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Transgenic Animals: Methods and Reasons For Creating Research Paper

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Updated: Apr 24th, 2022

Introduction

Transgenic animals are by-products of recent advancements in technology. Researchers feel that the technology is beneficial to resolve universal health challenges; whilst others feel it is an unethical practice. This paper examines the methods and reasons for creating transgenic animals, their societal impact and the ethical issues involved in the technology.

A transgenic animal refers to an animal that carries a foreign gene, which has been deliberately incorporated into its genome. Genome refers to the materials fully responsible for inherited characteristics. A foreign DNA is incorporated into the animal genome through recombinant DNA technology to the germ cell which ensures every germline contains the same transformed genetic information. The first “transgenic animal activity” was carried out three decades ago. This was when the first transgenic mice were produced through retrovirus infection of pre-implantation (Brinster, 1974). Since then, many gene transfer techniques have been developed such as “polymerase chain reaction (PCR), transgene reporters, DNA microarray, and fluorescent in situ hybridization” (Pinkert, 2002, p.364).

Animal models have been used throughout the history of biology to facilitate the understanding of pathogenesis mechanisms, and in the development of effective therapies. The animal models have also been used to evaluate safety and efficacy of vaccines and other various therapies. Transgenic technology has replaced the traditional genetic strategy that was tedious and time-consuming. The technology introduces a new era for animal modeling in biomedicine, accelerating better understanding and development of therapies for patients. Examples of transgenic animals include fruit flies such as Drosophila melanogaster, mosquitoes, bollworms (Pectinophora gossypiella), and mammals such as chimeras, cnidarians and fish (Pinkert, 2002).

Creating Transgenic Animals

There are various methods used in creating transgenic animals. However, the first step in all the techniques requires the creation of a transgene. Transgenes have three parts: “promoter- part responsible for dictating the gene to be made; transgene itself and termination sequence” (Pinkert, 2002, p. 364). The various methods used include “pronuclear microinjection, retrovirus infection, nuclear transfer and sperm mediated transfer” (Pinkert, 2002, p. 364).

The most-favored method is the microinjection: an egg isolated from an animal is fertilized in vitro. The constructed DNA carrying the foreign genome is injected using a fine needle into the nucleus of the ovum. Thus, the foreign DNA will be randomly inserted into the fertilized egg. The Ovum is then implanted into the oviduct of a surrogate animal where it develops. This method has been effectively used to create various types of transgenic animals. However, micro-injection technique efficiency in production of transgenic animals is noted below. The low efficiency is said to be a result of random fertilization insertion of the genome. Another crisis of this method includes the inability to control sites of integration or even the copy numbers of transgenes. Therefore, the random integration and multiple transgenes copies result in unregulated expression of transgenes, which are cytotoxic and thus will likely cause fatal side effects (Harper, 1999).

Retrovirus infection refers to retroviral infection of an embryo, usually at an early cleavage stage (blastocyst). This method results in only a proportion of cells carrying the transgene. The advantage of this method is in its ability to culture the cells to screen the uptake of the transgene (Pinkert, 2002).

To circumvent these challenges, a new technique that can deliver single copies of mutated genes to the specific target site was developed. Embryonic stem cell transfer technique facilitates the insertion of genes into specific sites in the genome of an animal. The method begins by isolating embryonic stem cells from the recipient animal. The stem cells are then grown in tissue culture flasks. Modification of cells is done by inserting foreign DNA carrying the gene of interest and sequence. The modified embryonic stem cells are then injected into the blastocyst stage of the developing recipient animal. Then, the modified blastocyst is implanted into the surrogate mother. The method is highly efficient as the genes get expressed more efficiently. This technology has brought two advantages. First, specific mutations are made in the embryonic stem cells through gene targeting procedures. This averts challenges associated with non-specific sites of transgene integration and production of transgenes multiple copies. Second, germ-line chimerism can be maintained in the heterozygote’s state in the offspring without jeopardizing the animals’ life. However, the technology has only been used to produce transgenic mice.

Another emerging technology in transgenesis is Somatic Cell Nuclear Transfer (SCNT). The technique involves the removal of somatic cell nucleus and egg chromosomes. The nucleus is microinjected into the chromosome-free egg. The embryo developed is genetically identical to the animal where the somatic cell originated. The first cloned mammal, Dolly sheep, was cloned using this technique. For transgenic animals, the nuclear donor cell comes from a culture of modified cells containing the transgene (Markoulaki et al., 2008).

Another method involves the use of viral vectors to insert foreign DNA into cells. However, this method is only used for transgenesis only if its pathogenic behavior can be controlled to avoid host cell infection or other detrimental effects. There are various viruses used for the process but the most commonly used are the retroviruses. The retrovirus has an RNA genome. It causes reverse transcription into the DNA making it become integrated into the host’s genome. The three main viral genes present in a retrovirus important for replication are gag, pol and env (Robbins, 1998).

