How do I use CRISPR Cas9

Gene editing: the 5 most important questions about CRISPR / Cas9

In genetic engineering, the trees grow back to the sky. A decade after the human genome project - in which the expectations of results turned out to be exaggerated - a new technology beckons again with supposed genetic omnipotence. CRISPR / Cas9 is the name of the bearer of hope - a pair of gene scissors that manipulate the DNA at freely selectable points with unprecedented accuracy. The process is already revolutionizing all areas of genetic engineering, and a Nobel Prize for women discoverers is a foregone conclusion. But the new procedure is not free from pitfalls either: Unwanted side effects, technical limits and even lawyers significantly limit the use of the gene editing system.

How does CRISPR / Cas9 work?

The CRISPR / Cas9 system, which is currently fundamentally changing genetic engineering, borrows from a sophisticated bacterial immune system that protects against viruses. It is based on an adaptive immune defense that "remembers" the DNA sequences of the pathogens and cuts their DNA if it is infected again.

This article is contained in Spektrum Kompakt, CRISPR / Cas - Intervention in the Human Genome

This combination of recognition and cutting is used in gene editing. The simplest variant involves injecting RNA into the cell, which encodes a protein called Cas9 and any recognition sequence. The cell uses the RNA to produce the protein, which finds the accompanying identification RNA and goes to work: Cas9 cuts double-stranded DNA - precisely at the point that the associated piece of RNA specifies. Since RNA can be produced artificially with any sequence, such a combination cuts any genome at any point, at least in theory.

The so-called CRISPR sequences have been known in the genome since the 1980s: The abbreviation stands for "clustered regularly interspaced short palindromic repeats", that is, short palindromic repetition sequences that are separated by other genetic material and occur in clusters in the genome at certain points. The pieces of genetic material between the repeated sequences, it turned out, often come from viruses - an indication that the CRISPR could be part of an antiviral system.

In the vicinity of CRISPR, the CRISPR-associated genes, called Cas, were later found in all bacteria with this system. They are the crucial element of the antiviral system. The CRISPR system "harvests" viral DNA and integrates pieces of it into the bacterial genome between the repeat sequences. As a result, the cell produces RNA counterparts to the virus DNA, which comes together with the Cas proteins. If a virus tries to infect the cell again with this DNA, the RNA "recognizes" the virus genome: The Cas proteins then cut up the viral genetic material so that it no longer causes any damage.

The origin of gene editing is the knowledge that the Cas proteins cut up any DNA, provided that they are given the appropriate identification RNA. CRISPR / Cas9 doesn't do more than that: After the cut, you rely on the cell's natural repair mechanisms, which now come into play by themselves.