Cut and Paste Genes Callum Sharma

Cut And Paste Genes Callum Sharma (Year 11, Churchill)

This article will present methods used by scientists to find cures for diseases through genetic editing using CRISPR. CRISPR technology is a simple yet powerful tool for editing genomes. It allows researchers to easily alter DNA sequences and modify gene function. Its many potential applications include correcting genetic defects, treating and preventing the spread of diseases and improving crops. However, its promise also raises ethical concerns.

1 BACKGROUND AND PROCEDURE

The genomes of organisms encode a series of messages and instructions within their DNA sequences. Genome editing involves changing those sequences, thereby changing the messages. CRISPR is a genetic engineering technique that targets genetic codes in order to edit the DNA. For example, it can be used to treat diseases such as HIV. When the target DNA is found, Cas9 – one of the enzymes that is part of the CRISPR system – binds to the DNA and cuts it, shutting the targeted gene off. The protein Cas9 is an enzyme that acts like a pair of molecular scissors, capable of cutting strands of DNA.1 CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats This means a series of ‘short’ ‘clustered’ repeating DNA sequences with “spacers” sitting in between them, and which mirror the next sequence like a ‘palindrome.’ These are the sequences that are used as a guide by the Cas-9 enzyme.

CRISPR technology was originally developed from the natural defence mechanisms of bacteria and archaea. These organisms use CRISPR with RNA and various Cas proteins, including Cas9, to stop attacks by viruses and other foreign bodies. 8 The Cas9 enzyme involves two RNA molecules which move the protein Cas9 to the targeted site, where it will make its cut, cutting both strands of the DNA double helix.

In bacteria, once the Cas9 has been guided to the CRISPR sequence, it can insert ‘spacers’. In the case of bacteria, the spacers are taken from viruses that previously attacked the organism. They serve as a bank of memories, which enables bacteria to recognize the viruses and fight off future attacks [1]. Once DNA is cut, the cell's natural repair mechanisms insert changes to the genome. This can happen in two different ways. One way is to join the two cuts back together. This method, also known as "non-homologous end joining," can cause flaws. Nucleotides can accidentally be inserted creating mutations, which could affect a gene. The second method is that the break is fixed by filling in the gap with nucleotides. To create this, the cell makes a short strand of DNA as a template. Scientists can supply the DNA template of their choosing to fix a mutation or to change a gene [8].

2 SCIENTIFIC HISTORY

The discovery of clustered DNA repeats was made by Yoshizumi Ashino in Osaka University in 1987 [1]. He accidentally discovered them by cloning a CRISPR sequence along with another gene that was the original target. The repeats were an unexpected finding, because repeats would usually be consecutive rather than in this case clustered. The CRISPR CAS-9 system was discovered by Jennifer Doudna, a professor at the University of California at Berkeley, and Emmanuel Charpentier. They discovered the CRISPR to create the CAS-9; which could locate and target the DNA specified by the guide RNA. Fusing two RNA molecules would create a single guide RNA molecule. They manipulated the nucleotide sequence of the RNA to program the CAS-9 [2].

In 2013, Feng Zhang, of the Broad Institute of MIT and Harvard, was the first scientist to adapt the CRISPR CAS-9 for editing eukaryotic cells. Zhang’s lab focused on Synthetic Biology and he had a central role in the development of CRISPR technologies. In 2011, Doctor Zhang started using the CRISPR system

Figure 1: CRISPR-CAS9 Gene Editing (Source: https://www.globalbiotechinsights.com/articles/10802/lookingbeyond-the-debate-of-who-owns-crispr-gene-editing-technology) on human cells, based on prior studies done by the Sylvain Moineau Lab. Zhang's group, using Doudna andCharpentier’s work, could effectively program the Cas9 to function in a human body. Zhang showed it could be used to target different locations in the genes at the same time. Moreover, he showed that CRISPR CAS-9 could be used for fixing issues in blood such as blood clots or the opposite, hemophilia [6].

In November 2018, a Chinese researcher He Jiankui altered embryos during fertility treatments and managed to delete receptors on the white blood cells of twin sisters using CRISPR CAS-9. By doing this he enhanced the resistance of the cells to HIV. The Chinese scientist claimed that he had altered a gene called CCR5, which allows the AIDS-causing virus to infect an important class of cells in the human immune system.

He Jiankui told The Associated Press that he carried out his experiment to protect the twin sisters from HIV infection later in life, as their father was HIV-positive [3].

3 ETHICS

A big safety issue with He Jian Kui’s experiments is their potential additional effects, as by using CRISPR, he might cause unintended, harmful mutations elsewhere in the genome. To ensure this had not happened, his team sequenced the entire genomes of both parents. They then removed 3 to 5 cells from each of the edited embryos before implantation in the mother and fully sequenced them, to check for unwanted mutations.

In addition, a caution of using CRISPR on embryos is something called mosaicism. If the eggs started dividing before the gene editing took place, the twin girls might have a mixture of cells with and without the edit [5]. Tests on the placenta and umbilical cord blood and tissue found exactly the same mutations in each sample for both twins, showing that mosaicism had not occurred. Mosaicism is an issue because if the offspring’s immune cells developed from non-edited cells, they would still be vulnerable to HIV [5].

