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Genetic Engineering in Animals with CRISPR and TALENs
Genetic engineering has reshaped the landscape of animal research, enabling scientists to precisely modify genomes for biomedical, pharmaceutical, and agricultural purposes. With tools like CRISPR-Cas9 and TALENs, researchers now generate genetically enhanced animals that model human diseases, produce therapeutic proteins, or exhibit desirable traits such as disease resistance. This article explores key genetic engineering techniques, applications in academic and industrial research, and ethical frameworks that guide this evolving field.
Fig.1 Animal genome editing techniques and applications.
CRISPR in Animal Genome Editing
CRISPR-Cas9, adapted from bacterial immune systems, enables rapid and accurate genome editing. It uses a guide RNA to target a specific DNA sequence, where the Cas9 enzyme introduces a double-strand break. Repair via non-homologous end joining (NHEJ) or homology-directed repair (HDR) allows for gene knockout or precise insertion.
In animal models, CRISPR components are often delivered into zygotes through microinjection, electroporation, or viral vectors. This approach ensures that genetic modifications are present in every cell, including germline cells. Due to its flexibility, CRISPR allows for multiplexed editing—the simultaneous targeting of multiple genes—expediting the creation of complex disease models.
Editing efficiency and specificity are key metrics. Mosaicism, where not all cells carry the same edit, is common in embryo editing. Thus, genotyping multiple offspring is standard to confirm the desired genotype.
CRISPR has significantly enhanced animal genome research by making gene editing more accessible, cost-effective, and efficient across species including mice, pigs, goats, and even chickens.
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TALENs in Animal Genome Editing
TALENs (Transcription Activator-Like Effector Nucleases) are engineered proteins that bind specific DNA sequences and introduce double-strand breaks using a FokI nuclease. Each TALEN pair binds opposite sides of the DNA, requiring dimerization for cleavage, which contributes to high specificity and reduced off-target activity.
TALENs have been widely used in livestock editing projects due to their reliability. For example, TALENs have enabled targeted gene insertion into bovine genomes to create hornless dairy cattle, thereby improving animal welfare and reducing the need for dehorning procedures.
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While TALENs require more effort to design compared to CRISPR, their precise targeting and lower off-target risks make them an important tool in animal genetic engineering, especially in regulatory-sensitive projects.
Genetically Engineered Animals for Disease Modeling
Animal models with precise genetic modifications provide critical insights into disease mechanisms and therapies.
Mice: The Backbone of Biomedical Research
- OncoMouse: The first patented transgenic animal, engineered with an activated oncogene to study tumor development.
- Alzheimer's Models: Mice expressing mutant human APP and tau genes develop amyloid plaques and neurofibrillary tangles, mirroring human pathology.
Large Animals: Bridging the Translational Gap
- Cystic Fibrosis Pigs: Engineered with CFTR mutations, these pigs exhibit lung infections and pancreatic defects absent in mouse models, enabling studies on airway clearance therapies.
- Nonhuman Primates: CRISPR-edited macaques with autism-linked SHANK3 mutations help unravel neural circuit dysfunctions.
Emerging Frontiers
- Zebrafish: Transparent embryos allow real-time visualization of cancer metastasis or cardiovascular development.
- Disease-Resistant Chickens: CRISPR edits to the ANP32A gene block avian influenza transmission, potentially preventing pandemics.
Biopharmaceutical Protein Production in Transgenic Animals
Genetically modified animals also serve as bioreactors for producing high-value proteins. This "gene pharming" strategy introduces human genes into livestock, enabling the expression of therapeutic proteins in milk, eggs, or blood.
A notable success is ATryn, an anticoagulant antithrombin protein produced in the milk of transgenic goats. Approved by the FDA, it marked a milestone in molecular farming, proving that genetically enhanced animals could meet regulatory standards for biologics.
Other examples include:
- Chickens engineered to produce human enzymes in egg whites.
- Rabbits that secrete therapeutic proteins in milk.
These platforms offer advantages over traditional cell cultures, including proper protein folding, post-translational modifications, and lower production costs. With scalable farming and non-invasive collection methods, transgenic animals provide a sustainable solution for complex protein manufacturing in biotech.
