Guide
According to foreign media reports, in less than five years, the genetic editing technology CRISPR has revolutionized the face and development of modern biology. This technology is capable of discovering, removing and replacing genetic material. Since its first report in 2012, scientists have published more than 5,000 papers on the technology. Biochemistry researchers embrace the technology and hope to use it to create better disease models. Numerous companies have invested this technology in the development of new drugs, therapies, foods, compounds and new materials in an attempt to gain new commercial benefits.
Usually, when we refer to CRISPR, it actually refers to the CRISPR/Cas system—consisting of a small piece of RNA and a highly efficient DNA cleavage enzyme (ie, nuclease), the full name of the palindrome repeat cluster /clustered regular interspaced short palindromic repeats/CRISPR-associated proteins. Its significance to biology is like the meaning of the Ford Model T for the manufacturing and transportation industries. Now, CRISPR has been used in the treatment of human cancer, and as far as 2018, the technology will be used in clinical trials such as hereditary diseases such as sickle-type red blood cell disease and type B thalassemia.
However, like the original Ford Model T, the classic CRISPR technology has become a bit crude, unreliable and even dangerous. It can't be combined with any part of the genome, and sometimes it cuts the wrong place. Moreover, it does not have a close button. If the Ford Model T is easy to overheat, then the classic CRISPR can be said to be easy to "eat too much."
Even with such limitations, the classic CRISPR system will remain a very important tool in biology in 2018 and beyond. However, in 2017, newer, faster genetic editing tools are available, and may soon eclipse the first generation of technology. Therefore, if you are interested in making a difference in this field, please be prepared, because "Gene Editing 2.0" is in sight!
Targeted cutting operations are a hallmark of CRISPR technology. However, while the Cas9 endonuclease cleaves two strands of DNA in an organism, it also poses some risk. Targeted cutting operations are a hallmark of CRISPR technology. However, while the Cas9 endonuclease cleaves two strands of DNA in an organism, it also poses some risk.
Rapid advance
Targeted cutting operations are a hallmark of CRISPR technology. However, while the Cas9 endonuclease cleaves two strands of DNA in an organism, it also poses some risk. Cells may make mistakes in repairing this severe genetic damage. This is why scientists want to design safer methods to achieve the same goal.
One method is to mutate the Cas9 nuclease to lose its ability to cleave, but still bind DNA. Next, use other proteins, such as proteins that activate gene expression, to bind to the Cas9 nuclease that loses some of its function, and jointly control the opening and closing of the gene without changing the DNA sequence (sometimes using light or chemical signals) ). This "epigenetic editor" may be used to treat diseases caused by a variety of genetic factors, while the classic CRISPR technique is best suited to dysfunction caused by a single mutation. In early December, researchers at the Salk Institute in the United States tried this new method in mice to treat serious diseases including diabetes, acute kidney disease and muscular dystrophy.
Scientists at Harvard University and the Broad Institute have even made bolder improvements to the CRISPR system: editing single base pairs. To achieve this, they must design a new, non-existing enzyme that chemically converts the paired adenine (A)-thymidine (T) to guanine (G)-cells. Pyrimidine (C). This change seems to be small, but it has a very significant meaning. Harvard chemist David Liu presided over the work, and he estimated that about half of the 32,000 pathogenic mutations known in the human body could be repaired by such a single site transformation. "I don't want the public to have a misunderstanding about this, that is, we can transform any DNA fragment of any human or any animal, even a cell in a petri dish, into another piece of DNA," David Liu said. "But, let us In terms of location, it also means a lot of responsibilities. The biggest question is, how much capacity can this era achieve, and how can we use these technologies to benefit society as quickly as possible?"
How to control risk?
The CRISPR/Cas system is an acquired immune mechanism found in most bacteria and most archaea. Its job is to discover the invading viral DNA and destroy it until the DNA is cleared. This system is an "accelerator" with no brakes and is therefore potentially dangerous – especially in clinical applications. The longer Cisco keeps in the cell, the greater the risk that it will treat certain fragments as target genes and cut them.
To minimize these off-target issues, scientists have been developing new tools to better control CRISPR. To date, researchers have identified 21 naturally occurring anti-Crisp (anti-CRISPR) protein families, protein molecules that inhibit gene-editing enzymes. However, scientists only understand the working mechanisms of a few of these proteins. Some proteins bind directly to Cas9, preventing it from attaching to DNA; others can activate enzymes that compete with Cas9 for genomic location. Currently, the University of California at Berkeley, the University of California at San Francisco, Harvard University, the Broad Institute, and the University of Toronto are working to develop ways to use these natural shutdown mechanisms to make them a codeable control tool.
In addition to medical applications, these protein families are also important for the continued development of the "gene drive" field. Gene-driven was first proposed in 2003 by Austin Burt, an evolutionary geneticist at Imperial College London, referring to a gene editing technique that rapidly spread specific traits into populations. If we can promote the evolution process in some way, it will be very beneficial for human beings to cope with many problems from epidemic diseases to climate change. For example, we can use this method to eliminate mosquitoes that cause malaria, or to eliminate harmful invasive species. However, in the wild environment, these means may also lose control and even have disastrous consequences. Just in 2017, the Defense Advanced Research Program (DARPA) under the US Department of Defense invested $65 million to find a safer genetically driven design, including an anti-CRISPR "close switch."
Progress of Cas enzyme
Despite the rapid advances in genetic technology for decades, many scientists do not understand why certain defects in DNA cause disease. Even if we know which genes are encoded into the cell in what order, it is much more difficult to know how the sequence information is passed, how it is translated (or not translated). This is why the team of Harvard and the Broad Institute's Zhang Feng (one of the discoverers of CRISPR-associated proteins) is looking for RNA-targeted Cas enzymes.
Since the genetic information that cells read when assembling proteins comes from RNA, they carry more basic genetic information about specific diseases. Moreover, because RNA is constantly being transcribed and translated, modifications to RNA help to better treat short-term diseases such as inflammation or trauma. This new system is called "REPAIR" and is called "RNA Editing for Programmable A to I Replacement". Currently, only a single nucleotide can be edited. Next, the researchers hope to try this technique in 11 other possible combinations.
Scientists have been discovering new Cas enzymes. The team at the Broad Institute studied the characteristics of the nuclease Cpf1. This enzyme has several key differences with other Cas enzymes, including the more active ends that are left when the DNA is cleaved, rather than the "blunt" ends. In February 2017, the research team at the University of California at Berkeley discovered Case and CasX, the most compact CRISPR system available. In the coming months or years, scientists hope to find more enzymes and discover more possibilities.
Only time will tell if the CRISPR-Cas9 system is the best genetic editing tool, or just the beginning of a scientific revolution. For different application areas, scientists need a lot of research to determine which tools are most suitable. What they can do now may only be to advance all of these systems. It may take many years to apply genetic editing techniques to human disease treatment, crop cultivation, and the prevention and treatment of disease-causing insects.
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