Transgenic animals - Definition, examples and characteristics

Content

• what is transgenesis
• What are transgenic animals
• Transgenesis by microinjection of zygotes
• Transgenesis by manipulation of embryonic cells
• Transgenesis by somatic cell transformation and nuclear transfer or cloning
• Examples of transgenic animals
• Transgenic animals: advantages and disadvantages
• Benefits
• Disadvantages

One of the most important events in scientific advances was the possibility of clone animals. There are great possibilities for medical and biotechnological use, as many diseases were eradicated thanks to these animals. But what are they actually? What are its advantages and disadvantages?

In this article by PeritoAnimal, we explain what are transgenic animals, what transgenesis consists of, and show examples and characteristics of some well-known transgenic animals.

what is transgenesis

Transgenesis is the procedure in which genetic information (DNA or RNA) is transferred from one organism to another, converting the second, and all its descendants, into transgenic organisms. The complete genetic material is not transferred, only one or more genes previously selected, extracted and isolated.

What are transgenic animals

Transgenic animals are those in which some characteristic has been genetically modified, which is very different from asexual reproduction among animals, also called clonal reproduction.

Theoretically, all living beings, and therefore all animals, can be genetically manipulated. The scientific literature records the use of animals such as sheep, goats, pigs, cows, rabbits, rats, mice, fish, insects, parasites and even humans. But the mouse it was the first animal used, and in which all tested techniques were successful.

The use of mice has become especially widespread because it is easy to introduce new genetic information into their cells, these genes are easily passed on to offspring, and they have very short life cycles and very numerous litters. In addition, it is a small animal, easy to handle and not very stressful, considering its physical and mental health. Finally, your genome is very similar to humans.

There are several techniques to produce transgenic animals:

Transgenesis by microinjection of zygotes

Using this technique, superovulation is first caused in the female, through hormonal treatment.Then, the fertilization, which can be in vitro or in vivo. Fertilized eggs are then collected and isolated. Here the first phase of the technique ends.

In the second stage, the zygotes (cells resulting from the union of an egg with a sperm naturally or through fertilization in vitro or in vivo) receive a microinjection with a solution containing the DNA we want to add to the genome.

Then, these already manipulated zygotes are reintroduced into the mother's uterus, so that the pregnancy occurs in a natural environment. Finally, once the puppies have grown up and been weaned, it's verified whether they incorporated the transgene (external DNA) into their genome.

Transgenesis by manipulation of embryonic cells

In this technique, instead of using zygotes, the transgene is introduced into the stem cells. These cells are removed from the developing blastula (a stage of embryonic development characterized by a single layer of cells) and placed in a solution that prevents the cells from differentiating and remaining as stem cells. Posteriorly, the foreign DNA is introduced, the cells are reimplanted in the blastula, and this is reintroduced into the maternal uterus.

The progeny you get with this technique is chimera, which means that some cells in your body will express the gene and others will not. For example, the "ovegoat", chimerism between sheep and goat, is an animal that has parts of the body with fur and other parts with wool. By further crossing the chimeras, individuals are obtained that will have the transgene in their germ cell line, that is, in their eggs or sperm.

Transgenesis by somatic cell transformation and nuclear transfer or cloning

Cloning consists of extracting embryonic cells of a blastula, cultivate them in vitro and then insert them into an oocyte (female germ cell) from which the nucleus has been removed. So they merge in such a way that the oocyte turns into an egg, having in the nucleus the genetic material of the original embryonic cell, and continuing its development as a zygote.

Examples of transgenic animals

Over the past 70 years, a series of research and experiments has been carried out to obtain genetically modified animals. However, despite the great fame of Dolly the sheep, she was not the first animal cloned in the world by the animal transgenics. Check out some examples of known transgenic animals below:

• Frogs: in 1952 it was performed the first cloning in history. It was the basis for cloning Dolly the sheep.
• THE dolly sheep: it is famous for being the first animal cloned through the technique of cellular nuclear transfer from an adult cell, and not for being the first animal to be cloned, as it wasn't. Dolly was cloned in 1996.
• Noto and Kaga cows: they were cloned in Japan thousands of times, as part of a project that sought to improve the quality and quantity of meat for human consumption.
• The Mira goat: this cloned goat in 1998, was the forerunner of cattle able to produce drugs useful for humans in your body.
• The Ombretta mouflon: first cloned animal for save an endangered species.
• The copycat cat: in 2001, the Genetic Savings & Clone company cloned a domestic cat with ends commercials.
• The Zhong Zhong and Hua Hua Monkeys: first cloned primates with the technique used in the Dolly sheep, in 2017.

Transgenic animals: advantages and disadvantages

Currently, transgenesis is a very controversial subject, and this controversy comes mainly from the lack of information about what transgenesis is, what its uses are, and what legislation regulates the technique and use of experimental animals.

In different countries around the world, biosafety is regulated by a set of specific laws, procedures or directives. In Brazil, biosafety legislation deals more specifically with recombinant DNA or RNA technology.

Law 8974, of January 5, 1995, Decree 1752, of December 20, 1995, and Provisional Measure 2191-9, of August 23, 2001^[1], establish safety standards and inspection mechanisms in the use of genetic engineering techniques in the construction, cultivation, handling, transport, marketing, consumption, release and disposal of genetically modified organism (GMO), aiming to protect the life and health of man, animals and plants, as well as the environment.^[2]

Among the advantages and disadvantages obtained with the use of transgenic animals, we find the following:

Benefits

• Improvement in research, from the standpoint of knowledge of the genome.
• Benefits for animal production and health.
• Advances in studies of diseases in animals and humans, such as cancer.
• Drug production.
• Organ and tissue donation.
• Creation of gene banks to prevent species extinction.

Disadvantages

• By modifying already existing species, we can put native species at risk.
• The expression of new proteins that did not previously exist in a given animal can lead to the appearance of allergies.
• Where in the genome the new gene will be placed can be undetermined in some cases, so the expected results can go wrong.
• Live animals are used, so it is essential to carry out an ethical review and determine how new and relevant the results of the experiment may be.

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