From restriction enzymes to crisper scissors, gene editing technology has revolutionized many fields, from improving food productivity to curing genetic diseases, but ethical debates and side effects are still far from settled.
Since the discovery of the existence of genes, attempts to edit them have been ongoing. The first conceptualization of genes occurred in the late 19th and early 20th centuries, and scientific efforts to understand their role and how they work have been ongoing ever since. In the 1950s, genetics took a quantum leap forward with the discovery of the double helix structure of DNA, and the possibility of gene editing began to be discussed. By the 1970s, the new field of genetic engineering was born, and specific research and experiments to make gene editing a reality began in earnest. It has already been successfully used to improve food productivity, and attempts are still being made to apply it to various fields.
Gene editing is the process of creating new recombinant DNA by inserting or removing specific genes. The process is divided into the following steps: cutting, separating, splicing, and replicating DNA, with the first step being the most important. Cutting the exact part you want is the first step and the key to gene editing. In this article, we’ll take a look at the past and present of this technology.
The first gene-cutting technology used was natural restriction enzymes. Restriction enzymes are enzymes that bacteria produce when they are attacked by a virus called a bacteriophage, which injects its own genes into the cell of the bacteria, and protects the bacteria by cutting the DNA that the bacteriophage injects. Restriction enzymes work by recognizing a special set of sequences called palindromes. Each restriction enzyme, derived from hundreds of different microorganisms, has a different recognition palindrome, which can be used to cut DNA into desired sections in a test tube. The use of restriction enzymes has opened up the field of genetic engineering by allowing humans to cut genes into desired regions, but it also has clear limitations. Restriction enzymes derived from microorganisms typically recognize six sequences, and when applied to the large chromosomes of higher organisms, they would cut the DNA too often, causing the cell to die. As a result, the technology was mostly limited to bacteria.
When restriction enzyme technology was first introduced, scientists realized that it could be used to manipulate the DNA of many organisms. In particular, Stanley Cohen and Herbert Boyer’s 1973 experiment, in which they created the first recombinant DNA using this technology, opened a new chapter in genetic engineering. This successful experiment proved that restriction enzymes could cut genes exactly where they were needed, paving the way for the free manipulation of genes.
The next gene-cutting technology used was man’s invention of artificial genetic scissors. Artificial genetic scissors were invented to solve problems with the cutting process of natural restriction enzymes. One of the most common genetic scissors used until recently is the Zinc Finger Nuclease. It has been in development since the 1980s. Zinc Finger Nuclease is a complex of six zinc-containing finger-like proteins called zinc fingers and a nuclease, an enzyme that acts on 34 nucleic acids. The zinc fingers recognize and bind to specific sequences, and an enzyme called Fok1 is responsible for deleting the binding sites. It’s a kind of dirty bomb. Whereas natural restriction enzymes recognize six or so sequences, the Zinc Finger Nuclease gene scissors recognize 18 to 24 base pairs. This allows them to cut the genome in only one or two places, and allows them to create many different variants of Zinc Fingers that can be customized to have different base sites recognized. This has made gene editing possible in higher animals, including humans, and has led to breakthroughs in the treatment of genetic diseases through gene editing.
Artificial genetic scissors, such as Zinc Finger Nuclease, were initially used primarily in laboratory research, but their applications have since expanded. For example, they have made significant contributions to agriculture, such as creating experimental mouse models with specific genetic defects to study diseases, and enhancing the disease resistance of certain crops through genetic modification. In the field of genetic disease treatment, gene editing has opened up the possibility of saving the lives of patients suffering from fatal genetic diseases.
The cutting technology currently in use is the recently invented crisper scissors. In addition to Zinc Finger Nuclease, TALE nuclease, RGE nuclease, and other genetic scissors have been invented one after another, but CRISPR-Cas9 has opened a new chapter in genetic engineering with its overwhelming performance. It was invented by researchers at a Danish yogurt company, based on the adaptive immune function of a sequence called CRISPR, which they discovered while studying lactic acid bacteria attacked by bacteriophages. In a nutshell, when viral DNA enters a bacterium, the Cas9 protein cuts it, and then transcribes an RNA that combines the cut viral sequence with the CRISPR sequence. The next time the same virus attacks, the RNA and Cas9 form a complex that defeats the virus much faster than before. By inserting the palindromic sequence you want to cut into CRISPR, you create an RNA that acts as a guide and combines it with the Cas9 protein to create a kind of genetic scissors. Unlike previous genetic scissors, this technology uses RNA rather than protein as a guide.
The Crisper scissors are revolutionary for several reasons. While previous genetic scissors required the creation of thousands of artificial genes to produce the desired protein, CRISPR uses RNA, which is much smaller than protein and can be produced with simple sequence manipulation, dramatically reducing production costs and allowing for mass production. The use of RNA also dramatically shortens the fertilization process, which previously required a very complicated process of manipulating an organism’s genes at the embryonic stem cell stage, injecting them back into the blastocyst, implanting them again, and verifying them. But with CRISPR, it’s a very simple process of injecting Cas9 and the desired RNA into a fertilized egg. This has given humans the ability to manipulate the genes of almost any organism, including ourselves. This has made previously unattainable research feasible thanks to increased efficiency and price competitiveness, and has led to a large amount of corporate investment in genetic engineering research.
The human touch is also reaching into areas that were considered the domain of the gods before the modern era. Within a century, genetic engineering has progressed from the rudimentary stage of editing bacteria to manipulating human genes. The promise is to increase food productivity, cure genetic diseases, restore endangered species, and treat certain diseases. However, the ethical debate about whether humanity can handle this new power and the possible side effects of gene editing is still in its infancy. While it’s important to study the use of the revolutionary genetic scissors called CRISPR, it’s also important to start a serious pan-human discussion about how to curb their indiscriminate use.
Since the advent of CRISPR, the revolutionary nature of the technology has reverberated far beyond the scientific community, particularly in the bioethics debate, as the ability to manipulate human embryos has spurred research. Not only scientists, but also lawyers, ethicists, and the general public have expressed various opinions on the issue, and in some cases, legal regulations on the criteria and limits of the use of Crisper technology have been discussed. This societal debate is based on the realization that Crisper scissors are not just a scientific tool, but a powerful force that can shape the future of humanity.
