(Cover Illustration by Leo Harris)
Introducing the Field of Genetic Engineering
Genetic engineering technology is one of the greatest breakthroughs in modern biology, transforming the possibilities of biomedical treatments. CRISPR, standing for “Clustered Regularly Interspaced Short Palindromic Repeats”, is a gene-editing system that relies on RNA, a single-stranded molecule containing genetic instructions. The RNA guides specialized proteins to precisely cut DNA, a double-stranded molecule containing genetic information. Since its discovery in 2012, CRISPR has revolutionized research and medicine, allowing scientists to edit genomes with unprecedented precision.
In 2025, a new player entered the field. TIGR-Tas is a freshly discovered, RNA-guided tool with the potential to surpass CRISPR in flexibility and safety. Researchers from the Zhang lab at Duke University identified TIGR-Tas in 2024 while mining microbial genomes of bacteria and phages (viruses that infect bacteria). The Duke team used a metagenomic screen—a technique where scientists sift through large amounts of genetic data from microbes to discover new genes. The TIGR-Tas system holds the next generation of genetic engineering in its hands.
The Details of TIGR-Tas
TIGR stands for Tandem Interspaced Guide RNAs, while Tas expands to TIGR-Associated System. In simple terms, TIGR-Tas functions as a dual-spacer, RNA-guided, DNA targeting system. That’s a lot of words; let’s break it down.
“RNA”: TIGR-Tas operates on messenger RNA (mRNA). mRNA carries instructions from DNA to the cell’s protein-making sites (ribosomes), ultimately acting as temporary genetic blueprints. Since TIGR-Tas only edits mRNA, the tool makes interim changes, reducing the risk of long-term harmful side effects. The mRNA editing process is a natural mechanism where the body’s enzymes convert the nucleotide (building blocks of genetic material) adenosine (A) into inosine (I), which cells interpret as guanine (G). The alterations simply change one of the base pairs, leading the ribosomes to interpret the mRNA differently. However, an entirely different protein is produced.
“RNA-guided”: Like CRISPR, TIGR-Tas is also RNA-guided, meaning the system uses a short RNA “guide” to find and bind to a specific DNA sequence. RNA works through complementary base pairing. If a scientist knows the sequence of a gene they want to target, they can design RNA to seek out its complementary stretch in DNA. Once bound, the system regulates which proteins are generated by the specific sequence. As proteins are the functional power of the cell, even a single base change in RNA can lead to distinct outcomes in the protein’s design and purpose.
“Dual-spacer”: TIGR-Tas uses two paired guide sequences, each capable of targeting one DNA strand. This specific quality increases both flexibility and precision, building cleaner edits while reducing off-target effects by requiring two simultaneous guide matches.
“Tas”: TIGR-Tas uses two proteins, TasR and TasH, to process and guide RNA. By contrast, CRISPR relies on the bulkier Cas9 protein. The smaller size of Tas proteins makes TIGR-Tas easier to deliver into cells—a major advantage for medicine, where oversized proteins often trigger immune reactions or face delivery challenges.
“PAM sequence”: TIGR-Tas is also unique in that it does not require a Protospacer Adjacent Motif (PAM) sequence— the short DNA sequence CRISPR requires to recognize its target.
Combined with its small size and flexibility, TIGR-Tas can be packaged into an Adeno-associated virus (AAV) vector—a widely used and efficient delivery method for gene therapies.
Differentiating TIGR-Tas from CRISPR
Although revolutionary, CRISPR has many limitations. One major challenge is its reliance on PAM sites. For CRISPR’s Cas9 protein to cut targeted DNA, a PAM sequence must be located next to the target. This requirement restricts where CRISPR can edit, as not every gene contains a conveniently placed PAM. TIGR-Tas works independently of PAMs, vastly broadening its editing range.
Tas proteins are smaller and more adaptable to delivery methods required for maximum impact. While Cas proteins are large, making them harder to deliver inside cells. TIGR-Tas is smaller and modular (its parts can be mixed and matched for targeting specific RNA sequences). This flexibility allows for novel forms of therapy delivery to patients, which could precisely target mutations cell by cell.