Enhancing Livestock Through Genetic Engineering
Genome editing is reshaping animal agriculture by introducing traits that improve productivity, disease resistance, and animal welfare. These developments showcase how genetic manipulation of animals enables faster, more precise improvements than conventional breeding, aligning with sustainability and productivity goals.
Disease Resistance
An exemplary case is the PRRS-resistant pig, engineered by knocking out the CD163 gene, which is essential for viral entry. These pigs remain healthy upon viral exposure, representing a breakthrough in reducing economic losses in swine production.
Animal Welfare
To eliminate painful dehorning procedures, researchers used TALENs to integrate the polled (hornless) allele into dairy cattle genomes. This gene edit mimics natural variation and results in offspring inheriting the hornless trait, improving safety and welfare in livestock operations.
Growth Efficiency
Targeting the myostatin (MSTN) gene has led to animals with increased muscle mass. CRISPR-mediated MSTN knockouts in goats and sheep have produced animals with higher meat yield. While such edits offer production benefits, they require monitoring for side effects like birthing difficulties.
Ethical Oversight in Animal Genome Research
The power of genome editing demands careful ethical governance. The 3Rs principle—Replacement, Reduction, and Refinement—remains the foundation of animal research ethics. Institutional Animal Care and Use Committees (IACUCs) rigorously review projects involving genetically modified animals to ensure ethical compliance.
For industrial applications, regulatory bodies such as the FDA assess gene-edited animals as if they were veterinary drugs. This includes evaluating the stability of edits, animal health, and food safety, ensuring public protection and trust.
Additionally, public debate shapes ethical boundaries. Concerns about animal suffering, ecological risks, and genetic ownership inform policy development. Transparent practices and responsible communication help maintain public support and regulatory clarity.
Ethics is not a barrier but a guide—ensuring that advances in animal genetic engineering benefit both science and society without compromising welfare.
BioVenic continues to support the development of reliable, efficient, and ethically responsible genetic tools for animal research and biotechnology. Learn more about our gene editing technologies and services
- CRISPR/Cas9
- TALENs
- ZFNs
- Genome Editing in Precision Animal Breeding
- Gene Delivery Solutions in Precision Animal Breeding
- Genome Modification Validation in Precision Animal Breeding
- Transgenesis in Precision Animal Breeding
- CRISPR Genome Editing in Precision Animal Breeding
- Custom CRISPR Libraries in Precision Animal Breeding
- Gene Knockout in Precision Animal Breeding
- Gene Knock-in in Precision Animal Breeding
FAQs
How do scientists validate off-target effects in CRISPR-edited animals?
Researchers typically use whole-genome sequencing, GUIDE-seq, or T7E1 assays to identify unintended edits and ensure genomic integrity before breeding or applying CRISPR-modified animals in research or industrial settings.
Are gene-edited animals more prone to health issues than wild-type counterparts?
Not necessarily. Edited animals undergo phenotypic monitoring and health assessments. Most edits mimic natural mutations, and rigorous screening ensures only viable, healthy lines are advanced for research or production.
What is the difference between TALENs and CRISPR?
TALENs use engineered proteins for DNA targeting, offering high specificity, while CRISPR relies on guide RNA and Cas9 protein, enabling faster design and multiplex editing but with potentially higher off-target risks.
References
- Nemudryi, A. A., et al. "TALEN and CRISPR/Cas genome editing systems: tools of discovery." Acta Naturae 6.3 (22) (2014): 19-40. https://doi.org/10.32607/20758251-2014-6-3-19-40
- Liu, Chang, et al. "Delivery strategies of the CRISPR-Cas9 gene-editing system for therapeutic applications." Journal of controlled release 266 (2017): 17-26. https://doi.org/10.1016/j.jconrel.2017.09.012
- Wang, Xiaolong, et al. "Generation of gene-modified goats targeting MSTN and FGF5 via zygote injection of CRISPR/Cas9 system." Scientific reports 5.1 (2015): 13878. https://doi.org/10.1038/srep13878