The newly engineered neobase editor significantly reduces the incidence of RNA editing.

In the long chain of DNA, the CRISPR/Cas gene editing technique known as "gene scissors" may be randomly taken away with several healthy fragments, known as "off-target effects", but the CRISPR base editor, which is compared to a "pencil", can "modify" the target fragment to the desired appearance.
however, the "pencil" may also be "Zhang Guan Li Dai", the original fragments replaced with other fragments. several CRISPR base editors developed in recent years have led to widespread OFF-targeting of RNA outside the target DNA, according to a team of researchers at Harvard University's Massachusetts General Hospital,
.
the team has also developed an engineered neobase editor that can significantly reduce the incidence of RNA editing and improve the accuracy of target DNA editing.
the results of the study published in the international authoritative journal Nature.
finding "wrong words" from 3 billion "words" to modify the treatment of human genetic diseases has been a biomedical difficulty.
so far, there are still many types of genetic diseases that do not have viable treatments;
"If you compare the whole sequence of DNA from the human genome to a book, there are about 3 billion words in this book, and each 'base' is like a word in this book." At
present, there are about 7,000 known human single-gene genetic diseases, most of which are caused by single-base mutations, said Dr. Liu Wen of Xiamen University's School of Pharmacy. Is there a better treatment strategy for
? "Correcting a single wrong base has the potential to cure these single-gene genetic diseases, so scientists hope to find a molecular tool that can accurately target modification simply of a single base."
, " Liu said, but it's very difficult, like finding the word accurately and quickly from 3 billion words and modifying it.
"It is precisely because of this precise targeting capability that the CRISPR/Cas9 system has been developed as an efficient gene editing tool.
Professor Yuan Jing of Xiamen University's School of Life Sciences told reporters that the CRISPR/Cas9 system, like a "scissor" that can accurately cut off double-stranded DNA, has achieved efficient gene knockout in many species and has played a revolutionary role in biomedical research.
but it also causes double-stranded DNA to break, introducing a potential risk of random insertion and missing mutations, known as DNA off-target effects.
2017, Harvard University's Liu Ruqian research team published in the journal Nature, the first innovative based on the CRISPR/Cas9 system, the first generation of base editor BE1.
the researchers further used this system to accurately replace the nucleotides of The Alzheimer's disease-causing gene APOE4 and the cancer-causing gene TP53 in in vitro cells, and verified the feasibility of the technique.
"CRISPR base editor, more like a can modify the single base 'pencil', will not cause double-stranded DNA fracture, in theory can cause hundreds of disease-causing genomic monobase mutations fixed-point correction, thus avoiding potential risks, in clinical medical research and crop breeding and other fields have great potential and important application value.
," said Professor Zhang Jisen, executive vice director of the Genomics and Biotechnology Research Center at Fujian University of Agriculture and Forestry.
RNA level off-target effect is also urgent to pay attention to science and technology is sometimes also a "double-edged sword", the base editor unexpected off-target effect can not be ignored. According to liu Wen,
, it is like a typo that was meant to be modified on the first page, but a correct word on page three has been modified due to the off-target effect, which can lead to the occurrence of potential diseases.
"Since the advent of the monobase editor, most investigations into off-target gene editing have focused on DNA, but we found that this technique can also induce a large number of RNA changes."
, said Dr. Keith, author of the article and a department of pathology at Harvard University's Massachusetts General Hospital.
at first, Dr. Keith speculated that the base editor that fuses rat cytosine nucleomine disaminase rAPOBEC1 as a "pencil" may be altered in cells to have the target nucleotide base of the DNA molecule, as well as specific nucleotide sites on RNA molecules.
if this is true, a large number of mRNA molecules from different genes in cells may be modified by the base editor, resulting in off-target RNA effects.
their experiment confirmed the hypothesis.
, Dr. Ren Chong of the Chinese Academy of Sciences told Science daily, the researchers conducted RNA off-target analysis of the widely used CBE base editor and the recently developed ABE base editor, and found that both editors caused a wide range of base editing at RNA levels, suggesting that the base editor not only has the editing activity of THE DNA level, but also the editing activity of THE RNA level, which is often overlooked in the study.
", "the existing base editor, the widespread off-target effect on RNA molecules, for its clinical application has a great risk, in the future medical clinical applications, we need it to achieve both accurate attack on the enemy, but not to harm the innocent."
" Liang Zhenchang, a researcher at the Chinese Academy of Sciences, said that at this stage, scientists around the world are continuing their efforts to continuously improve the efficiency and accuracy of gene modification technology and reduce off-targeting.
screened for a more precise new "pencil" first-generation single-base editor BE1, most scientists in the field focused on two improvements: first, to improve the single base replacement activity of the base editor, making this "pencil" more efficient to use;
" improvements in both areas are critical to clinical applications.
," Yuan Jing said.
found a widespread RNA off-target defect in the base editor, Dr. Keith's team redesigned the original CBE base editor to screen two improved "new pencils" from 16 mutant proteins - the base editor "BE3-R33A" and "BE3-R33A/K34A".
the modified base editor had the same DNA editing activity as the original CBE editor, but RNA levels were edited at least 390 times and 3800 times less frequently, respectively.
"constructanding and screening favorable (low RNA off-target effect) base editor is an effective way to reduce off-target effect.
," Liang said.
any technology is not perfect in its infancy. "
The latest study has made us aware of the shortcomings of the base editor and reminds researchers that they need to have a more comprehensive understanding of the technology and the advantages and drawbacks of any new technology in future research," Zhang said.
Yuan Jing believes that the treatment of human genetic diseases, if drug treatment is playing a cure, then through gene editing technology, especially the base editor, the genetic disease patients causether error genetic information, fundamentally corrected, can play the purpose of the cure.
this path holds hope, but it must be long and full of difficult twists and turns.
Source: Science Daily.