Overview
CRISPR gene editing is a genetic manipulation tool in molecular biology that enables alteration of the genomes of living organisms by this particular technique. While at this point it can not be considered an innovative technology, CRISPR already needs to exploit its potential, which will have a much broader and more positive effect on our lives. [3]
▲(simplified image of gene editing. “Do CRISPR Risks Outweigh Rewards?” (GEN) [4])
What is CRISPR?
“CRISPR” stands for Clustered Regularly Interspaced Short Palindromic Repeats and is a class of DNA sequences present in prokaryotic organism genomes such as bacteria and archaea. Such sequences are extracted from bacteriophageal DNA fragments that originally infected the prokaryote, and are used during subsequent infections to identify and kill DNA from related bacteriophages. The words “CRISPR” or “CRISPR-Cas9” are also used simply to refer to the various CRISPR-Cas9 and -CPF1, devices that can be designed to modify particular genetic code sequences and to change or alter DNA at different sites, as well as for other purposes. The Cas9 (or “CRISPR-associated”) protein is an enzyme that behaves like a pair of molecular scissors, capable of breaking DNA sequences. By using CRISPR, one can permanently modify genes in living cells and organisms and, in the future, enable the correction of mutations at precise locations in the human genome to treat genetic causes of disease. [1] [4] [6]
Why CRISPR-Cas9?
While there are many Cas and Gene editing methods, CRISPR-Cas9 stands out for its high degree of precision and accuracy in cutting and pasting DNA together with relatively low cost and the potential to add or delete more than one gene. Moreover, as the CRISPR-Cas9 device itself can cut DNA strands, CRISPRs do not need to be combined with different cleaving enzymes as do other methods. They can also easily align sequences of a reference RNA (gRNA) programmed to direct them to their DNA targets. Tens of thousands of these gRNA sequences have already been developed, and the research community is open. [2] [3]
History
The first definition of what would later be called CRISPR is from researcher Yoshizumi Ishino and his colleagues at the University of Osaka in 1987. We mistakenly cloned part of a CRISPR sequence along with the gene “iap,” which was their initial target. The gene tended to have five small, repeated fragments of DNA separated by short, non-repeating sequences of ‘spacer’ DNA. However, in 2002 a team of Dutch scientists led by Rudd Jansen at the University of Utrecht coined The term. [2] [9]
How Does it Work?
▲How CRISPR works. “CRISPR: Implications for Materials Science.” (Cambridge Core) [3]
By injecting the Cas9 nuclease complexed with a synthetic RNA guide (gRNA) into a cell , the cell genome may be cut at the desired spot, allowing for the removal of existing genes and/or inserting new ones. When the DNA is sliced, researchers use the cell’s own DNA repair mechanism to attach or remove fragments of genetic material, or make improvements to the DNA by replacing an existing fragment with a new DNA strand. This process, in other words, creates a break in both strands of the DNA molecule which causes the cell to repair the break, sensing a problem. Instead, this repair might correct an error or even implant a new gene which is a much more complicated operation. Cells usually patch a break in their DNA by gluing back together the broken ends. [1] [3] [5]
Precedents/Uses
CRISPR genome editing allows scientists to rapidly create model cells and organisms that can be used by researchers to facilitate studies into diseases such as cancer and mental illness. Furthermore, CRISPR is now being used as a rapid diagnostic. CRISPR is used by Japanese scientists to alter the flower color of a typical garden plant. Researchers have programmed CRISPR in the Japanese morning glory to attack a specific gene, known as the DFR-B gene. They also introduced the CRISPR device into plant embryos in the laboratory. The gene-editing method effectively interrupted the gene DFR-B and thus transformed the signature violet color of the plant to green. A scientist in Oregon made headlines when he reported that his team used CRISPR to snip out a genetic error in dozens of human embryos that caused heart disease. Since the procedure was for scientific purposes only and none of the embryos were inserted into the uterus of a woman with the intent to establish a child, it demonstrates the potential for CRISPR use. [6] [7]
Potential Applications
Genome editing is also critical for the prevention and treatment of human diseases. Most work on genome editing is currently conducted to explain diseases using animal and cell models. Scientists continue to work to establish if this method is healthy and appropriate for use in humans. [3]
Through studies on a wide variety of diseases, it is being discussed including single-gene conditions such as cystic fibrosis, hemophilia, and sickle cell disease. This also retains promise to cure and eliminate more common illnesses, such as cancer , heart disease, psychiatric illness and infection with the human immunodeficiency virus (HIV). [2]
One firm, eGenesis, which is spun out of the laboratory of Harvard geneticist George Church, uses CRISPR to make pigs ideal organ donors for humans. Many pig organs, such as the lungs and the heart, are comparable in size to human ones. The organization is now using CRISPR to change genes that are active in the immune system to prevent the tissue from being destroyed by the human body. [8]
CRISPR would be an effective method to domesticate new crops, improve food nutrient value and help protect crops against severe weather and climate change. CRISPR is also being used as a way of breeding cacao trees to be immune to diseases that potentially threaten the production of chocolates. [6]
[1] “CRISPR Enables Gene Editing on an Unprecedented Scale.” WhatisBiotechnology.org, www.whatisbiotechnology.org/index.php/science/summary/crispr. Last Accessed: 2019/12/14
[2] “CRISPR Gene Editing.” Wikipedia, Wikimedia Foundation, 15 Jan. 2020, en.wikipedia.org/wiki/CRISPR_gene_editing#Predecessors. Last Accessed: 2019/12/14
[3] “CRISPR: Implications for Materials Science.” Cambridge Core, www.cambridge.org/core/journals/mrs-bulletin/news/crispr-implications-for-materials-science. Last Accessed: 2019/12/14
[4] “Do CRISPR Risks Outweigh Rewards?” GEN, 5 Nov. 2018, www.genengnews.com/magazine/328/do-crispr-risks-outweigh-rewards/. Last Accessed: 2019/12/14
[5] Makarova, Kira S, and Eugene V Koonin. “Annotation and Classification of CRISPR-Cas Systems.” Methods in molecular biology (Clifton, N.J.) vol. 1311 (2015): 47-75. doi:10.1007/978-1-4939-2687-9_4 Last Accessed: 2019/12/14
[6] Mullin, Emily. “The 7 Craziest Ways CRISPR Is Being Used Right Now.” Medium, OneZero, 11 Oct. 2019, onezero.medium.com/the-7-craziest-ways-crispr-is-being-used-right-now-bcf3bd203f23. Last Accessed: 2019/12/14
[7] “Questions and Answers about CRISPR.” Broad Institute, 4 Aug. 2018, www.broadinstitute.org/what-broad/areas-focus/project-spotlight/questions-and-answers-about-crispr. Last Accessed: 2019/12/14
[8] “What Are Genome Editing and CRISPR-Cas9? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, ghr.nlm.nih.gov/primer/genomicresearch/genomeediting. Last Accessed: 2019/12/14
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