Transgenic Animals

What are the Transgenic Animals?

• Organisms containing integrated sequences of cloned DNA (transgenes), transferred using techniques of genetic engineering (to include those of gene transfer and gene substitution) are called transgenic animals. 
• Transgenesis is the phenomenon in which a foreign gene with desired characteristics is introduced into the genome of the target animal. The foreign gene that is introduced is known as the transgene, and the animal whose genome is altered is known as transgenic. 
• These genes are passed on to successive generations.

Transgenic Animals Methods of Creating 

• Chemical Transfection: In this method, the target DNA is taken up in the presence of calcium phosphate. The DNA and calcium phosphate co-precipitates, which facilitates DNA uptake. The mammalian cells possess the ability to take up foreign DNA from the culture medium.
• Retrovirus-Mediated Gene Transfer:The gene is transferred by means of a vector. Since retroviruses have the ability to infect the host cell, they are used as vectors to transfect the gene of interest into the target genome.
• Bactofection:It is the process by which the gene of interest is transferred into the target gene with the help of bacteria.
• Viral Vectors:Viruses are used to transfect rDNA into the animal cell. The viruses possess the ability to infect the host cell, express well and replicate efficiently.
• Physical Transfection:
• • The gene of interest is directly injected into the pronucleus of a fertilized ovum. It is the very first method that proved to be effective in mammals. 
  • Other methods of physical transfection include particle bombardment, ultrasound and electroporation.

Applications of transgenic animals:

• Transgenic animals can be prepared by keeping in view the economically signifi­cant traits, such as efficient feed utiliza­tion, faster growth rate, production of lean meat, increased production and enhanced immune-competence.
• Attempts have been made for exploiting the mammary gland to produce pharmaceutical proteins in milk.
• Transgenic sheep armed with genes in­volved in cysteine synthesis from dietary serine exhibited significant positive effect on wool production.
• A heterologous protein, such as a variant of human tissue plasminogen activator has also been produced in goat which is being used in patients suffering from thrombosis, for dissolving blood clots.
• The long term goal of companies develop­ing transgenic animals is to create a new generation of medicines based on gene products, rather than on drugs engineered by chemicals.
• Transgenic processes have been adopted to increase the disease resistance in ani­mals, such as genetic immunization with recombinant plasmid containing gene for antigen of interest has been attempted for prevention of infectious diseases, e.g., ra­bies, pseudorabies virus, etc.
• Breeding of pigs with humanized organs for use in xenotransplantation has become an important application of transgenic approach.The gene construct used to create the transgenic pigs containing the human beta-globin locus control gene may be suit­able substitute for obtaining blood.
• Transgenic animals are also used for test­ing drugs or to undertake studies which is always not possible on human beings.
• Transgenic animals have also been pro­duced to serve as models to understand particular diseases like cystic fibrosis. This is caused by a defective gene which can be mimicked in a transgenic mouse. Such transgenic animals allow the testing of drugs or to undertake studies not always possible on humans.