Animals that have had foreign genes purposefully added to their genomes are known as transgenic animals. These genes, also referred to as transgenes, are inserted to imitate human diseases, enhance livestock, create medications, or investigate gene function. Usually, genetic engineering methods are used to create transgenic animals.

While bacteria can successfully create a number of recombinant proteins used in medicine, some proteins require a eukaryotic animal host in order to be processed properly. As a result, genes have been cloned and expressed in mice, sheep, goats, and chickens. Transgenic animals are those that have been modified to express recombinant DNA.

Steps to Produce Transgenic Animals

1.Identification and Isolation of the Gene

A donor organism—such as bacteria, plants, or animals—is used to identify a particular gene of interest.
In order to guarantee expression in the intended organism, the gene is extracted and prepared with regulatory sequences, including a promoter and a terminator.

2.Preparation of the Vector

To make it easier for the gene to enter the animal’s genome, it is placed into a vector (such a plasmid or viral vector). To regulate the location and timing of gene expression, regulatory sequences are incorporated, such as constitutive or tissue-specific promoters.

3. Gene Transfer Techniques

• • Microinjection :A thin glass needle is used to inject the gene straight into the pronucleus of a fertilized egg.To create a transgenic animal, the altered egg is inserted into a surrogate mother. For instance, transgenic mice are used in biomedical research.
  • Gene Transfer Mediated by Retroviruses  : The desired gene is inserted into a retrovirus that infects embryonic cells. Stable expression is ensured by the virus’s integration of the gene into the host DNA.
  • Embryonic Stem (ES) Cell-Mediated Gene Transfer : In vitro, the transgene is inserted into embryonic stem cells.Early-stage embryos are then placed into a surrogate mother after modified stem cells have been added.
    In order to produce fully transgenic animals, additional breeding may be necessary if the progeny are chimeric.
  • Gene editing using CRISPR-Cas9 CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) are the repeated DNA sequences found in bacterial genomes. They serve as a memory of past viral infections by storing fragments of viral DNA  which are called spacers.The ground-breaking gene-editing tool CRISPR-Cas9 is based on a defense system naturally present in bacteria and archaea. It enables the precise addition, deletion, or change of particular genetic sequences to an organism’s DNA. Because of CRISPR-Cas9’s effectiveness, adaptability, and relative simplicity, it has emerged as a key component of modern biotechnology.
  • Sperm-Mediated Gene Transfer (SMGT) : Sperm cells are used as carriers to transfer foreign DNA into an egg during fertilization in a process known as sperm-mediated gene transfer (SMGT). Compared to previous techniques for creating transgenic animals, this method is comparatively easy and non-invasive.

4. Selection and Screening

Molecular methods like PCR (Polymerase Chain Reaction) , Southern blotting and western blotting ( to detect the expressed proteins) are used to screen the progeny to verify the transgene’s existence and expression.

5. Breeding

In order to guarantee that the transgene is heritable and expressed consistently in succeeding generations, transgenic animals are bred to create a stable line.

“Methods to produce Transgenic mice” by John W. Kimball via source content is licensed under CC BY 3.0

Applications of Transgenic Animals

Increased Productivity in Agriculture
Transgenic animals are designed to grow more quickly, produce more milk, and use feed more efficiently.
As an illustration, consider transgenic cows that provide milk with increased casein content for improved cheesemaking.
Resistance to Disease
Antibiotics and other treatments are less necessary when animals are resistant to particular diseases. Porcine Reproductive and Respiratory Syndrome (PRRS)-resistant pigs are one example.

Human Disease Models

Researchers can better understand disease causes and create treatments by using transgenic animals to imitate human diseases. For example: Mice genetically altered to develop cancer or Alzheimer’s disease.

Gene Knockouts

A genetically modified mouse known as a “knockout mouse” is one in which a particular gene has been totally deactivated, or “knocked out,” in order to examine its function. This is accomplished by causing the gene to become dysfunctional or non-expressed. In biomedical research, knockout mice are incredibly useful tools that are frequently employed to simulate human diseases, investigate gene function, and test novel treatments.

Drug Testing

New medications are tested for safety and efficacy using transgenic animals. For instance, drug-target interactions can be ascertained by using knockout mice deficient in particular genes.

Manufacturing Biopharmaceuticals

Therapeutic proteins are produced in the milk, blood, or eggs of transgenic animals. For instance, goats that have been genetically modified to generate the blood-clotting protein antithrombin in their milk.

Xenotransplantation

In order to decrease organ rejection during transplants, transgenic animals—especially pigs—are genetically engineered to produce organs that are compatible with humans. Pigs deficient in specific antigens, for instance, can shield humans from immunological rejection.

Industrial Applications-Biomaterial Production

Transgenic animals are created to produce industrially useful materials like spider silk in their milk or wool.
For instance, goats produce spider silk proteins in their milk, which are then used to make strong, lightweight fabrics.

Conservation

Through improved disease resistance or environmental adaptation, transgenic approaches are being investigated to conserve endangered species.

Examples of Transgenic Animals

Challenges and Ethical Considerations

• Possible problems with transgenic animals’ welfare.
• Unanticipated ecological effects of releasing transgenic animals into the wild.
• Ethical considerations for manipulating animal genomes for human benefit.

Although there is great potential for transgenic animals to improve science, medicine, and agriculture, they must be carefully regulated to address ethical, environmental, and health concerns.

Watch the video from Fuse school to know about GMOs ( Genetically Modified Organisms)

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