CRISPR: The Gene Editing Revolution

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Very few things have excited the scientific community in recent years more than CRISPR technology, due to its wide range of applications and fairly simple method. The concept involves the use of a bacterial enzyme, Cas 9, which is usually used to protect bacteria from viral infection, by cutting up the invading virus’s DNA. Biologists have been applying this same principle, of DNA splicing to develop CRISPR.

In the lab, scientists can use the CRISPR Cas 9 enzyme in various different processes, but usually resulting in one of two end results – a knock-out or a knock-in. A knock-out is where you cut a region of genetic code to remove the functionality. The original function is knocked out, whereas a knock-in cuts the region and then adds in a new length of DNA to modify the function.

The entire human genetic code is billions of bases. Made up of the alphabet for life, DNA is comprised of C (Cytosine), A (Adenine), T (Thymine) and G (Guanine). Due to the length of the DNA, there are many places where the Cas9 enzyme can cut and modify the gene. A recent study in China has been performed to knock-out the gene CCR5, which is involved in HIV infection, and this leads to the birth of genetically edited babies. It may seem like a potential answer to curing HIV; however, there are some major disadvantages. The Cas9 enzyme is not specific enough to attack a single site, such as the CCR5 gene, hence it may also attack elsewhere, known as off-target effects. These off-target effects can have a substantial impact on the genetically edited individual, leading to possible disability and genetic conditions, as the genome is not fully understood yet. It has also been shown in CRISPR studies involving mice that the CCR5 gene is involved elsewhere in the body, such as cognitive ability. The study showed that there was an increase in cognitive ability in individuals with the CCR5 knock-out.

There are so many ethical considerations with gene editing. The one that most people think of is “designer babies”, a phrase which has been around for years and is more relevant than ever. The use of gene editing for therapeutics and the use of them for building an individual are two very different things, as the technology at the moment is purely therapeutic, but cosmetic gene editing is not far off. A line must be drawn and new legislation thought up around the use of gene editing in humans. However, most examples of gene editing aren’t in humans.

Recently, scientists have been exploiting the Cas9 enzyme to vary the ratios of male and female cattle. The Cas9 was produced by the egg, and upon fusing with the cell, the enzyme would knock out the Y chromosome, causing the embryo to self-abort, which increase the number of female offspring to 90% of the total offspring. This means less veal are being slaughtered and is therefore making farming more ethically stable.

Another example of CRISPR done right is in the banana. The Cavendish banana is the one we all see on the shelves in the local supermarket. However, there is a virus that threatens many of the plantations they are grown in, which reduces the amount of successful bananas, and hence increases the price. Hope is not lost though, as another species of banana, Gonja Manjaya, has a gene which makes it immune from the virus. By doing a knock-in of the Gonja Manjaya into the common Cavendish banana, it will also make them resistant to the virus, hence surviving the epidemic which threatens to increase the value of the humble banana.

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