INTRODUCTION
“CRISPR” is the short form for "Clusters of Regularly Interspaced Short Palindromic Repeats" which is a new and powerful gene-editing tool capable of altering the DNA sequence and allowing modification of gene functions. CRISPR has been successfully used in curing many genetic defects, treating and preventing the spread of diseases and improving crops. The process of undertaking this procedure was not clear until 2017, when nature (the journal) published a paper on its actions for the very first time. This also brings up an implication of this method which is, being able to alter the gene of our interest in a human DNA and modify it according to our need such that the person would be able to do things that would not be humanly possible without the need of external help.
CRISPR-CAS9
CRISPR is that specialized region of the DNA which has two distinct characteristics, viz, the presence of nucleotide repeats and spacers. The building blocks of DNA, which are the repeated sequences of nucleotides, are distributed throughout a CRISPR region.
This technology was inspired from the natural defense mechanisms of bacteria and several single celled organisms. These organisms use RNA derived via CRISPR and various other Cas proteins, like Cas9, to protect themselves from the attack of viruses and other foreign bodies. They carry this out primarily by chopping up and destroying the DNA of a foreign invader. When these components are transferred into another, more complex organism, it allows for the manipulation of genes or gene editing. The Cas9 protein is an enzyme that cuts foreign DNA by typically binding to the two RNA molecules: crRNA and another called tracrRNA which then guides the Cas9 to the target site where it will eventually make its cut. Ca9 cuts both the strands of the DNA double helix, using two separate domains, and makes what is known to us as the “double stranded break”. Short DNA sequences, known as PAMs (Protospacer Adjacent Motifs) sit adjacent to the target DNA sequence and act as very specific tags. Thus the Cas9 won’t just cut anywhere in a genome.
In 2012, two pivotal research papers were published in the journals Science and PNAS, which helped transform bacterial CRISPR-Cas9 into a simple, programmable genome-editing tool. The studies thus concluded that Cas9 could be directed to cut any region of DNA. This could be done by just changing the nucleotide sequence of crRNA, which binds to a complementary DNA target. In 2012, Martin Jinek and colleagues further simplified the system by fusing crRNA and tracrRNA to make one "guide RNA." Thus, there are only two requirements for genome editing : the Cas9 protein and the guide RNA.
A representation of how CRISPR makes genetic changes is depicted here with the help of the following image:
UTILITY AND LIMITATIONS
The first and foremost use is in the therapeutic application. Studies using in vitro and animal models of human disease have demonstrated that the technology can be effective in correcting genetic defects and also diseases like cystic fibrosis, cataracts and Fanconi anemia.
CRISPR technology has been applied in the food and agricultural industries to engineer useful cultures and to vaccinate industrial cultures against viruses. It is also being applied in the agricultural field to improve the crop yield, drought tolerance and nutritional properties.
Another application is to create gene drives. These are genetic systems, which increase the chances of a particular trait being passed on from parent to offspring and eventually, over the course of generations, the trait spreads through the entire population.
A representation of how CRISPR technology can be administered in a real life situation in the permanent treatment of a patient suffering from sickle cell disease is depicted and explained with the help of the following image:
Limitations:
CRISPR is not a hundred percent efficient technique and moreover, the genome-editing efficiencies could vary and reach upto as high as 80%.
There is a phenomenon called "off-target effects", where the DNA is cut at sites other than the intended target. This can lead to the introduction of vague mutations that are not required and lead to ‘genome vandalism’.
CRISPR AND THE IDEA OF SUPERHUMANS:
Although there has been several studies and theories proposed on the use of CRISPR to produce genetically modified humans or basically superhumans, but this becoming a reality is a long way to go, and so the alteration of human DNA, at present, in order to possess superhuman powers remains something seemingly fictional. In the present time, the use of CRISPR in humans is purely therapeutic, i.e., fixing genetic mutations rather than creating them. And such therapies are giving individuals special abilities above those that the DNA they were born with gave them and they are becoming the first genetically modified humans.
With trials at a spread of stages, from in vitro to animal models to early clinical use, the therapeutic use of CRISPR in humans is probably going to extend as more and more successful and beneficial effects are being demonstrated. Edits within the genome are giving these individuals ‘powers’ as they do to the superheroes of fiction, but just on a significantly smaller scale and not just like the basic thought of the power to save the world.
RECENT BREAK-THROUGHS:
(1) Victoria Gray is a 34-year-old woman from Forest, Mississippi, who is the first person in the United States to have her sickle cell disease treated with a gene-editing technique on July 2, 2019. The researchers conducting the study stated that it's too soon to reach any firm conclusions about the long-term safety and effectiveness of the approach but until now its been really successful and promising. The company that executed the procedure, also revealed that a second sickle cell patient along with three other beta-thalassemia patients was under treatment as part of their research program.
(2) Scientists at the Casey Eye Institute at Oregon Health & Science University, Portland, have tried on the new CRISPR-based medicine in the treatment of a patient who has an inherited form of blindness. This was an experimental approach toward the treatment of the genetically inherited disease - ‘Leber congenital amaurosis’, which is caused by a faulty gene that causes blindness from the early stages of life. This disease nearly affects around one in every 40,000 births, making it a very much required approach. In the treatment, the patient was administered with a dose of experimental drug, AGN-151587, via an injection in the eye. And now the patient seems to be very much cured. Further that, the CRISPR edit is permanent, thus patients may only need a single dose and be hazel free for the rest of their life.
CONCLUSION:
This article was mainly focused on the CRISPR technique, its methodology and the brief insight on the process. This technique at the present time has several applications in varying fields, but in case of human trials, it is limited only up to therapeutic applications and its applications in the medical field is only increasing day by day and thus opening up a new scope of creating a genetically modified superhuman. But this idea is not yet ethically accepted and thus the superhumans exist only as fictional characters, as per now. But we can surely say that the CRISPR technology might turn out to be a very useful and powerful tool, in the coming future, which would be accepted across the globe and thus would enable us to manipulate human DNA, for the better.
- Neha Unni
Dept. of Biochemistry and Biotechnology
St. Xavier’s college, Ahmedabad
REFERENCES: