What are transgenic animals? What are the key techniques used in the creation of transgenic animals, and how do these methods contribute to advancements in fields such as medicine and agriculture?

Transgenic animals are animals whose genetic material has been intentionally altered by introducing genes from another species. These genes, known as transgenes, are inserted into the animal's genome, causing it to express new traits or characteristics that were not originally present. The foreign genes can come from different species or even be synthetic. The goal is to create animals that possess certain beneficial traits, which can serve a variety of purposes in research, medicine and agriculture.

Transgenic animals are also a critical tool in understanding how genes influence development, disease processes and behavior. One of the main purposes of producing transgenic animals is to replicate human diseases in animal models, which allows researchers to study those diseases and test possible treatments in ways that would be impossible or unethical in humans.

In the past few decades, transgenic animals have revolutionized the fields of genetics, biotechnology and pharmaceuticals, enabling the development of genetically modified organisms (GMOs) that play significant roles in human health and food production. This advanced technology has led to the creation of animals used in drug production, disease modeling and agricultural improvements.

Key Techniques Used in the Creation of Transgenic Animals

Several techniques have been developed to create transgenic animals, each with its own set of advantages and challenges. The following methods represent the main techniques currently used in genetic engineering for animals:

1. Pronuclear Injection

Pronuclear injection is a commonly used method for creating transgenic animals, especially in mice. In this technique, a fertilized egg (embryo) is collected from a female animal, and the foreign DNA or transgene, is directly injected into the pronucleus. The pronucleus is the nucleus of the egg or sperm before they combine to form the zygote (fertilized egg).

After injecting the foreign gene into the pronucleus, the embryo is implanted into a surrogate mother. As the embryo grows and develops into a fetus, the introduced gene becomes integrated into the animal's DNA. When the animal is born, scientists test its cells to check if the transgene has been successfully passed down to the offspring. This technique allows researchers to produce genetically modified animals with new traits, such as increased resistance to diseases or the ability to produce specific proteins.

Pronuclear injection is effective, but it is more challenging to perform in larger animals. Therefore, it is most commonly used with mice, where the procedure is easier to carry out. Despite its technical challenges, this method has proven to be an essential tool in genetic research and the creation of transgenic animals.

2. Embryonic Stem (ES) Cell Method

The embryonic stem (ES) cell method is a more advanced and precise technique used to create genetically modified animals, especially for producing knockout or knock-in transgenic animals. It is widely used in mice but can be applied to other species as well. In this method:

• Embryonic Stem Cells (ES cells) are isolated from early-stage embryos. These cells are undifferentiated, meaning they have the potential to develop into any type of tissue in the body.

• The Embryonic Stem cells are cultured in a laboratory. The foreign DNA is introduced into these cells either through electroporation (an electric shock) or chemical methods. This foreign DNA can either add a new gene to the genome (for knock-ins) or remove or disable an existing gene (for knockouts).

• After the DNA is successfully integrated into the stem cells, the modified ES cells are injected into early-stage embryos of a recipient animal. These embryos, containing a mix of normal and modified cells, are then implanted into a surrogate mother.

Once the embryos develop and are born, the offspring are examined to check if the new gene has been successfully integrated into their genome. The ES cell method allows scientists to make very precise changes in the animal's genetic material. For knock-ins, a specific gene is inserted at a precise location, while for knockouts, a gene is completely removed or disabled. This method is invaluable for creating animals with specific genetic traits and is particularly useful for studying gene function and disease models.

3. Viral Vector-Mediated Gene Transfer

Viral vector-mediated gene transfer is a method that uses viruses to deliver foreign genetic material into an animal's cells. This technique is often used when other methods are less effective or feasible. In this method:

• Viruses, such as retroviruses, adenoviruses, or lentiviruses, are genetically engineered to carry the foreign DNA (the transgene). These viruses are modified so they can no longer cause disease, but they retain their ability to infect cells.

• The engineered viruses are then used to infect cells in the animal or directly infect the embryos of the animal. Once inside the host cells, the virus integrates the foreign gene into the host genome. The viral vector essentially acts as a vehicle to deliver the genetic material, allowing it to become part of the animal's DNA.

