Posted by on February 19, 2018 7:25 pm
Categories: Baidu

Source: Cell Rep:explain why CRISPR-Cas9 presence of off-target effects

2018 2 November 18/bio Valley BIOON/—Cas9 protein found simplifies genome editing, and may even in the near future to eliminate many hereditary diseases. The use of Cas9, scientists were able to cut the cell DNA, thereby correcting the mutated gene, or the new genetic material introduced into this new cut of the bit point. Initially, the CRISPR-Cas9 system seems to be very accurate. However, today, it is obvious that Cas9 also sometimes cut with its targeted sequence is similar to other DNA sequences. In a new study, from the Netherlands Delft University of technology researchers have developed a mathematical model to explain why the Cas9 will cleave some DNA sequences, while allowing the other of the DNA sequence remains intact. Related research results published in 2018 2 May 6, the Cell Reports journal, The paper entitled“Hybridization Kinetics Explains the CRISPR-Cas Off-Targeting Rules”.


the picture from the TU Delft. div>

CRISPR-Cas9 system is a protection of bacteria from viruses of the defense mechanisms. If viruses invade bacteria, but does not take over the bacterial cell, then this defense system from viruses,cut out some of the genetic material and store it in the bacteria’s own genome. This built-in viral DNA plays a genetic memory of the role. If this is the same virus again attack the bacteria or its descendants, then it will quickly identify such an attack of the virus, and the delivery of Cas9 protein to track it. The use of such stored genetic material to produce viral RNA(CRISPR RNA, crRNA as a“cheat table cheat sheet”, the Cas9 looking for this bacterial cells are not friendly DNA. If a match is found the viral DNA, then the CRISPR-Cas9 system will cut the viral DNA, eliminating the virus once again invade the threat.< p>unwanted effects

scientists initially believed that the CRISPR-Cas9 to cut a piece of DNA sequence, the DNA sequence should be and it carries the speed of the look-up table to match exactly. However, this speculation has now been proven to be wrong. Cas9 is sometimes cut with it is looking for the target DNA similar to the DNA sequence, but these similar DNA sequences containing a plurality of different bases. According to Tu Delft researcher Martin Depken argument, from an evolutionary point of view, cutting these slightly different DNA sequences is very reasonable. He said,“the virus continues to mutate, it is possible to have a different Cas9 looking for the target genome. By also cutting a slightly different DNA sequences, the CRISPR-Cas9 system is able to track the virus’s evolution and to better protect the bacteria from which the attacker attacks.”

In this case, this bacteria is beneficial, but the human it is harmful. If we want to use Cas9 to edit genes, then in addition to cutting the researchers want to target the gene, the other gene will not be cutting is very necessary. Destroy the other’s genetic material can produce terrible consequences.

there have been experiments show that compared to other gene editing tool CRISPR-Cas9 is more likely to cut some of the non-matching sequence.

by the PhD student Misha Klein LED Depken team want to know to decide this preference the basic physics of what is. Depken said, that everything is about to depart from the RNA template by base pairing to the cost of energy.

Depken explains,“when the Cas9 identification of a DNA sequence matches, it is from this chain start end inspection. Then, it will sequentially check the chain all the bases. For each nucleotide match, Cas9 will gain energy, and any mismatch will consume energy. A DNA sequence contains no matching of the bases more, and these mismatched bases closer to this sequence at the beginning, Cas9 less likely for it to be cut, on the contrary, it will from the DNA, fall down and continue looking for a better able to match its RNA template to the DNA sequence.

better prediction

according to Depken of the argument, surprisingly, his team developed this simple mathematical model very well predicted the existing��The Cas9 cutting behavior of the data. If it does not match the nucleotide in a segment of DNA sequence at the end, then in order to increase the cutting possibilities, Cas9 may need to gathering enough energy to overcome this barrier. The model also explains Cas9 in a segment of DNA sequence at the start of the encounter does not match the base, or two mismatched bases close enough, why is it not on this piece of DNA sequence to be cut.

when it comes to a piece of DNA sequence is cut when the possibility of, the Cas9 protein itself, the physical properties also play a role. Depken and his colleagues are now considering this variable is integrated into their model. Ultimately, this model should be able to better predict the Cas9 may be generated by the cutting error. Depken said,“sometimes, in the repair genes, to choose the accurate site to be cut, and our model will help determine the target to which site is most appropriate.” This model provides the physical understanding also helps to edit the DNA to avoid the occurrence of life-threatening errors. Biological Valley


Misha Klein, Behrouz Eslami-Mossallam, Dylan Gonzalez Arroyo et al. Hybridization Kinetics Explains the CRISPR-Cas Off-Targeting Rules. Cell Reports, 6 February 2018, 22(6):1413-1423, doi:10.1016/j. celrep. 2018. 01. 045

Published at Mon, 19 Feb 2018 19:26:41 +0000

Leave a Reply