Figure 2: He Jian Kui defending his stance on Genetic Editing (Source: https://www.theguardian.com/science/2018/nov/28/scientist-in-china-defends-human-embryo-gene-editing)

A third issue is that disabling the CCR5 gene does not provide complete protection against HIV and the broader consequences of knocking out this gene – which is involved in immune function – are unclear. The twins are not completely vulnerable but rather not completely protected.

He Jian Kui was criticised for experimenting when the risks to otherwise healthy children were unclear, and for acting against Chinese law. There was also anger because HIV can be treated and there was barely any risk of it being passed from the HIV-positive father to his children.

The Chinese authorities investigated and concluded that Professor He had acted illegally in pursuit of fame and fortune. Professor He has always defended his experiments and at a summit in Hong Kong said he was "proud" of his gene-editing work.

The Core Guiding Principles for Genome Editing in Human Embryos which were created by He Jian Kiu and he abided by during his experiment are as follows:

Mercy for the families who need the editing. A broken gene, infertility, or a preventable disease should not stop life. For a few families, early gene surgery may be the only way to heal disease and save a child from suffering.

Only to be used to cure serious diseases, not for vanity. Gene surgery is a serious medical procedure that should never be used for aesthetics.

To respect a child’s autonomy. After gene surgery, a child has equal rights. No obligations exist to his or her parents or any organization, including paying for the procedure.

Genes do not define you. Our DNA does not predetermine our purpose or what we could achieve. We flourish from our own hard work. Whatever our genes may be, we are equal in potential.

Everyone deserves freedom from genetic disease. Wealth should not determine health. Organizations developing genetic cures have a moral obligation to serve families of every background [4].

Some scientists accept the use of genome editing and tests and investigations on humans have been carried out in Europe, the US and Canada to see how this new technology could treat blood disorders like anemia. However, after He’s tests on the twin daughters, genome editing became quite a controversial subject that led to concern in the scientific community. Scientists say that changes to the embryo’s

genomes could be passed down generations and potentially cause disease or have other negative effects. After He’s experiment, Chinese scientists stated that "We as biomedical researchers strongly oppose and condemn any attempts on editing human embryo genes without scrutiny on ethics and safety!" Even the scientists involved in the discovery of CRISPR opposed He’s tests [9].

"This work is a break from the cautious and transparent approach of the global scientific community's application of Crispr-Cas9 for human germline editing," stated Jennifer Doudna,. Her concern was that people might exploit genome editing to create ‘designer babies’, where the parents would choose its traits or characteristics such as blond hair [9].

In conclusion, genetic editing can benefit the human race substantially. However, it also has its downsides as it can result in mutations or even infant mortality. I believe He Jian Kui’s experiment was ethical and helpful for other genetic scientists. I believe this because it was to stop the daughters having to suffer later in life, which I think should be the only reason it should be used, to try to prevent illness or unnecessary death. This should be even more pertinent in the current Covid-19 situation as it spreads around the world. People with diabetes or a cardiovascular disease have a severe risk, but by using Genome Editing it could reduce the likelihood of the person getting it from birth.

GLOSSARY

Archaea: Nucleotide: RNA:

Genome:

Spacer: single-celled microorganisms, different from bacteria molecules which are joined together in long chains to make DNA and RNA ribonucleic acid; long, single-stranded chain of nucleotides that carry genetic information and are involved in processing proteins a genome is the genetic material of an organism; the genome sequence of an individual is the complete list of the nucleotides that make up all of their chromosomes short sequences of DNA that are interspersed among repeated sequences, and do not code for any genes

BIBLIOGRAPHY

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7. Vidyasagar, Aparna. “What Is CRISPR?” LiveScience, Purch, 21 Apr. 2018, www.livescience. com/58790-crispr-explained.html. Institute, Broad. “Questions and Answers about CRISPR.” Broad Institute, 4 Aug. 2018, www. broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr. NormileNov, Dennis, et al. “CRISPR Bombshell: Chinese Researcher Claims to Have Created GeneEdited Twins.” Science, 27 Nov. 2018, www.sciencemag.org/news/2018/11/crispr-bombshell-chineseresearcher-claims-have-created-gene-edited-twins. http://www.youtube.com/watch?v=MyNHpMoPkIg Page, Michael Le. “CRISPR Babies: More Details on the Experiment That Shocked the World.” New Scientist, 28 Nov. 2018, www.newscientist.com/article/2186911-crispr-babies-more-details-on-theexperiment-that-shocked-the-world/. Institute, Broad. “CRISPR Timeline.” Broad Institute, 7 Dec. 2018, www.broadinstitute.org/whatbroad/areas-focus/project-spotlight/crispr-timeline. Ramsey, Lydia. “A Scientist Who Genetically Edited Babies to Be HIV-Resistant Was Just Sentenced to 3 Years in Prison. Here's How He Did It and Why Scientists around the World Are Outraged.” Business Insider, Business Insider, 30 Dec. 2019, www.businessinsider.com/he-jiankui-sentenced-to3-years-in-prison-for-gene-editing-embryos-2019-12.