New RNA Editor
Geneticists have learned to edit RNA 900 times more accurately
Anna Kaznadzei, N+1
Geneticists have developed a new system for editing RNA without cutting based on the CRISPR-Cas13 system, and then improved it, reducing the number of mistakes it makes by 900 times. The study was published in Science.
RNA editing, unlike DNA editing, allows, firstly, to make changes to the cell at specified time intervals, and secondly, it does not cause so many questions and problems related to the ethics of genomic editing in general. RNA degrades over time, and all changes associated with it are thus reversible. You can read more about the CRISPR-Cas13 system, which allows you to edit RNA, here.
Scientists from Harvard and MIT systematically analyzed a number of proteins of the Cas13 family to find the most effective form of this protein, and selected a candidate belonging to a bacterium of the genus Prevotella, which was called PspCas13b. Compared to all his orthologs, he most effectively found and inactivated the necessary RNA by cutting it. This in itself was already a useful find, since the new effective "scissors" could be used in other types of experiments. In this project, scientists created a modified form of a protein that successfully found its target, but was not able to cut it.
After that, the Cas13b protein was "cross–linked" with the ADAR2 protein - adenosine RNA deaminase, which is capable of converting adenosine into inosine. Inosine is regarded by the cell as guanosine – thus, this mechanism is equivalent to replacing And on G. As a result, the right place is found using the CRISPR-Cas13b system, but the RNA is not cleaved, but is deaminated using ADAR2. This system was called REPAIR (RNA Editing for Programmable A to I Replacement); its efficiency averaged from 20 to 40 percent, and in some cases this number reached 89 percent.
The scheme of the REPAIR system (David B.T. Cox et al / Science, 2017)
Using protein engineering techniques, the scientists then created an improved version of the system, which they called REPAIRv2. It demonstrated 900 times greater specificity to target mutations – thus, the number of editing errors significantly decreased. In order to test the operation of the new system, long RNA molecules with known mutations were used. The efficiency of REPAIRv2 was still from 20 to 40 percent, but the new version practically did not affect non-target targets. Thus, in particular, it was possible to edit mutations in HEK293FT cell culture that cause congenital aplastic anemia and nephrogenic diabetes insipidus in humans.
The system successfully edits the specified sets of mutations, which cannot cure genetic diseases by themselves, but can have a very significant impact on their development, scientists believe. Among the diseases that are associated with mutations of G in A are Duchenne muscular dystrophy, Parkinson's disease and focal epilepsy.
In the future, scientists are going to improve the efficiency of the REPAIRv2 system and develop techniques that allow such systems to be directed to specified tissues.
And you can read about another work of a group of scientists from Harvard and MIT, published simultaneously on deaminases and editing, but concerning DNA and the technique that for the first time made it possible to turn A-T pairs into G-C pairs, here.
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