, resulting in a chimeric animal
Unlike the other two methods, which require live transgenic offspring to test for the presence of the desired transgene, this method allows testing for transgenes at the cell stage. Different steps in transgenic animal production - Gene of interest is isolated in a strand of DNA.
- DNA is cut specific points by restriction enzymes. The enzymes recognize certain sequences of bases on the DNA strand and cut where the sequences appear.
- The cut DNA is jointed with a vector, which may be a virus (e.g.Retro viral vector) or a plasmid. The vector carries the gene of interest into organisms that will produce the protein.
- When the genes are transferred in this way they get expressed in the desired organ of animals. In addition to vector method, direct microinjection of nuclear material into invitro fertilized (IVF) embryos, and genetically modified embryonic stem cell transfer are effective techniques for transgenic animal production. Among these methods, transgenic animal production through stem cell transfer is very specific in locating the organ of desired action. Transgenic milk can be prepared by two ways. One way is by inserting an extra gene into cow embryos, modifying their genetic make-up. Another method is to mate ‘normal’ cows with genetically modified bulls so that the next generation of calves will produce the desired protein. Although the genetic code is essentially the same for all organisms, the fine details of gene control differ. A gene from a bacterium will not often work correctly if it is introduced unmodified into a eukaryotic animal cell. The genetic engineer first of all constructs a transgene containing the gene of interest plus some extra DNA that correctly controls the function of the gene in the new animal. This transgene has then to be inserted into a new animal. Many genes are only expressed in particular tissues and are controlled by special segment of DNA next to the gene called promoter sequence. When constructing a transgene, scientists generally substitute the donor’s promoter sequence with one that is specially designed to ensure that the gene will function in the correct tissues of the recipient animal. This is crucial when, for example the gene need to be expressed in milk of animal.
Transgenic Animals and Milk
Milk-producing transgenic animals are especially useful for production of medicines, nutritional supplements and pharmaceuticals. Products such as insulin, growth hormone, and blood anti-clotting factors have already been obtained from the milk of transgenic cows, sheep, or goats. Research is also underway to manufacture milk through transgenesis for treatment of debilitating diseases such as phenylketonuria (PKU), hereditary emphysema, and cystic fibrosis. Milk composition can be altered in several ways – changing the concentration of unsaturated fatty acids, reducing the lactose content, removing ß- lactoglobulin and combining nutraceuticals in milk. By combining nutritional and genetic interventions, researchers are now hoping to develop ‘medicine milk’ rich in specific milk components that have implications in health as well as treatment. Cows, goats and sheep are utilized for the production of more than 60 therapeutic proteins, including plasma proteins, monoclonal antibodies and vaccines. In 1997, the first transgenic cow, Rosie, produced human alpha-lactalbumin -enriched milk at 2.4 grams per litre. This transgenic milk is a more nutritionally balanced product than natural bovine milk and could be given to babies or the elderly with special nutritional or digestive needs. Lactoferrin, the iron-binding protein plays an important role in stimulating the immune system and acting as a first line of defence against infection. Its level in human milk is about 1 g/l (in human colostrums about 7 g/l) and that in cow’s milk is only about onetenth that in human milk. A New Zealand research group developed a genetically modified dairy herd capable of producing ‘medicinal milk’ containing recombinant human lactoferrin (rhLF) by transgenic technology. Now Argentinean scientists have developed a cow which can secrete human insulin in its milk. This insulin will be purified from cow milk and used for treatment of Diabetes Mellitus. When compared to conventional methods of insulin production this method is much more cost effective. In 2001, two scientists in Canada spliced spider genes into the cells of lactating goats. The goats began to manufacture silk along with their milk and secrete tiny silk strands from their body by the bucketful. By extracting polymer strands from the milk and weaving them into thread, the scientists can create a light, tough, flexible material that could be used in such applications as military uniforms, medical micro sutures, and tennis racket strings. The major advantage of transgenic technology is that proteins can be produced at a low cost compared to the method using mammalian cell culture. However various ethical, legal and social aspects of biotechnological research need to be addressed before the implementation of transgenic herds.
Transgenic cows for human breast milk?
Some of us may have been breastfed when we were babies, and scientific researches do show that breastfeeding is actually more beneficial than supplements for development and in establishing immune system in infants. However, some mothers are unable to provide this and hence rely on supplements. In early 2011, Chinese scientists have inserted human genes into the DNA of dairy cow embryos and approximately what is known as ‘hybrid’, more specifically ‘transgenic cows’ have been produced.
The process of creating transgenic cows is very similar to that which was to create Dolly the Sheep. The researchers used cloning technology to introduce human genes into the DNA of Holstein dairy cows before the genetically modified embryos were implanted into surrogate cows.
According to Professor Ning Li, the scientist who led the research claimed that the milk tastes stronger and ‘nicer’ than normal milk and that these cows can produce milk that is virtually identical to human breast milk as the milk contained few of proteins that are actually found in human breast milk. First is lysozyme. It was quite sensational, as lysozyme is an antimicrobial protein naturally found in large quantities in human breast milk and it helps to protect infants from bacterial infections during their early stages of life. Second is lactoferrin, which helps to boost the number of immune cells in babies. Third is alpha-lactalbumin which increases the production of lactose.
Also, the scientists also revealed at an exhibition at the China Agricultural University that they have boosted milk fat content by 20 percent and have also changed the levels of milk solids, making it closer to the composition of human milk as well as having the same immune-boosting properties. Not only this, but the transgenic cows are physically identical to ordinary cows and Professor Li said their work has shown it was possible to ‘humanise’ cows’ milk.
