Transgenic Animals

Transgenic Animal

There are various definitions for the term transgenic animal.

A transgenic animal is one whose genome has been changed to carry genes from other species.

The nucleus of all cells in every living organism contains genes made up of DNA.

These genes store information that regulates how our bodies form and function.

Genes can be altered artificially, so that some characteristics of an animal are changed.

For example, an embryo can have an extra, functioning gene from another source artificially introduced into it, or a gene introduced which can knock out the functioning of another particular gene in the embryo.

Animals that have their DNA manipulated in this way are known as transgenic animals.

The majority of transgenic animals produced so far are mice, the animal that pioneered the technology.

The first successful transgenic animal was a mouse. A few years later, it was followed by rabbits, pigs, sheep, and cattle.

How are transgenic animals produced?

To date, there are three basic methods of producing transgenic animals:

(i) DNA microinjection

(ii) Retrovirus-mediated gene transfer

(iii) 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 offsprings 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.

How do transgenic animals contribute to human welfare?

The benefits of these animals to human welfare can be grouped into following areas:

(1) Agriculture (2) Medicine (3) Industry

The examples below are not intended to be complete but only to provide a sampling of the benefits.

1. Agricultural Applications

(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.

(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.

(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.

2. Medical Applications

(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.

(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 transgenics 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 -lactalbumin.

(c) Vaccine safety: Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humans. Transgenic mice are being used to test the safety of the polio vaccine. If successful and found to be reliable, they could replace the use of monkeys to test the safety of batches of the vaccine.

3. 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.

The anthrax bacterium sent through letters after September 2001.

Mass-produced pathogens or their toxins are delivered either as powder or in the form of spray, using a variety of delivery devices.

Bioweapons (a) are low-cost weapons, (b) cause for more casualities than chemical or conventional weapons, and (c) bioweapon agents are invisible, and extremely difficult to detect.

These features make bioweapon agents very convenient for use by terrorists and even governments, and both have used them on a limited scale.

The possible defences against bioweapons include the use of respirator or gas mask, vaccination, administration of appropriate antibiotics, and decontamination. In addition, sensitive detection systems should be develped to control and minimise damage.