CRISPR Technology for Gene Editing - A Paradigm of Possibilities
Clustered Regularly Interspaced Short Palindromic Repeats or CRISPR is a genome editing tool that has proved to be a breakthrough in science. CRISPR is one of the fastest and most accurate technologies for DNA editing.
The development of CRISPR genome editing technology was awarded a Nobel Prize in chemistry in the year 2020. The technology makes it possible to alter the traits of significant crops and animals and manipulate the genomes of model organisms in scientific experiments.
CRISPR has potentially revolutionized research, especially in the medical field. It was instrumental in detecting COVID RNA and holds potential in treating genetic diseases.
Emmanuelle Charpentier and Jennifer A. Doudna were awarded Nobel Prize in chemistry in the year 2020. [Image source: Wikimedia Commons]
The Crispr cas9 system comprises two significant molecules that can help modify the DNA:
- Cas9: Cas9 is an enzyme that acts as a ‘molecular scissor’ which can cut the strands of DNA.
- Guide RNA or gRNA: This is a sequence of RNA that has been already designed and used as a guide for cas9. The guide RNA assures that the Cas9 genome puts a cut at an appropriate point of the genome.
History and development of CRISPR
Japanese molecular biologist, Yoshizumi Ishino first discovered CRISPR in 1987 from DNA sequences of Escherichia coli. Then, due to the unavailability of sufficient sequences, especially for mobile genetic elements, it was impossible to speculate its potential biological functions.
Later, in the year 1993, the archeal CRISPR repeat was discovered for the first time by Francisco Mojica. With this revelation, the genome sequences of many archaea and bacteria were analyzed, and it was discovered that this unusual structure is widespread in prokaryotes.
In the early 2000s it was discovered that the CRISPR repeats possess a common set of properties which are now known to be the hallmarks of CRISPR. Subsequently, in 2005, it was discovered that these sequences matched fragments of bacteriophage genomes. This discovery helped in hypothesizing that CRISPR is an adaptive immune system.
Today it is estimated that 40% of bacteria and 90% of archaea have CRISPR repeats. The term CRISPR was first coined by Ruud Jansen and Mojica in the year 2001. Cas 9 was discovered by Alexandar Bolotin in the year 2005. While studying the bacteria Streptococcus thermophilus a CRISPR locus was found that had novel Cas genes and one that encoded a large protein. This protein was hypothesized to have nuclease activity and is currently known as Cas9.
Several experimental studies have been conducted to reveal the ability of CRISPR to act on DNA targets. It was discovered that Cas9 was the protein that was responsible for cleavage in the CRISPR Cas9 system and that CRISPR systems can perform heterologous functions in other species. Subsequent discoveries and biochemical characterization of Cas9 made it possible to harness the CRISPR Cas9 system for editing the genome.
Applications of CRISPR
- Medical Science: CRISPR-Cas9 has been used in studying several genetic diseases including Duchenne muscular dystrophy, hemophilia, loss of hearing, etc. The CRISPR-Cas9 system can help rectify genetic errors in stem cells that bring about genetic diseases. CRISPR has an advantage in the treatment of bacterial and antiviral diseases as it functions as a bacterial immune system against invasive genetic agents. CRISPR has also been employed in targeting tumor suppressor genes to inhibit tumorigenesis.
- CRISPR as a testing and diagnostic tool: Reportedly, CRISPR diagnostic tools have achieved considerable recognition for nucleic acid molecular testing because of their specificity and high sensitivity. CRISPR Cas12, Cas13, and Cas14 have shown promising features such as unique collateral cleavage activity which can help simplify detection methods by distinguishing the positive and negative samples. FDA in the year 2022 gave authorization to a novel rapid test for COVID-19 that has been developed with the help of CRISPR. This technology enables to process thousands of samples in a single day.
- Plant science: CRISPR-Cas9 has been employed in genome editing of crop varieties. CRISPR with plant breeding techniques has shown promising results such as increased yield, enhanced quality of the yield, resistance to disease, and improvement in nutrition. Advancements such as super grains, which produce up to 10% increased yields, tastier greens that are rich in flavor and nutrients along with the removal of bitterness have been made.
- Greener fuels: The use of CRISPR genome editing techniques has been proven to improve the production of biofuels by algae. The Strains of algae that produce twice the amounts of fats have been created, which can generate biodiesel. With this modification, the efficiency of converting CO2 into biofuel has also increased.
Future of CRISPR
In the future, there is a huge potential for CRISPR to be used as a treatment and not just as a tool to study diseases.
CRISPR has the potential to induce mutations in embryos that are known to develop diseases. Much debate has been going on around the ethical implications of human cell editing particularly germ cells with the potential of inheritance in future generations. Another prospect CRISPR holds is immune cell therapy. Studies have been going on to investigate the modification of DNA to kill cancerous cells. Agricultural issues that have a direct impact on food security such as citrus greening diseases will be solved in the future with the help of CRISPR genome editing.
Researchers are putting in efforts to bring back extinct species with the help of CRISPR genome editing technology. Allegedly, the passenger pigeon’s genes from North American forests would be transferred to its modern relative, the band tail pigeon.
Although advances in CRISPR only started a decade ago, we are beginning to see remarkable breakthroughs that show we cannot predict the potential of CRISPR at this point. There are numerous potential features, and applications, that we still have to discover.
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