This technique is especially useful for introducing genes into cells that are difficult to modify by other methods. For example, some cell types that are hard to modify using other techniques can be more easily altered with viral vectors. Additionally, viral vectors are commonly used to create gene therapy models, where therapeutic genes are introduced into animal models to study human diseases and test potential treatments.

4. Sperm-Mediated Gene Transfer (SMGT)

Sperm-mediated gene transfer (SMGT) is a relatively newer method for creating transgenic animals, and it is less commonly used. In SMGT:

• Foreign DNA (the transgene) is introduced into sperm cells using techniques like electroporation, where an electric current is used to create temporary pores in the sperm cell membrane, allowing the foreign DNA to enter. The DNA becomes integrated into the sperm's genetic material, thus modifying its genome.

• Once the sperm cells have been genetically modified, they are used to fertilize eggs collected from a female animal. The fertilization process is natural, with the modified sperm carrying the introduced transgene into the egg. This results in the formation of a zygote (fertilized egg), which now contains the foreign gene in its genome.

• The fertilized eggs are then implanted into a surrogate mother, where they develop into transgenic offspring. After the offspring are born, they are tested to confirm the presence of the foreign gene in their genome. This testing ensures that the transgene has been successfully integrated into the animal's DNA and the animal is genetically modified.

SMGT is considered a simpler and less harmful method than other gene transfer techniques, like pronuclear injection. It is mainly used in species like fish and poultry, where sperm manipulation is easier. However, it is less effective in species with difficult sperm manipulation. Despite limitations, SMGT is valuable in aquaculture and agriculture for creating transgenic animals with traits such as disease resistance or faster growth.

Contributions of Transgenic Animals to Medicine and Agriculture

The creation of transgenic animals has significant implications for both medicine and agriculture, providing critical tools for understanding disease, developing new treatments and improving agricultural practices.

1. In Medicine

Transgenic animals play a pivotal role in advancing medical research and treatments:

• Disease Models: Transgenic animals, particularly mice, serve as models for studying human diseases. By introducing human genes or mutations into animals, scientists can replicate diseases like cancer, diabetes, Alzheimer's disease and heart disease. These animal models provide valuable insights into disease mechanisms and progression, allowing researchers to test new treatments before applying them to humans.

• Gene Therapy Research: Transgenic animals are essential for the development of gene therapy approaches, where faulty or absent genes in humans are replaced with functional ones. For example, animals are genetically modified to express human versions of defective genes, which can then be tested for therapeutic efficacy.

• Production of Therapeutic Proteins: Transgenic animals can be engineered to produce valuable proteins in their milk, blood, or other tissues. This process, known as pharming, is used to produce proteins such as human growth hormone, insulin, antithrombin and tissue plasminogen activator (tPA). These proteins have important medical uses, such as treating genetic disorders or blood-clotting issues.

• Vaccine Development: Transgenic animals can also be used to produce vaccines or to test new vaccines. For example, transgenic rabbits can produce human proteins necessary for creating vaccines, or transgenic mice can be used to evaluate vaccine efficacy against infectious diseases.

2. In Agriculture

Transgenic animals contribute significantly to improvements in agricultural practices and food production:

• Improved Livestock: Transgenic animals are used to create livestock that exhibit improved traits, such as enhanced growth rates, better disease resistance, or higher productivity. For example, transgenic salmon have been engineered to grow faster and reach market size more quickly than their wild counterparts.

• Disease Resistance: Some transgenic animals, particularly pigs, have been modified to be resistant to specific diseases. An example is the modification of pigs to resist the PRRS (Porcine Reproductive and Respiratory Syndrome), a devastating disease in pig farming.

• Higher Productivity: Transgenic animals can also be bred for enhanced production traits. For example, transgenic cows may be modified to produce more milk, or cows may be engineered to produce milk with enhanced nutritional value or altered composition.

• Environmental Benefits: Transgenic animals with enhanced traits may also contribute to sustainability. For example, genetically modified animals with increased disease resistance can reduce the need for antibiotics in farming, contributing to lower environmental pollution and healthier food products.