• Urooza Sarma

CRISPR: More than just a cut, copy and paste

by Urooza Sarma, Rahul Rao, Varun Rao and Yasir Aheer


Summary:

  • CRISPR has caused a tremendous shift in the way science is done, opening the possibilities for using this gene editing technology in medicine, agriculture and the environment.

  • By harnessing a mechanism found in bacteria, CRISPR has been adapted to laboratories to carry out gene editing in a rapid, inexpensive and precise manner.

  • It is also being used in agriculture to create more ‘elite’ or ‘resilient’ crops that can withstand dramatic changes in climate and disease.

  • It is currently being used to understand genetic origins of disease and allow for better genetically targeted drug discovery for diseases such as Cystic Fibrosis and Huntington’s Disease.

  • The success of CRISPR relies on scientific collaboration and communication to the wider audience.

Genes maketh humans, just like they do other animals, birds, trees and even viruses and bacteria. For years, the dogma has been that we are just products of our genetic make-up, whether it is genes for eye colour and hair, or those that can cause lasting impacts on health and disease. It was generally accepted that editing these genes with a cut, copy and paste mechanism was something only encountered in science fiction such as the dystopian futures imagined in the 1932 novel, Brave New World by Aldous Huxley or the 1997 film Gattaca. The ability to feasibly change an organism’s DNA, which once seemed futuristic and impossible, is now within reach. Cue, CRISPR.


The combination of CRISPR (Clustered regulated interspaced short palindromic repeats) and CRISPR-associated protein 9 (Cas9) is a powerful gene editing technology which has led to a quantum leap in genetic science. From treating neurological disorders and developing personalised medicine, to optimising agriculture, or developing biological sources of plastic, CRISPR may be the biological system that could disrupt and change all of our current systems.



What is CRISPR?

The technique of CRISPR, now widely used in laboratories, arose from a genome editing system used by bacteria, to protect themselves from invasion by viruses. Simply, the CRISPR system in bacteria recognise genes found in viruses, and destroy them. When viruses invade bacteria, they expel their genetic material, in the form of DNA or RNA, and exploit the host’s machinery to make proteins. In bacteria, infection by viruses results in the production of enzymes that fight off the intruder. This results in bacteria building a ‘library’ known as CRISPR arrays, containing snippets of RNA or information from previously invading viruses. This CRISPR array acts as a “blacklist” for bacteria, so if there is a re-invasion of the same virus or a similar one, it can produce RNA segments from these CRISPR arrays and use it to target and destroy the virus’ DNA using enzymes such as Cas9. Simply put, Cas9 is the bacterium’s prison guard - it traverses the cell carrying a “blacklist”, which is the CRISPR array, with the names and faces of “viral criminals” in the form of RNA. If the virus’s RNA matches the information the Cas9 has, it arrests it and neutralises its threat to the bacterium.


Figure 1: How CRISPR can be used in the lab to delete or insert a gene (Source: Vox.com)


The translation of the CRISPR system from bacterium to widespread laboratory use has been an epic tale of collaboration amongst the scientific world, transforming our ability to remove undesirable genes and add desirable ones. How is this achieved? The gene of interest is added to the “blacklist” or CRISPR array possessed by Cas9. Unable to tell viral DNA apart from others, Cas9 carries out its function on this information, just as it would on viral DNA.


In the lab, this has been adapted and refined to a two-component system:

1. Designing a sequence that recognises the gene of interest and

2. Cas9 enzymatic activity, that cuts the targeted sequence and removes it.


Currently, gene removal through CRISPR has high success rates. Gene replacement, whereby ‘bad’ genes are replaced with ‘good’ can also be done at much higher precision rate than other gene editing technologies. CRISPR has changed the way we can edit genes in an inexpensive and precise manner, and its uses are widespread, from food technology to disease understanding.



CRISPR can change the supply chain of food production

CRISPR is gaining momentum in the field of agriculture, giving food crops all of the benefits of ‘survival of the fittest’ at the hands of scientists. CRISPR technology is being used to identify traits that make crops more desirable, including increasing crop yield, quality of fruit and genetically altering crops to repel insects or become more tolerant to extreme weather conditions.


