Transgenic Animals| Genetically modified animals| Applications of transgenic animals

Transgenic Animals

Transgenic Animals are genetically modified animals with a trans gene inserted in them. There are techniques of gene transfer to produce transgenic animals.  In this article, you will also know about the medical, agricultural, and industrial applications of transgenic animals for the benefit of humanity.

Transgenic Animals 

Transgenic Animals are those genetically modified animals in which foreign genes have been inserted, the gene which is inserted is known as a transgene and the process is known as transgenesis.  This is the technique in which desired gene of interest is inserted in the target animal’s genome which alters the genetic makeup of that genome. Previously selective breeding techniques were used to improve genetic traits but now transgenesis is used to enhance the genetic characteristics of the genome of the target animals.

Methods of Gene Transfer

The common techniques of gene transfer to produce transgenic animals are:

Physical method of gene transfer

Physical methods can be performed by particle bombardment, electroporation, Ultrasonic waves, and DNA microinjection. It is a direct method of gene transfer and is applied to a variety of animal species. DNA microinjection involves a single gene or selected gene construct from another specie or the same specie with a different member that is directly injected into the pronucleus of the fertilized ovule.

The expression of the gene in another organism would be unknown for example the inserted gene would be over-expressed, under-expressed, or would be unique to the animal species showing similar characteristics as the host specie. The fertilized ovule is afterward placed in the host female animal. This was the first technique performed which get successful on animals.

The first transgenic animal cloned was Dolly sheep. Dolly sheep were produced through the electroporation method. An unfertilized egg was taken and the nucleus was removed and injected into the udder cells of white sheep. Electric pulses were given to fuse the cells of white sheep with the enucleated eggs of black sheep. The embryo was produced which was cultivated for one week. Then embryo was inserted into different black sheep which gave birth to dolly sheep.

Chemical Method of gene transfer

Chemical transfection is one of the methods of gene transfer. The target DNA is introduced in the presence of calcium phosphate. DNA is absorbed and precipitated by the use of calcium phosphate. DNA is catalyzed through the cross-membrane which facilitates DNA uptake. Mammalian cells present in culture media take the foreign DNA.

Vector-based Gene transfer

Different vectors are used to transfer genes such as viral vectors, and bacterial vectors. Foreign DNA can be introduced to animal cells through viruses. The viruses have the capacity to transfect the host cell, express themselves, and multiply within the host cell. Bacterial vectors can also be used to infect target DNA into the host cell.

Retroviral-based Gene transfer

The most common method of gene transfer is Retrovirus gene transfer.  Retroviruses are RNA-based vectors that are used to transfer genes of interest into host organisms because of their ability to transfect host cells. This technique uses retrovirus to infect the host cell. During transfection, retroviral RNA is converted to DNA which is then introduced into the foreign DNA of the host organism. 

The offspring produced in this technique would be in a chimeric condition which indicates that not all cells contain retrovirus because retrovirus incorporates transgene into a few of the germ cells. These chimeras specie produce are cross-bred for several generations and if the transgene gets incorporated in every cell, it will express in every cell resulting in homozygous transgenic animals.

Embryonic Stem cell gene transfer

This technique inserts the target DNA sequence (transgene) through in vitro embryonic stem cells. Stem cells are an undifferentiated mass of cells that can develop into any cell, resulting in the development of a whole organism. At the embryonic stage of development, the tissue of the desired organism is integrated into an embryo. This technique is effective on mice. This method is helpful in targeting specific gene mutations.

Genetically modified animals

Applications of Transgenic Animals

The vast applications of transgenic animals for the benefit of human welfare have been classified into three groups:

Agriculture

Medical

Industrial

Agricultural Applications

Selective breeding allows producing animals with desired features such as increased milk and meat production, better nutritional food, and a high growth rate. Previously conventional breeding was labor-intensive, time-consuming, and require more force to be performed.  But nowadays, due to the advancement in technology, farming techniques have become precise and quicker. 

Genetic engineering has enabled farmers to boost production and increase livestock growth. For Example, transgenic cows produce more milk with less lactose. Cattle with goats and sheep produce more meat and sheep produce more wool.

Some of the animals have developed in such a way that they are immune to diseases while in past this was impossible such as pigs that are resistant to flu. Scientists are still striving to breed disease-resistant organisms.

Medical Applications

The milk-producing transgenic cows have benefited in many ways such as by producing products like insulin, growth hormone, and blood anti-clotting agents. The chemical which promotes the growth of red blood cells is produced by transgenic cows. Studies are being conducted to produce milk by transgenesis for the treatment of genetic disorders like phenylketonuria, and cystic fibrosis. These transgenic animals are used as models for the treatment of disorders, and for the creation of pharmaceutical products.

One of the medical applications is gene therapy a person who has a defective gene can be placed with a normal copy of the gene. Therefore, these animals examine how genes are regulated and how they affect the body.  Transgenic mice have been useful in developing cures for many genetic disorders. A calf with a transgene has been created that helps in the formation of human red blood cells.

Transgenic animals are used as research models for studying drugs and their effects. Before a particular drug or vaccination is given to humans, it is first tested for safety on transgenic animals as model organisms.  By inserting the genes in transgenic animals, scientists can find the gene expression of a particular gene.

Industrial Applications

In Canada,  they perform an experiment in which spider silk genes were taken from spiders and inserted in goats to produce transgenic goats. This goat produces silk along with milk. Scientists can secrete silk strands from the body of a goat. These silk strands from milk have been extracted and weaved into a thread to produce materials that would be used in making things like military uniforms, tennis rackets, and medical microsurgical products.