They claimed that the human breast milk provides us just the basic source of nutrition; just right proportions of proteins, carbohydrates, fats, minerals and vitamins for an infant’s optimal growth and development. Also, professor Li said that even with cow’s milk it provides just the adequate amounts and digestion and absorption problems made it not the perfect food possible for human beings. Therefore, the researchers believe the modified milk is a possible substitute for not only human breast milk, but they can also modify this further to create a possible substitute for cow’s milk, as the results indicated much higher nutritional content.
Although there are many controversies surrounding this, and many believe that it is rather unethical and even a violation against the nature’s providence, scientists believe that the genetically modified milk can help many – from infants to even elderly, in providing nutrition. They hope to have huge herds of these cows producing an alternative to human breast milk and cow’s milk, and they hope to have this sold in global supermarkets within next 3 years.
HOW DO TRANSGENIC ANIMALS CONTRIBUTE TO HUMAN WELFARE?
Through genetic engineering, it is possible to make specific alterations to animals‟ genome that seems and is impossible to achieve through conventional selective breeding. In the present scenario, we easily think of manipulating the properties of animals; be that with meat, milk, egg, wool, excretory products, other behavioral, psychological, physiological or any other responses .In fact, one of the first applications of these transgenically produced large farm animals was that they could produce altered or novel proteins in their milk .
The process of transgenesis with the production of transgenic animals promises following general advantages:
Increased growth rate in meat animals (Beef, pigs, chicken, etc) Increased muscle mass Increased feed conversion rates Improved nutritional quality Increased disease resistance in animals Improved wool quality Disease models Xenotransplantation Bioreactors However, with transgenesis, it is not the end for conventional animal breeding procedures, but these two processes will need to be taken in conjunction for better animal production. These aspects include that of feed optimization, reproductive improvement, disease control, efficient production alongside other common goals.
The benefits of these animals to human welfare can be grouped into areas:
• Agriculture
• Medicine
• Industry
The examples below are not intended to be complete but only to provide a sampling of the benefits.
- Agricultural Applications
Transgenesis will allow larger herds with specific traits.
a) breeding
Farmers have always used selective breeding to produce animals that exhibit desired traits (e.g., increased milk production, high growth rate).Traditional breeding is a time-consuming, difficult task. When technology using molecular biology was developed, it became possible to develop traits in animals in a shorter time and with more precision. In addition, it offers the farmer an easy way to increase yields.
Scientists can improve the size of livestock genetically.
b) quality
Transgenic cows exist that produce more milk or milk with less lactose or cholesterol, pigs and cattle that have more meat on them, and sheep that grow more wool. In the past, farmers used growth hormones to spur the development of animals but this technique was problematic, especially since residue of the hormones remained in the animal product.
Disease-resistant livestock is not a reality just yet.
c) disease resistance
Scientists are attempting to produce disease-resistant animals, such as influenza-resistant pigs, but a very limited number of genes are currently known to be responsible for resistance to diseases in farm animals. - Medical Applications
Transplant organs may soon come from transgenic animals.
a) xenotransplantation
Patients die every year for lack of a replacement heart, liver, or kidney. For example, about 5,000 organs are needed each year in the United Kingdom alone. Transgenic pigs may provide the transplant organs needed to alleviate the shortfall. Currently, xenotransplantation is hampered by a pig protein that can cause donor rejection but research is underway to remove the pig protein and replace it with a human protein.
Milk-producing transgenic animals are especially useful for medicines.
b) nutritional supplements and pharmaceuticals
Products such as insulin, growth hormone, and blood anti-clotting factors may soon be or have already been obtained from the milk of transgenic cows, sheep, or goats. Research is also underway to manufacture milk through transgenesis for treatment of debilitating diseases such as phenylketonuria (PKU), hereditary emphysema, and cystic fibrosis.
In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk at 2.4 grams per litre. This transgenic milk is a more nutritionally balanced product than natural bovine milk and could be given to babies or the elderly with special nutritional or digestive needs. Rosie’s milk contains the human gene alpha-lactalbumin.
A transgenic cow exists that produces a substance to help human red cells grow.
c) human gene therapy
Human gene therapy involves adding a normal copy of a gene (transgene) to the genome of a person carrying defective copies of the gene. The potential for treatments for the 5,000 named genetic diseases is huge and transgenic animals could play a role. For example, the A. I. Virtanen Institute in Finland produced a calf with a gene that makes the substance that promotes the growth of red cells in humans.
Uses in industry include material fabrication and safety tests of chemicals. - Industrial Applications
In 2001, two scientists at Nexia Biotechnologies in Canada spliced spider genes into the cells of lactating goats. The goats began to manufacture silk along with their milk and secrete tiny silk strands from their body by the bucketful. By extracting polymer strands from the milk and weaving them into thread, the scientists can create a light, tough, flexible material that could be used in such applications as military uniforms, medical microsutures, and tennis racket strings.
Toxicity-sensitive transgenic animals have been produced for chemical safety testing. Microorganisms have been engineered to produce a wide variety of proteins, which in turn can produce enzymes that can speed up industrial chemical reactions.
Throughout history, transgenic animal has made significant contributions to human health and well-being. The recent advances in reproductive technologies (in vitro production of embryos, sperm sexing, somatic nuclear transfer, Lentiviral transfer of oocytes and zygotes, Chimera generation by injecting the pluripotent cells) adds a new dimension to animal breeding. The application of transgenic animals showed that within the next five to eight years genetically modified animals will play a significant and important role in the biomedical field, in particular via the production of valuable pharmaceutical proteins and the supply of xenografts. New and exciting techniques being developed will continue to expand this important and useful area of experimentation.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
Image-Courtesy-Google
Reference-On Request.
