Tech UPTechnologyThey create the most accurate technique to correct genetic...

They create the most accurate technique to correct genetic mutations

A new form of the celebrated CRISPR-Cas9 genome editing tool appears to significantly expand the range of diseases that could be treated with this technology, by allowing scientists to precisely change any of the four “letters” in DNA and insert or delete any DNA stretching, plus more efficiently and accurately than previous versions of CRISPR . As if this were not enough, the scientists state in their study, which is collected by the journal Nature, that it achieves all this without making genomic coding cuts in the double helix, as does the classic CRISPR and many of its ramifications. Great news for medicine.


Few discoveries have the capacity to transform a discipline so much, but something that seemed unimaginable before is now possible thanks to CRISPR.


The system, called prime editing or quality editing , avoids double-stranded DNA breaks and, in principle, “could correct around 89% of known human genetic variants associated with diseases,” the scientists explain; that is, it is capable of directly editing human cells in a precise, efficient and highly versatile way, expanding the scope of gene editing for biological and therapeutic research.

“An important aspiration in molecular life sciences is the ability to accurately make any change in the genome anywhere. We believe that prime editing brings us closer to that goal,” says David Liu, director of the Merkin Institute for Transformative Technologies in Health at the Broad Institute of MIT and Harvard. “We know of no other mammalian cell editing technology that offers this level of versatility and precision with so few by-products.”


How did they do it?


The experts combined the Cas9 enzyme with a second enzyme called reverse transcriptase. The resulting molecular machine, combined with a guide RNA, is capable of locating a specific DNA site and, at the same time, replacing the specific DNA sequence, cutting a single modified DNA strand to avoid unwanted mutations.


And is that the ability to rewrite the genetic code is one of the most surprising scientific advances in recent years. The most common approach, known as Crispr-Cas9 (“molecular scissors”), they focus on a particular DNA sequence and then cut it in two. The procedure allows scientists to disable specific genes and even correct harmful mutations by providing cells with new strands of DNA with which to repair the cut.

However, Crispr-Cas9 is not perfect. It often leads to cells with a random mix of edits, including extra pieces of DNA called insertions, or missing pieces of genetic code called deletions. These are less problematic when scientists work on cells in vitro , because the affected ones can be discarded. But when genome editing is used to rewrite faulty genes in people’s lungs, hearts, and other tissues, much more precision is needed. Now it is possible with this super precise tool from Crispr.


Scientists made more than 175 edits on human cells, including correcting the genetic causes of sickle cell anemia and Tay-Sachs disease. The results put on the table that it is “the technique is more effective, produces fewer unwanted effects and has less erroneous editing than that carried out with Cas9”, explains David Liu, leader of the work.


You can think of the prime editor as a word processor , capable of searching for specific DNA sequences and very precisely replacing them with edited DNA sequences,” the expert clarifies.


Scientists are really excited

Liu’s team intends to continue optimizing quality editing, including maximizing its efficiency in many different cell types, further investigating the possible effects of this editing on cells, further testing in cell and animal disease models, and exploring delivery mechanisms in animals to provide a potential pathway for human therapeutic applications.

Researchers and the Broad Institute are making this technology freely available to academic and nonprofit communities , including by sharing vectors through the nonprofit Addgene.


Referencia: Andrew V. Anzalone et al. Search-and-replace genome editing without double-strand breaks or donor DNA. Nature (2019) DOI: 10.1038/s41586-019-1711-4


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