Another key difference is that CRISPR edits DNA permanently, while TIGR-Tas only temporarily modifies RNA. Without disturbing any neighboring nucleotides, TIGR-Tas can swap a single mRNA letter, making it safer and much more precise than CRISPR.
Real-world Applications of TIGR-Tas—in Theory
The potential applications of TIGR-Tas are vast, but its theoretical use in medicine is especially urgent, as this new system may be able to cure lifelong illnesses that were once considered incurable.
Within the realm of neurological diseases, TIGR-Tas can edit RNA in neurons without altering their DNA. This is important for conditions like ALS, Huntington’s disease, and epilepsy, which often arise from single-point mutations (single errors in copying DNA, leading to mutated copies of cells), or toxic protein production (one-time instances of incorrect DNA copying, leading to incorrect mRNA, and build up of necessary proteins in cells), and can lead to a lifetime of disease. Neurons are difficult to target with DNA editing technology, such as CRISPR, because cutting DNA can trigger dangerous immune responses. With neurons having a very rare regeneration mechanism, there is a high risk of irreparable damage. By targeting RNA, TIGR-Tas may prevent the production of harmful proteins.
TIGR-Tas also has potential in the field of genetic metabolic disorders. A proof-of-concept study from Duke University demonstrated TIGR-Tas correcting mutations linked to ornithine transcarbamylase deficiency (OTCD), an X-linked urea cycle disorder that causes ammonia buildup in the blood (causing swelling in brain cells and disrupting neurotransmitters). OTCD may be fatal in infants. Remarkably, TIGR-Tas corrected the mutation in human liver cells without introducing off-target errors.
A leading hope for TIGR-Tas is that it can treat cancer. Cancer is another single-point mutation which carries into a deadly, and often unstoppable, domino effect. This disease arises when errors occur during DNA replication (copying DNA for cell division), leading to mutations in tumor suppressor genes or to the activation of oncogenes (overactive cell growth gene, causes uncontrolled cell division). Cell division en masse at unprecedented rates leads to the buildup of cells, known as tumors. TIGR-Tas may silence mistakes in both tumor suppressors and cancer-causing transcriptions at the RNA level—without permanently altering the genome.
By avoiding DNA alterations, TIGR-Tas creates opportunities for personalized therapies to treat rare diseases. Physicians may design RNA edits tailored to an individual patient’s needs, targeting only the harmful transcripts while leaving the rest of the genome intact.
Limitations
Currently, TIGR-Tas remains experimental. Most studies have been conducted in cell lines and animal models, with human applications (see Real-World Applications section) on the horizon. Delivering RNA guides to the correct tissues remains a challenge, since RNA is fragile and often degrades before reaching its target. Although non-viral delivery systems are being tested, viral vectors (like AAV) still dominate in terms of accuracy and impact. Long-term safety studies are necessary to evaluate unwanted immune responses and side effects over time.
The Bigger Picture
The discovery of TIGR-Tas may shift the future of genetic medicine. Instead of cutting and permanently altering DNA, TIGR-Tas represents a more versatile approach: temporarily rewriting RNA base sequences. Opening the door to therapies that are both safer and more adaptable, TIGR-Tas suggests a future where gene editing is not focused on managing diseases with ongoing treatments, but curing them by correcting errors at their source. TIGR-Tas may be the next major leap forward in making genetic engineering more targeted and personalized. TIGR-Tas marks a turning point in medicine, transforming how we approach, treat, and ultimately cure disease.
Sources
https://www.science.org/doi/10.1126/science.adl4630
https://today.duke.edu/2024/10/tigr-tas
https://www.fiercebiotech.com/research/dukes-tigr-tas-programmable-rna-editor
https://www.nature.com/articles/s41576-023-00600-z
https://www.cell.com/cell-reports-methods/fulltext/S2667-2375(24)00098-3
https://www.statnews.com/2024/10/28/rna-editing-therapies-hope-tigr-tas/
https://www.cell.com/trends/biotechnology/fulltext/S0167-7799(23)00155-4