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What the hell is gene editing technology?
First, let's introduce the concept of gene editing. In fact, the word "gene editing" is relatively simplified. Strictly speaking, it should be called "genome fixed-point editing technology" Here we should pay attention to two key words, one is "genome", which should be in the genome of the nucleus.
The other is "fixed-point editing" because different genes have different sites in the genome of the nucleus. If we don't talk about the editing of specific genome sites, it is actually very different from the technology we are discussing now. Because there are many other technologies that can change the DNA composition in cells. Such as mitochondrial gene replacement technology. Another is to introduce foreign genes with recombinant specific viruses, but they cannot be fixed. It is randomly placed in the genome, which is different from the gene editing technology we are going to discuss today. Gene editing technology, namely "genome site-specific editing technology", refers to the knockout, addition and site-specific mutation of specific DNA fragments.
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The History of Gene Editing Technology
In fact, gene editing technology is not a new concept, and it began to exist as early as the 1990s. So far, it has gone through three generations.
The first generation of gene editing technology is to establish knock-out and knock-in gene mutation models through homologous recombination. As the name implies, knockout refers to knocking out some genes from the original animal genome through certain techniques; Knock-in is the integration of genes that do not exist at a certain point in the animal genome through certain techniques. Knockout and knock-in are accomplished by homologous recombination of DNA. This is a very complicated technology. If we want to make a successful animal gene knock-out and knock-in mutation model, it will take about two to three years and more money will be invested. In addition, this technology is generally used to establish animal models for genetic diseases research, and it is difficult to be used in clinic or in large-scale application in agriculture and animal husbandry.
The second generation gene editing technology is ZFN and Taran technology. The principle of these two technologies is to establish a system by combining DNA nucleic acid binding protein with endonuclease. Because these protein can recognize certain nucleotide sequences, the system formed by certain design can knock out and mutate specific genes.
The third generation gene editing technology is a very popular CRISPR/Cas9 system recently. Its principle is to use ribosome structure for gene editing. CRISPR/Cas9 system can be combined with the target gene through certain design, and then the target gene can be knocked out, site-directed mutation or new foreign gene can be introduced for gene editing.
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Why is the third generation gene editing technology concerned?
To be exact, these three generations of gene editing technologies have certain technical limitations so far. The first obvious limitation is the miss effect. So what is the miss effect? For example, the original design is to edit a DNA target, but it has been looking for it, but it has not found the right target. In fact, it has come to this step to form a similar site, leading to off-target.