Transposons are DNA sequences with unique ability to transpose to different locations of a genome. They can also be used for transgenic animal production. The transposase gene is usually replaced with the foreign transgene (Houdebine, 2002).

Sperm-mediated transgenesis technique is rarely used to create transgenic animals. The technique uses modified sperm cells as vectors during in vitro fertilization. The sperms are cultured with foreign DNA. The DNA binds to the plasma membrane, and the sperm is then implanted in an egg through in vitro fertilization. The technique results in random integration of the genome (Bosch 2004).

Currently, various strategies are being initiated to improve gene targeting technology and to permit more and more sophisticated genetic experiments to be carried out on animals. Transgenic mice generated by pro-nuclear DNA injection are still in use for various biological inquiries such as consequences of overexpression and ectopic expression of various molecules in animals. Current progress in this field involves the use of designs for pro-nuclear DNA injection and Gene targeting methods.

The future of transgenic animals involves fine-tuning of gene-targeting procedures and in the aggregation method used in the introduction of embryo stem cells into embryos. Therefore, future development of genetic manipulation in animals must project in the following technical challenges: first, seek adequate information concerning the regulatory mechanism of certain gene expression in animals and second, develop a simplified aggregation technique (Conklin & Stilwell, 2007).

Benefits of Using Transgenic Animals

Transgenic animals have been very useful to man especially in acting as models for diseases, for assessing pharmaceuticals’ products, alternatives for human organ donations, agriculture benefits and other biological models.

Transgenic animals have been used for pharmaceuticals’ purposes. Most of these drugs are produced through milk from the transgenic animals. Milk is the most common means through which transgenetic-generated proteins are secreted. However, there exist other approaches such as kidney. Mammary glands remain popular in the manipulation because no detectable effects have been identified as yet. The transformed protein is removed from the animal’s body through milk secretion, and the secreted protein has no risk of contamination (Keefer, 2004). Example of transformers is the transgenic sheep to secrete a human clotting factor IX (FIX). FIX is a protein used for blood clotting in humans. Previously, it was obtained from human plasma providing risks for HIV and Hepatitis C virus. Others include ATryn produced by transgenic goats and the production of Lactoferrin in cows (King, 2009).

Transgenic diseases models are the most common application for transgenic animals. Human diseases are studied to learn more mechanisms behind them in order to develop therapies. Some of the diseases include Alzheimer’s, HIV/AIDS, and oncomouse diseases. Valuable information has been collected through the use of such models. For example, Alzheimer’s disease transgenic mice have been used to show the genetic impact of the disease. Professor Dave Adams was the first to successfully develop an AD mouse who aided in understanding that beta-amyloid production caused AD. Other mice engineered subsequently expressed mutant genes commonly associated with AD. These genes include PS1, PS2, tau protein and ApoE. Current investigations show that mutant human genes in transgenic mice have a high deposition of beta-amyloid with reduced cognitive function. Various therapies are being used on the mice to stop the progression of the disease (Janus & Westaway, 2001). Transgenic mice have also played great role in the study of cancer through expressing the oncogene which causes cell proliferation or through eliminating tumor suppressor genes (Pinkert, 2002).

Transgenic animals have eased the global food crisis issues. The animals are modified to have desirable traits. Two of the most engineered animals are the pigs and fish. Transgenesis aims at producing animals, which are larger for food sources. Other genetically modified animals such as Enviropig of the University of Guelph in Canada can help in a reduction of agricultural waste. Such like transgenic animals also facilitate the flushing out of agricultural pests. This is a good strategy to obtain a sustainable environment with no pollution from toxic substances (Parekh, 2004).

Organ failure is a global health crisis. Organ transplants are extremely costly and rare. However, xenotransplantation has become the solution to this quandary. This involves the use of animal organs for human transplants. Grafts can be done through the use of organs from the same species (concordant xenografts) or different species (discordant xenografts). However, transgenic animals such as pigs have the ability to reproduce faster and have large numbers of litter that can be used to grow organs of their recipient. Transgenic pigs have been modified such that complement regulatory proteins have the ability to decrease activation (Dwyer et al., 2002).

Ethical Issues involved with Using Transgenic Animals

Despite the many benefits associated with transgenesis in various technologies such as organ transplants, pharmaceuticals, resolving the food crisis and understanding pathogenesis mechanisms; there are concerns raised over the use of this technology. Ethical debates have been raised over the uses and in determining the extent the animals should be used for research.