CRISPR technology has literally ‘gone bananas’ in this field. Since late 2019, a deadly fungus called Fusarium oxysporum f.sp. cubense has been tearing through the Americas and destroying the banana crop, threatening its future supply. Scientists across the globe have been using CRISPR to edit the genome of the humble banana, to insert a fungal resistant gene into its genome. Whilst some may point out that we have been creating genetically modified crops for a while, what makes the banana a particularly interesting candidate for CRISPR technology is its evolution as a genetically modified organism. The common banana consumed around the world is a sterile genetically modified organism (GMO) and is currently only propagated through cloning, meaning currently the genes that make it susceptible to death by fungi are passed on across generations. By using CRISPR, scientists can tweak the current known genome of the banana to introduce fungal resistant genes, prolonging its livelihood and making it safer to consume.


In its absolute natural state, years of cross-breeding between wild strains of crop may result in a crop that is ‘elite’ and a natural product of years of selection pressures. However, the rate at which food is supplied and consumed in the growing population across the world is not conducive to this process, and risks completely losing species of crops. As we experience more dramatic changes in climate and exposure to microbes, it is critical to harness the power of biotechnologies such as CRISPR to give us the best chance at maintaining a food supply chain that can keep up with these changes. CRISPR has the ability to produce elite crops from wild strains in a rapid, precise and sustainable way. As with matters of medicine, to increase the public’s trust in CRISPR-edited food, the discussion around this technology and its uses needs to be open and clearly communicated to give its best chance of surviving regulations and appealing to consumers. Think GMOs, rebranded.



CRISPR as a tool to understand genetic diseases

The discovery of CRISPR in laboratories has paved the way for innovation and possibilities across health, environmental and agricultural spheres. CRISPR is being used to unlock a wealth of knowledge and broaden our understanding of genetic mechanisms of disease. It has also enhanced our understanding of genetic diseases such as Huntington’s Disease and Cystic Fibrosis, and has helped develop drugs to target these for better health outcomes. CRISPR has also been tried in the immune cells that are directly attacked by the Human Immunodeficiency Virus (HIV) and may be a way for us to target other viral epidemics, such as Sars-Cov-2. The mechanism appears simple: find the gene of interest, develop guides to locate it within the nucleus of a cell and use enzymes such as Cas9 to remove the culprit.


However, some may argue that marketing CRISPR in such a manner is a case of rose-tinted glasses. There are several hurdles to overcome, including improving precision in identifying the gene of interest and reducing off-target effects, causing unintended consequences. Currently, there is no definite way for scientists to predict all of the off-target effects of the system, meaning gene editing of this sort could result in cancers and other adverse effects. But with power comes great responsibility and while CRISPR has revolutionised the way we can edit genes in an inexpensive and precise manner, it isn’t perfect yet. In its imperfection, lies fear of misuse or abuse.



CRISPR and the impossible future of ‘designer babies’

“Designer babies” is a highly charged term that gets thrown around when discussing CRISPR. Can we use gene editing tools to alter embryos? Remove a gene here, add a gene there? The simple answer to this is no. Technologically, we just aren’t there yet, and ethically it’s a whole different ball game. In 2018, in a move that was considered to be jumping the gun from the otherwise ongoing collaborative effort in the field, scientist He Jiakui claimed to have used CRISPR to create live HIV resistant human twin babies. This resulted in outcry from academics in the field, along with banning of his work.


We do not yet fully understand the off-target effect of changing one gene, or the effect it can have on the full genome of the individual. The technical capability of CRISPR requires significant improvement before it can be safely used in embryos. Quite apart from the technical aspects, the use of CRISPR in this field requires serious ethical considerations. Most scientists advocate for a slow and steady approach here, to keep the discussion about CRISPR open, in efforts to keep the public’s trust. While there is a lot that can be done, there is still plenty we need to do before we can even begin to jiggle the lock on that Pandora’s box.



From labs to our lives

There is no doubt that CRISPR technology has enhanced our ability to perform lab-based science, while also seeing varied real-word uses, from medicine to agriculture. From a technical aspect, this technology is still evolving and is very much a work in progress. Its scientific progress relies on collaborative and open discourse between scientists, but its possibilities are immense.


However, CRISPR’s ultimate success in delivering on those promises relies on how it is communicated to the public. Laying out all the information in a clear and concise manner, and easing uncertainties about its effects is essential to give society a chance to grapple with the regulatory and ethical issues that may arise from it.

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Disclaimer: This article is based on our personal opinion and does not reflect or represent any organisation that we might be associated with.