The interest for the so-called “gene editing” technology has grown rapidly, becoming a hot topic nowadays. But what exactly is gene editing? When talking about it, we usually say that gene editing is to DNA what a text editing programme is to a text file. DNA is a molecule able to encode information, like which colour our eyes should be or how big a tree should grow, in a way that our cells can read. It is made up of units called bases which belong to four types and which are arranged in sequence, just like letters in a text. If we imagine DNA as a text, gene editing allows us to alter a specific part of the text, erasing some “letters” (bases) or introducing new text. As DNA contains the instructions for living beings to function, this, in turn, will affect the characteristics of an organism. In contrast with gene editing, traditional gene engineering inserts some text that we know is useful (like “how to resist drought”) at some random point in the text that we cannot control. Surprisingly, the latter does work, but that’s another story. What is clear is that a finer control of how we manipulate genetic material can have huge potential to develop applications in any field involving living systems.

However, you may wonder how it is possible to “edit” DNA if it is a molecule and not really a text. To answer this, we have to look at how cells manage their genetic information. Cells need genetic information to remain the same because if the cell is functioning properly, a change can mean something not working. Unfortunately, DNA can easily be altered by factors in the environment such as UV light or X-rays. Because of that, through millions of years of evolution, cells have developed what we call “DNA repair” mechanisms. These are special molecules that detect errors in the DNA and fix it the best they can.

How do scientists take advantage of this? There is a system called CRISPR-Cas, which you may have heard of, a weapon that bacteria use against viruses that infect them (yes, bacteria can be infected by viruses, too!). Viruses, too, have DNA and they need it to carry out an infection. The CRISPR-Cas system is able to detect the DNA from the virus by looking for a specific sequence of bases belonging to said virus and make a cut. DNA is read continuously, so if the molecule is cut, the information can no longer be retrieved and the virus is unable to infect.

Now, back to gene-editing, because DNA works in the same way in any living being, scientists can artificially deploy this system in any cell, like a plant cell and make a specific cut in the plant’s DNA. Why would we want to do that? Didn’t we say that this renders DNA impossible to read? Yes, that is true. Here is where the DNA repair comes into play. When the cell detects that its DNA is broken it quickly activates these mechanisms to join the two DNA pieces resulting from the cut at all costs. There are two ways of dealing with a break. In the first one, the cell simply joins the two pieces of DNA. However, the process is not perfect and it may cause some information to be lost. If this happens, a gene can become non-functional or altered (or not). A gene is a specific part of the DNA that contains a distinct piece of information, such as eye colour. This is a way in which we can do gene editing, as we know that turning off some genes can be beneficial in certain contexts. For example, plants sacrifice part of their energy to protect themselves against disease, so if we turn off the genes responsible for fighting off microbes, this energy can be used towards growth and their yield may be increased.

There is a second interesting possibility. To avoid the aforementioned loss of information, cells have developed a mechanism called “recombination” in which they repair DNA by following a template. For example, chromosomes have two arms, which are completely identical, so, if one of them breaks, the other can be used to copy the missing information and ensure that the fixed version is not altered, as happened with the first method of simply joining the DNA pieces. Furthermore, cells look for identical copies by looking for a similar sequence to the ends of the broken pieces of DNA. We can exploit this by providing the template ourselves, using a template including the information we wish to introduce at that particular place surrounded by sequences similar to these ends to “trick” the cell. This is indeed a wonderful approach. However, multicellular organisms usually prefer the former joining mechanism and rarely use this recombination strategy, even though they have the capacity to do so. This is a problem because some of the most interesting organisms to apply this technology, like plants or animals, are multicellular. Consequently, we still need to make further improvements. Still, gene editing is already a reality and CRISPR-Cas has already been used to create edited plants or animals in the lab.

As you can see, gene editing is a very powerful technique, which properly used can revolutionise agriculture, healthcare and many other areas. Because of this, we need society to be informed about its potential and pitfalls. In this way, we will be able to jointly make rational decisions to ensure it is used safely and under proper regulations, just like any other technology.