CRISPR/Cas9 genome editing technology
CRISPR gene target
Gene editing is a group of technologies that scientists use to change an organism’s DNA. These technologies allow genetic material to be added, removed, or modified at particular locations in the genome. Several approaches to genome editing have been developed over the years. Recently, one editing technology that has got the attention of all is the CRISPR/Cas9. CRISPR and Cas9 are acronyms for Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), and CRISPR-associated protein 9 (Cas9) respectively. The CRISPR/Cas9 system has generated a lot of excitement in the scientific community because it is faster, cheaper, more accurate, and more efficient than other existing genome editing methods.
How CRISPR/Cas9 works
CRISPR-Cas9 was adapted from a naturally occurring genome editing system in bacteria. The bacteria capture snippets of DNA from invading viruses and use them to create DNA segments known as CRISPR arrays. The CRISPR arrays allow the bacteria to “remember” the viruses (or closely related ones). If the viruses attack again, the bacteria produce RNA segments from the CRISPR arrays to target the viruses’ DNA. The bacteria then use Cas9 or a similar enzyme to cut the DNA apart, which disables the virus.
The CRISPR/Cas9 similarly is replicated in the lab. Scientists create a small piece of RNA with a short”guide” sequence that binds to a specific target sequence of DNA in a genome. The RNA also binds to the Cas9 enzyme. Just like in bacteria, the modified RNA is used to recognize the DNA sequence, and the Cas9 enzyme cuts the DNA at the targeted location.
Alternatives to CRISPR/Cas9
Although Cas9 is the enzyme that is used most often, other enzymes (for example, cas2a, Cpf1, etc) can also be used. Once the DNA is cut, researchers use the cell’s own DNA repair machinery to add or delete pieces of genetic material, or to make changes to the DNA by replacing an existing segment with a newly customized DNA sequence.
CRISPR and disease prevention
Genome editing is of great interest in the prevention and treatment of human diseases. Currently, most research on genome editing is done to understand diseases using cells and animal models. Scientists are still working to determine whether this approach is safe and effective for use in people. It is being explored in research on a wide variety of diseases, including single-gene disorders such as cystic fibrosis, haemophilia, and sickle cell disease. It also holds promise for the treatment and prevention of more complex diseases, such as cancer, heart disease, mental illness, and human immunodeficiency virus (HIV) infection.
Who discovered CRISPR
Emmanuelle Charpentier and Jennifer Doudna made groundbreaking discoveries related to the CRISPR-Cas9 system. They were jointly awarded the 2020 Nobel Prize. This historic recognition marked the first time in history that the Nobel Prize was bestowed upon two women for their remarkable contributions to the field of DNA manipulation.
Ethical concerns of genome editing
Ethical concerns arise when genome editing, using technologies such as CRISPR/Cas9, is used to alter human genomes. Most of the changes introduced with genome editing are limited to somatic cells, which are cells other than egg and sperm cells. These changes affect only certain tissues and are not passed from parent to offspring. On the other side, changes made to genes in egg or sperm cells (sex cells) or in the genes of an embryo could be passed to future generations. Sex cell and embryonic genome editing stirs a number of ethical debates, including whether it would be permissible to use this technology to enhance normal human traits (such as durability, height or intelligence).
Due to the global debate centred on genome editing involving sex cells, many countries have currently prohibited such moves. You probably heard about a Chinese faculty who got fired for editing genes at the embryonic stage.