Transgenic animals advocates accentuate the tremendous benefit they offer to humans. These include the ability to comprehend various disease mechanisms such as AIDS, Alzheimer’s and Parkinson’s disease. The models have also aided to circumvent various roadblocks in animal research for therapies, vaccines and treatment. Other advantages include the ability to harvest uncontaminated pharmaceutical products from transgenic animals. The technology is so sustainable since the animal remains unhurt as the proteins are produced through mammary glands and through their secretions’ products like milk. In xenotransplantations, transgenic pigs have been used to knock out genes that result in graft rejection (U.S. Transplantation Data, 2010). Another beneficial use includes agricultural processes. Various livestock, including cows, pigs, goats, and poultry have been modified genetically to grow bigger in a short duration. Transgenic sheep are used for increased wool growth, cows for more milk and poultry for better eggs (Margawati, 2003).

However, there are various concerns raised about using transgenic animals. First is the human safety. Some feel that effectiveness of treatments and therapies on an animal model may produce undesirable outcomes when applied to humans. However, various organizations are responsible for ensuring all transformed drugs are safe for human consumption (FDA, 2009). Others feel that the transgenic model can have the disease that can accidentally be realized in the world. This argument is far-fetched because disease models are known to breed at a slower rate compared to the wild type. The possibility of creating an animal that is difficult to handle or contain would only become a threat to humans if the animal escapes into the wilderness (Almond, 2000). Cruelty to animals has become a major concern in research ethics. PETA and other organizations for protection of animals strongly reject animals being used as models for studying human diseases. There have been other issues that animals do not always express properly. This implies that a great number of animals are created without any scientific benefits (Pinkert, 2002).

Religious concerns range from the sacredness of some animals to the opposing side of viewing animals to be inferior to human beings. Religions preserve their position that animals must be used only if they are not subjected to pain by the name of research. Other religions view transgenesis as “playing God”. They argue that God created everything purposefully. Therefore, inserting foreign genes into animals is an act of rebelling against God’s will of creation. Each religion has its own views on animal research (Pinkert, 2002).

Conclusion

The ethical debate surrounding transgenic animal research is here to stay. Society will remain divided with some advocating for transgenic animals due to their benefits delineated in this paper whereas the opposing side will continue fighting for and in the protection of animals from being used in experimentation or manipulation. This paper has shown that all transgenesis procedures such as transpharming are carefully done with minimal risks incurred. The transgenic processes are also geared towards saving human life rather than harming it. Each of the described transgenic animal applications has its advantages and disadvantages. However, each failure, can be viewed as an opportunity in the scientific research world to find more information.

References

Almond, B. (2000). Commodifying animals: ethical issues in genetic engineering of animals. Health, Risk and Society, 2(1), 95-105.

Bosch, P. (2004). Generation of transgenic livestock by somatic cell nuclear transfer. Biotechnologia Aplicada, 21(1), 128-136.

Brinster, R. (1974). The effect of cells transferred into mouse blastocyst on subsequent development. Journal of Experimental Medicine, 1(1), 1049-1056.

Conklin, A., & Stilwell, T. (2007). World food: production and use. New York, NY: John Wiley and Sons Inc.

Dwyer et al. (2002). Xenotransplantation: past achievements and future promise. Heart, lung and circulation, 11(1), 33-41.

FDA. (2009). Guidance for industry Regulation of Genetically Engineered Animals Containing Heritable Recombinant DNA constructs- Final Guidance. Federal and Drugs Authority. Web.

Harper, B. (1999). How transgenic are produced. FDA Veterinarian Newsletter, 14(1), 1.

Houdebine, L. (2002). The Methods to Generate Transgene Expression. Journal of Biotechnology, 98(1), 145-160.

Janus, C., & Westway, D. (2001). Transgenic mouse models of Alzheimer’s disease. Physiology and Behavior, 73(1), 873-886.

Keefer, C. (2004). Production of bio products through the use of transgenic models. Animal Reproduction Science, 82(1), 5-12.

King, J. (2009). First US approval for transgenic animal drug. Nature Biotechnology, 27(1), 301-303.

Margawati, E. (2003). Transgenic Animals; their benefits to Human welfare. Action Bioscience. Web.

Markoulaki et al. (2008). Somatic cell Nuclear Transfer and Derivation of Embryonic Stem Cells in the Mouse. Methods, 45(1), 101-114.

Parekh, S. (2004). The GMO hand book: Genetically modified Animals, Microbes, and plants in biotechnology: Human press. New Jersey, NJ: Prentice Hall.

Pinkert, C. (2002). Transgenic animal technology: a laboratory handbook. San Diego, SA: Gulf professional publishing.

Robbins, P. (1998). Viral Vectors for gene therapy. Pharmacology and Therapeutics, 80(1), 35-47.

U.S. Transplantation Data. (2009). Data. United Network for Organ sharing. Web.

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